Add `agx_white`, `agx_contrast` and HDR support to the AgX tonemapper.

Also optimize all tonemappers to perform less calculations per-pixel.

Note: unlike `white`, `agx_white` is limited to a minimum of `2.0` and defaults to `16.29`. When using a RGB10A2 render buffer, `agx_white` will be ignored and a value of `2.0` will be used instead to ensure good behavior on the Mobile renderer.

doc/classes/Environment.xml

@@ -315,6 +315,13 @@
 		<member name="ssr_max_steps" type="int" setter="set_ssr_max_steps" getter="get_ssr_max_steps" default="64">
 			The maximum number of steps for screen-space reflections. Higher values are slower.
 		</member>
+		<member name="tonemap_agx_contrast" type="float" setter="set_tonemap_agx_contrast" getter="get_tonemap_agx_contrast" default="1.25">
+			Increasing [member tonemap_agx_contrast] will make dark values darker and bright values brighter. Produces a higher quality result than [member adjustment_contrast] without any additional performance cost, but is only available when using the [constant TONE_MAPPER_AGX] tonemapper.
+		</member>
+		<member name="tonemap_agx_white" type="float" setter="set_tonemap_agx_white" getter="get_tonemap_agx_white" default="16.29">
+			The white reference value for tonemapping, which indicates where bright white is located in the scale of values provided to the tonemapper. For photorealistic lighting, it is recommended to set [member tonemap_agx_white] to at least [code]6.0[/code]. Higher values result in less blown out highlights, but may make the scene appear lower contrast. [member tonemap_agx_white] is the same as [member tonemap_white], but is only effective with the [constant TONE_MAPPER_AGX] tonemapper. See also [member tonemap_exposure].
+			[b]Note:[/b] When using the Mobile renderer with [member Viewport.use_hdr_2d] disabled, [member tonemap_agx_white] is ignored and a white value of [code]2.0[/code] will always be used instead.
+		</member>
 		<member name="tonemap_exposure" type="float" setter="set_tonemap_exposure" getter="get_tonemap_exposure" default="1.0">
 			Adjusts the brightness of values before they are provided to the tonemapper. Higher [member tonemap_exposure] values result in a brighter image. See also [member tonemap_white].
 			[b]Note:[/b] Values provided to the tonemapper will also be multiplied by [code]2.0[/code] and [code]1.8[/code] for [constant TONE_MAPPER_FILMIC] and [constant TONE_MAPPER_ACES] respectively to produce a similar apparent brightness as [constant TONE_MAPPER_LINEAR].
@@ -323,8 +330,8 @@
 			The tonemapping mode to use. Tonemapping is the process that "converts" HDR values to be suitable for rendering on an LDR display. (Godot doesn't support rendering on HDR displays yet.)
 		</member>
 		<member name="tonemap_white" type="float" setter="set_tonemap_white" getter="get_tonemap_white" default="1.0">
-			The white reference value for tonemapping, which indicates where bright white is located in the scale of values provided to the tonemapper. For photorealistic lighting, recommended values are between [code]6.0[/code] and [code]8.0[/code]. Higher values result in less blown out highlights, but may make the scene appear lower contrast. See also [member tonemap_exposure].
-			[b]Note:[/b] [member tonemap_white] is ignored when using [constant TONE_MAPPER_LINEAR] or [constant TONE_MAPPER_AGX].
+			The white reference value for tonemapping, which indicates where bright white is located in the scale of values provided to the tonemapper. For photorealistic lighting, it is recommended to set [member tonemap_white] to at least [code]6.0[/code]. Higher values result in less blown out highlights, but may make the scene appear lower contrast. [member tonemap_agx_white] will be used instead when using the [constant TONE_MAPPER_AGX] tonemapper. See also [member tonemap_exposure].
+			[b]Note:[/b] [member tonemap_white] must be set to [code]2.0[/code] or lower on the Mobile renderer to produce bright images.
 		</member>
 		<member name="volumetric_fog_albedo" type="Color" setter="set_volumetric_fog_albedo" getter="get_volumetric_fog_albedo" default="Color(1, 1, 1, 1)">
 			The [Color] of the volumetric fog when interacting with lights. Mist and fog have an albedo close to [code]Color(1, 1, 1, 1)[/code] while smoke has a darker albedo.
@@ -431,8 +438,7 @@
 			[b]Note:[/b] This tonemapping operator is called "ACES Fitted" in Godot 3.x.
 		</constant>
 		<constant name="TONE_MAPPER_AGX" value="4" enum="ToneMapper">
-			Uses a film-like tonemapping curve and desaturates bright values for a more realistic appearance. Better than other tonemappers at maintaining the hue of colors as they become brighter. The slowest tonemapping option.
-			[b]Note:[/b] [member tonemap_white] is fixed at a value of [code]16.29[/code], which makes [constant TONE_MAPPER_AGX] unsuitable for use with the Mobile rendering method.
+			Uses an adjustable film-like tonemapping curve and desaturates bright values for a more realistic appearance. Better than other tonemappers at maintaining the hue of colors as they become brighter. The slowest tonemapping option.
 		</constant>
 		<constant name="GLOW_BLEND_MODE_ADDITIVE" value="0" enum="GlowBlendMode">
 			Adds the glow effect to the scene.

doc/classes/RenderingServer.xml

@@ -1523,6 +1523,14 @@
 				Sets the variables to be used with the "tonemap" post-process effect. See [Environment] for more details.
 			</description>
 		</method>
+		<method name="environment_set_tonemap_agx_contrast">
+			<return type="void" />
+			<param index="0" name="env" type="RID" />
+			<param index="1" name="agx_contrast" type="float" />
+			<description>
+				See [member Environment.tonemap_agx_contrast] for more details.
+			</description>
+		</method>
 		<method name="environment_set_volumetric_fog">
 			<return type="void" />
 			<param index="0" name="env" type="RID" />
@@ -5509,8 +5517,7 @@
 			[b]Note:[/b] This tonemapping operator is called "ACES Fitted" in Godot 3.x.
 		</constant>
 		<constant name="ENV_TONE_MAPPER_AGX" value="4" enum="EnvironmentToneMapper">
-			Uses a film-like tonemapping curve and desaturates bright values for a more realistic appearance. Better than other tonemappers at maintaining the hue of colors as they become brighter. The slowest tonemapping option.
-			[b]Note:[/b] [member Environment.tonemap_white] is fixed at a value of [code]16.29[/code], which makes [constant ENV_TONE_MAPPER_AGX] unsuitable for use with the Mobile rendering method.
+			Uses an adjustable film-like tonemapping curve and desaturates bright values for a more realistic appearance. Better than other tonemappers at maintaining the hue of colors as they become brighter. The slowest tonemapping option.
 		</constant>
 		<constant name="ENV_SSR_ROUGHNESS_QUALITY_DISABLED" value="0" enum="EnvironmentSSRRoughnessQuality">
 			Lowest quality of roughness filter for screen-space reflections. Rough materials will not have blurrier screen-space reflections compared to smooth (non-rough) materials. This is the fastest option.

drivers/gles3/rasterizer_scene_gles3.cpp

@@ -2380,9 +2380,12 @@ void RasterizerSceneGLES3::render_scene(const Ref<RenderSceneBuffers> &p_render_
 		}
 
 		tonemap_ubo.exposure = environment_get_exposure(render_data.environment);
-		tonemap_ubo.white = environment_get_white(render_data.environment);
 		tonemap_ubo.tonemapper = int32_t(environment_get_tone_mapper(render_data.environment));
-
+		RendererEnvironmentStorage::TonemapParameters params = environment_get_tonemap_parameters(render_data.environment, false);
+		tonemap_ubo.tonemapper_params[0] = params.tonemapper_params[0];
+		tonemap_ubo.tonemapper_params[1] = params.tonemapper_params[1];
+		tonemap_ubo.tonemapper_params[2] = params.tonemapper_params[2];
+		tonemap_ubo.tonemapper_params[3] = params.tonemapper_params[3];
 		tonemap_ubo.brightness = environment_get_adjustments_brightness(render_data.environment);
 		tonemap_ubo.contrast = environment_get_adjustments_contrast(render_data.environment);
 		tonemap_ubo.saturation = environment_get_adjustments_saturation(render_data.environment);
@@ -2840,7 +2843,7 @@ void RasterizerSceneGLES3::_render_post_processing(const RenderDataGLES3 *p_rend
 		glow_hdr_bleed_threshold = environment_get_glow_hdr_bleed_threshold(p_render_data->environment);
 		glow_hdr_bleed_scale = environment_get_glow_hdr_bleed_scale(p_render_data->environment);
 		glow_hdr_luminance_cap = environment_get_glow_hdr_luminance_cap(p_render_data->environment);
-		srgb_white = environment_get_white(p_render_data->environment);
+		srgb_white = environment_get_white(p_render_data->environment, false);
 	}
 
 	if (glow_enabled) {

drivers/gles3/rasterizer_scene_gles3.h

@@ -449,14 +449,14 @@ private:
 
 		struct TonemapUBO {
 			float exposure = 1.0;
-			float white = 1.0;
 			int32_t tonemapper = 0;
 			int32_t pad = 0;
-
 			int32_t pad2 = 0;
+			float tonemapper_params[4] = { 0.0, 0.0, 0.0, 0.0 };
 			float brightness = 1.0;
 			float contrast = 1.0;
 			float saturation = 1.0;
+			int32_t pad3 = 0;
 		};
 		static_assert(sizeof(TonemapUBO) % 16 == 0, "Tonemap UBO size must be a multiple of 16 bytes");
 

drivers/gles3/shaders/effects/post.glsl

@@ -164,7 +164,7 @@ void main() {
 	color.rgb *= s4ao(uv_interp); // The USE_SSAO_X controls the number of samples.
 #endif
 
