iOS-利用CADisplayLink计算FPS

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CADisplayLink会在每次刷新屏幕的时候，执行Delegate，从而计算出FPS，检测CPU的卡顿。

注意，需要加入到RunLoop中:

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#import <SpriteKit/SpriteKit.h>

_link = [CADisplayLink displayLinkWithTarget:self selector:@selector(tick:)];
[_link addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];

CFTimeInterval lastTime = 0;
int count = 0;
- (void)tick:(CADisplayLink *)link {
    if (lastTime == 0) {
        lastTime = link.timestamp;
        return;
    }
    
    count++;
    NSTimeInterval delta = link.timestamp - lastTime;
    if (delta < 1) return;
    lastTime = link.timestamp;
    float fps = count / delta;
    count = 0;
    
    NSLog(@"FPS::%d", (int)round(fps));
}

运行结果如下:

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FPS::59
FPS::60
FPS::60
FPS::60
FPS::60
FPS::60

单独使用CADisplayLink,只能检测CPU的FPS，对于GPU长时间进行视图混合造成的卡顿，无法检测，因此引入一个空像素点的SKView, 当GPU出现卡顿时，依然会触发CADisplayLink回调。

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SKScene *scene = [SKScene new];
_sceneView = [[SKView alloc] initWithFrame:CGRectMake(0.0, 0.0, 1.0, 1.0)];
[_sceneView presentScene:scene];
[[UIApplication sharedApplication].keyWindow addSubview:sceneView];