Add AGX tone-mapping function

With "punchy" variant as well.

Author: jonathanhogg

docs/shaders.md

@@ -361,11 +361,12 @@ image (luminance > $0.5$).
 adjustments, Values less than 1 will lighten the output image and values
 greater than 1 will darken it.
 
-`tonemap=` [ `:reinhard` | `:aces` ]
+`tonemap=` [ `:reinhard` | `:aces` | `:agx` | `:agx_punchy` ]
 : If specified, then a tone-mapping function will be applied to map high
 dynamic range images into the $[0,1]$ range. The supported tone-mapping
-functions are: the Reinhard curve function, and a (close approximation of) the
-ACES filmic function. Default is no tone-mapping.
+functions are: the Reinhard curve function, a (close approximation of) the
+ACES filmic function and a (close approximation) of the AGX and AGX "Punchy"
+tone-mapping functions. Default is no tone-mapping.
 
 If `tonemap=:reinhard` then an additional attribute is supported:
 

src/flitter/render/window/glsl/color_functions.glsl

@@ -8,23 +8,64 @@ float srgb_luminance(vec3 c) {
     return dot(c, vec3(0.2126, 0.7152, 0.0722));
 }
 
-vec3 tonemap_reinhard(vec3 c, float whitepoint) {
-    vec3 cd = c / (1.0 + c);
+vec3 tonemap_reinhard(vec3 color, float whitepoint) {
+    vec3 cd = color / (1.0 + color);
     if (whitepoint > 1.0) {
-        cd *= (1.0 + c / (whitepoint * whitepoint));
+        cd *= (1.0 + color / (whitepoint * whitepoint));
     }
     return cd;
 }
 
+// This function based on https://github.com/TheRealMJP/BakingLab/blob/master/BakingLab/ACES.hlsl
+//
 vec3 tonemap_aces(vec3 color)
 {
-    // This function based on https://github.com/TheRealMJP/BakingLab/blob/master/BakingLab/ACES.hlsl
-    //
     color = mat3(0.59719, 0.076, 0.0284, 0.35458, 0.90834, 0.13383, 0.04823, 0.01566, 0.83777) * color;
     color = (color * (color + 0.0245786) - 0.000090537) / (color * (0.983729 * color + 0.4329510) + 0.238081);
     return mat3(1.60475, -0.10208, -0.00327, -0.53108, 1.10813, -0.07276, -0.07367, -0.00605, 1.07602) * color;
 }
 
+// These functions based on https://iolite-engine.com/blog_posts/minimal_agx_implementation
+//
+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;
+}
+
+vec3 agx(vec3 color) {
+    const mat3 agx_mat = mat3(0.842479062253094, 0.0423282422610123, 0.0423756549057051,
+                              0.0784335999999992, 0.878468636469772, 0.0784336,
+                              0.0792237451477643, 0.0791661274605434, 0.879142973793104);
+	const float min_ev = -12.47393;
+	const float max_ev = 4.026069;
+    color = agx_mat * color;
+    color = (clamp(log2(color), min_ev, max_ev) - min_ev) / (max_ev - min_ev);
+    return agx_default_contrast_approx(color);
+}
+
+vec3 agx_eotf(vec3 color) {
+    const mat3 agx_mat_inv = mat3(1.19687900512017, -0.0528968517574562, -0.0529716355144438,
+                                  -0.0980208811401368, 1.15190312990417, -0.0980434501171241,
+                                  -0.0990297440797205, -0.0989611768448433, 1.15107367264116);
+    return agx_mat_inv * color;
+}
+
+vec3 tonemap_agx(vec3 color)
+{
+    color = agx(color);
+    return agx_eotf(color);
+}
+
+vec3 tonemap_agx_punchy(vec3 color)
+{
+    color = agx(color);
+    float luma = srgb_luminance(color);
+    color = pow(color, vec3(1.35));
+    color = luma + 1.4 * (color - luma);
+    return agx_eotf(color);
+}
+
 vec3 rgb_to_hsv(vec3 color) {
     vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
     vec4 p = mix(vec4(color.bg, K.wz), vec4(color.gb, K.xy), step(color.b, color.g));
@@ -35,7 +76,7 @@ vec3 rgb_to_hsv(vec3 color) {
 }
 
 vec3 hsv_to_rgb(vec3 color) {
-    vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
+    const vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
     vec3 p = abs(fract(color.xxx + K.xyz) * 6.0 - K.www);
     return color.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), color.y);
 }

src/flitter/render/window/shaders.py

@@ -43,15 +43,15 @@ def render(self, node, references, **kwargs):
 
 class Adjust(Shader):
     DEFAULT_FRAGMENT_SOURCE = TemplateLoader.get_template('adjust.frag')
-    TONEMAP_FUNCTIONS = {'reinhard', 'aces'}
+    TONEMAP_FUNCTIONS = {'reinhard', 'aces', 'agx', 'agx_punchy'}
 
     def render(self, node, references, **kwargs):
         tonemap = node.get('tonemap', 1, str)
         if tonemap not in self.TONEMAP_FUNCTIONS:
             tonemap = None
         super().render(node, references, exposure=0, contrast=1, brightness=0, shadows=0, highlights=0,
                        hue=0, saturation=1, color_matrix=(1, 0, 0, 0, 1, 0, 0, 0, 1),
-                       gamma=1, tonemap_function=tonemap, **kwargs)
+                       gamma=1, tonemap_function=tonemap, whitepoint=0, **kwargs)
 
 
 class Blur(Shader):