Add AgX tonemapper option to Environment

Technical implementation notes:

- Moved linearization step to before the outset matrix is applied and
  changed polynomial contrast curve approximation.
  - This does *not* implement Blender's chroma rotation to address hue shift.
    This hue rotation was found to have a significant performance impact.
- Improved performance by combining the AgX outset matrix with the Rec 2020 matrix.

Co-authored-by: Allen Pestaluky <allenpestaluky@gmail.com>
Co-authored-by: Clay John <claynjohn@gmail.com>

doc/classes/Environment.xml

@@ -321,6 +321,7 @@
 		</member>
 		<member name="tonemap_white" type="float" setter="set_tonemap_white" getter="get_tonemap_white" default="1.0">
 			The white reference value for tonemapping (also called "whitepoint"). Higher values can make highlights look less blown out, and will also slightly darken the whole scene as a result. Only effective if the [member tonemap_mode] isn't set to [constant TONE_MAPPER_LINEAR]. See also [member tonemap_exposure].
+			[b]Note:[/b] [member tonemap_white] is ignored when using [constant TONE_MAPPER_AGX].
 		</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.
@@ -425,6 +426,9 @@
 			Use the Academy Color Encoding System tonemapper. ACES is slightly more expensive than other options, but it handles bright lighting in a more realistic fashion by desaturating it as it becomes brighter. ACES typically has a more contrasted output compared to [constant TONE_MAPPER_REINHARDT] and [constant TONE_MAPPER_FILMIC].
 			[b]Note:[/b] This tonemapping operator is called "ACES Fitted" in Godot 3.x.
 		</constant>
+		<constant name="TONE_MAPPER_AGX" value="4" enum="ToneMapper">
+			Use the AgX tonemapper. AgX is slightly more expensive than other options, but it handles bright lighting in a more realistic fashion by desaturating it as it becomes brighter. AgX is less likely to darken parts of the scene compared to [constant TONE_MAPPER_ACES] and can match the overall scene brightness of [constant TONE_MAPPER_FILMIC] more closely.
+		</constant>
 		<constant name="GLOW_BLEND_MODE_ADDITIVE" value="0" enum="GlowBlendMode">
 			Additive glow blending mode. Mostly used for particles, glows (bloom), lens flare, bright sources.
 		</constant>

doc/classes/RenderingServer.xml

@@ -5365,6 +5365,9 @@
 			Use the Academy Color Encoding System tonemapper. ACES is slightly more expensive than other options, but it handles bright lighting in a more realistic fashion by desaturating it as it becomes brighter. ACES typically has a more contrasted output compared to [constant ENV_TONE_MAPPER_REINHARD] and [constant ENV_TONE_MAPPER_FILMIC].
 			[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">
+			Use the AgX tonemapper. AgX is slightly more expensive than other options, but it handles bright lighting in a more realistic fashion by desaturating it as it becomes brighter. AgX is less likely to darken parts of the scene compared to [constant ENV_TONE_MAPPER_ACES], and can match [constant ENV_TONE_MAPPER_FILMIC] more closely.
+		</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.
 		</constant>

drivers/gles3/shaders/tonemap_inc.glsl

@@ -27,6 +27,14 @@ 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 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)
@@ -76,18 +84,79 @@ vec3 tonemap_aces(vec3 color, float p_white) {
 	return color_tonemapped / p_white_tonemapped;
 }
 
-// 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 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);
+// Mean error^2: 3.6705141e-06
+vec3 agx_default_contrast_approx(vec3 x) {
+	vec3 x2 = x * x;
+	vec3 x4 = x2 * x2;
+
+	return +15.5 * x4 * x2 - 40.14 * x4 * x + 31.96 * x4 - 6.868 * x2 * x + 0.4298 * x2 + 0.1191 * x - 0.00232;
+}
+
+const mat3 LINEAR_REC2020_TO_LINEAR_SRGB = mat3(
+		vec3(1.6605, -0.1246, -0.0182),
+		vec3(-0.5876, 1.1329, -0.1006),
+		vec3(-0.0728, -0.0083, 1.1187));
+
+const mat3 LINEAR_SRGB_TO_LINEAR_REC2020 = mat3(
+		vec3(0.6274, 0.0691, 0.0164),
+		vec3(0.3293, 0.9195, 0.0880),
+		vec3(0.0433, 0.0113, 0.8956));
+
+vec3 agx(vec3 val) {
+	const mat3 agx_mat = mat3(
+			0.856627153315983, 0.137318972929847, 0.11189821299995,
+			0.0951212405381588, 0.761241990602591, 0.0767994186031903,
+			0.0482516061458583, 0.101439036467562, 0.811302368396859);
+
+	const float min_ev = -12.47393;
+	const float max_ev = 4.026069;
+
+	// Do AGX in rec2020 to match Blender.
+	val = LINEAR_SRGB_TO_LINEAR_REC2020 * val;
+	val = max(val, vec3(0.0));
+
+	// Input transform (inset).
+	val = agx_mat * val;
+
+	// Log2 space encoding.
+	val = max(val, 1e-10);
+	val = clamp(log2(val), min_ev, max_ev);
+	val = (val - min_ev) / (max_ev - min_ev);
+
+	// Apply sigmoid function approximation.
+	val = agx_default_contrast_approx(val);
+
+	return val;
+}
+
+vec3 agx_eotf(vec3 val) {
+	const mat3 agx_mat_out = mat3(
+			1.1271005818144368, -0.1413297634984383, -0.1413297634984383,
+			-0.1106066430966032, 1.1578237022162720, -0.1106066430966029,
+			-0.0164939387178346, -0.0164939387178343, 1.2519364065950405);
+
+	val = agx_mat_out * val;
+
+	// Convert back to linear so we can escape Rec 2020.
+	val = pow(val, vec3(2.4));
+
+	val = LINEAR_REC2020_TO_LINEAR_SRGB * val;
+
+	return val;
+}
+
+// Adapted from https://iolite-engine.com/blog_posts/minimal_agx_implementation
+vec3 tonemap_agx(vec3 color) {
+	color = agx(color);
+	color = agx_eotf(color);
+	return color;
 }
 
