我正在使用CoreGraphics来实现对我来说工作正常的自由手绘图,现在我想为此绘图实现撤消功能,以便用户可以清除其最后一个笔画。使用CoreGraphics绘图
这是我工作UITouchesBegin和UITouchesMoved的绘图方法。
-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event{
UITouch *touch = [touches anyObject];
previousPoint2 = previousPoint1;
previousPoint1 = [touch previousLocationInView:self];
currentPoint = [touch locationInView:self];
// calculate mid point
CGPoint mid1 = midPoint(previousPoint1, previousPoint2);
CGPoint mid2 = midPoint(currentPoint, previousPoint1);
CGMutablePathRef path = CGPathCreateMutable();
CGPathMoveToPoint(path, NULL, mid1.x, mid1.y);
CGPathAddQuadCurveToPoint(path, NULL, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y);
CGRect bounds = CGPathGetBoundingBox(path);
CGPathRelease(path);
drawBox = bounds;
//Pad our values so the bounding box respects our line width
drawBox.origin.x -= self.lineWidth * 2;
drawBox.origin.y -= self.lineWidth * 2;
drawBox.size.width += self.lineWidth * 4;
drawBox.size.height += self.lineWidth * 4;
UIGraphicsBeginImageContext(drawBox.size);
[self.layer renderInContext:UIGraphicsGetCurrentContext()];
curImage = UIGraphicsGetImageFromCurrentImageContext();
[curImage retain];
UIGraphicsEndImageContext();
[self setNeedsDisplayInRect:drawBox];
}
-(void)drawRect:(CGRect)rect {
[curImage drawAtPoint:CGPointMake(0, 0)];
CGPoint mid1 = midPoint(previousPoint1, previousPoint2);
CGPoint mid2 = midPoint(currentPoint, previousPoint1);
context = UIGraphicsGetCurrentContext();
[self.layer renderInContext:context];
CGContextMoveToPoint(context, mid1.x, mid1.y);
// Use QuadCurve is the key
CGContextAddQuadCurveToPoint(context, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y);
CGContextSetLineCap(context, kCGLineCapRound);
CGContextSetLineWidth(context, self.lineWidth);
CGContextSetStrokeColorWithColor(context, self.lineColor.CGColor);
CGContextStrokePath(context);
[super drawRect:rect];
}
http://stackoverflow.com/questions/5741880/iphone-paint-application – 2012-04-09 10:49:59
我试图在问题的代码,但不能这样做成功。 [Here](http://stackoverflow.com/questions/6689600/undo-drawing-in-paint-application) – 2012-04-09 10:50:58