Add "simplified" grain option, for extra performance.

Uses PRNG calls instead of texture fetches, so it tends to look more harsh and have patterning issues depending on the GPU.

gldefs.txt

@@ -23,6 +23,18 @@ HardwareShader postprocess scene
 	Uniform int nb
 	Texture NoiseTexture "textures/mfxnoise.png"
 }
+HardwareShader postprocess scene
+{
+	Name "mfx_grain_simple"
+	Shader "shaders/glsl/mfx_grain_simple.fp" 330
+	Uniform float Timer
+	Uniform float nf
+	Uniform float ni
+	Uniform float ns
+	Uniform float np
+	Uniform float bnp
+	Uniform int nb
+}
 
 HardwareShader postprocess scene
 {