在我的iOS应用程序中,我试图用CoreGraphics绘制曲线.绘图本身工作正常,但在视网膜显示器上,图像使用相同的分辨率绘制,不会使像素倍增.结果是像素化图像.
我正在绘制使用以下功能：
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
UITouch *touch = [touches anyObject];
CGPoint currentPoint = [touch locationInView:self.canvasView];
UIGraphicsBeginImageContext(self.canvasView.frame.size);
[canvasView.image drawInRect:self.canvasView.frame];
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextSetShouldAntialias(ctx,YES);
CGContextSetLineCap(ctx,kCGLineCapRound);
CGContextSetlinewidth(ctx,5.0);
CGContextSetRGBstrokeColor(ctx,1.0,0.0,1.0);
CGContextBeginPath(ctx);
CGContextMovetoPoint(ctx,lastPoint.x,lastPoint.y);
CGContextAddLinetoPoint(ctx,currentPoint.x,currentPoint.y);
CGContextstrokePath(ctx);
canvasView.image = UIGraphicsGetimageFromCurrentimageContext();
UIGraphicsEndImageContext();
lastPoint = currentPoint;
// some code omitted from this example
}
我发现的建议是use the scaleFactor property,或CGContextSetShouldAntialias() function,但这两个都没有帮助到目前为止. (虽然我可能不正确地使用它们)
任何帮助将不胜感激.
解决方法
您需要用UIGraphicsBeginImageContext替换
if (UIGraphicsBeginImageContextWithOptions != NULL) {
UIGraphicsBeginImageContextWithOptions(size,NO,0.0);
} else {
UIGraphicsBeginImageContext(size);
}
UIGraphicsBeginImageContextWithOptions是在4.x软件中引入的.如果要在3.x设备上运行此代码,则需要使用弱链接UIKit框架.如果您的部署目标是4.x或更高版本,您可以使用UIGraphicsBeginImageContextWithOptions,而无需任何额外的检查.