PFont f;
int ypos;
int xpos, xpos2;

PGraphics masker;
PImage img;
String basetext = "LOVEYOULOVEYOULOVEYOULOVEYOULOVEYOU";
String masktext = "YOULOVEYOULOVEYOULOVEYOULOVEYOULOVE";
void setup() {
  size(600, 480);
  img = createImage();
  f = createFont("serif", 500);
  textFont(f);
  masker = createGraphics(width, height);
  ypos = height*.9;
  xpos = width*.5;
  xpos2 = (width*.5)-textWidth(basetext);
  frameRate(30);
  smooth();
}
void draw () {
  background(255);

  masker.beginDraw();
  //  masker.textAlign(CENTER);
  masker.textFont(f);
  masker.background(255);
  masker.fill(0);
  masker.text(masktext, xpos, ypos);
  masker.endDraw();

  //  textAlign(CENTER);
  textFont(f);
  fill(0);
  text(basetext, xpos2, ypos);
  img = masker.get();
  blend(img, 0, 0, masker.width, masker.height, 0, 0, width, height, ADD);

  xpos -= 2;
  xpos2 += 1;

  if (xpos < -textWidth(masktext)) {
    xpos = 0;
    xpos2 = -textWidth(basetext);
  }
}