I think I am misunderstanding how fragment shaders work.  I thought that this shader would not do anything.  Simply set the color of each pixel to whatever it was before:

2. #define PROCESSING_TEXTURE_SHADER
3. 
   
4. uniform sampler2D texture;
5. varying vec4 vertColor;
6. varying vec4 vertTexCoord;
7. 
   
8. void main() 
9. {
10. vec4 rgba = texture2D(texture, vertTexCoord.st).rgba;
11. gl_FragColor = rgba;
13. }
14. 
    

But it seems to do something more than that.  As I apply this filter to my red PGraphics instance it becomes gray over time.  

Why is that?

Best,

Sammi