-	color.rgb = apply_tonemapping(color.rgb, white);
+	color.rgb = apply_tonemapping(color.rgb);
 
 #ifdef USE_BCS
 	// Apply brightness:

drivers/gles3/shaders/scene.glsl

@@ -2534,7 +2534,7 @@ void main() {
 	// Tonemap before writing as we are writing to an sRGB framebuffer
 	frag_color.rgb *= exposure;
 #ifdef APPLY_TONEMAPPING
-	frag_color.rgb = apply_tonemapping(frag_color.rgb, white);
+	frag_color.rgb = apply_tonemapping(frag_color.rgb);
 #endif
 	frag_color.rgb = linear_to_srgb(frag_color.rgb);
 
@@ -2806,7 +2806,7 @@ void main() {
 	// Tonemap before writing as we are writing to an sRGB framebuffer
 	additive_light_color *= exposure;
 #ifdef APPLY_TONEMAPPING
-	additive_light_color = apply_tonemapping(additive_light_color, white);
+	additive_light_color = apply_tonemapping(additive_light_color);
 #endif
 	additive_light_color = linear_to_srgb(additive_light_color);
 

drivers/gles3/shaders/sky.glsl

@@ -265,7 +265,7 @@ void main() {
 
 	color *= exposure;
 #ifdef APPLY_TONEMAPPING
-	color = apply_tonemapping(color, white);
+	color = apply_tonemapping(color);
 #endif
 	color = linear_to_srgb(color);
 

drivers/gles3/shaders/tonemap_inc.glsl

@@ -1,13 +1,13 @@
 layout(std140) uniform TonemapData { //ubo:0
 	float exposure;
-	float white;
 	int tonemapper;
 	int pad;
-
 	int pad2;
+	vec4 tonemapper_params;
 	float brightness;
 	float contrast;
 	float saturation;
+	int pad3;
 };
 
 // This expects 0-1 range input.
@@ -28,17 +28,18 @@ vec3 srgb_to_linear(vec3 color) {
 #ifdef APPLY_TONEMAPPING
 
 // Based on Reinhard's extended formula, see equation 4 in https://doi.org/cjbgrt
-vec3 tonemap_reinhard(vec3 color, float p_white) {
-	float white_squared = p_white * p_white;
+vec3 tonemap_reinhard(vec3 color) {
+	float white_squared = tonemapper_params.x;
 	vec3 white_squared_color = white_squared * color;
 	// Equivalent to color * (1 + color / white_squared) / (1 + color)
 	return (white_squared_color + color * color) / (white_squared_color + white_squared);
 }
 
-vec3 tonemap_filmic(vec3 color, float p_white) {
-	// exposure bias: input scale (color *= bias, white *= bias) to make the brightness consistent with other tonemappers
-	// also useful to scale the input to the range that the tonemapper is designed for (some require very high input values)
-	// has no effect on the curve's general shape or visual properties
+vec3 tonemap_filmic(vec3 color) {
+	// These constants must match the those in the C++ code that calculates the parameters.
+	// exposure_bias: Input scale (color *= bias, env->white *= bias) to make the brightness consistent with other tonemappers.
+	// Also useful to scale the input to the range that the tonemapper is designed for (some require very high input values).
+	// Has no effect on the curve's general shape or visual properties.
 	const float exposure_bias = 2.0f;
 	const float A = 0.22f * exposure_bias * exposure_bias; // bias baked into constants for performance
 	const float B = 0.30f * exposure_bias;
@@ -48,14 +49,14 @@ vec3 tonemap_filmic(vec3 color, float p_white) {
 	const float F = 0.30f;
 
 	vec3 color_tonemapped = ((color * (A * color + C * B) + D * E) / (color * (A * color + B) + D * F)) - E / F;
-	float p_white_tonemapped = ((p_white * (A * p_white + C * B) + D * E) / (p_white * (A * p_white + B) + D * F)) - E / F;
 
-	return color_tonemapped / p_white_tonemapped;
+	return color_tonemapped / tonemapper_params.x;
 }
 
 // Adapted from https://github.com/TheRealMJP/BakingLab/blob/master/BakingLab/ACES.hlsl
 // (MIT License).
-vec3 tonemap_aces(vec3 color, float p_white) {
+vec3 tonemap_aces(vec3 color) {
+	// These constants must match the those in the C++ code that calculates the parameters.
 	const float exposure_bias = 1.8f;
 	const float A = 0.0245786f;
 	const float B = 0.000090537f;
@@ -78,46 +79,46 @@ vec3 tonemap_aces(vec3 color, float p_white) {
 	vec3 color_tonemapped = (color * (color + A) - B) / (color * (C * color + D) + E);
 	color_tonemapped *= odt_to_rgb;
 
-	p_white *= exposure_bias;
-	float p_white_tonemapped = (p_white * (p_white + A) - B) / (p_white * (C * p_white + D) + E);
-
-	return color_tonemapped / p_white_tonemapped;
+	return color_tonemapped / tonemapper_params.x;
 }
 
-// Polynomial approximation of EaryChow's AgX sigmoid curve.
-// x must be within the range [0.0, 1.0]
-vec3 agx_contrast_approx(vec3 x) {
-	// Generated with Excel trendline
-	// Input data: Generated using python sigmoid with EaryChow's configuration and 57 steps
-	// Additional padding values were added to give correct intersections at 0.0 and 1.0
-	// 6th order, intercept of 0.0 to remove an operation and ensure intersection at 0.0
-	vec3 x2 = x * x;
-	vec3 x4 = x2 * x2;
-	return 0.021 * x + 4.0111 * x2 - 25.682 * x2 * x + 70.359 * x4 - 74.778 * x4 * x + 27.069 * x4 * x2;
+// allenwp tonemapping curve; developed for use in the Godot game engine.
+// Source and details: https://allenwp.com/blog/2025/05/29/allenwp-tonemapping-curve/
+// Input must be a non-negative linear scene value.
+vec3 allenwp_curve(vec3 x) {
+	const float output_max_value = 1.0; // SDR always has an output_max_value of 1.0
+
+	// These constants must match the those in the C++ code that calculates the parameters.
+	// 18% "middle gray" is perceptually 50% of the brightness of reference white.
+	const float awp_crossover_point = 0.18;
+	// When output_max_value and/or awp_crossover_point are no longer constant,
+	// awp_shoulder_max can be calculated on the CPU and passed in as tonemap_e.
+	const float awp_shoulder_max = output_max_value - awp_crossover_point;
+
+	float awp_contrast = tonemapper_params.x;
+	float awp_toe_a = tonemapper_params.y;
+	float awp_slope = tonemapper_params.z;
+	float awp_w = tonemapper_params.w;
+
+	// Reinhard-like shoulder:
+	vec3 s = x - awp_crossover_point;
+	vec3 slope_s = awp_slope * s;
+	s = slope_s * (1.0 + s / awp_w) / (1.0 + (slope_s / awp_shoulder_max));
+	s += awp_crossover_point;
+
+	// Sigmoid power function toe:
+	vec3 t = pow(x, vec3(awp_contrast));
+	t = t / (t + awp_toe_a);
+
+	return mix(s, t, lessThan(x, vec3(awp_crossover_point)));
 }
 
 // This is an approximation and simplification of EaryChow's AgX implementation that is used by Blender.
 // This code is based off of the script that generates the AgX_Base_sRGB.cube LUT that Blender uses.
 // Source: https://github.com/EaryChow/AgX_LUT_Gen/blob/main/AgXBasesRGB.py
+// Colorspace transformation source: https://www.colour-science.org:8010/apps/rgb_colourspace_transformation_matrix
 vec3 tonemap_agx(vec3 color) {
-	// Combined linear sRGB to linear Rec 2020 and Blender AgX inset matrices:
-	const mat3 srgb_to_rec2020_agx_inset_matrix = mat3(
-			0.54490813676363087053, 0.14044005884001287035, 0.088827411851915368603,
-			0.37377945959812267119, 0.75410959864013760045, 0.17887712465043811023,
-			0.081384976686407536266, 0.10543358536857773485, 0.73224999956948382528);
-
-	// Combined inverse AgX outset matrix and linear Rec 2020 to linear sRGB matrices.
-	const mat3 agx_outset_rec2020_to_srgb_matrix = mat3(
-			1.9645509602733325934, -0.29932243390911083839, -0.16436833806080403409,
-			-0.85585845117807513559, 1.3264510741502356555, -0.23822464068860595117,
-			-0.10886710826831608324, -0.027084020983874825605, 1.402665347143271889);
-
-	// LOG2_MIN      = -10.0
-	// LOG2_MAX      =  +6.5
-	// MIDDLE_GRAY   =  0.18
-	const float min_ev = -12.4739311883324; // log2(pow(2, LOG2_MIN) * MIDDLE_GRAY)
-	const float max_ev = 4.02606881166759; // log2(pow(2, LOG2_MAX) * MIDDLE_GRAY)
-
+	// Input color should be non-negative!
 	// Large negative values in one channel and large positive values in other
 	// channels can result in a colour that appears darker and more saturated than
 	// desired after passing it through the inset matrix. For this reason, it is
@@ -125,31 +126,43 @@ vec3 tonemap_agx(vec3 color) {
 	// This is done before the Rec. 2020 transform to allow the Rec. 2020
 	// transform to be combined with the AgX inset matrix. This results in a loss
 	// of color information that could be correctly interpreted within the
-	// Rec. 2020 color space as positive RGB values, but it is less common for Godot
-	// to provide this function with negative sRGB values and therefore not worth
+	// Rec. 2020 color space as positive RGB values, but is often not worth
 	// the performance cost of an additional matrix multiplication.
-	// A value of 2e-10 intentionally introduces insignificant error to prevent
-	// log2(0.0) after the inset matrix is applied; color will be >= 1e-10 after
-	// the matrix transform.
-	color = max(color, 2e-10);
-
-	// Do AGX in rec2020 to match Blender and then apply inset matrix.
-	color = srgb_to_rec2020_agx_inset_matrix * color;
-
-	// Log2 space encoding.
-	// Must be clamped because agx_contrast_approx may not work
-	// well with values outside of the range [0.0, 1.0]
-	color = clamp(log2(color), min_ev, max_ev);
-	color = (color - min_ev) / (max_ev - min_ev);
-
-	// Apply sigmoid function approximation.
-	color = agx_contrast_approx(color);
-
-	// Convert back to linear before applying outset matrix.
-	color = pow(color, vec3(2.4));
-
-	// Apply outset to make the result more chroma-laden and then go back to linear sRGB.
-	color = agx_outset_rec2020_to_srgb_matrix * color;
+	//
+	// Additionally, this AgX configuration was created subjectively based on
+	// output appearance in the Rec. 709 color gamut, so it is possible that these
+	// matrices will not perform well with non-Rec. 709 output (more testing with
+	// future wide-gamut displays is be needed).
+	// See this comment from the author on the decisions made to create the matrices:
+	// https://github.com/godotengine/godot-proposals/issues/12317#issuecomment-2835824250
+
+	// Combined Rec. 709 to Rec. 2020 and Blender AgX inset matrices:
+	const mat3 rec709_to_rec2020_agx_inset_matrix = mat3(
+			0.544814746488245, 0.140416948464053, 0.0888104196149096,
+			0.373787398372697, 0.754137554567394, 0.178871756420858,
+			0.0813978551390581, 0.105445496968552, 0.732317823964232);
+
+	// Combined inverse AgX outset matrix and Rec. 2020 to Rec. 709 matrices.
+	const mat3 agx_outset_rec2020_to_rec709_matrix = mat3(
+			1.96488741169489, -0.299313364904742, -0.164352742528393,
+			-0.855988495690215, 1.32639796461980, -0.238183969428088,
+			-0.108898916004672, -0.0270845997150571, 1.40253671195648);
+
+	const float output_max_value = 1.0; // SDR always has an output_max_value of 1.0
+
+	// Apply inset matrix.
+	color = rec709_to_rec2020_agx_inset_matrix * color;
+
+	// Use the allenwp tonemapping curve to match the Blender AgX curve while
+	// providing stability across all variable dyanimc range (SDR, HDR, EDR).
+	color = allenwp_curve(color);
+
+	// Clipping to output_max_value is required to address a cyan colour that occurs
+	// with very bright inputs.
+	color = min(vec3(output_max_value), color);
+
+	// Apply outset to make the result more chroma-laden and then go back to Rec. 709.
+	color = agx_outset_rec2020_to_rec709_matrix * color;
 
