objective-c - Cocos2d中如何实现zoom效果？

Question

我现在用cocos2d引擎设计游戏，并加载了全部的精灵（sprite），但是由于一部分精灵高度要大于320像素，所以很难将它们完全加载进来。为了方便，我打算实现ZOOM IN和ZOOM out效果，ZOOM IN可以瞬间让全部精灵最小化，ZOOM out则会让它们恢复最初的状态。
怎么样才能创造出这种效果吗？同时，希望大家也可以为我讲一下有关pinch zoom的内容。

黄舟 · Answer

答：Michael Fredrickson
（最佳答案）
想实现zoom的效果很容易，只要设定游戏的main layer的scale属性即可，但是仍然有一些细节需要注意。
在缩放layer时，会整体提高layer的位置，如果在游戏中想要实现滚动的效果，你需要作出如下设定：
可以将layer中的anchorPoint设定成ccp(0.0f, 0.0f)，然后算出layer上升的距离，再重新设定参数，让它回复原状。

- (void) scale:(CGFloat) newScale scaleCenter:(CGPoint) scaleCenter {
    // scaleCenter is the point to zoom to.. 
    // If you are doing a pinch zoom, this should be the center of your pinch.

    // Get the original center point.
    CGPoint oldCenterPoint = ccp(scaleCenter.x * yourLayer.scale, scaleCenter.y * yourLayer.scale); 

    // Set the scale.
    yourLayer.scale = newScale;

    // Get the new center point.
    CGPoint newCenterPoint = ccp(scaleCenter.x * yourLayer.scale, scaleCenter.y * yourLayer.scale); 

    // Then calculate the delta.
    CGPoint centerPointDelta  = ccpSub(oldCenterPoint, newCenterPoint);

    // Now adjust your layer by the delta.
    yourLayer.position = ccpAdd(yourLayer.position, centerPointDelta);
}

实现Pinch zoom很简单，只要检测touchesMoved，然后调用滚动路线（scaling routine）即可。

- (void) ccTouchesMoved:(NSSet*)touches withEvent:(UIEvent*)event {

    // Examine allTouches instead of just touches.  Touches tracks only the touch that is currently moving...
    //   But stationary touches still trigger a multi-touch gesture.
    NSArray* allTouches = [[event allTouches] allObjects];

    if ([allTouches count] == 2) {            
        // Get two of the touches to handle the zoom
        UITouch* touchOne = [allTouches objectAtIndex:0];
        UITouch* touchTwo = [allTouches objectAtIndex:1];

        // Get the touches and previous touches.
        CGPoint touchLocationOne = [touchOne locationInView: [touchOne view]];
        CGPoint touchLocationTwo = [touchTwo locationInView: [touchTwo view]];  

        CGPoint previousLocationOne = [touchOne previousLocationInView: [touchOne view]];
        CGPoint previousLocationTwo = [touchTwo previousLocationInView: [touchTwo view]];

        // Get the distance for the current and previous touches.
        CGFloat currentDistance = sqrt(
                                       pow(touchLocationOne.x - touchLocationTwo.x, 2.0f) + 
                                       pow(touchLocationOne.y - touchLocationTwo.y, 2.0f));

        CGFloat previousDistance = sqrt(
                                        pow(previousLocationOne.x - previousLocationTwo.x, 2.0f) + 
                                        pow(previousLocationOne.y - previousLocationTwo.y, 2.0f));

        // Get the delta of the distances.
        CGFloat distanceDelta = currentDistance - previousDistance;

        // Next, position the camera to the middle of the pinch.
        // Get the middle position of the pinch.
        CGPoint pinchCenter = ccpMidpoint(touchLocationOne, touchLocationTwo);

        // Then, convert the screen position to node space... use your game layer to do this.
        pinchCenter = [yourLayer convertToNodeSpace:pinchCenter];

        // Finally, call the scale method to scale by the distanceDelta, pass in the pinch center as well.
        // Also, multiply the delta by PINCH_ZOOM_MULTIPLIER to slow down the scale speed.      
        // A PINCH_ZOOM_MULTIPLIER of 0.005f works for me, but experiment to find one that you like.
        [self scale:yourlayer.scale - (distanceDelta * PINCH_ZOOM_MULTIPLIER)
            scaleCenter:pinchCenter];
    }    
}

答：Andrew
如果所有的精灵都来自同一个parent，你可以将其进行缩放设置，协调不同parent，保证它们之间的关联性。

答：mohammad alabid
以下代码可以将layer的位置缩放2倍，

[layer setScale:2];
layer.position=ccp(240/2+40,160*1.5);
double dx=(touchLocation.x*2-240);
double dy=(touchLocation.y*2-160);
layer.position=ccp(inGamePlay.position.x-dx,inGamePlay.position.y-dy);