我有很多CALayer在我的应用程序运行时动态创建，我需要能够生成这些的一个位图，稍后将被屏蔽。
当我需要创建蒙版时，CALayers已经被绘制到背景中（也使用了shouldRasterize = YES），并且使用renderInContext我能够获得位图。但是，随着CAlayers数量的增加，renderInContext引起的暂停变得越来越长。有没有我可以使用renderInContext的替代方法，或者我可以使用它来阻止我的应用暂时冻结？
理想情况是直接从内存/缓冲区/缓存中访问已经绘制的像素数据而不使用OpenGL，但我不确定CoreAnimation是否可以实现。
谢谢，任何其他信息都非常有用！
答案 0 :(得分：8)
Rob认为renderInContext:是在这里使用的正确方法是正确的。渲染上下文实际上将图层的像素数据渲染到上下文中。这是一个示例应用程序，它将在后台线程上绘制10,000个图层......
该应用程序执行以下操作：
这是代码......
首先，创建一个包含大量图层的子视图：
@implementation C4WorkSpace {
UIView *v;
dispatch_queue_t backgroundRenderQueue;
CFTimeInterval beginTime;
NSTimer *timer;
NSInteger timerCallCount;
}
-(void)setup {
//create a view to hold a bunch of CALayers
v = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 400, 400)];
v.center = CGPointMake(384,512);
//create a buch of CALayers and add them to a view
for(int i = 0; i < 10000; i++) {
CALayer *l = [[CALayer alloc] init];
l.frame = CGRectMake([self random:390],[self random:390],10,10);
l.backgroundColor = [UIColor blueColor].CGColor;
l.borderColor = [UIColor orangeColor].CGColor;
l.borderWidth = 2.0f;
[v.layer addSublayer:l];
}
//add the view to the application's main view
[self.view addSubview:v];
}
-(NSInteger)random:(NSInteger)value {
srandomdev();
return ((NSInteger)random())%value;
}
其次，创建一个启动计时器然后触发渲染的方法......
-(void)touchesBegan {
timer = [NSTimer scheduledTimerWithTimeInterval:0.03f target:self selector:@selector(printTime) userInfo:nil repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:timer forMode:NSDefaultRunLoopMode];
[self render];
}
-(void)printTime {
NSLog(@"%d (main thread running)",++timerCallCount);
}
第三，使用回调方法创建一个渲染循环，该方法在渲染完成后将图像放在屏幕上。
-(void)render {
NSLog(@"render was called");
//create the queue
backgroundRenderQueue = dispatch_queue_create("backgroundRenderQueue",DISPATCH_QUEUE_CONCURRENT);
//create a async call on the background queue
dispatch_async(backgroundRenderQueue, ^{
//create a cgcontext
NSUInteger width = (NSUInteger)v.frame.size.width;
NSUInteger height = (NSUInteger)v.frame.size.height;
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
NSUInteger bytesPerPixel = 4;
NSUInteger bytesPerRow = bytesPerPixel * width;
unsigned char *rawData = malloc(height * bytesPerRow);
NSUInteger bitsPerComponent = 8;
CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast | kCGBitmapByteOrder32Big);
//render the layer and its subviews
[v.layer renderInContext:context];
//create a callback async on the main queue when rendering is complete
dispatch_async(dispatch_get_main_queue(), ^{
//create an image from the context
UIImage *m = [UIImage imageWithCGImage:CGBitmapContextCreateImage(context)];
UIImageView *uiiv = [[UIImageView alloc] initWithImage:m];
//add the image view to the main view
[self.view addSubview:uiiv];
CGColorSpaceRelease(colorSpace);
CGContextRelease(context);
NSLog(@"rendering complete");
[timer invalidate];
});
});
}
注意：如果您的图层不在同一个子图层中，您可以轻松调用for循环，将上下文与每个CALayer的原点相互转换，并将每个图层单独绘制到上下文中< / p>
当我运行时，我得到以下输出：
2013-03-18 07:14:28.617 C4iOS[21086:907] render was called
2013-03-18 07:14:28.648 C4iOS[21086:907] 1 (main thread running)
2013-03-18 07:14:28.680 C4iOS[21086:907] 2 (main thread running)
2013-03-18 07:14:28.709 C4iOS[21086:907] 3 (main thread running)
2013-03-18 07:14:28.737 C4iOS[21086:907] 4 (main thread running)
2013-03-18 07:14:28.767 C4iOS[21086:907] 5 (main thread running)
2013-03-18 07:14:28.798 C4iOS[21086:907] 6 (main thread running)
2013-03-18 07:14:28.828 C4iOS[21086:907] 7 (main thread running)
2013-03-18 07:14:28.859 C4iOS[21086:907] 8 (main thread running)
2013-03-18 07:14:28.887 C4iOS[21086:907] 9 (main thread running)
2013-03-18 07:14:28.917 C4iOS[21086:907] 10 (main thread running)
2013-03-18 07:14:28.948 C4iOS[21086:907] 11 (main thread running)
2013-03-18 07:14:28.978 C4iOS[21086:907] 12 (main thread running)
2013-03-18 07:14:29.010 C4iOS[21086:907] 13 (main thread running)
2013-03-18 07:14:29.037 C4iOS[21086:907] 14 (main thread running)
2013-03-18 07:14:29.069 C4iOS[21086:907] 15 (main thread running)
2013-03-18 07:14:29.097 C4iOS[21086:907] 16 (main thread running)
2013-03-18 07:14:29.130 C4iOS[21086:907] 17 (main thread running)
2013-03-18 07:14:29.159 C4iOS[21086:907] 18 (main thread running)
2013-03-18 07:14:29.189 C4iOS[21086:907] 19 (main thread running)
2013-03-18 07:14:29.217 C4iOS[21086:907] 20 (main thread running)
2013-03-18 07:14:29.248 C4iOS[21086:907] 21 (main thread running)
2013-03-18 07:14:29.280 C4iOS[21086:907] 22 (main thread running)
2013-03-18 07:14:29.309 C4iOS[21086:907] 23 (main thread running)
2013-03-18 07:14:29.337 C4iOS[21086:907] 24 (main thread running)
2013-03-18 07:14:29.369 C4iOS[21086:907] 25 (main thread running)
2013-03-18 07:14:29.397 C4iOS[21086:907] 26 (main thread running)
2013-03-18 07:14:29.405 C4iOS[21086:907] rendering complete
答案 1 :(得分：3)
renderInContext:是这里最好的工具，但您不需要在主线程上运行它。只需将其移至后台线程，它就会停止冻结您的应用。