UIBezierPath数组渲染问题（如何使用CGLayerRef进行优化）

问题描述

朋友，我正在使用UIBezierPaths进行自由手绘，并且一切正常，为此，我将路径存储在路径数组中，一切正常，而在渲染时，我正在遍历整个数组并渲染路径，但是一旦数组数量增加，绘制时就会出现延迟，下面是我的drawRect代码。请帮我找出问题所在

friends, I am working with UIBezierPaths, for free hand drawing , and everything works fine, for this I am storing my paths in a path array, everything works fine, while rendering, I am looping the whole array and rendering the paths,but soon as the array count increases, I see a lag while drawing, below is my drawRect code. please help me out in finding where I am going wrong

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

    UITouch *mytouch=[[touches allObjects] objectAtIndex:0];

    m_previousPoint2 = m_previousPoint1;
    m_previousPoint1 = [mytouch previousLocationInView:self];
    m_currentPoint = [mytouch locationInView:self];

    CGPoint mid1    = midPoint(m_previousPoint1, m_previousPoint2); 
    CGPoint mid2    = midPoint(m_currentPoint, m_previousPoint1);  

    testpath = CGPathCreateMutable();
    CGPathMoveToPoint(testpath, NULL, mid1.x, mid1.y);

    CGPathAddQuadCurveToPoint(testpath, NULL, m_previousPoint1.x, m_previousPoint1.y, mid2.x, mid2.y);      


    CGRect bounds = CGPathGetBoundingBox(testpath);   

    CGPathRelease(testpath);


    CGRect 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;


    CGContextRef context = UIGraphicsGetCurrentContext();
    context = CGLayerGetContext(myLayerRef);


    [self.layer renderInContext:UIGraphicsGetCurrentContext()];      

    [self setNeedsDisplayInRect:drawBox];    

}


- (void)drawRect:(CGRect)rect
{   
    CGContextRef context = UIGraphicsGetCurrentContext();

    if(myLayerRef == nil)
    {            
        myLayerRef = CGLayerCreateWithContext(context, self.bounds.size, NULL);
    }

    [self.layer renderInContext:context];   


    CGPoint mid1 = midPoint(m_previousPoint1, m_previousPoint2); 
    CGPoint mid2 = midPoint(m_currentPoint, m_previousPoint1);


    CGContextMoveToPoint(context, mid1.x, mid1.y);
    CGContextAddQuadCurveToPoint(context, m_previousPoint1.x, m_previousPoint1.y, mid2.x, mid2.y); 
    CGContextSetLineCap(context, kCGLineCapRound);
    CGContextSetLineWidth(context, self.lineWidth);
    CGContextSetStrokeColorWithColor(context, self.lineColor.CGColor);

    CGContextSetFlatness(context, 0.1);

    CGContextSetAllowsAntialiasing(context, true);

    CGContextStrokePath(context);

    [super drawRect:rect];  

 }

根据@borrrden的以下讨论更新了代码

Code updated according to the below discussion by @borrrden

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Ranjit

RegardsRanjit

推荐答案

WWDC 2012会议上讨论了这个确切的问题。我认为这被称为iOS性能：图形或类似的东西。你一定要看。

There is an excellent session in the WWDC 2012 sessions about this exact problem. I think it is called iOS performance: Graphics or something similar. You should definitely watch it.

摘要是，请勿将其存储在路径中。无需保留此路径信息。存储一个单独的上下文（最好使用CGLayer）并在其中进行绘制（就像您将点添加到路径，将点添加到上下文界面一样）。然后在drawRect中，只需将该层绘制到当前图形上下文中即可。另外，请确保仅在已更改的矩形上调用 setNeedsDisplay ，否则您很可能在高分辨率设备上遇到问题。

The summary is, DON'T store it in a path. There is no need to keep this path information around. Store a separate context (CGLayer is best) and draw into that (just like you add points to the path, add points to the context intead). Then in your drawRect, simply draw that layer into the current graphics context. Also be sure to only call setNeedsDisplay on the rectangle that changed, or you will most likely run into problems on a high resolution device.

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