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    3.14a
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  • Shapes and strokes on a plane in P3D/OpenGL
    Rendering several overlapping shapes on a plane in 3D seems to be quite tricky using P3D/OpenGL (in Processing 2.0). Without the right hints there is either "z-fighting" of the different shapes visible (causing headaches) and the strokes of all shapes are visible (including the covered ones).



    I searched quite a while for a solution, eventually with the wrong key words, but in the end I found a solution that may is of use to some of the readers.

    So if you draw several shapes on the same plane add the two following hints:
    1. hint(DISABLE_DEPTH_TEST); // avoids z-fighting
    2. hint(ENABLE_ACCURATE_2D); // strokes are drawn correctly
    A small example

    1. void setup() {
    2.   size(200, 200, OPENGL);
    3. }

    5. void draw() {
    6.   background(255);
    7.   smooth();
    8.   hint(DISABLE_DEPTH_TEST); // avoids z-fighting
    9.   hint(ENABLE_ACCURATE_2D); // strokes are drawn correctly
    10.   // some motion
    11.   translate(width/2, height/2, -200);
    12.   rotateY(frameCount * 0.01);
    13.   rotateX(frameCount * 0.01);
    14.   stroke(150);
    15.   strokeWeight(6); // increase the thickness
    16.   fill(220, 0, 0);
    17.   rect(-50, -50, 200, 200); 
    18.   fill(220, 220, 0);
    19.   rect(-100, -100, 200, 200); 
    20. }