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
}