add tonemapping shaders

shader/Functions/gamma.glsl

@@ -0,0 +1,21 @@
+const float GAMMA = 2.2;
+const float INV_GAMMA = 1.0 / GAMMA;
+
+// linear to sRGB approximation
+// see http://chilliant.blogspot.com/2012/08/srgb-approximations-for-hlsl.html
+vec3 linearTosRGB(vec3 color)
+{
+    return pow(color, vec3(INV_GAMMA));
+}
+
+// sRGB to linear approximation
+// see http://chilliant.blogspot.com/2012/08/srgb-approximations-for-hlsl.html
+vec3 sRGBToLinear(vec3 srgbIn)
+{
+    return vec3(pow(srgbIn.xyz, vec3(GAMMA)));
+}
+
+vec4 sRGBToLinear(vec4 srgbIn)
+{
+    return vec4(sRGBToLinear(srgbIn.xyz), srgbIn.w);
+}