 	// Blender's lusRGB.compensate_low_side is too complex for this shader, so
 	// simply return the color, even if it has negative components. These negative
@@ -163,17 +176,21 @@ vec3 tonemap_agx(vec3 color) {
 #define TONEMAPPER_ACES 3
 #define TONEMAPPER_AGX 4
 
-vec3 apply_tonemapping(vec3 color, float p_white) { // inputs are LINEAR
-	// Ensure color values passed to tonemappers are positive.
-	// They can be negative in the case of negative lights, which leads to undesired behavior.
+vec3 apply_tonemapping(vec3 color) { // inputs are LINEAR
 	if (tonemapper == TONEMAPPER_LINEAR) {
 		return color;
-	} else if (tonemapper == TONEMAPPER_REINHARD) {
-		return tonemap_reinhard(max(vec3(0.0f), color), p_white);
+	}
+
+	// Ensure color values passed to tonemappers are positive.
+	// They can be negative in the case of negative lights, which leads to undesired behavior.
+	color = max(vec3(0.0), color);
+
+	if (tonemapper == TONEMAPPER_REINHARD) {
+		return tonemap_reinhard(color);
 	} else if (tonemapper == TONEMAPPER_FILMIC) {
-		return tonemap_filmic(max(vec3(0.0f), color), p_white);
+		return tonemap_filmic(color);
 	} else if (tonemapper == TONEMAPPER_ACES) {
-		return tonemap_aces(max(vec3(0.0f), color), p_white);
+		return tonemap_aces(color);
 	} else { // TONEMAPPER_AGX
 		return tonemap_agx(color);
 	}

scene/resources/environment.cpp

@@ -227,12 +227,30 @@ float Environment::get_tonemap_white() const {
 	return tonemap_white;
 }
 
+void Environment::set_tonemap_agx_white(float p_white) {
+	tonemap_agx_white = p_white;
+	_update_tonemap();
+}
+
+float Environment::get_tonemap_agx_white() const {
+	return tonemap_agx_white;
+}
+
+void Environment::set_tonemap_agx_contrast(float p_agx_contrast) {
+	tonemap_agx_contrast = p_agx_contrast;
+	RS::get_singleton()->environment_set_tonemap_agx_contrast(environment, p_agx_contrast);
+}
+
+float Environment::get_tonemap_agx_contrast() const {
+	return tonemap_agx_contrast;
+}
+
 void Environment::_update_tonemap() {
 	RS::get_singleton()->environment_set_tonemap(
 			environment,
 			RS::EnvironmentToneMapper(tone_mapper),
 			tonemap_exposure,
-			tonemap_white);
+			tone_mapper == TONE_MAPPER_AGX ? tonemap_agx_white : tonemap_white);
 }
 
 // SSR
@@ -1116,7 +1134,14 @@ void Environment::_validate_property(PropertyInfo &p_property) const {
 	}
 
 	if (p_property.name == "tonemap_white" && (tone_mapper == TONE_MAPPER_LINEAR || tone_mapper == TONE_MAPPER_AGX)) {
-		// Whitepoint adjustment is not available with AgX or linear as it's hardcoded there.
+		p_property.usage = PROPERTY_USAGE_NO_EDITOR;
+	}
+
+	if (p_property.name == "tonemap_agx_white" && tone_mapper != TONE_MAPPER_AGX) {
+		p_property.usage = PROPERTY_USAGE_NO_EDITOR;
+	}
+
+	if (p_property.name == "tonemap_agx_contrast" && tone_mapper != TONE_MAPPER_AGX) {
 		p_property.usage = PROPERTY_USAGE_NO_EDITOR;
 	}
 
@@ -1252,11 +1277,17 @@ void Environment::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_tonemap_exposure"), &Environment::get_tonemap_exposure);
 	ClassDB::bind_method(D_METHOD("set_tonemap_white", "white"), &Environment::set_tonemap_white);
 	ClassDB::bind_method(D_METHOD("get_tonemap_white"), &Environment::get_tonemap_white);
+	ClassDB::bind_method(D_METHOD("set_tonemap_agx_white", "white"), &Environment::set_tonemap_agx_white);
+	ClassDB::bind_method(D_METHOD("get_tonemap_agx_white"), &Environment::get_tonemap_agx_white);
+	ClassDB::bind_method(D_METHOD("set_tonemap_agx_contrast", "contrast"), &Environment::set_tonemap_agx_contrast);
+	ClassDB::bind_method(D_METHOD("get_tonemap_agx_contrast"), &Environment::get_tonemap_agx_contrast);
 
 	ADD_GROUP("Tonemap", "tonemap_");
 	ADD_PROPERTY(PropertyInfo(Variant::INT, "tonemap_mode", PROPERTY_HINT_ENUM, "Linear,Reinhard,Filmic,ACES,AgX"), "set_tonemapper", "get_tonemapper");
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "tonemap_exposure", PROPERTY_HINT_RANGE, "0,4,0.01,or_greater"), "set_tonemap_exposure", "get_tonemap_exposure");
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "tonemap_white", PROPERTY_HINT_RANGE, "1,16,0.01,or_greater"), "set_tonemap_white", "get_tonemap_white");
+	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "tonemap_agx_white", PROPERTY_HINT_RANGE, "2,16.5,0.01,or_greater"), "set_tonemap_agx_white", "get_tonemap_agx_white");
+	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "tonemap_agx_contrast", PROPERTY_HINT_RANGE, "1.0,2.0,0.01,or_greater"), "set_tonemap_agx_contrast", "get_tonemap_agx_contrast");
 
 	// SSR
 

scene/resources/environment.h

@@ -115,6 +115,8 @@ private:
 	ToneMapper tone_mapper = TONE_MAPPER_LINEAR;
 	float tonemap_exposure = 1.0;
 	float tonemap_white = 1.0;
+	float tonemap_agx_white = 16.29; // Default to Blender's AgX white.
+	float tonemap_agx_contrast = 1.25; // Default to approximately Blender's AgX contrast.
 	void _update_tonemap();
 
 	// SSR
@@ -271,6 +273,10 @@ public:
 	float get_tonemap_exposure() const;
 	void set_tonemap_white(float p_white);
 	float get_tonemap_white() const;
+	void set_tonemap_agx_white(float p_white);
+	float get_tonemap_agx_white() const;
+	void set_tonemap_agx_contrast(float p_agx_contrast);
+	float get_tonemap_agx_contrast() const;
 
 	// SSR
 	void set_ssr_enabled(bool p_enabled);

servers/rendering/renderer_rd/effects/tone_mapper.cpp

@@ -147,6 +147,10 @@ void ToneMapper::tonemapper(RID p_source_color, RID p_dst_framebuffer, const Ton
 	}
 
 	tonemap.push_constant.tonemapper = p_settings.tonemap_mode;
+	tonemap.push_constant.tonemapper_params[0] = p_settings.tonemapper_params[0];
+	tonemap.push_constant.tonemapper_params[1] = p_settings.tonemapper_params[1];
+	tonemap.push_constant.tonemapper_params[2] = p_settings.tonemapper_params[2];
+	tonemap.push_constant.tonemapper_params[3] = p_settings.tonemapper_params[3];
 	tonemap.push_constant.flags |= p_settings.use_auto_exposure ? TONEMAP_FLAG_USE_AUTO_EXPOSURE : 0;
 	tonemap.push_constant.exposure = p_settings.exposure;
 	tonemap.push_constant.white = p_settings.white;
@@ -237,6 +241,11 @@ void ToneMapper::tonemapper_mobile(RID p_source_color, RID p_dst_framebuffer, co
 	tonemap_mobile.push_constant.white = p_settings.white;
 	tonemap_mobile.push_constant.luminance_multiplier = p_settings.luminance_multiplier;
 
