据我目前了解,每当我在UIView的drawRect:方法中绘制任何内容时,整个上下文都会被擦除然后重新绘制。
因此,我必须像这样做才能绘制一系列点:
方法A:在每次调用时重新绘制所有内容
- (void)drawRect:(CGRect)rect {
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextDrawImage(context, self.bounds, maskRef); //draw the mask
CGContextClipToMask(context, self.bounds, maskRef); //respect alpha mask
CGContextSetBlendMode(context, kCGBlendModeColorBurn); //set blending mode
for (Drop *drop in myPoints) {
CGContextAddEllipseInRect(context, CGRectMake(drop.point.x - drop.size/2, drop.point.y - drop.size/2, drop.size, drop.size));
}
CGContextSetRGBFillColor(context, 0.5, 0.0, 0.0, 0.8);
CGContextFillPath(context);
}
这意味着我必须存储所有的点(这是可以接受的),并每次想添加一个新点时重新绘制它们。不幸的是,这会导致我的性能非常差,我相信有其他更有效的方法来完成这个任务。编辑:使用MrMage的代码,我尝试了以下方法,但速度仍然很慢,颜色混合也无效。有没有其他方法可以尝试? 方法B:将先前绘制的内容保存在UIImage中,仅绘制新内容和该图像
- (void)drawRect:(CGRect)rect
{
//draw on top of the previous stuff
UIGraphicsBeginImageContext(self.frame.size);
CGContextRef ctx = UIGraphicsGetCurrentContext(); // ctx is now the image's context
[cachedImage drawAtPoint:CGPointZero];
if ([myPoints count] > 0)
{
Drop *drop = [myPoints objectAtIndex:[myPoints count]-1];
CGContextClipToMask(ctx, self.bounds, maskRef); //respect alpha mask
CGContextAddEllipseInRect(ctx, CGRectMake(drop.point.x - drop.dropSize/2, drop.point.y - drop.dropSize/2, drop.dropSize, drop.dropSize));
CGContextSetRGBFillColor(ctx, 0.5, 0.0, 0.0, 1.0);
CGContextFillPath(ctx);
}
[cachedImage release];
cachedImage = [UIGraphicsGetImageFromCurrentImageContext() retain];
UIGraphicsEndImageContext();
//draw on the current context
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextDrawImage(context, self.bounds, maskRef); //draw the mask
CGContextSetBlendMode(context, kCGBlendModeColorBurn); //set blending mode
[cachedImage drawAtPoint:CGPointZero]; //draw the cached image
}
编辑: 最终,我将下面提到的方法之一与仅在新矩形中重绘相结合。结果是: 快速方法:
- (void)addDotAt:(CGPoint)point
{
if ([myPoints count] < kMaxPoints) {
Drop *drop = [[[Drop alloc] init] autorelease];
drop.point = point;
[myPoints addObject:drop];
[self setNeedsDisplayInRect:CGRectMake(drop.point.x - drop.dropSize/2, drop.point.y - drop.dropSize/2, drop.dropSize, drop.dropSize)]; //redraw
}
}
- (void)drawRect:(CGRect)rect
{
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextDrawImage(context, self.bounds, maskRef); //draw the mask
CGContextClipToMask(context, self.bounds, maskRef); //respect alpha mask
CGContextSetBlendMode(context, kCGBlendModeColorBurn); //set blending mode
if ([myPoints count] > 0)
{
Drop *drop = [myPoints objectAtIndex:[myPoints count]-1];
CGPathAddEllipseInRect (dotsPath, NULL, CGRectMake(drop.point.x - drop.dropSize/2, drop.point.y - drop.dropSize/2, drop.dropSize, drop.dropSize));
}
CGContextAddPath(context, dotsPath);
CGContextSetRGBFillColor(context, 0.5, 0.0, 0.0, 1.0);
CGContextFillPath(context);
}
谢谢大家!