void setup(){
size(600, 600,P3D);
frameRate(60);
}
float rX = 0;
float rY = 0;
void draw(){
colorMode(RGB,255);
background(255, 255, 255, 255);
float size = 5;
int num = 20;
pushMatrix();
translate(width/2, height/2, 300);
noStroke();
rotateY(rY);
rotateX(rX);
for (int i = 0; i<num; i++){
for (int j = 0; j<num; j++){
for (int k = 0; k<num; k++){
pushMatrix();
translate(i*size - num*size/2, j*size - num*size/2, k*size - num*size/2);
fill((float)i/num * 255, (float)j/num * 255, (float)k/num * 255);
box(size, size, size);
popMatrix();
}
}
}
popMatrix();
}
void mouseDragged(){
rY += (mouseX - pmouseX) * 0.01;
rX += -(mouseY - pmouseY) * 0.01;}

camera位置一直没变，只是用来rotateY()和rotateX()来旋转了一下而已
mouseDragged()是当拖动鼠标时自动呼出的函数，
类似的还有mouseClicked(), mouseMoved(), mousePressed(), mouseReleased(), keyPressed(), keyReleased(), keyTyped()