OpenGL2: Speed up tonemap shader.

code/renderergl2/glsl/tonemap_vp.glsl

@@ -2,12 +2,26 @@ attribute vec3 attr_Position;
 attribute vec4 attr_TexCoord0;
 
 uniform mat4   u_ModelViewProjectionMatrix;
+uniform vec3   u_ToneMinAvgMaxLinear;
 
 varying vec2   var_TexCoords;
+varying float  var_InvWhite;
 
+float FilmicTonemap(float x)
+{
+	const float SS  = 0.22; // Shoulder Strength
+	const float LS  = 0.30; // Linear Strength
+	const float LA  = 0.10; // Linear Angle
+	const float TS  = 0.20; // Toe Strength
+	const float TAN = 0.01; // Toe Angle Numerator
+	const float TAD = 0.30; // Toe Angle Denominator
+
+	return ((x*(SS*x+LA*LS)+TS*TAN)/(x*(SS*x+LS)+TS*TAD)) - TAN/TAD;
+}
 
 void main()
 {
 	gl_Position = u_ModelViewProjectionMatrix * vec4(attr_Position, 1.0);
 	var_TexCoords = attr_TexCoord0.st;
+	var_InvWhite = 1.0 / FilmicTonemap(u_ToneMinAvgMaxLinear.z - u_ToneMinAvgMaxLinear.x);
 }