Linearize colors in frag shader

ocornut#4890

backends/vulkan/glsl_shader.frag

@@ -8,7 +8,16 @@ layout(location = 0) in struct {
     vec2 UV;
 } In;
 
+vec4 to_linear(vec4 sRGB)
+{
+    bvec3 cutoff = lessThan(sRGB.rgb, vec3(0.04045));
+    vec3  higher = pow((sRGB.rgb + vec3(0.055)) / vec3(1.055), vec3(2.4));
+    vec3  lower  = sRGB.rgb / vec3(12.92);
+
+    return vec4(mix(higher, lower, cutoff), sRGB.a);
+}
+
 void main()
 {
-    fColor = In.Color * texture(sTexture, In.UV.st);
+    fColor = to_linear(In.Color) * to_linear(texture(sTexture, In.UV.st));
 }