+	tonemap_mobile.push_constant.tonemapper_params[0] = p_settings.tonemapper_params[0];
+	tonemap_mobile.push_constant.tonemapper_params[1] = p_settings.tonemapper_params[1];
+	tonemap_mobile.push_constant.tonemapper_params[2] = p_settings.tonemapper_params[2];
+	tonemap_mobile.push_constant.tonemapper_params[3] = p_settings.tonemapper_params[3];
+
 	uint32_t spec_constant = 0;
 	spec_constant |= p_settings.use_bcs ? TONEMAP_MOBILE_FLAG_USE_BCS : 0;
 	spec_constant |= p_settings.use_glow ? TONEMAP_MOBILE_FLAG_USE_GLOW : 0;
@@ -324,6 +333,11 @@ void ToneMapper::tonemapper_subpass(RD::DrawListID p_subpass_draw_list, RID p_so
 	tonemap_mobile.push_constant.white = p_settings.white;
 	tonemap_mobile.push_constant.luminance_multiplier = p_settings.luminance_multiplier;
 
+	tonemap_mobile.push_constant.tonemapper_params[0] = p_settings.tonemapper_params[0];
+	tonemap_mobile.push_constant.tonemapper_params[1] = p_settings.tonemapper_params[1];
+	tonemap_mobile.push_constant.tonemapper_params[2] = p_settings.tonemapper_params[2];
+	tonemap_mobile.push_constant.tonemapper_params[3] = p_settings.tonemapper_params[3];
+
 	uint32_t spec_constant = TONEMAP_MOBILE_ADRENO_BUG;
 	spec_constant |= p_settings.use_bcs ? TONEMAP_MOBILE_FLAG_USE_BCS : 0;
 	//spec_constant |= p_settings.use_glow ? TONEMAP_MOBILE_FLAG_USE_GLOW : 0;

servers/rendering/renderer_rd/effects/tone_mapper.h

@@ -122,6 +122,8 @@ private:
 		float white; //  4 - 88
 		float auto_exposure_scale; //  4 - 92
 		float luminance_multiplier; //  4 - 96
+
+		float tonemapper_params[4]; //  16 - 112
 	};
 
 	struct TonemapPushConstantMobile {
@@ -135,6 +137,8 @@ private:
 		float glow_map_strength; //  4 - 40
 		float exposure; //  4 - 44
 		float white; //  4 - 48
+
+		float tonemapper_params[4]; //  16 - 64
 	};
 
 	/* tonemap actually writes to a framebuffer, which is
@@ -171,6 +175,7 @@ public:
 		RID glow_map;
 
 		RS::EnvironmentToneMapper tonemap_mode = RS::ENV_TONE_MAPPER_LINEAR;
+		float tonemapper_params[4] = { 0.0, 0.0, 0.0, 0.0 };
 		float exposure = 1.0;
 		float white = 1.0;
 

servers/rendering/renderer_rd/renderer_scene_render_rd.cpp

@@ -722,8 +722,19 @@ void RendererSceneRenderRD::_render_buffers_post_process_and_tonemap(const Rende
 		tonemap.texture_size = Vector2i(color_size.x, color_size.y);
 
 		if (p_render_data->environment.is_valid()) {
+			// When we are using RGB10A2 render buffer format, our scene
+			// is limited to a maximum of 2.0. In this case we should limit
+			// the max white of tonemappers, specifically AgX which defaults
+			// to a high white value.
+			bool limit_agx_white = rb->get_base_data_format() == RD::DATA_FORMAT_A2B10G10R10_UNORM_PACK32;
+
 			tonemap.tonemap_mode = environment_get_tone_mapper(p_render_data->environment);
-			tonemap.white = environment_get_white(p_render_data->environment);
+			RendererEnvironmentStorage::TonemapParameters params = environment_get_tonemap_parameters(p_render_data->environment, limit_agx_white);
+			tonemap.tonemapper_params[0] = params.tonemapper_params[0];
+			tonemap.tonemapper_params[1] = params.tonemapper_params[1];
+			tonemap.tonemapper_params[2] = params.tonemapper_params[2];
+			tonemap.tonemapper_params[3] = params.tonemapper_params[3];
+			tonemap.white = environment_get_white(p_render_data->environment, limit_agx_white);
 			tonemap.exposure = environment_get_exposure(p_render_data->environment);
 		}
 
@@ -882,9 +893,20 @@ void RendererSceneRenderRD::_post_process_subpass(RID p_source_texture, RID p_fr
 	RendererRD::ToneMapper::TonemapSettings tonemap;
 
 	if (p_render_data->environment.is_valid()) {
+		// When we are using RGB10A2 render buffer format, our scene
+		// is limited to a maximum of 2.0. In this case we should limit
+		// the max white of tonemappers, specifically AgX which defaults
+		// to a high white value.
+		bool limit_agx_white = rb->get_base_data_format() == RD::DATA_FORMAT_A2B10G10R10_UNORM_PACK32;
+
 		tonemap.tonemap_mode = environment_get_tone_mapper(p_render_data->environment);
+		RendererEnvironmentStorage::TonemapParameters params = environment_get_tonemap_parameters(p_render_data->environment, limit_agx_white);
+		tonemap.tonemapper_params[0] = params.tonemapper_params[0];
+		tonemap.tonemapper_params[1] = params.tonemapper_params[1];
+		tonemap.tonemapper_params[2] = params.tonemapper_params[2];
+		tonemap.tonemapper_params[3] = params.tonemapper_params[3];
 		tonemap.exposure = environment_get_exposure(p_render_data->environment);
-		tonemap.white = environment_get_white(p_render_data->environment);
+		tonemap.white = environment_get_white(p_render_data->environment, limit_agx_white);
 	}
 
 	// We don't support glow or auto exposure here, if they are needed, don't use subpasses!

servers/rendering/renderer_rd/shaders/effects/tonemap.glsl

@@ -82,23 +82,26 @@ layout(push_constant, std430) uniform Params {
 	float white;
 	float auto_exposure_scale;
 	float luminance_multiplier;
+
+	vec4 tonemapper_params;
 }
 params;
 
 layout(location = 0) out vec4 frag_color;
 
 // Based on Reinhard's extended formula, see equation 4 in https://doi.org/cjbgrt
-vec3 tonemap_reinhard(vec3 color, float white) {
-	float white_squared = white * white;
+vec3 tonemap_reinhard(vec3 color) {
+	float white_squared = params.tonemapper_params.x;
 	vec3 white_squared_color = white_squared * color;
 	// Equivalent to color * (1 + color / white_squared) / (1 + color)
 	return (white_squared_color + color * color) / (white_squared_color + white_squared);
 }
 
-vec3 tonemap_filmic(vec3 color, float white) {
-	// exposure bias: input scale (color *= bias, white *= bias) to make the brightness consistent with other tonemappers
-	// also useful to scale the input to the range that the tonemapper is designed for (some require very high input values)
-	// has no effect on the curve's general shape or visual properties
+vec3 tonemap_filmic(vec3 color) {
+	// These constants must match the those in the C++ code that calculates the parameters.
+	// exposure_bias: Input scale (color *= bias, env->white *= bias) to make the brightness consistent with other tonemappers.
+	// Also useful to scale the input to the range that the tonemapper is designed for (some require very high input values).
+	// Has no effect on the curve's general shape or visual properties.
 	const float exposure_bias = 2.0f;
 	const float A = 0.22f * exposure_bias * exposure_bias; // bias baked into constants for performance
 	const float B = 0.30f * exposure_bias;
@@ -108,14 +111,14 @@ vec3 tonemap_filmic(vec3 color, float white) {
 	const float F = 0.30f;
 
 	vec3 color_tonemapped = ((color * (A * color + C * B) + D * E) / (color * (A * color + B) + D * F)) - E / F;
-	float white_tonemapped = ((white * (A * white + C * B) + D * E) / (white * (A * white + B) + D * F)) - E / F;
 
-	return color_tonemapped / white_tonemapped;
+	return color_tonemapped / params.tonemapper_params.x;
 }
 
 // Adapted from https://github.com/TheRealMJP/BakingLab/blob/master/BakingLab/ACES.hlsl
 // (MIT License).
-vec3 tonemap_aces(vec3 color, float white) {
+vec3 tonemap_aces(vec3 color) {
+	// These constants must match the those in the C++ code that calculates the parameters.
 	const float exposure_bias = 1.8f;
 	const float A = 0.0245786f;
 	const float B = 0.000090537f;
@@ -138,46 +141,46 @@ vec3 tonemap_aces(vec3 color, float white) {
 	vec3 color_tonemapped = (color * (color + A) - B) / (color * (C * color + D) + E);
 	color_tonemapped *= odt_to_rgb;
 
-	white *= exposure_bias;
-	float white_tonemapped = (white * (white + A) - B) / (white * (C * white + D) + E);
-
-	return color_tonemapped / white_tonemapped;
+	return color_tonemapped / params.tonemapper_params.x;
 }
 
