想加个图片背景怎么加？

String message = "HAPPY 2018!";
PFont font1;
PFont font2;
PFont font3;
char[] letters;
float[] x;
void setup(){
background(255,255,255);
size(1200,1000);
font1 = loadFont("Chalkboard-70.vlw");
textFont(font1);
letters = message.toCharArray();
x = new float[letters.length];
x[0]=100;
for(int i=1; i<letters.length; i++){
x[i] = x[i-1] + textWidth(letters[i-1]);
}
font2 = loadFont("BrushScriptMT-70.vlw");
textFont(font2);
letters = message.toCharArray();
x = new float[letters.length];
x[0]=100;
for(int i=1; i<letters.length; i++){
x[i] = x[i-1] + textWidth(letters[i-1]);
}
font3 = loadFont("BrushScriptMT-70.vlw");
textFont(font3);
letters = message.toCharArray();
x = new float[letters.length];
x[0]=100;
for(int i=1; i<letters.length; i++){
x[i] = x[i-1] + textWidth(letters[i-1]);
}
}
void draw(){
background(0);
for(int i=0;i<letters.length;i++){
if(mouseX>x[i] && mouseX<(x[i]+textWidth(letters[i])) &&
mouseY>200 && mouseY<300){
if(i%2==0){
textFont(font2);
}
else{
textFont(font3);
}
fill(i*15,100,255);
text(letters[i], x[i], 250);
}
else{
fill(0,0,255);
textFont(font1);
text(letters[i], x[i], 300);
}
}
}