Grayscale Frag Shader is killing my frame rate

[mer10]

Granted it's expected.... but I'm looking for suggestions on what I could do to improve the performance. Currently it's causing my app to dip just below 30 FPS(normally at 50 or 60 FPS but I cap it at 30).

Here is the code for GrayScale.fsh

varying lowp vec4 colorVarying;
varying mediump vec2 TextureCoordOut;
uniform sampler2D Sampler;
varying lowp vec4 ColorOut;
lowp vec4 fragColor;
lowp float luminance;
void main()
{
fragColor=texture2D(Sampler, TextureCoordOut)*ColorOut;
luminance=fragColor.r*.2126+fragColor.g*.7152+.072 2*fragColor.b;
gl_FragColor=vec4(luminance,luminance,luminance,fr agColor.a);
}

Help is greatly appreciated!

[Duncan C]

Originally Posted by mer10

Granted it's expected.... but I'm looking for suggestions on what I could do to improve the performance. Currently it's causing my app to dip just below 30 FPS(normally at 50 or 60 FPS but I cap it at 30).

Here is the code for GrayScale.fsh

varying lowp vec4 colorVarying;
varying mediump vec2 TextureCoordOut;
uniform sampler2D Sampler;
varying lowp vec4 ColorOut;
lowp vec4 fragColor;
lowp float luminance;
void main()
{
fragColor=texture2D(Sampler, TextureCoordOut)*ColorOut;
luminance=fragColor.r*.2126+fragColor.g*.7152+.072 2*fragColor.b;
gl_FragColor=vec4(luminance,luminance,luminance,fr agColor.a);
}

Help is greatly appreciated!

Are you sure it's the shader that's doing it? Try setting your fragment color to a fixed value (commenting out your texture and your luminance value) and test that. I bet there's no difference in speed. Fragment shaders are farmed out to the compute units on the GPU, and run VERY fast.

[mer10]

Originally Posted by Duncan C

Are you sure it's the shader that's doing it? Try setting your fragment color to a fixed value (commenting out your texture and your luminance value) and test that. I bet there's no difference in speed. Fragment shaders are farmed out to the compute units on the GPU, and run VERY fast.

I tried that. My original frag shader only had this line in main() and didn't have the fragColor or Luminance in it. Worked well.

gl_FragColor=texture2D(Sampler, TextureCoordOut)*ColorOut;

All of the changes I made when comparing the two were in the frag shader. Perhaps I'm doing something wrong??

[Duncan C]

Originally Posted by mer10

I tried that. My original frag shader only had this line in main() and didn't have the fragColor or Luminance in it. Worked well.

gl_FragColor=texture2D(Sampler, TextureCoordOut)*ColorOut;

All of the changes I made when comparing the two were in the frag shader. Perhaps I'm doing something wrong??

Dunno. I'm a neophyte when it comes to OpenGL shaders. It might be that one of the calculations you're doing is causing the compute units in the GPU to thrash. Maybe you're asking to do double precision math, for example, or convert parameters to different precision? I understand that can be slow.

[mer10]

Originally Posted by Duncan C

Dunno. I'm a neophyte when it comes to OpenGL shaders. It might be that one of the calculations you're doing is causing the compute units in the GPU to thrash. Maybe you're asking to do double precision math, for example, or convert parameters to different precision? I understand that can be slow.

Maybe...i'll have to look into it more. Thanks!