-// Polynomial approximation of EaryChow's AgX sigmoid curve.
-// x must be within the range [0.0, 1.0]
-vec3 agx_contrast_approx(vec3 x) {
-	// Generated with Excel trendline
-	// Input data: Generated using python sigmoid with EaryChow's configuration and 57 steps
-	// Additional padding values were added to give correct intersections at 0.0 and 1.0
-	// 6th order, intercept of 0.0 to remove an operation and ensure intersection at 0.0
-	vec3 x2 = x * x;
-	vec3 x4 = x2 * x2;
-	return 0.021 * x + 4.0111 * x2 - 25.682 * x2 * x + 70.359 * x4 - 74.778 * x4 * x + 27.069 * x4 * x2;
+// allenwp tonemapping curve; developed for use in the Godot game engine.
+// Source and details: https://allenwp.com/blog/2025/05/29/allenwp-tonemapping-curve/
+// Input must be a non-negative linear scene value.
+vec3 allenwp_curve(vec3 x) {
+	const float output_max_value = 1.0; // SDR always has an output_max_value of 1.0
+
+	// These constants must match the those in the C++ code that calculates the parameters.
+	// 18% "middle gray" is perceptually 50% of the brightness of reference white.
+	const float awp_crossover_point = 0.18;
+	// When output_max_value and/or awp_crossover_point are no longer constant,
+	// awp_shoulder_max can be calculated on the CPU and passed in as params.tonemap_e.
+	const float awp_shoulder_max = output_max_value - awp_crossover_point;
+
+	float awp_contrast = params.tonemapper_params.x;
+	float awp_toe_a = params.tonemapper_params.y;
+	float awp_slope = params.tonemapper_params.z;
+	float awp_w = params.tonemapper_params.w;
+
+	// Reinhard-like shoulder:
+	vec3 s = x - awp_crossover_point;
+	vec3 slope_s = awp_slope * s;
+	s = slope_s * (1.0 + s / awp_w) / (1.0 + (slope_s / awp_shoulder_max));
+	s += awp_crossover_point;
+
+	// Sigmoid power function toe:
+	vec3 t = pow(x, vec3(awp_contrast));
+	t = t / (t + awp_toe_a);
+
+	return mix(s, t, lessThan(x, vec3(awp_crossover_point)));
 }
 
 // This is an approximation and simplification of EaryChow's AgX implementation that is used by Blender.
 // This code is based off of the script that generates the AgX_Base_sRGB.cube LUT that Blender uses.
 // Source: https://github.com/EaryChow/AgX_LUT_Gen/blob/main/AgXBasesRGB.py
+// Colorspace transformation source: https://www.colour-science.org:8010/apps/rgb_colourspace_transformation_matrix
 vec3 tonemap_agx(vec3 color) {
-	// Combined linear sRGB to linear Rec 2020 and Blender AgX inset matrices:
-	const mat3 srgb_to_rec2020_agx_inset_matrix = mat3(
-			0.54490813676363087053, 0.14044005884001287035, 0.088827411851915368603,
-			0.37377945959812267119, 0.75410959864013760045, 0.17887712465043811023,
-			0.081384976686407536266, 0.10543358536857773485, 0.73224999956948382528);
-
-	// Combined inverse AgX outset matrix and linear Rec 2020 to linear sRGB matrices.
-	const mat3 agx_outset_rec2020_to_srgb_matrix = mat3(
-			1.9645509602733325934, -0.29932243390911083839, -0.16436833806080403409,
-			-0.85585845117807513559, 1.3264510741502356555, -0.23822464068860595117,
-			-0.10886710826831608324, -0.027084020983874825605, 1.402665347143271889);
-
-	// LOG2_MIN      = -10.0
-	// LOG2_MAX      =  +6.5
-	// MIDDLE_GRAY   =  0.18
-	const float min_ev = -12.4739311883324; // log2(pow(2, LOG2_MIN) * MIDDLE_GRAY)
-	const float max_ev = 4.02606881166759; // log2(pow(2, LOG2_MAX) * MIDDLE_GRAY)
-
+	// Input color should be non-negative!
 	// Large negative values in one channel and large positive values in other
 	// channels can result in a colour that appears darker and more saturated than
 	// desired after passing it through the inset matrix. For this reason, it is
@@ -185,31 +188,43 @@ vec3 tonemap_agx(vec3 color) {
 	// This is done before the Rec. 2020 transform to allow the Rec. 2020
 	// transform to be combined with the AgX inset matrix. This results in a loss
 	// of color information that could be correctly interpreted within the
-	// Rec. 2020 color space as positive RGB values, but it is less common for Godot
-	// to provide this function with negative sRGB values and therefore not worth
+	// Rec. 2020 color space as positive RGB values, but is often not worth
 	// the performance cost of an additional matrix multiplication.
-	// A value of 2e-10 intentionally introduces insignificant error to prevent
-	// log2(0.0) after the inset matrix is applied; color will be >= 1e-10 after
-	// the matrix transform.
-	color = max(color, 2e-10);
-
-	// Do AGX in rec2020 to match Blender and then apply inset matrix.
-	color = srgb_to_rec2020_agx_inset_matrix * color;
-
-	// Log2 space encoding.
-	// Must be clamped because agx_contrast_approx may not work
-	// well with values outside of the range [0.0, 1.0]
-	color = clamp(log2(color), min_ev, max_ev);
-	color = (color - min_ev) / (max_ev - min_ev);
-
-	// Apply sigmoid function approximation.
-	color = agx_contrast_approx(color);
-
-	// Convert back to linear before applying outset matrix.
-	color = pow(color, vec3(2.4));
-
-	// Apply outset to make the result more chroma-laden and then go back to linear sRGB.
-	color = agx_outset_rec2020_to_srgb_matrix * color;
+	//
+	// Additionally, this AgX configuration was created subjectively based on
+	// output appearance in the Rec. 709 color gamut, so it is possible that these
+	// matrices will not perform well with non-Rec. 709 output (more testing with
+	// future wide-gamut displays is be needed).
+	// See this comment from the author on the decisions made to create the matrices:
+	// https://github.com/godotengine/godot-proposals/issues/12317#issuecomment-2835824250
+
+	// Combined Rec. 709 to Rec. 2020 and Blender AgX inset matrices:
+	const mat3 rec709_to_rec2020_agx_inset_matrix = mat3(
+			0.544814746488245, 0.140416948464053, 0.0888104196149096,
+			0.373787398372697, 0.754137554567394, 0.178871756420858,
+			0.0813978551390581, 0.105445496968552, 0.732317823964232);
+
+	// Combined inverse AgX outset matrix and Rec. 2020 to Rec. 709 matrices.
+	const mat3 agx_outset_rec2020_to_rec709_matrix = mat3(
+			1.96488741169489, -0.299313364904742, -0.164352742528393,
+			-0.855988495690215, 1.32639796461980, -0.238183969428088,
+			-0.108898916004672, -0.0270845997150571, 1.40253671195648);
+
+	const float output_max_value = 1.0; // SDR always has an output_max_value of 1.0
+
+	// Apply inset matrix.
+	color = rec709_to_rec2020_agx_inset_matrix * color;
+
+	// Use the allenwp tonemapping curve to match the Blender AgX curve while
+	// providing stability across all variable dyanimc range (SDR, HDR, EDR).
+	color = allenwp_curve(color);
+
+	// Clipping to output_max_value is required to address a cyan colour that occurs
+	// with very bright inputs.
+	color = min(vec3(output_max_value), color);
+
+	// Apply outset to make the result more chroma-laden and then go back to Rec. 709.
+	color = agx_outset_rec2020_to_rec709_matrix * color;
 
 	// Blender's lusRGB.compensate_low_side is too complex for this shader, so
 	// simply return the color, even if it has negative components. These negative
@@ -233,17 +248,21 @@ vec3 srgb_to_linear(vec3 color) {
 #define TONEMAPPER_ACES 3
 #define TONEMAPPER_AGX 4
 
-vec3 apply_tonemapping(vec3 color, float white) { // inputs are LINEAR
-	// Ensure color values passed to tonemappers are positive.
-	// They can be negative in the case of negative lights, which leads to undesired behavior.
+vec3 apply_tonemapping(vec3 color) { // inputs are LINEAR
 	if (params.tonemapper == TONEMAPPER_LINEAR) {
 		return color;
-	} else if (params.tonemapper == TONEMAPPER_REINHARD) {
-		return tonemap_reinhard(max(vec3(0.0f), color), white);
+	}
+
+	// Ensure color values passed to tonemappers are positive.
+	// They can be negative in the case of negative lights, which leads to undesired behavior.
+	color = max(vec3(0.0), color);
+
+	if (params.tonemapper == TONEMAPPER_REINHARD) {
+		return tonemap_reinhard(color);
 	} else if (params.tonemapper == TONEMAPPER_FILMIC) {
-		return tonemap_filmic(max(vec3(0.0f), color), white);
+		return tonemap_filmic(color);
 	} else if (params.tonemapper == TONEMAPPER_ACES) {
-		return tonemap_aces(max(vec3(0.0f), color), white);
+		return tonemap_aces(color);
 	} else { // TONEMAPPER_AGX
 		return tonemap_agx(color);
 	}
@@ -876,7 +895,7 @@ void main() {
 
 	// Tonemap to lower dynamic range.
 
-	color.rgb = apply_tonemapping(color.rgb, params.white);
+	color.rgb = apply_tonemapping(color.rgb);
 
 	// Post-tonemap glow.
 
