working with shaders in py5

[Maltiec]

Has anyone worked with shaders in py5? is there any special rules for shaders which will be used in apply_filter()? I've tried some examples with calling py5.shader() and using set method of Shader class - and it was a success, but apply_filter() works in a very strange way (black window most of the time).

[hx2A]

Yes, I have used shaders extensively, and have spent much of today with that. apply_filter() should also work. Not sure why you are getting a black window. Can you provide some examples? What shader are you passing to apply_filter()?

[hx2A]

I looked at some code I wrote that uses apply_filter() and I recall the shader needs to work a bit differently than regular shaders. Normally when you create a vert and frag shader it is for drawing triangles and the shader has no information about pixels it is being drawn on top of. apply_filter() is different in that you have access to the all of the pixels in the window.

The following fragment shader could be used with apply_filter().

// filename: data/red.glsl

// processing supplied variables
uniform sampler2D texture;
varying vec4 vertColor;
varying vec4 vertTexCoord;

void main() {
  // get original color for this pixel
  vec4 originalColor = texture2D(texture, vertTexCoord.st) * vertColor;

  // remove green and blue, leaving red
  vec4 color = vec4(originalColor.r, 0.0, 0.0, 1.0);

  // gl_FragColor needs to be set to something
  gl_FragColor = color;
}

Test code:

def setup():
    py5.size(400, 400, py5.P2D)
    py5.rect(10, 10, 300, 300)
    shader = py5.load_shader('red.glsl')
    py5.apply_filter(shader)

Shaders take some time and effort to understand, and Processing Shaders add some complexity because of the Processing framework. Once you get the hang of them, they are super useful.

[Maltiec]

Thanks a lot! I've tried some examples from https://webgl-shaders.com/ And those shaders really differ from processing-specific ones.

[hx2A]

You are welcome.

Those shaders might work with Processing but will take some effort and knowledge of what Processing Shaders need & want to integrate them into Processing's framework.