ios - iOS:在CGContext上绘制最终会模糊

我有一个应用程序，该应用程序显示在其顶部具有UIImage的文档，您可以在其中绘制线条等以突出显示内容。

如果我一直画线(触摸，画图，抬起手指，然后在屏幕的其他区域重复)

线条逐渐模糊。

这是我的触摸代码，我将 kCGBlendModeCopy 用于blendmode，但已使用 kCGBlendModeNormal 。 DrawingView是一个UIImageView。

更新
这是我已经画过的线，它们越老，模糊的程度就越多，这就像每增加一条线都会衰减旧的线。在iPad 2 ios8上测试iPad mini Retina ios7

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

    mouseSwiped = NO;

    if ( self.drawingEnabled )
    {
        UITouch *touch = [touches anyObject];
        lastPoint = [touch locationInView:self.drawingView];

        UIGraphicsBeginImageContext(self.drawingView.frame.size);
        [self.drawingView.image drawInRect:CGRectMake(0, 0, self.drawingView.frame.size.width, self.drawingView.frame.size.height) blendMode:kCGBlendModeCopy alpha:1.0];
    }
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {

    if ( self.drawingEnabled )
    {
        mouseSwiped = YES;
        UITouch *touch = [touches anyObject];

        CGPoint currentPoint = [touch locationInView:self.drawingView];

        CGContextRef ctxt = UIGraphicsGetCurrentContext();
        CGContextMoveToPoint(ctxt, lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(ctxt, currentPoint.x, currentPoint.y);
        CGContextSetLineCap(ctxt, kCGLineCapRound);
        CGContextSetLineWidth(ctxt, self.brush );
        CGContextSetRGBStrokeColor(ctxt, self.redColour, self.greenColour, self.blueColour, OPACITY);

        if (self.eraserOn)
        {
            CGContextSetBlendMode(ctxt,kCGBlendModeClear);
        }
        else
        {
            CGContextSetBlendMode(ctxt,kCGBlendModeCopy);
        }

        CGContextStrokePath(ctxt);
        self.drawingView.image = UIGraphicsGetImageFromCurrentImageContext();

        lastPoint = currentPoint;
    }
}

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event
{


    [super touchesCancelled:touches withEvent:event];

    UIGraphicsEndImageContext();

    if(!mouseSwiped)
    {
        //self.drawingView.image = nil;
    }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {


    if ( self.drawingEnabled )
    {

        if(!mouseSwiped) {
            UIGraphicsEndImageContext();

            UIGraphicsBeginImageContext(self.drawingView.frame.size);
            [self.drawingView.image drawInRect:CGRectMake(0, 0, self.drawingView.frame.size.width, self.drawingView.frame.size.height)];
            CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
            CGContextSetLineWidth(UIGraphicsGetCurrentContext(), self.brush);
            CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), self.redColour, self.greenColour, self.blueColour, OPACITY);
            CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
            CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
            CGContextStrokePath(UIGraphicsGetCurrentContext());
            CGContextFlush(UIGraphicsGetCurrentContext());
            self.drawingView.image = UIGraphicsGetImageFromCurrentImageContext();
            UIGraphicsEndImageContext();
        }

        if (self.delegate)
        {
            [self.delegate drawingUpated];
        }

        //NSLog(@"%@  ---  %@", NSStringFromCGRect(self.frame) , NSStringFromCGRect(self.drawingView.frame) );
    }
}

最佳答案

事实证明，这与我如何设置自我框架有关。 drawingView和内部图像的大小。

图像是1005 x 720
drawingView是719.9的1004.2，因此存在一个舍入问题。每次我画一条新线，它都会四舍五入。