[PD] shaders + erosion filter

[hi]

I made a shader, and i don't understand why it does not work. 
I used Hias example for the background substraction provided with the Kinect examples, and modified it with an erosion part.

I will post my shader here, maybe anybody already can spot easily whats wrong..

#extension GL_ARB_texture_rectangle : enable

uniform float xmin;
uniform float xmax;
uniform float ymin;
uniform float ymax;
uniform float zmin;
uniform float zmax;
uniform int N; // size of eroding element can be scaled from outside


uniform sampler2DRect sourceTexture; // DEPTHMAP


void main (void)
{
	vec2 pos = (gl_TextureMatrix[0] * gl_TexCoord[0]).st;
	
	vec4 color = texture2DRect(sourceTexture,  pos);

	vec3 real = vec3 (0.0, 0.0, 0.0);

	// COMPUTE REAL COORDINATES
	// in mm 
	
	// z component
	real.z = color.r * 65536.0 + color.g * 256.0; // depth_mode 4 or 5
    
	// x component
	float FovH = 1.0144686707507438;
	float XtoZ = tan(FovH / 2.0) * 2.0;
	real.x = ((pos.x / 640.0) - 0.5) * real.z * XtoZ;

	// y component
	float FovV=0.78980943449644714;
	float YtoZ = tan(FovV / 2.0) * 2.0;
	real.y = (0.5 - (pos.y / 480.0)) * real.z * YtoZ;

    
    // I used erosion example from:
    // https://sourceforge.net/p/glmixer/Source/197/tree/trunk/shaders/imageProcessing_fragment.glsl

    int i = 0;
    int j = 0;
  
    vec3 minValue = vec3(1.0);
    vec3 tmp = vec3(0.0);
    
    float step_w = 0.0;
    step_w = 1.0 / 640.0;
    float step_h = 0.0;
    step_h = 1.0 / 480.0;
    
    for (i = -(N-1)/2; i< (N+1)/2 ; i++){
        for (j = -(N-1)/2; j< (N+1)/2; j++) {
            tmp = texture2DRect(sourceTexture, vec2 ( pos.s + float(i)*step_w, pos.t + float(j)*step_h ) ).rgb;
            real.z = tmp.r * 65536.0 + tmp.g * 256.0;
            
            minValue = min(tmp, minValue);  // take smaller of any position or minValue,
                                            // if minValue is 0 for any of the pixel of erosion,
                                            // it will allways be smaller in the whole erosion step
                                            // and therefor the whole block should be 0
                                            // -> DOES NOT WORK! Why?
           
            if ((real.z <= zmin) || (real.z >= zmax)) // compare values against depth boundries
            {
                 minValue = vec3 (0.0, 0.0, 0.0);
            }
           
        }
    }

    if (minValue == vec3(0.0)){

    gl_FragColor =  vec4(minValue, 1.0);
    }
    else{
        gl_FragColor = vec4(color.r, color.g, 1.0, 1.0);
    }
}

Am 07.07.2017 um 12:51 schrieb cyrille henry <ch at chnry.net>:

> hello,
> 
> you can render the 1st shader in a framebuffer, and use it as a texture to render the 2nd shader.
> have a look at example in 10.glsl folder for more informations
> 
> cheers
> C
> 
> 
> Le 07/07/2017 à 01:09, hi via Pd-list a écrit :
>> Dear list!
>> is it possible to run 2 pixel shaders right after each other? how? With the first I would like to do some background supstraction and with the second some erosion filtering.
>> Or can it be done in one?
>> Did any of you implement any morphology filter as a shader in Pd?
>> best,
>> jonas
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