Qt: Fix builtin post shaders

data/resources/shaders/simple-brightness.glsl

@@ -0,0 +1,36 @@
+/*
+[configuration]
+
+[OptionRangeFloat]
+GUIName = Brightness Scale
+OptionName = BRIGHTNESS_SCALE
+MinValue = 0.1
+MaxValue = 5.0
+StepAmount = 0.1
+DefaultValue = 1.0
+
+[/configuration]
+*/
+
+void main()
+{
+  float4 color = Sample();
+  float brightness_scale = GetOption(BRIGHTNESS_SCALE);
+
+  // rgb->yuv
+  float3 yuv;
+  yuv.r = dot(color.rgb, float3(0.299f, 0.587f, 0.114f));
+  yuv.g = dot(color.rgb, float3(-0.14713f, -0.28886f, 0.436f));
+  yuv.b = dot(color.rgb, float3(0.615f, -0.51499f, -0.10001f));
+
+  // apply brightness to y
+  yuv.r = saturate(yuv.r * brightness_scale);
+
+  // yuv->rgb
+  color.r = dot(yuv, float3(1.0f, 0.0f, 1.13983f));
+  color.g = dot(yuv, float3(1.0f, -0.39465f, -0.58060f));
+  color.b = dot(yuv, float3(1.0f, 2.03211f, 0.0f));
+  color.rgb = saturate(color.rgb);
+
+  SetOutput(saturate(color));
+}