如果在场景iphone上出现两个以上的精灵（来自spritesheet），像素完美碰撞无法正常工作？

Question

我正在用iPhone开发游戏中的像素完美碰撞只有在场景中出现一个精灵才会起作用，否则它就无法工作了。你能提供一些信息吗？

我使用此代码进行动画精灵（spritesheet）之间的像素完美碰撞。

 -(BOOL) isCollisionBetweenSpriteA:(CCSprite*)spr1 spriteB:(CCSprite*)spr2 pixelPerfect:(BOOL)pp


  {

BOOL isCollision = NO;

CGRect intersection = CGRectIntersection([spr1 boundingBox], [spr2 boundingBox]);

// Look for simple bounding box collision
if (!CGRectIsEmpty(intersection))
{
    // If we're not checking for pixel perfect collisions, return true
    if (!pp) {return YES;}

    CGPoint spr1OldPosition = spr1.position;
    CGPoint spr2OldPosition = spr2.position;

    spr1.position = CGPointMake(spr1.position.x - intersection.origin.x, spr1.position.y - intersection.origin.y);
    spr2.position = CGPointMake(spr2.position.x - intersection.origin.x, spr2.position.y - intersection.origin.y);

    intersection = CGRectIntersection([spr1 boundingBox], [spr2 boundingBox]);

    // Assuming that the spritebatchnode of both sprites is the same, I just use one. If each sprite has a different sprite batch node as parent you should modify the code to get the spriteBatchNode for each sprite and visit them.
    CCSpriteBatchNode* _sbnMain =(CCSpriteBatchNode*) spr1.parent;

    //NOTE: We are assuming that the spritebatchnode is always at 0,0

    // Get intersection info
    unsigned int x = (intersection.origin.x)* CC_CONTENT_SCALE_FACTOR();
    unsigned int y = (intersection.origin.y)* CC_CONTENT_SCALE_FACTOR();
    unsigned int w = intersection.size.width* CC_CONTENT_SCALE_FACTOR();
    unsigned int h = intersection.size.height* CC_CONTENT_SCALE_FACTOR();
    unsigned int numPixels = w * h;// * CC_CONTENT_SCALE_FACTOR();

    // create render texture and make it visible for testing purposes
    int renderWidth = w+1;
    int renderHeight = h+1;

    if(renderWidth<32)
    {
        renderWidth =32;
    }

    if(renderHeight < 32)
    {
        renderHeight =32;
    }

    renderTexture = [[CCRenderTexture alloc] initWithWidth:renderWidth height:renderHeight pixelFormat:kCCTexture2DPixelFormat_RGBA8888];

    //rt is always going to be at 0,0 - can't change it.
    renderTexture.position = CGPointMake(0, 0);
    [self addChild:renderTexture];
    renderTexture.visible = NO;

    //NSLog(@"\nintersection = (%u,%u,%u,%u), area = %u",x,y,w,h,numPixels);

    // Draw into the RenderTexture
    [renderTexture beginWithClear:0 g:0 b:0 a:0];

    // Render both sprites: first one in RED and second one in GREEN
    glColorMask(1, 0, 0, 1);
    [_sbnMain visitSprite:spr1];
    glColorMask(0, 1, 0, 1);
    [_sbnMain visitSprite:spr2];
    glColorMask(1, 1, 1, 1);

    // Get color values of intersection area
    ccColor4B *buffer = malloc( sizeof(ccColor4B) * numPixels );
    glReadPixels(x, y, w, h, GL_RGBA, GL_UNSIGNED_BYTE, buffer);

    [renderTexture end];

    // Read buffer
    unsigned int step = 1;
    for(unsigned int i=0; i<numPixels; i+=step)
    {
        ccColor4B color = buffer[i];

        if (color.r > 0 && color.g > 0)
        {
            isCollision = YES;
            break;
        }
    }
    // Free buffer memory
    free(buffer);
    spr1.position = spr1OldPosition; 
    spr2.position = spr2OldPosition;

    [renderTexture release];
    [self removeChild:renderTexture cleanup:YES];
} return isCollision;}