[英]Capturing (animated) screen behind UIView
最近我問了一個類似的問題,關於如何向UIView添加半透明效果,並獲得了很好的答復。
但是,它使用了大量的CPU能力進行處理,因此我使用了答案背后的一些想法,但是使用了效率更高的GPUImage進行了過濾。
它適用於靜態屏幕,但是我想用動畫更改背景UIImageView
的圖像。 但是,當我將UIView
設置為在過渡期間對背景進行采樣時,似乎會忽略過渡並在動畫開始之前顯示新的Image。
相關代碼如下(如果需要更多,請詢問!):
包含自定義UIView
和UIImageView
背景的超級視圖:
//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子類中:
- (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];
}
如何獲得背景以跟隨動畫?
我認為問題在於,一旦更改圖像,就會調用displayLayer(不考慮進行中的過渡),因此新圖像將用於半透明。
您應該修改updateViewBG
以便它不會在過渡完成之前更新圖層內容。 例如,您可以將標記添加到類中,在開始轉換時進行設置,並在轉換完成時將其重置。 設置標志后,請勿調用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];
}
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