Initiation aux Shaders avec Processing

uniform mat4 transformMatrix;
 
attribute vec4 position;
attribute vec4 color;
 
varying vec4 vertColor;
 
void main() {
  gl_Position = transformMatrix * position;
 
  vertColor = color;
}

#ifdef GL_ES
precision mediump float;
precision mediump int;
#endif
 
varying vec4 vertColor;
 
void main() {
  gl_FragColor = vertColor;
}

PShader myShader;
int margin = 32;
 
void setup() {
 size(800, 600, P2D); 
 
 myShader = loadShader("frag.glsl", "vert.glsl");
 noStroke();
}
 
void draw() {
  background(0);
  shader(myShader);
  fill(230, 120, 0);
  rect(margin, margin, width - 2*margin, height - 2*margin);
  resetShader();    // Désactive le shader, permet de redessiner normalement
}