Add Gambatte color GLSL port by RiskyJumps

handheld/shaders/color/gbc-gambatte-color.slang

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+#version 450
+
+/*
+   Gambatte Color
+   A Slang/GLSL port of the color correction option on Gambatte emulator
+   Ported by: RiskyJumps
+   License: Public domain
+*/
+
+/*
+OPTIONS:
+
+INT_OPS (default: Disabled)
+It's supposed to be more "accurate" but it's a waste. Not recommended
+*/
+//#define INT_OPS
+
+/*
+SIMULATE_INT (default: Disabled)
+Only meaningful if INT_OPS is disabled. It truncates floats. Then
+again, it's supposed to be more "accurate" but it looks just
+too similar. It's still a waste. Not recommended.
+*/
+//#define SIMULATE_INT
+
+layout(std140, set = 0, binding = 0) uniform UBO
+{
+     mat4 MVP;
+     vec4 OutputSize;
+     vec4 OriginalSize;
+     vec4 SourceSize;
+} global;
+
+#pragma stage vertex
+layout(location = 0) in vec4 Position;
+layout(location = 1) in vec2 TexCoord;
+layout(location = 0) out vec2 vTexCoord;
+
+void main()
+{
+     gl_Position = global.MVP * Position;
+     vTexCoord = TexCoord;
+}
+
+#pragma stage fragment
+layout(location = 0) in vec2 vTexCoord;
+layout(location = 0) out vec4 FragColor;
+layout(set = 0, binding = 2) uniform sampler2D Source;
+
+void main()
+{
+     vec4 color = texture(Source, vTexCoord);
+
+#ifdef INT_OPS
+     color.rgb *= 255.0;
+
+     int r = (int)color.r;
+     int g = (int)color.g;
+     int b = (int)color.b;
+
+     int R = (r * 13 + g * 2 + b) >> 4;
+     int G = (g *  3 + b) >> 2;
+     int B = (r *  3 + g * 2 + b * 11) >> 4;
+
+     color.rgb = vec3((float)R, (float)G, (float)B);
+     color.rgb /= 255.0;
+
+     FragColor = color;
+     return;
+
+#else
+     mat3 color_correction = mat3(
+          13.0,  2.0,   1.0,
+           0.0,  3.0,   1.0,
+           3.0,  2.0,  11.0
+     );
+
+     mat3 scale = mat3(
+          1.0/16.0,      0.0,       0.0,
+               0.0,  1.0/4.0,       0.0,
+               0.0,      0.0,  1.0/16.0
+     );
+
+     color_correction *= scale;
+
+#ifdef SIMULATE_INT
+     color.rgb *= 255.0;
+     color.rgb = floor(color.rgb);
+     color.rgb *= color_correction;
+     color.rgb = floor(color.rgb);
+     color.rgb /= 255.0;
+     FragColor = color;
+     return;
+
+#else
+     color.rgb *= color_correction;
+     FragColor = color;
+     return;
+
+#endif
+
+#endif
+}