使用 CGAffineTransformMakeRotation 来回滑动触摸中的图像旋转会使 fps 下降一半

Question

在 3D 游戏中，优化后我在 iPad2 上达到了 60fps，主运行循环位于辅助线程中， 使用界面构建器在主线程上构建UI，（这个问题是关于主线程的UI）

我有两个控制器，一个油门向上，和一个用于在使用触摸交互的UI中滚动的摇杆，你可以看到摇杆在下面这张图片中。

它有 180 度的旋转运动，正如您可以从该图像

如果我运行游戏，并且然后用我的拇指在这根棍子上来回擦洗，（从 0 度疯狂滚动到 -180 度） fps 下降到 33fps 而不是 60fps..

只需从下面的代码列表中注释掉下面的这一行，就可以将 fps 恢复到60fps，（我用拇指擦洗，游戏确实在滚动，但是这根棍子的图像当然不会移动），因此可以在不更新这根棍子的图像的情况下以全帧速率玩游戏，（表明它仅是这个例程吗）用这种方法更新和转换图像极大地影响了我的帧率。请参阅下面的代码，您认为有办法解决此性能问题吗？ （否则我将不得不有一些通用的圆形区域，其中只有一个圆圈代表触摸区域，以给出您在某些游戏中看到的滚动概念，例如我认为的《无限之剑》..但我更愿意拥有这个交互式图像显示真正的目的。您是否看到我需要更改的内容？

  joypadCap.transform = CGAffineTransformMakeRotation(touchAngle); //rotation in radians

这是已设置的 viewController 的相关代码，“joypad”是您在上面看到的图像，油门是一个不同的图像，它会影响 fps，但不会影响到上面这个单一调用的程度，因为油门只是将图像移动到正确的位置，而不是使用这个 CGAffineTransformMakeRotation，但该操作确实使 fps 下降了大约 8fps。

@interface stickController : UIViewController
{
    IBOutlet UIImageView *throttleStickCap;
    IBOutlet UIImageView *joypadCap;
etc......

@implementation stickController

@synthesize frontViewButton, backViewButton, leftViewButton, rightViewButton, upViewButton, gunSight;

//------------------------------------------------------------------------------------
- (void)viewDidLoad
{
NSLog(@"viewDidLoad");
    [super viewDidLoad];
    throttleStick = throttleStickCap.frame;
    throttleStickCenterx = throttleStickCap.center.x;
    throttleStickCentery = throttleStickCap.center.y;
    throttleStickMax = 72.0f;
    throttleStickMin = -7.0f;

    joypad = joypadCap.frame;
    joypadCenterx = joypadCap.center.x;
    joypadCentery = joypadCap.center.y;
    joypadMax = 50.0f;
    joypadMin = -50.0f;

    theStickController = self;
}

//------------------------------------------------------------------------------------
- (void)touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event
{
    NSSet *allTouches = [event allTouches];
    for (UITouch *touch in allTouches)
    {
        CGPoint touchLocation = [touch locationInView:self.view];

        if (CGRectContainsPoint(throttleStick, touchLocation))
        {
            throttleStickTouchHash = [touch hash];
        }

        if (CGRectContainsPoint(joypad, touchLocation))
        {
            joypadTouchHash = [touch hash];

            CGPoint touchLocation = [touch locationInView:self.view];
            float dx = touchLocation.x - (float)joypadCenterx;
            float dy = touchLocation.y - (float)joypadCentery;

            distance = sqrtf(powf(dx, 2.0f) + powf(dy, 2.0f));

            if (distance > joypadMax)
            {
                enoughDistance = shootDistance;
                createBulletSet();
            }
        }
    }
}

//------------------------------------------------------------------------------------
- (void)touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event
{
    NSSet *allTouches = [event allTouches];

    for (UITouch *touch in allTouches)
    {
        if ([touch hash] == throttleStickTouchHash)
        {
            CGPoint touchLocation = [touch locationInView:self.view];

            distance = throttleStickCentery - touchLocation.y;

            if (distance > throttleStickMax)
            {
                throttleStickCap.center = CGPointMake(throttleStickCenterx, throttleStickCentery - throttleStickMax);
                throttle = throttleStickMax;
            }
            else if (distance < throttleStickMin)
            {
                throttleStickCap.center = CGPointMake(throttleStickCenterx, throttleStickCentery - throttleStickMin);
                throttle = throttleStickMin;
            }
            else
            {
                throttleStickCap.center = CGPointMake(throttleStickCap.center.x, touchLocation.y);
                throttle = distance;
            }
            throttle *= .10;
            throttleStick = throttleStickCap.frame;
        }

        if ([touch hash] == joypadTouchHash)
        {
            CGPoint touchLocation = [touch locationInView:self.view];
            float dx = touchLocation.x - (float)joypadCenterx;
            float dy = touchLocation.y - (float)joypadCentery;

            distance = sqrtf(powf(dx, 2.0f) + powf(dy, 2.0f));

            if (distance > joypadMax) createBulletSet();
                else enoughDistance = shootDistance;

            if (dx > joypadMax) roll = joypadMax;
                else if (dx < joypadMin) roll = joypadMin;
                else roll = dx;

            joypad = joypadCap.frame;

            touchAngle = atan2(dy, dx) + 1.570796;

            if ((dx < 0.0f) && (dy > 0.0f)) touchAngle = -1.570796;
            else if ((dx > 0.0f) && (dy > 0.0f)) touchAngle = 1.570796;

    //      joypadCap.transform = CGAffineTransformMakeRotation(touchAngle); //rotation in radians
        }
    }
}

//------------------------------------------------------------------------------------
- (void)forceTouchesEnd
{
    throttleStickMoving = NO;
    throttleStickTouchHash = 0;
    throttle = 0.0f;
    throttleStickCap.center = CGPointMake(throttleStickCenterx, throttleStickCentery);
    throttleStick = throttleStickCap.frame;

    joypadMoving = NO;
    joypadTouchHash = 0;
    roll = 0.0f;
    joypadCap.transform = CGAffineTransformMakeRotation(0.0f); //rotation in radians
    joypad = joypadCap.frame;
}

//------------------------------------------------------------------------------------
- (void)touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event
{
    for (UITouch *touch in touches)
    {
        if ([touch hash] == throttleStickTouchHash)
        {
            throttleStickTouchHash = 0;
        }

        if ([touch hash] == joypadTouchHash)
        {
            joypadTouchHash = 0;
            roll = 0.0f;

            joypad = joypadCap.frame;

            return;
        }
    }
}