objective-c – 从夹点位置缩放在CGContext上绘制的图像

这个问题是来自另一个SO问题的后续问题： zooming using pinch but not using transform methods.我让缩放工作非常接近完美,但它仍然会使绘制的图像“跳转”,因为我一直在调用它.代码中最重要的部分如下：

当观察到夹点事件时,会调用此方法：

[code snippet 1]

- (IBAction)handlePinchGesture:(UIGestureRecognizer *)sender {
    float previousZoomLevel = zoomLevel;
    UIPinchGestureRecognizer *pinch = (UIPinchGestureRecognizer *)sender;

    float zoomIncreaseFactor = [self getZoomFactor:[pinch scale]]; //= 13 or 7 or 10
    float estimatedDelta = (previousZoomLevel * zoomIncreaseFactor) / 150;

    if ([pinch scale] > previousScale) {
        zoomLevel += estimatedDelta;
    }

    if ([pinch scale] < previousScale) {
        zoomLevel -= estimatedDelta;
    }

    previousScale = [pinch scale];

    if (zoomLevel < MIN_ZOOM_LEVEL) {
        zoomLevel = MIN_ZOOM_LEVEL;
    }

    if (zoomLevel > MAX_ZOOM_LEVEL) {
        zoomLevel = MAX_ZOOM_LEVEL;
    }

    CGPoint loc = [pinch locationInView:self];

    NSLog(@"loc: {%.1f,%.1f},lastPinchLoc: {%.1f,%.1f}",loc.x,loc.y,lastPinchLocation.x,lastPinchLocation.y);

    //uncomment the below part to always zoom from the first zoom location.
    //if (lastPinchLocation.x != 0 && lastPinchLocation.y != 0) {
        //loc.x += lastPinchLocation.x - loc.x;
        //loc.y += lastPinchLocation.y - loc.y;
    //}

    //NSLog(@"newLastPinchLocation: {%.1f,loc.y);

    lastPinchLocation = loc;

    hasBeenMoved = YES;

    if (zoomLevel != previousZoomLevel) {
        [self setNeedsDisplay];
    }
}

当我捏住整个屏幕时,上面的NSLog给出了以下打印：

2012-10-16 10:15:19.357 App[2609:907] loc: {147.0,232.0},lastPinchLoc: {0.0,0.0}
2012-10-16 10:15:19.391 App[2609:907] loc: {147.0,231.0},lastPinchLoc: {147.0,232.0}
2012-10-16 10:15:19.436 App[2609:907] loc: {148.0,231.0}
2012-10-16 10:15:19.457 App[2609:907] loc: {148.0,lastPinchLoc: {148.0,232.0}
2012-10-16 10:15:19.474 App[2609:907] loc: {148.0,233.0},232.0}
2012-10-16 10:15:19.507 App[2609:907] loc: {147.0,233.0}
2012-10-16 10:15:19.573 App[2609:907] loc: {103.0,355.0},233.0}
2012-10-16 10:15:20.324 App[2609:907] loc: {585.0,710.0},lastPinchLoc: {103.0,355.0}
2012-10-16 10:15:20.340 App[2609:907] loc: {584.0,709.0},lastPinchLoc: {585.0,710.0}
2012-10-16 10:15:20.356 App[2609:907] loc: {584.0,lastPinchLoc: {584.0,709.0}
2012-10-16 10:15:20.374 App[2609:907] loc: {584.0,710.0}
2012-10-16 10:15:20.407 App[2609:907] loc: {583.0,710.0}
2012-10-16 10:15:20.456 App[2609:907] loc: {512.0,811.0},lastPinchLoc: {583.0,710.0}
2012-10-16 10:15:21.056 App[2609:907] loc: {645.0,163.0},lastPinchLoc: {512.0,811.0}
2012-10-16 10:15:21.090 App[2609:907] loc: {647.0,164.0},lastPinchLoc: {645.0,163.0}
2012-10-16 10:15:21.107 App[2609:907] loc: {647.0,165.0},lastPinchLoc: {647.0,164.0}
2012-10-16 10:15:21.156 App[2609:907] loc: {602.0,249.0},165.0}
2012-10-16 10:15:21.839 App[2609:907] loc: {153.0,702.0},lastPinchLoc: {602.0,249.0}
2012-10-16 10:15:21.856 App[2609:907] loc: {157.0,703.0},lastPinchLoc: {153.0,702.0}
2012-10-16 10:15:21.874 App[2609:907] loc: {159.0,704.0},lastPinchLoc: {157.0,703.0}
2012-10-16 10:15:21.890 App[2609:907] loc: {160.0,lastPinchLoc: {159.0,704.0}
2012-10-16 10:15:21.906 App[2609:907] loc: {123.0,796.0},lastPinchLoc: {160.0,704.0}
2012-10-16 10:15:21.923 App[2609:907] loc: {125.0,794.0},lastPinchLoc: {123.0,796.0}
2012-10-16 10:15:22.706 App[2609:907] loc: {368.0,303.0},lastPinchLoc: {125.0,794.0}
2012-10-16 10:15:22.723 App[2609:907] loc: {369.0,307.0},lastPinchLoc: {368.0,303.0}
2012-10-16 10:15:22.725 App[2609:907] loc: {369.0,lastPinchLoc: {369.0,307.0}
2012-10-16 10:15:22.739 App[2609:907] loc: {371.0,312.0},307.0}
2012-10-16 10:15:22.756 App[2609:907] loc: {374.0,lastPinchLoc: {371.0,312.0}
2012-10-16 10:15:22.773 App[2609:907] loc: {338.0,392.0},lastPinchLoc: {374.0,312.0}

就在CGContext上绘制项目之前,将x和y放入此方法中,然后在返回的位置上绘制项目.类变量’zoomTouchLocation’与上面代码段中的’lastPinchLocation’具有相同的值.

[code snippet 2]

- (CGPoint)handleCoordinatesX:(float)x y:(float)y {
    x -= zoomTouchLocation.x;
    y -= zoomTouchLocation.y;

    x = x * zoomLevel;
    y = y * zoomLevel;

    x += zoomTouchLocation.x;
    y += zoomTouchLocation.y;

    return CGPointMake(x,y);
}

如果我每次按预期工作时捏在大致相同的位置,但是当我在整个屏幕上捏捏时,图像会疯狂地跳转.

现在基本上我的问题是,是否有人可以帮助我解决这个“跳转”问题并让图像从我放大的位置缩放而不会跳转.如果您需要更多信息,请在下面的评论中提问.

(而且我确实知道我的代码跳转发生是很正常的,我只是找不到阻止它这样做的方法)