@@ -888,7 +907,7 @@ void main() {
 		if (params.glow_map_strength > 0.001) {
 			glow = mix(glow, texture(glow_map, uv_interp).rgb * glow, params.glow_map_strength);
 		}
-		glow = apply_tonemapping(glow, params.white);
+		glow = apply_tonemapping(glow);
 		color.rgb = apply_glow(color.rgb, glow, params.white);
 	}
 

servers/rendering/renderer_rd/shaders/effects/tonemap_mobile.glsl

@@ -89,23 +89,26 @@ layout(push_constant, std430) uniform Params {
 	float glow_map_strength;
 	float exposure;
 	float white;
+
+	vec4 tonemapper_params;
 }
 params;
 
 layout(location = 0) out vec4 frag_color;
 
 // Based on Reinhard's extended formula, see equation 4 in https://doi.org/cjbgrt
-vec3 tonemap_reinhard(vec3 color, float white) {
-	float white_squared = white * white;
+vec3 tonemap_reinhard(vec3 color) {
+	float white_squared = params.tonemapper_params.x;
 	vec3 white_squared_color = white_squared * color;
 	// Equivalent to color * (1 + color / white_squared) / (1 + color)
 	return (white_squared_color + color * color) / (white_squared_color + white_squared);
 }
 
-vec3 tonemap_filmic(vec3 color, float white) {
-	// exposure bias: input scale (color *= bias, white *= bias) to make the brightness consistent with other tonemappers
-	// also useful to scale the input to the range that the tonemapper is designed for (some require very high input values)
-	// has no effect on the curve's general shape or visual properties
+vec3 tonemap_filmic(vec3 color) {
+	// These constants must match the those in the C++ code that calculates the parameters.
+	// exposure_bias: Input scale (color *= bias, env->white *= bias) to make the brightness consistent with other tonemappers.
+	// Also useful to scale the input to the range that the tonemapper is designed for (some require very high input values).
+	// Has no effect on the curve's general shape or visual properties.
 	const float exposure_bias = 2.0f;
 	const float A = 0.22f * exposure_bias * exposure_bias; // bias baked into constants for performance
 	const float B = 0.30f * exposure_bias;
@@ -115,14 +118,14 @@ vec3 tonemap_filmic(vec3 color, float white) {
 	const float F = 0.30f;
 
 	vec3 color_tonemapped = ((color * (A * color + C * B) + D * E) / (color * (A * color + B) + D * F)) - E / F;
-	float white_tonemapped = ((white * (A * white + C * B) + D * E) / (white * (A * white + B) + D * F)) - E / F;
 
-	return color_tonemapped / white_tonemapped;
+	return color_tonemapped / params.tonemapper_params.x;
 }
 
 // Adapted from https://github.com/TheRealMJP/BakingLab/blob/master/BakingLab/ACES.hlsl
 // (MIT License).
-vec3 tonemap_aces(vec3 color, float white) {
+vec3 tonemap_aces(vec3 color) {
+	// These constants must match the those in the C++ code that calculates the parameters.
 	const float exposure_bias = 1.8f;
 	const float A = 0.0245786f;
 	const float B = 0.000090537f;
@@ -145,46 +148,46 @@ vec3 tonemap_aces(vec3 color, float white) {
 	vec3 color_tonemapped = (color * (color + A) - B) / (color * (C * color + D) + E);
 	color_tonemapped *= odt_to_rgb;
 
-	white *= exposure_bias;
-	float white_tonemapped = (white * (white + A) - B) / (white * (C * white + D) + E);
-
-	return color_tonemapped / white_tonemapped;
+	return color_tonemapped / params.tonemapper_params.x;
 }
 
-// Polynomial approximation of EaryChow's AgX sigmoid curve.
-// x must be within the range [0.0, 1.0]
-vec3 agx_contrast_approx(vec3 x) {
-	// Generated with Excel trendline
-	// Input data: Generated using python sigmoid with EaryChow's configuration and 57 steps
-	// Additional padding values were added to give correct intersections at 0.0 and 1.0
-	// 6th order, intercept of 0.0 to remove an operation and ensure intersection at 0.0
-	vec3 x2 = x * x;
-	vec3 x4 = x2 * x2;
-	return 0.021 * x + 4.0111 * x2 - 25.682 * x2 * x + 70.359 * x4 - 74.778 * x4 * x + 27.069 * x4 * x2;
+// allenwp tonemapping curve; developed for use in the Godot game engine.
+// Source and details: https://allenwp.com/blog/2025/05/29/allenwp-tonemapping-curve/
+// Input must be a non-negative linear scene value.
+vec3 allenwp_curve(vec3 x) {
+	const float output_max_value = 1.0; // SDR always has an output_max_value of 1.0
+
+	// These constants must match the those in the C++ code that calculates the parameters.
+	// 18% "middle gray" is perceptually 50% of the brightness of reference white.
+	const float awp_crossover_point = 0.18;
+	// When output_max_value and/or awp_crossover_point are no longer constant,
+	// awp_shoulder_max can be calculated on the CPU and passed in as params.tonemap_e.
+	const float awp_shoulder_max = output_max_value - awp_crossover_point;
+
+	float awp_contrast = params.tonemapper_params.x;
+	float awp_toe_a = params.tonemapper_params.y;
+	float awp_slope = params.tonemapper_params.z;
+	float awp_w = params.tonemapper_params.w;
+
+	// Reinhard-like shoulder:
+	vec3 s = x - awp_crossover_point;
+	vec3 slope_s = awp_slope * s;
+	s = slope_s * (1.0 + s / awp_w) / (1.0 + (slope_s / awp_shoulder_max));
+	s += awp_crossover_point;
+
+	// Sigmoid power function toe:
+	vec3 t = pow(x, vec3(awp_contrast));
+	t = t / (t + awp_toe_a);
+
+	return mix(s, t, lessThan(x, vec3(awp_crossover_point)));
 }
 
 // This is an approximation and simplification of EaryChow's AgX implementation that is used by Blender.
 // This code is based off of the script that generates the AgX_Base_sRGB.cube LUT that Blender uses.
 // Source: https://github.com/EaryChow/AgX_LUT_Gen/blob/main/AgXBasesRGB.py
+// Colorspace transformation source: https://www.colour-science.org:8010/apps/rgb_colourspace_transformation_matrix
 vec3 tonemap_agx(vec3 color) {
-	// Combined linear sRGB to linear Rec 2020 and Blender AgX inset matrices:
-	const mat3 srgb_to_rec2020_agx_inset_matrix = mat3(
-			0.54490813676363087053, 0.14044005884001287035, 0.088827411851915368603,
-			0.37377945959812267119, 0.75410959864013760045, 0.17887712465043811023,
-			0.081384976686407536266, 0.10543358536857773485, 0.73224999956948382528);
-
-	// Combined inverse AgX outset matrix and linear Rec 2020 to linear sRGB matrices.
-	const mat3 agx_outset_rec2020_to_srgb_matrix = mat3(
-			1.9645509602733325934, -0.29932243390911083839, -0.16436833806080403409,
-			-0.85585845117807513559, 1.3264510741502356555, -0.23822464068860595117,
-			-0.10886710826831608324, -0.027084020983874825605, 1.402665347143271889);
-
-	// LOG2_MIN      = -10.0
-	// LOG2_MAX      =  +6.5
-	// MIDDLE_GRAY   =  0.18
-	const float min_ev = -12.4739311883324; // log2(pow(2, LOG2_MIN) * MIDDLE_GRAY)
-	const float max_ev = 4.02606881166759; // log2(pow(2, LOG2_MAX) * MIDDLE_GRAY)
-
+	// Input color should be non-negative!
 	// Large negative values in one channel and large positive values in other
 	// channels can result in a colour that appears darker and more saturated than
 	// desired after passing it through the inset matrix. For this reason, it is
@@ -192,31 +195,43 @@ vec3 tonemap_agx(vec3 color) {
 	// This is done before the Rec. 2020 transform to allow the Rec. 2020
 	// transform to be combined with the AgX inset matrix. This results in a loss
 	// of color information that could be correctly interpreted within the
-	// Rec. 2020 color space as positive RGB values, but it is less common for Godot
-	// to provide this function with negative sRGB values and therefore not worth
+	// Rec. 2020 color space as positive RGB values, but is often not worth
 	// the performance cost of an additional matrix multiplication.
-	// A value of 2e-10 intentionally introduces insignificant error to prevent
-	// log2(0.0) after the inset matrix is applied; color will be >= 1e-10 after
-	// the matrix transform.
-	color = max(color, 2e-10);
-
-	// Do AGX in rec2020 to match Blender and then apply inset matrix.
-	color = srgb_to_rec2020_agx_inset_matrix * color;
-
-	// Log2 space encoding.
-	// Must be clamped because agx_contrast_approx may not work
-	// well with values outside of the range [0.0, 1.0]
-	color = clamp(log2(color), min_ev, max_ev);
-	color = (color - min_ev) / (max_ev - min_ev);
-
-	// Apply sigmoid function approximation.
-	color = agx_contrast_approx(color);
-
-	// Convert back to linear before applying outset matrix.
-	color = pow(color, vec3(2.4));
-
-	// Apply outset to make the result more chroma-laden and then go back to linear sRGB.
-	color = agx_outset_rec2020_to_srgb_matrix * color;
+	//
+	// Additionally, this AgX configuration was created subjectively based on
+	// output appearance in the Rec. 709 color gamut, so it is possible that these
+	// matrices will not perform well with non-Rec. 709 output (more testing with
+	// future wide-gamut displays is be needed).
+	// See this comment from the author on the decisions made to create the matrices:
+	// https://github.com/godotengine/godot-proposals/issues/12317#issuecomment-2835824250
+
+	// Combined Rec. 709 to Rec. 2020 and Blender AgX inset matrices:
+	const mat3 rec709_to_rec2020_agx_inset_matrix = mat3(
+			0.544814746488245, 0.140416948464053, 0.0888104196149096,
+			0.373787398372697, 0.754137554567394, 0.178871756420858,
+			0.0813978551390581, 0.105445496968552, 0.732317823964232);
+
+	// Combined inverse AgX outset matrix and Rec. 2020 to Rec. 709 matrices.
+	const mat3 agx_outset_rec2020_to_rec709_matrix = mat3(
+			1.96488741169489, -0.299313364904742, -0.164352742528393,
+			-0.855988495690215, 1.32639796461980, -0.238183969428088,
+			-0.108898916004672, -0.0270845997150571, 1.40253671195648);
+
+	const float output_max_value = 1.0; // SDR always has an output_max_value of 1.0
+
+	// Apply inset matrix.
+	color = rec709_to_rec2020_agx_inset_matrix * color;
+
+	// Use the allenwp tonemapping curve to match the Blender AgX curve while
+	// providing stability across all variable dyanimc range (SDR, HDR, EDR).
+	color = allenwp_curve(color);
+
+	// Clipping to output_max_value is required to address a cyan colour that occurs
+	// with very bright inputs.
+	color = min(vec3(output_max_value), color);
+
+	// Apply outset to make the result more chroma-laden and then go back to Rec. 709.
+	color = agx_outset_rec2020_to_rec709_matrix * color;
 
