GPUImage recalculateViewGeometry

原因：
更新xocde11.4之后发现GPUImage视频画面渲染特别慢，并且控制台输出如下信息：

Main Thread Checker: UI API called on a background thread: -[UIView bounds]
PID: 7360, TID: 1812926, Thread name: (none), Queue name: com.sunsetlakesoftware.GPUImage.openGLESContextQueue, QoS: 0
Backtrace:
4   KXLive                              0x0000000100e12e60 __39-[GPUImageView recalculateViewGeometry]_block_invoke + 52
5   KXLive                              0x0000000100dec788 runSynchronouslyOnVideoProcessingQueue + 108
6   KXLive                              0x0000000100e12e0c -[GPUImageView recalculateViewGeometry] + 108
7   KXLive                              0x0000000100e13804 __37-[GPUImageView setInputSize:atIndex:]_block_invoke + 312
8   KXLive                              0x0000000100dec788 runSynchronouslyOnVideoProcessingQueue + 108
9   KXLive                              0x0000000100e136ac -[GPUImageView setInputSize:atIndex:] + 136
10  KXLive                              0x0000000100e0ee38 -[GPUImageVideoCamera updateTargetsForVideoCameraUsingCacheTextureAtWidth:height:time:] + 660
11  KXLive                              0x0000000100e0fb48 -[GPUImageVideoCamera processVideoSampleBuffer:] + 2120
12  KXLive                              0x0000000100e106c4 __74-[GPUImageVideoCamera captureOutput:didOutputSampleBuffer:fromConnection:]_block_invoke + 180
13  libdispatch.dylib                   0x0000000105e5d260 _dispatch_call_block_and_release + 24
14  libdispatch.dylib                   0x0000000105e5d220 _dispatch_client_callout + 16
15  libdispatch.dylib                   0x0000000105e6be80 _dispatch_queue_serial_drain + 768
16  libdispatch.dylib                   0x0000000105e60730 _dispatch_queue_invoke + 328
17  libdispatch.dylib                   0x0000000105e6cdd8 _dispatch_root_queue_drain_deferred_wlh + 352
18  libdispatch.dylib                   0x0000000105e73ebc _dispatch_workloop_worker_thread + 676
19  libsystem_pthread.dylib             0x0000000181e6fe70 _pthread_wqthread + 860
20  libsystem_pthread.dylib             0x0000000181e6fb08 start_wqthread + 4

意思是在子线程中UIView对象调用了bounds ，导致视频画面迟迟渲染不出来。
查找发现GPUImageView的视频渲染类的

(void)recalculateViewGeometry;

方法中有两处调用了bounds。
解决办法：
在GPUImageView中声明一个属性viewBounds来保存view的bounds值，在- (void)layoutSubviews方法中给viewBounds赋值，用viewBounds代替bounds就可以了，此时可以很快的调起摄像头并且渲染出画面。

- (void)layoutSubviews {
    [super layoutSubviews];
    self.viewBounds = self.bounds;
    // The frame buffer needs to be trashed and re-created when the view size changes.
    if (!CGSizeEqualToSize(self.bounds.size, boundsSizeAtFrameBufferEpoch) &&
        !CGSizeEqualToSize(self.bounds.size, CGSizeZero)) {
        runSynchronouslyOnVideoProcessingQueue(^{
            [self destroyDisplayFramebuffer];
            [self createDisplayFramebuffer];
            [self recalculateViewGeometry];
        });
    }
}

- (void)recalculateViewGeometry;
{
    runSynchronouslyOnVideoProcessingQueue(^{
        CGFloat heightScaling, widthScaling;
        
        CGSize currentViewSize = self.viewBounds.size;
        
        //    CGFloat imageAspectRatio = inputImageSize.width / inputImageSize.height;
        //    CGFloat viewAspectRatio = currentViewSize.width / currentViewSize.height;
        
        CGRect insetRect = AVMakeRectWithAspectRatioInsideRect(inputImageSize, self.viewBounds);

在xcode11和iOS13开始，系统对在子线程中做UI操作要求更加严格。千万不要在子线程中使用与UI相关的代码