sending array to Shader, unexpected error

edited June 2016 in GLSL / Shaders

So I am trying to get a simple particle system to work with shaders.

my processing code looks like this

PShader pointShader;
int COUNT = 300;

float[] sourceX = new float[COUNT];
float[] sourceY = new float[COUNT];

void setup()
  size(600, 600, P3D);


void draw() {
 // background(0);
    for (int i = 0; i < COUNT; i++) {
    sourceX[i] = random(0, width);
    sourceY[i] = random(0, height);

  pointShader = loadShader("point.glsl");
  pointShader.set("sourceX", sourceX);
  pointShader.set("sourceY", sourceY);
  rect(0, 0, width, height);


my shader:


#ifdef GL_ES
precision mediump float;
precision mediump int;

uniform float[300] sourceX;
uniform float[300] sourceY;

void main() {
    float intensity = 0.0;

    // sum the distances from the points
    for(int i = 0; i < 300; i++) {
        float d = distance(gl_FragCoord.xy, vec2(sourceX[i], sourceY[i]));
        intensity += exp(-0.05 * d * d);

    // map the colours

        gl_FragColor = vec4(0.0, intensity * 1, 1.0, 1.0);


this works without a problem but as soon as I up the particle count to 1000 I get the error:

Screen Shot 2016-06-28 at 23.45.59

Where am I going wrong here? Is this not the right way to do this?

Ultimately my intention is to send the point cloud data from a Kinect2 to the shader. I have a working sketch for that (without the shader) but instead of sending the Kinect points into a class I would like to send it to a shader. I'm hoping I can have a much higher particle count that way.

Thank you for your help!



  • edited June 2016

    Are you sure the error is array related? Try commenting out bits until the error goes away.

    I am suspicious of line 5 but can't test anything here / now.

    (Oh, sorry, didn't see the bit about the 1000 particles. That does seem odd)

  • I don't have the solution, but only questions :) Does this produce 1000 iterations for every single pixel on the screen? Is it slower when you increase the number of particles? Would the effect look very different if you had 1000 quads with a radial texture applied to them, and maybe using blend mode ADD?

  •     float d = distance(gl_FragCoord.xy, vec2(sourceX[i], sourceY[i]));
        intensity += exp(-0.05 * d * d);

    you could get rid of the 300 expensive sqrts per fragment by not calling distance() - you square the result again immediately so why bother?

    something like

    float d2 = myDistance2(gl_FragCoord.xy, vec2(sourceX[i], sourceY[i]));
    intensity += exp(-.05 * d2);

    where myDistance2 is something like

    myDistance2(vec2 a, vec2 b) {
      return (a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y);

    (massively untested)

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