图像在处理中旋转时消失

Question

I'm using the Processing language to do a little game, but I'm having trouble with images and rotation. My sprite displays fine if I apply no rotation to it, but it disappears completely if it is rotated. Here's the rotation code:

void display(boolean alternate) {
    pushMatrix();
    if(!isHead && !isTail && alternate) rotate(radians(180));
    rotate(radians(90*direction));
    image(snake, x, y, linkSize, linkSize);
    popMatrix();
}

When direction is 0, or alternate is true and direction is 2, then the image displays. Otherwise, no image is displayed. I'm not sure if it matters or not, but snake is a.png image with an alpha transparency. The declaration for snake is snake = loadImage("SnakeLink.png"); .

Answer 1

You are actually rotating the image from it's origin (top left corner), so it disappears from the screen. You have to translate to the center of the image, rotate, translate back to it's origin and then display it.

translate(image.width/2, image.height/2);
rotate(radians);
translate(-image.width/2, -image.height/2);