 #define TONEMAPPER_LINEAR 0
 #define TONEMAPPER_REINHARD 1
 #define TONEMAPPER_FILMIC 2
 #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.
@@ -98,8 +167,10 @@ vec3 apply_tonemapping(vec3 color, float p_white) { // inputs are LINEAR
 		return tonemap_reinhard(max(vec3(0.0f), color), p_white);
 	} else if (tonemapper == TONEMAPPER_FILMIC) {
 		return tonemap_filmic(max(vec3(0.0f), color), p_white);
-	} else { // TONEMAPPER_ACES
+	} else if (tonemapper == TONEMAPPER_ACES) {
 		return tonemap_aces(max(vec3(0.0f), color), p_white);
+	} else { // TONEMAPPER_AGX
+		return tonemap_agx(color);
 	}
 }
 

scene/resources/environment.cpp

@@ -1120,7 +1120,8 @@ void Environment::_validate_property(PropertyInfo &p_property) const {
 		}
 	}
 
-	if (p_property.name == "tonemap_white" && tone_mapper == TONE_MAPPER_LINEAR) {
+	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;
 	}
 
@@ -1275,7 +1276,7 @@ void Environment::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("get_tonemap_white"), &Environment::get_tonemap_white);
 
 	ADD_GROUP("Tonemap", "tonemap_");
-	ADD_PROPERTY(PropertyInfo(Variant::INT, "tonemap_mode", PROPERTY_HINT_ENUM, "Linear,Reinhard,Filmic,ACES"), "set_tonemapper", "get_tonemapper");
+	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, "0,16,0.01"), "set_tonemap_exposure", "get_tonemap_exposure");
 	ADD_PROPERTY(PropertyInfo(Variant::FLOAT, "tonemap_white", PROPERTY_HINT_RANGE, "0,16,0.01"), "set_tonemap_white", "get_tonemap_white");
 
@@ -1580,6 +1581,7 @@ void Environment::_bind_methods() {
 	BIND_ENUM_CONSTANT(TONE_MAPPER_REINHARDT);
 	BIND_ENUM_CONSTANT(TONE_MAPPER_FILMIC);
 	BIND_ENUM_CONSTANT(TONE_MAPPER_ACES);
+	BIND_ENUM_CONSTANT(TONE_MAPPER_AGX);
 
 	BIND_ENUM_CONSTANT(GLOW_BLEND_MODE_ADDITIVE);
 	BIND_ENUM_CONSTANT(GLOW_BLEND_MODE_SCREEN);

scene/resources/environment.h

@@ -67,6 +67,7 @@ class Environment : public Resource {
 		TONE_MAPPER_REINHARDT,
 		TONE_MAPPER_FILMIC,
 		TONE_MAPPER_ACES,
+		TONE_MAPPER_AGX,
 	};
 
 	enum SDFGIYScale {

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

@@ -207,6 +207,14 @@ vec4 texture2D_bicubic(sampler2D tex, vec2 uv, int p_lod) {
 
 #endif // !USE_GLOW_FILTER_BICUBIC
 
+// 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 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)
@@ -256,12 +264,74 @@ vec3 tonemap_aces(vec3 color, float white) {
 	return color_tonemapped / white_tonemapped;
 }
 
