Question

我最近问过一个类似的问题，关于如何为UIView添加半透明效果，并得到了很好的回应。

然而，它使用了大量的CPU处理能力，因此我使用了答案背后的一些想法，但使用GPUImage进行了过滤，效率更高。

它适用于静态屏幕，但我想用动画更改背景UIImageView的图像。但是，当我设置UIView以在过渡期间对背景进行采样时，似乎忽略了过渡并在动画开始之前显示新的图像。
相关代码如下（询问您是否需要更多！）：

包含自定义UIView和UIImageView背景的超级视图：

//The Transition
[contentView setScheduled:YES]; //Starts the sampling every 0.2 seconds

//bg is the UIImageView and contentView is the 'translucent' UIView subclass
[UIView transitionWithView:bg duration:1.0 options:UIViewAnimationOptionTransitionCrossDissolve animations:^{
    [bg setImage:newImage];
}completion:^(BOOL finished){
    [contentView setScheduled:NO];
}];

然后在UIView子类中：

- (UIImage *)snapshotOfSuperview:(UIView *)superview
{
CGFloat scale = 0.5;
if (([UIScreen mainScreen].scale > 1 || self.contentMode == UIViewContentModeScaleAspectFill))
{
    CGFloat blockSize = 12.0f/5;
    scale = blockSize/MAX(blockSize * 2, floor(self.blurRadius));
}
UIGraphicsBeginImageContextWithOptions(self.bounds.size, YES, scale);
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextTranslateCTM(context, -self.frame.origin.x, -self.frame.origin.y);
self.hidden=YES; //Don't take a snapshot of the view
[superview.layer renderInContext:context];
self.hidden=NO;
UIImage *snapshot = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return snapshot;
}

-(void)updateViewBG{
UIImage *superviewImage = [self snapshotOfSuperview:self.superview];

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{
    GPUImageGaussianBlurFilter* filter = [[GPUImageGaussianBlurFilter alloc] init];
    filter.blurSize = 0.8f;
    UIImage* newBG = [self applyTint:self.tintColour image:[filter imageByFilteringImage:superviewImage]];

    dispatch_async(dispatch_get_main_queue(), ^{
        self.layer.contents = (id)newBG.CGImage;
        self.layer.contentsScale = newBG.scale;
    });
});
}

-(UIImage*)applyTint:(UIColor*)colour image:(UIImage*)inImage{
UIImage *newImage;
if (colour) {
    UIGraphicsBeginImageContext(inImage.size);

    CGContextRef ctx = UIGraphicsGetCurrentContext();
    CGRect area = CGRectMake(0, 0, inImage.size.width, inImage.size.height);

    CGContextScaleCTM(ctx, 1, -1);
    CGContextTranslateCTM(ctx, 0, -area.size.height);
    CGContextSaveGState(ctx);
    CGContextClipToMask(ctx, area, inImage.CGImage);
    [colour set];
    CGContextFillRect(ctx, area);
    CGContextRestoreGState(ctx);
    CGContextSetBlendMode(ctx, kCGBlendModeLighten);
    CGContextDrawImage(ctx, area, inImage.CGImage);
    newImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
}else{
    newImage = inImage;
}
return newImage;
}

-(void)displayLayer:(CALayer *)layer{
[self updateViewBG];
}

如何获得跟随动画的背景？

Answer 1

我认为问题在于，只要更改图像，就会调用displayLayer（忽略正在进行的转换），因此新图像用于半透明。

您应该修改updateViewBG，以便在转换完成之前不会更新图层内容。例如，您可以在类中添加一个标志，在开始转换时设置它，并在完成时重置它。设置标志后，您不要拨打updateViewBG。

[UIView transitionWithView:bg duration:1.0 options:UIViewAnimationOptionTransitionCrossDissolve animations:^{

    self.isTransitionInProgress = YES;
    [bg setImage:newImage];

}completion:^(BOOL finished){

    [contentView setScheduled:NO];

    self.isTransitionInProgress = NO;
    [contentView.layer setNeedsDisplay];

}];



-(void)displayLayer:(CALayer *)layer{
    if (!self.isTransitionInProgress)
        [self updateViewBG];
}

在UIView背后捕捉（动画）屏幕

1 个答案: