shader to make white background transparent

MartinVDL

For one of my sketches I need to take a black an white PImage and remove all the white pixels. I did it using the usual pixel array method but this slows down my sketch considerably (its already computing the physiscs for 1000 particles). I really want to learn how to use the GLSL shaders but as I'm not skilled in C thats going to take some time. For now can someone give me a quick solution?

TIA

MartinVDL

Figured it out. In case anyone else ever needs this, here's a simple shader I made:

#ifdef GL_ES
precision mediump float;
precision mediump int;
#endif


varying vec4 vertTexCoord;
uniform sampler2D texture;

void main(void)
{
    vec3 col = texture2D(texture, vertTexCoord.st).rgb;

    float a = 1.0 - col.r ; // make white transparent
    col.rgb = 1.0 - col.rgb; // invert if wanted

    gl_FragColor = vec4(col, a);
}