PImage txtr;
PVector off;
PVector scl;

void setup() {
  size(512, 256, P3D);
  textureMode(NORMAL);
  textureWrap(REPEAT);
  noStroke();

  txtr = loadImage("txtr.png");
  off = new PVector();
  float aspect = width / (float)height;
  scl = new PVector(3 * aspect, 3);
}

void draw() {
  background(0xffffffff);

  beginShape();
  texture(txtr);
  vertex(0, 0, 0, off.x, off.y);
  vertex(width, 0, 0, off.x + scl.x, off.y);
  vertex(width, height, 0, off.x + scl.x, off.y + scl.y);
  vertex(0, height, 0, off.x, off.y + scl.y);
  endShape(CLOSE);

  off.x += 0.01;
  off.y += 0.005;
}