 	// Blender's lusRGB.compensate_low_side is too complex for this shader, so
 	// simply return the color, even if it has negative components. These negative
@@ -234,17 +249,21 @@ vec3 srgb_to_linear(vec3 color) {
 	return mix(pow((color.rgb + a) * (1.0f / (vec3(1.0f) + a)), vec3(2.4f)), color.rgb * (1.0f / 12.92f), lessThan(color.rgb, vec3(0.04045f)));
 }
 
-vec3 apply_tonemapping(vec3 color, float white) { // inputs are LINEAR
-	// Ensure color values passed to tonemappers are positive.
-	// They can be negative in the case of negative lights, which leads to undesired behavior.
+vec3 apply_tonemapping(vec3 color) { // inputs are LINEAR
 	if (tonemapper_linear) {
 		return color;
-	} else if (tonemapper_reinhard) {
-		return tonemap_reinhard(max(vec3(0.0f), color), white);
+	}
+
+	// Ensure color values passed to tonemappers are positive.
+	// They can be negative in the case of negative lights, which leads to undesired behavior.
+	color = max(vec3(0.0), color);
+
+	if (tonemapper_reinhard) {
+		return tonemap_reinhard(color);
 	} else if (tonemapper_filmic) {
-		return tonemap_filmic(max(vec3(0.0f), color), white);
+		return tonemap_filmic(color);
 	} else if (tonemapper_aces) {
-		return tonemap_aces(max(vec3(0.0f), color), white);
+		return tonemap_aces(color);
 	} else { // tonemapper_agx
 		return tonemap_agx(color);
 	}
@@ -748,7 +767,7 @@ void main() {
 
 	// Tonemap to lower dynamic range.
 
-	color.rgb = apply_tonemapping(color.rgb, params.white);
+	color.rgb = apply_tonemapping(color.rgb);
 
 #ifndef SUBPASS
 	// Post-tonemap glow.
@@ -761,7 +780,7 @@ void main() {
 		if (use_glow_map) {
 			glow = mix(glow, texture(glow_map, uv_interp).rgb * glow, params.glow_map_strength);
 		}
-		glow = apply_tonemapping(glow, params.white);
+		glow = apply_tonemapping(glow);
 		color.rgb = apply_glow(color.rgb, glow, params.white);
 	}
 #endif

servers/rendering/renderer_scene_cull.h

@@ -1240,9 +1240,10 @@ public:
 
 	// Tonemap
 	PASS4(environment_set_tonemap, RID, RS::EnvironmentToneMapper, float, float)
+	PASS2(environment_set_tonemap_agx_contrast, RID, float)
 	PASS1RC(RS::EnvironmentToneMapper, environment_get_tone_mapper, RID)
 	PASS1RC(float, environment_get_exposure, RID)
-	PASS1RC(float, environment_get_white, RID)
+	PASS2RC(float, environment_get_white, RID, bool)
 
 	// Fog
 	PASS11(environment_set_fog, RID, bool, const Color &, float, float, float, float, float, float, float, RS::EnvironmentFogMode)

servers/rendering/renderer_scene_render.cpp

@@ -373,8 +373,20 @@ float RendererSceneRender::environment_get_exposure(RID p_env) const {
 	return environment_storage.environment_get_exposure(p_env);
 }
 
-float RendererSceneRender::environment_get_white(RID p_env) const {
-	return environment_storage.environment_get_white(p_env);
+float RendererSceneRender::environment_get_white(RID p_env, bool p_limit_agx_white) const {
+	return environment_storage.environment_get_white(p_env, p_limit_agx_white);
+}
+
+void RendererSceneRender::environment_set_tonemap_agx_contrast(RID p_env, float p_agx_contrast) {
+	environment_storage.environment_set_tonemap_agx_contrast(p_env, p_agx_contrast);
+}
+
+float RendererSceneRender::environment_get_tonemap_agx_contrast(RID p_env) const {
+	return environment_storage.environment_get_tonemap_agx_contrast(p_env);
+}
+
+RendererEnvironmentStorage::TonemapParameters RendererSceneRender::environment_get_tonemap_parameters(RID p_env, bool p_limit_agx_white) const {
+	return environment_storage.environment_get_tonemap_parameters(p_env, p_limit_agx_white);
 }
 
 // Fog

servers/rendering/renderer_scene_render.h

@@ -137,7 +137,10 @@ public:
 	void environment_set_tonemap(RID p_env, RS::EnvironmentToneMapper p_tone_mapper, float p_exposure, float p_white);
 	RS::EnvironmentToneMapper environment_get_tone_mapper(RID p_env) const;
 	float environment_get_exposure(RID p_env) const;
-	float environment_get_white(RID p_env) const;
+	float environment_get_white(RID p_env, bool p_limit_agx_white) const;
+	void environment_set_tonemap_agx_contrast(RID p_env, float p_agx_contrast);
+	float environment_get_tonemap_agx_contrast(RID p_env) const;
+	RendererEnvironmentStorage::TonemapParameters environment_get_tonemap_parameters(RID p_env, bool p_limit_agx_white) const;
 
 	// Fog
 	void environment_set_fog(RID p_env, bool p_enable, const Color &p_light_color, float p_light_energy, float p_sun_scatter, float p_density, float p_height, float p_height_density, float p_aerial_perspective, float p_sky_affect, RS::EnvironmentFogMode p_mode);

servers/rendering/rendering_method.h

@@ -185,10 +185,11 @@ public:
 
 	// Tonemap
 	virtual void environment_set_tonemap(RID p_env, RS::EnvironmentToneMapper p_tone_mapper, float p_exposure, float p_white) = 0;
+	virtual void environment_set_tonemap_agx_contrast(RID p_env, float p_agx_contrast) = 0;
 
 	virtual RS::EnvironmentToneMapper environment_get_tone_mapper(RID p_env) const = 0;
 	virtual float environment_get_exposure(RID p_env) const = 0;
-	virtual float environment_get_white(RID p_env) const = 0;
+	virtual float environment_get_white(RID p_env, bool p_limit_agx_white) const = 0;
 
 	// Fog
 	virtual void environment_set_fog(RID p_env, bool p_enable, const Color &p_light_color, float p_light_energy, float p_sun_scatter, float p_density, float p_height, float p_height_density, float p_aerial_perspective, float p_sky_affect, RS::EnvironmentFogMode p_mode = RS::EnvironmentFogMode::ENV_FOG_MODE_EXPONENTIAL) = 0;

servers/rendering/rendering_server.cpp

@@ -3102,6 +3102,7 @@ void RenderingServer::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("environment_set_ambient_light", "env", "color", "ambient", "energy", "sky_contribution", "reflection_source"), &RenderingServer::environment_set_ambient_light, DEFVAL(RS::ENV_AMBIENT_SOURCE_BG), DEFVAL(1.0), DEFVAL(0.0), DEFVAL(RS::ENV_REFLECTION_SOURCE_BG));
 	ClassDB::bind_method(D_METHOD("environment_set_glow", "env", "enable", "levels", "intensity", "strength", "mix", "bloom_threshold", "blend_mode", "hdr_bleed_threshold", "hdr_bleed_scale", "hdr_luminance_cap", "glow_map_strength", "glow_map"), &RenderingServer::environment_set_glow);
 	ClassDB::bind_method(D_METHOD("environment_set_tonemap", "env", "tone_mapper", "exposure", "white"), &RenderingServer::environment_set_tonemap);
+	ClassDB::bind_method(D_METHOD("environment_set_tonemap_agx_contrast", "env", "agx_contrast"), &RenderingServer::environment_set_tonemap_agx_contrast);
 	ClassDB::bind_method(D_METHOD("environment_set_adjustment", "env", "enable", "brightness", "contrast", "saturation", "use_1d_color_correction", "color_correction"), &RenderingServer::environment_set_adjustment);
 	ClassDB::bind_method(D_METHOD("environment_set_ssr", "env", "enable", "max_steps", "fade_in", "fade_out", "depth_tolerance"), &RenderingServer::environment_set_ssr);
 	ClassDB::bind_method(D_METHOD("environment_set_ssao", "env", "enable", "radius", "intensity", "power", "detail", "horizon", "sharpness", "light_affect", "ao_channel_affect"), &RenderingServer::environment_set_ssao);

servers/rendering/rendering_server.h

@@ -1284,6 +1284,7 @@ public:
 	};
 
 	virtual void environment_set_tonemap(RID p_env, EnvironmentToneMapper p_tone_mapper, float p_exposure, float p_white) = 0;
+	virtual void environment_set_tonemap_agx_contrast(RID p_env, float p_agx_contrast) = 0;
 	virtual void environment_set_adjustment(RID p_env, bool p_enable, float p_brightness, float p_contrast, float p_saturation, bool p_use_1d_color_correction, RID p_color_correction) = 0;
 
 	virtual void environment_set_ssr(RID p_env, bool p_enable, int p_max_steps, float p_fade_in, float p_fade_out, float p_depth_tolerance) = 0;

servers/rendering/rendering_server_default.h

@@ -831,6 +831,7 @@ public:
 	FUNC1(environment_glow_set_use_bicubic_upscale, bool)
 
 	FUNC4(environment_set_tonemap, RID, EnvironmentToneMapper, float, float)
+	FUNC2(environment_set_tonemap_agx_contrast, RID, float)
 