-// 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 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);
+// Polynomial approximation of EaryChow's AgX sigmoid curve.
+// In Blender's implementation, numbers could go a little bit over 1.0, so it's best to ensure
+// this behaves the same as Blender's with values up to 1.1. Input values cannot be lower than 0.
+vec3 agx_default_contrast_approx(vec3 x) {
+	// Generated with Excel trendline
+	// Input data: Generated using python sigmoid with EaryChow's configuration and 57 steps
+	// 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 -0.20687445 * x + 6.80888933 * x2 - 37.60519607 * x2 * x + 93.32681938 * x4 - 95.2780858 * x4 * x + 33.96372259 * x4 * x2;
+}
+
+const mat3 LINEAR_SRGB_TO_LINEAR_REC2020 = mat3(
+		vec3(0.6274, 0.0691, 0.0164),
+		vec3(0.3293, 0.9195, 0.0880),
+		vec3(0.0433, 0.0113, 0.8956));
+
+// 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
+vec3 tonemap_agx(vec3 color) {
+	const mat3 agx_inset_matrix = mat3(
+			0.856627153315983, 0.137318972929847, 0.11189821299995,
+			0.0951212405381588, 0.761241990602591, 0.0767994186031903,
+			0.0482516061458583, 0.101439036467562, 0.811302368396859);
+
+	// Combined inverse AgX outset matrix and linear Rec 2020 to linear sRGB matrices.
+	const mat3 agx_outset_rec2020_to_srgb_matrix = mat3(
+			1.9648846919172409596, -0.29937618452442253746, -0.16440106280678278299,
+			-0.85594737466675834968, 1.3263980951083531115, -0.23819967517076844919,
+			-0.10883731725048386702, -0.02702191058393112346, 1.4025007379775505276);
+
+	// 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)
+
+	// Do AGX in rec2020 to match Blender.
+	color = LINEAR_SRGB_TO_LINEAR_REC2020 * color;
+
+	// Preventing negative values is required for the AgX inset matrix to behave correctly.
+	// This could also be done before the Rec. 2020 transform, allowing the transform to
+	// be combined with the AgX inset matrix, but doing this causes a loss of color information
+	// that could be correctly interpreted within the Rec. 2020 color space.
+	color = max(color, vec3(0.0));
+
+	color = agx_inset_matrix * color;
+
+	// Log2 space encoding.
+	color = max(color, 1e-10); // Prevent log2(0.0). Possibly unnecessary.
+	// Must be clamped because agx_blender_default_contrast_approx may not work well with values above 1.0
+	color = clamp(log2(color), min_ev, max_ev);
+	color = (color - min_ev) / (max_ev - min_ev);
+
+	// Apply sigmoid function approximation.
+	color = agx_default_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;
+
+	// Simply hard clip instead of Blender's complex lusRGB.compensate_low_side.
+	color = max(color, vec3(0.0));
+
+	return color;
 }
 
 vec3 linear_to_srgb(vec3 color) {
@@ -275,6 +345,7 @@ vec3 linear_to_srgb(vec3 color) {
 #define TONEMAPPER_REINHARD 1
 #define TONEMAPPER_FILMIC 2
 #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.
@@ -285,8 +356,10 @@ vec3 apply_tonemapping(vec3 color, float white) { // inputs are LINEAR
 		return tonemap_reinhard(max(vec3(0.0f), color), white);
 	} else if (params.tonemapper == TONEMAPPER_FILMIC) {
 		return tonemap_filmic(max(vec3(0.0f), color), white);
-	} else { // TONEMAPPER_ACES
+	} else if (params.tonemapper == TONEMAPPER_ACES) {
 		return tonemap_aces(max(vec3(0.0f), color), white);
+	} else { // TONEMAPPER_AGX
+		return tonemap_agx(color);
 	}
 }
 

servers/rendering_server.cpp

@@ -3072,6 +3072,7 @@ void RenderingServer::_bind_methods() {
 	BIND_ENUM_CONSTANT(ENV_TONE_MAPPER_REINHARD);
 	BIND_ENUM_CONSTANT(ENV_TONE_MAPPER_FILMIC);
 	BIND_ENUM_CONSTANT(ENV_TONE_MAPPER_ACES);
+	BIND_ENUM_CONSTANT(ENV_TONE_MAPPER_AGX);
 
 	BIND_ENUM_CONSTANT(ENV_SSR_ROUGHNESS_QUALITY_DISABLED);
 	BIND_ENUM_CONSTANT(ENV_SSR_ROUGHNESS_QUALITY_LOW);

servers/rendering_server.h

@@ -1243,7 +1243,8 @@ class RenderingServer : public Object {
 		ENV_TONE_MAPPER_LINEAR,
 		ENV_TONE_MAPPER_REINHARD,
 		ENV_TONE_MAPPER_FILMIC,
-		ENV_TONE_MAPPER_ACES
+		ENV_TONE_MAPPER_ACES,
+		ENV_TONE_MAPPER_AGX,
 	};
 
 	virtual void environment_set_tonemap(RID p_env, EnvironmentToneMapper p_tone_mapper, float p_exposure, float p_white) = 0;