修改GPUImageView中的recalculateViewGeometry方法

一、定义一个viewBounds属性来保存bounds

/// 解决首次启动很慢的问题
@property (nonatomic, assign) CGRect viewBounds;

二、修改layoutSubviews

- (void)layoutSubviews {
    [super layoutSubviews];
// 记录bounds
    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];
        });
    }
}

三、修改recalculateViewGeometry

- (void)recalculateViewGeometry;
{
    runSynchronouslyOnVideoProcessingQueue(^{
        CGFloat heightScaling, widthScaling;
        
// 修改这句
        CGSize currentViewSize = self.viewBounds.size;
        
        //    CGFloat imageAspectRatio = inputImageSize.width / inputImageSize.height;
        //    CGFloat viewAspectRatio = currentViewSize.width / currentViewSize.height;
        
// 修改这句
        CGRect insetRect = AVMakeRectWithAspectRatioInsideRect(inputImageSize, self.viewBounds);
        
        switch(_fillMode)
        {
            case kGPUImageFillModeStretch:
            {
                widthScaling = 1.0;
                heightScaling = 1.0;
            }; break;
            case kGPUImageFillModePreserveAspectRatio:
            {
                widthScaling = insetRect.size.width / currentViewSize.width;
                heightScaling = insetRect.size.height / currentViewSize.height;
            }; break;
            case kGPUImageFillModePreserveAspectRatioAndFill:
            {
                //            CGFloat widthHolder = insetRect.size.width / currentViewSize.width;
                widthScaling = currentViewSize.height / insetRect.size.height;
                heightScaling = currentViewSize.width / insetRect.size.width;
            }; break;
        }
        
        imageVertices[0] = -widthScaling;
        imageVertices[1] = -heightScaling;
        imageVertices[2] = widthScaling;
        imageVertices[3] = -heightScaling;
        imageVertices[4] = -widthScaling;
        imageVertices[5] = heightScaling;
        imageVertices[6] = widthScaling;
        imageVertices[7] = heightScaling;
    });
    
//    static const GLfloat imageVertices[] = {
//        -1.0f, -1.0f,
//        1.0f, -1.0f,
//        -1.0f,  1.0f,
//        1.0f,  1.0f,
//    };
}

参考文章：
GPUImage recalculateViewGeometry卡UI线程问题