Add hue and saturation controls on !adjust

docs/shaders.md

@@ -326,6 +326,16 @@ range around 0.5.
 double the color value of each pixel, an adjustment of `-1` will half the value
 of each pixel. Default is `0`.
 
+`hue=` *DELTA*
+: Specifies a positive or negative hue adjustment in the useful range
+$(-0.5,0.5)$. All colors will be rotated around the standard HSV hue cylinder
+by this amount.
+
+`saturation=` *MULTIPLIER*
+: Specifies an amount to multiple the saturation of each pixel by. Values
+less than `1` will desaturate the image and values greater than `1` will
+over-saturate it. A value of `0` will convert the image to grayscale.
+
 `shadows=` *STOPS*
 : Specifies an exposure adjustment to apply to the darker parts of the input
 image (luminance < $0.25$).
@@ -358,6 +368,7 @@ The `!adjust` filter works in the following order:
 
 - un-premultiply alpha
 - apply `color_matrix`
+- apply `hue` and `saturation`
 - apply `exposure`
 - apply `brightness` and `contrast`
 - apply `shadows` and `highlights`

src/flitter/render/window/glsl/adjust.frag

@@ -9,6 +9,8 @@ uniform float contrast;
 uniform float brightness;
 uniform float shadows;
 uniform float highlights;
+uniform float hue;
+uniform float saturation;
 uniform mat3 color_matrix;
 % if tonemap_function == 'reinhard':
 uniform float whitepoint;
@@ -30,8 +32,10 @@ void main() {
 %         endif
 %     endfor
     vec3 col = merged.a > 0.0 ? merged.rgb / merged.a : vec3(0.0);
-    col = color_matrix * col;
-    col = filter_adjust(col, exposure, contrast, brightness, shadows, highlights);
+    vec3 hsv = rgb_to_hsv(color_matrix * col);
+    hsv.x += hue;
+    hsv.y *= saturation;
+    col = filter_adjust(hsv_to_rgb(hsv), exposure, contrast, brightness, shadows, highlights);
     col = max(vec3(0.0), col);
 %     if gamma != 1:
     col = pow(col, vec3(gamma));

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

@@ -24,3 +24,18 @@ vec3 tonemap_aces(vec3 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;
 }
+
+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));
+    vec4 q = mix(vec4(p.xyw, color.r), vec4(color.r, p.yzx), step(p.x, color.r));
+    float d = q.x - min(q.w, q.y);
+    const float e = 1.0e-10;
+    return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), d / (q.x + e), q.x);
+}
+
+vec3 hsv_to_rgb(vec3 color) {
+    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

@@ -50,7 +50,7 @@ def render(self, node, references, **kwargs):
         if tonemap not in self.TONEMAP_FUNCTIONS:
             tonemap = None
         super().render(node, references, exposure=0, contrast=1, brightness=0, shadows=0, highlights=0,
-                       color_matrix=(1, 0, 0, 0, 1, 0, 0, 0, 1),
+                       hue=0, saturation=1, color_matrix=(1, 0, 0, 0, 1, 0, 0, 0, 1),
                        gamma=1, tonemap_function=tonemap, **kwargs)