// display the message, first as a single string,
// and then one character at a time
size(600,300);

float pad = 20;

String msg = "This is a test";

textSize(80);
textAlign(LEFT, CENTER);
fill(0);

text(msg, pad, 100);

float x=pad;

for (int k=0; k < msg.length(); k++) {
  noFill();
  rect(x,160,textWidth(msg.charAt(k)),80);
  fill(0);
  text(msg.charAt(k), x, 200);
  x += textWidth(msg.charAt(k));  
}