 	FUNC7(environment_set_adjustment, RID, bool, float, float, float, bool, RID)
 

servers/rendering/storage/environment_storage.cpp

@@ -208,13 +208,7 @@ void RendererEnvironmentStorage::environment_set_tonemap(RID p_env, RS::Environm
 	ERR_FAIL_NULL(env);
 	env->exposure = p_exposure;
 	env->tone_mapper = p_tone_mapper;
-	if (p_tone_mapper == RS::ENV_TONE_MAPPER_LINEAR) {
-		env->white = 1.0; // With HDR output, this should be the output max value instead.
-	} else if (p_tone_mapper == RS::ENV_TONE_MAPPER_AGX) {
-		env->white = 16.29;
-	} else {
-		env->white = MAX(1.0, p_white); // Glow with screen blend mode does not work when white < 1.0.
-	}
+	env->white = p_white;
 }
 
 RS::EnvironmentToneMapper RendererEnvironmentStorage::environment_get_tone_mapper(RID p_env) const {
@@ -229,10 +223,124 @@ float RendererEnvironmentStorage::environment_get_exposure(RID p_env) const {
 	return env->exposure;
 }
 
-float RendererEnvironmentStorage::environment_get_white(RID p_env) const {
+float RendererEnvironmentStorage::environment_get_white(RID p_env, bool p_limit_agx_white) const {
 	Environment *env = environment_owner.get_or_null(p_env);
 	ERR_FAIL_NULL_V(env, 1.0);
-	return env->white;
+
+	const float output_max_value = 1.0; // SDR always has an output_max_value of 1.0.
+
+	// Glow with screen blend mode does not work when white < 1.0, so make sure
+	// it is at least 1.0 for all tonemappers:
+	if (env->tone_mapper == RS::ENV_TONE_MAPPER_LINEAR) {
+		return output_max_value;
+	} else if (env->tone_mapper == RS::ENV_TONE_MAPPER_FILMIC || env->tone_mapper == RS::ENV_TONE_MAPPER_ACES) {
+		// Filmic and ACES only support SDR; their white is stable regardless
+		// of output_max_value.
+		return MAX(1.0, env->white);
+	} else if (env->tone_mapper == RS::ENV_TONE_MAPPER_AGX) {
+		// AgX works best with a high white. 2.0 is the minimum required for
+		// good behavior with Mobile rendering method.
+		if (p_limit_agx_white) {
+			return 2.0;
+		} else {
+			float agx_white = MAX(2.0, env->white);
+			// Instead of constraining by matching the output_max_value, constrain
+			// by multiplying to ensure the desired non-uniform scaling behavior
+			// is maintained in the shoulder.
+			return agx_white * output_max_value;
+		}
+	} else { // Reinhard
+		// The Reinhard tonemapper is not designed to have a white parameter
+		// that is less than the output max value. This is especially important
+		// in the variable Extended Dynamic Range (EDR) paradigm where the
+		// output max value may change to be greater or less than the white
+		// parameter, depending on the available dynamic range.
+		return MAX(output_max_value, env->white);
+	}
+}
+
+void RendererEnvironmentStorage::environment_set_tonemap_agx_contrast(RID p_env, float p_agx_contrast) {
+	Environment *env = environment_owner.get_or_null(p_env);
+	ERR_FAIL_NULL(env);
+	env->tonemap_agx_contrast = p_agx_contrast;
+}
+
+float RendererEnvironmentStorage::environment_get_tonemap_agx_contrast(RID p_env) const {
+	Environment *env = environment_owner.get_or_null(p_env);
+	ERR_FAIL_NULL_V(env, 1.0);
+	return env->tonemap_agx_contrast;
+}
+
+RendererEnvironmentStorage::TonemapParameters RendererEnvironmentStorage::environment_get_tonemap_parameters(RID p_env, bool p_limit_agx_white) const {
+	Environment *env = environment_owner.get_or_null(p_env);
+	ERR_FAIL_NULL_V(env, TonemapParameters());
+
+	const float output_max_value = 1.0; // SDR always has an output_max_value of 1.0.
+
+	float white = environment_get_white(p_env, p_limit_agx_white);
+	TonemapParameters tonemap_parameters = TonemapParameters();
+
+	if (env->tone_mapper == RS::ENV_TONE_MAPPER_LINEAR) {
+		// Linear has no tonemapping parameters
+	} else if (env->tone_mapper == RS::ENV_TONE_MAPPER_REINHARD) {
+		tonemap_parameters.white_squared = white * white;
+	} else if (env->tone_mapper == RS::ENV_TONE_MAPPER_FILMIC) {
+		// These constants must match those in the shader code.
+		// exposure_bias: Input scale (color *= bias, white *= bias) to make the brightness consistent with other tonemappers
+		// also useful to scale the input to the range that the tonemapper is designed for (some require very high input values).
+		// Has no effect on the curve's general shape or visual properties.
+		const float exposure_bias = 2.0f;
+		const float A = 0.22f * exposure_bias * exposure_bias; // bias baked into constants for performance
+		const float B = 0.30f * exposure_bias;
+		const float C = 0.10f;
+		const float D = 0.20f;
+		const float E = 0.01f;
+		const float F = 0.30f;
+
+		tonemap_parameters.white_tonemapped = ((white * (A * white + C * B) + D * E) / (white * (A * white + B) + D * F)) - E / F;
+	} else if (env->tone_mapper == RS::ENV_TONE_MAPPER_ACES) {
+		// These constants must match those in the shader code.
+		const float exposure_bias = 1.8f;
+		const float A = 0.0245786f;
+		const float B = 0.000090537f;
+		const float C = 0.983729f;
+		const float D = 0.432951f;
+		const float E = 0.238081f;
+
+		white *= exposure_bias;
+		float white_tonemapped = (white * (white + A) - B) / (white * (C * white + D) + E);
+		tonemap_parameters.white_tonemapped = white_tonemapped;
+	} else if (env->tone_mapper == RS::ENV_TONE_MAPPER_AGX) {
+		// Calculate allenwp tonemapping curve parameters on the CPU to improve shader performance.
+		// Source and details: https://allenwp.com/blog/2025/05/29/allenwp-tonemapping-curve/
+
+		// These constants must match the those in the shader code.
+		// 18% "middle gray" is perceptually 50% of the brightness of reference white.
+		const float awp_crossover_point = 0.18;
+		// When output_max_value and/or awp_crossover_point are no longer constant, awp_shoulder_max can
+		// be calculated on the CPU and passed in as tonemap_parameters.tonemap_e.
+		const float awp_shoulder_max = output_max_value - awp_crossover_point;
+
+		float awp_high_clip = white;
+
+		// awp_toe_a is a solution generated by Mathematica that ensures intersection at awp_crossover_point.
+		float awp_toe_a = ((1.0 / awp_crossover_point) - 1.0) * pow(awp_crossover_point, env->tonemap_agx_contrast);
+		// Slope formula is simply the derivative of the toe function with an input of awp_crossover_point.
+		float awp_slope_denom = pow(awp_crossover_point, env->tonemap_agx_contrast) + awp_toe_a;
+		float awp_slope = (env->tonemap_agx_contrast * pow(awp_crossover_point, env->tonemap_agx_contrast - 1.0) * awp_toe_a) / (awp_slope_denom * awp_slope_denom);
+
+		float awp_w = awp_high_clip - awp_crossover_point;
+		awp_w = awp_w * awp_w;
+		awp_w = awp_w / awp_shoulder_max;
+		awp_w = awp_w * awp_slope;
+
+		tonemap_parameters.awp_contrast = env->tonemap_agx_contrast;
+		tonemap_parameters.awp_toe_a = awp_toe_a;
+		tonemap_parameters.awp_slope = awp_slope;
+		tonemap_parameters.awp_w = awp_w;
+	}
+
+	return tonemap_parameters;
 }
 
 // Fog

servers/rendering/storage/environment_storage.h

@@ -34,6 +34,30 @@
 #include "servers/rendering/rendering_server.h"
 
 class RendererEnvironmentStorage {
+public:
+	union TonemapParameters {
+		// Shader vec4:
+		float tonemapper_params[4];
+
+		// Reinhard:
+		struct {
+			float white_squared;
+		};
+
+		// Filmic and ACES:
+		struct {
+			float white_tonemapped;
+		};
+
+		// AgX:
+		struct {
+			float awp_contrast;
+			float awp_toe_a;
+			float awp_slope;
+			float awp_w;
+		};
+	};
+
 private:
 	static RendererEnvironmentStorage *singleton;
 
@@ -62,6 +86,7 @@ private:
 		RS::EnvironmentToneMapper tone_mapper;
 		float exposure = 1.0;
 		float white = 1.0;
+		float tonemap_agx_contrast = 1.25; // Default to approximately Blender's AgX contrast
 
 		// Fog
 		bool fog_enabled = false;
@@ -202,7 +227,10 @@ public:
 	void environment_set_tonemap(RID p_env, RS::EnvironmentToneMapper p_tone_mapper, float p_exposure, float p_white);
 	RS::EnvironmentToneMapper environment_get_tone_mapper(RID p_env) const;
 	float environment_get_exposure(RID p_env) const;
-	float environment_get_white(RID p_env) const;
+	float environment_get_white(RID p_env, bool p_limit_agx_white) const;
+	void environment_set_tonemap_agx_contrast(RID p_env, float p_agx_contrast);
+	float environment_get_tonemap_agx_contrast(RID p_env) const;
+	TonemapParameters environment_get_tonemap_parameters(RID p_env, bool p_limit_agx_white) const;
 
 	// Fog
 	void environment_set_fog(RID p_env, bool p_enable, const Color &p_light_color, float p_light_energy, float p_sun_scatter, float p_density, float p_height, float p_height_density, float p_aerial_perspective, float p_sky_affect, RS::EnvironmentFogMode p_mode);