Memory management in Coregraphics (iOS)

Question

I am working on a drawing application, I am using CGlayers for drawing, So I open my canvas for drawing on click of a button,

I am using UIBezierPath and then converting it to CGPath in touchesMoved below and then using it to draw

 -(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
    {           
        if (ctr == 4)
        {
            m_touchMoved = true;

            self.currentPath = [[DrawingPath alloc] init];

            [self.currentPath setPathColor:self.lineColor];
            self.currentPath.pathWidth = [NSString stringWithFormat:@"%f",self.lineWidth];


             pts[3] = midPoint(pts[2], pts[4]);// move the endpoint to the middle of the line joining the second control point of the first Bezier segment and the first control point of the second Bezier segment
            [self.currentPath.path moveToPoint:pts[0]];
            [self.currentPath.path addCurveToPoint:pts[3] controlPoint1:pts[1] controlPoint2:pts[2]];

            CGPathRef cgPath = self.currentPath.path.CGPath;
            mutablePath = CGPathCreateMutableCopy(cgPath);        

            [self setNeedsDisplay];

            pts[0] = pts[3];
            pts[1] = pts[4];
            ctr = 1;
        }

    }

This is my drawRect method

- (void)drawRect:(CGRect)rect
    {
       switch (m_drawStep)
       {
           case DRAW:
           {

               CGContextRef context = UIGraphicsGetCurrentContext();//Get a reference to current context(The context to draw)


               if(currentDrawingLayer == nil)
               {
                   CGFloat scale = self.contentScaleFactor;
                   CGRect bounds = CGRectMake(0, 0, self.bounds.size.width * scale, self.bounds.size.height * scale);
                   CGLayerRef layer = CGLayerCreateWithContext(context, bounds.size, NULL);
                   CGContextRef layerContext = CGLayerGetContext(layer);
                   CGContextScaleCTM(layerContext, scale, scale);
                   //currentDrawingLayer = layer;
                   [self setCurrentDrawingLayer:layer];
                   CGLayerRelease(currentDrawingLayer);
               }




               CGContextRef layerContext = CGLayerGetContext(currentDrawingLayer);
               CGContextBeginPath(layerContext);
               CGContextAddPath(layerContext, mutablePath);
               CGContextSetLineWidth(layerContext, self.lineWidth);
               CGContextSetLineCap(layerContext, kCGLineCapRound);
               CGContextSetLineJoin(layerContext, kCGLineJoinRound);
               CGContextSetAllowsAntialiasing(layerContext, YES);
               CGContextSetShouldAntialias(layerContext, YES);
               CGContextSetStrokeColorWithColor(layerContext, self.lineColor.CGColor);
               CGContextSetFillColorWithColor(layerContext, self.lineColor.CGColor);
               CGContextSetBlendMode(layerContext,kCGBlendModeNormal);
               CGContextStrokePath(layerContext);
               CGPathRelease(mutablePath);

              CGContextDrawLayerInRect(context, self.bounds, currentDrawingLayer );
           }
               break;

    }

I have manually created setter method

-(void)setCurrentDrawingLayer:(CGLayerRef)layer
{
    CGLayerRetain(layer);
    CGLayerRelease(currentDrawingLayer);
    currentDrawingLayer = layer;
}

Now when user clicks on savebutton, I get image out of the canvas this way

-(void)getImageFromCanvas
{
    UIGraphicsBeginImageContextWithOptions(self.bounds.size, NO,0.0);//Creates a bitmap based graphics context with
                                                                         //specified options
        [self.layer renderInContext:UIGraphicsGetCurrentContext()];//Renders the reciever and its layers into specified
                                                                   //context.
        m_curImage = UIGraphicsGetImageFromCurrentImageContext();  
        UIGraphicsEndImageContext();//Removes the current context from top of stack

     if(currentDrawingLayer)
     {
            CGLayerRelease(currentDrawingLayer);
     }

  [m_delegate performSelectorOnMainThread:@selector(getCanVasViewImage:)
                                 withObject:m_curImage
                              waitUntilDone:NO];


}

I get the image and show it on a grid on the screen with resized image, But when I perform these operations, my memory usage always spikes up, and it is not decreasing,here is the screen shot after creating three drawings

To resize image , I use this, I run this in a separate thread

dispatch_async(dispatch_get_global_queue(0,0), ^{
    UIGraphicsBeginImageContextWithOptions(newSize, NO, 0.0);

     [image1 drawInRect:CGRectMake(0,0,newSize.width,newSize.height)];


     UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext();

     UIGraphicsEndImageContext();
});

memory goes on increasing, and finally after creating some 30 drawings, my app crashes, because memory spikes upto 550MB

So, I am not understanding where I am going wrong, How I can manage memory issues while drawing.

Answer 1

Your mutablePath leak, because you release the previous one in -drawRect: (and only if m_drawStep == DRAW). As -setNeedDisplay just marks the view as needing to be redrawn. -drawRect: is only send on the next drawing cycle, so several -touchesMoved:withEvent: may append between, drawing cycles. There is also some leak, that can happen when m_drawStep != DRAW.

So remove CGPathRelease(mutablePath) from -drawRect: method and release it in -touchesMoved:withEvent:

CGPathRef cgPath = self.currentPath.path.CGPath;
CGPathRelease(mutablePath);
mutablePath = CGPathCreateMutableCopy(cgPath);        

[self setNeedsDisplay];

Also release the CGLayerRef you create after setting it in -setCurrentDrawingLayer: because you retain it in -setCurrentDrawingLayer:.

if(currentDrawingLayer == nil)
{
    // ...
    CGLayerRef layer = CGLayerCreateWithContext(context, bounds.size, NULL); // layer is created, refCount == 1
    // ...
    [self setCurrentDrawingLayer:layer]; // layer is retained by -setCurrentDrawingLayer:, refCount == 2
     CGLayerRelease(layer); // release layer, refCount == 1

     // without it the previous release layer refCount still == 2, so in -setCurrentDrawingLayer:
     // CGLayerRelease(currentDrawingLayer) decrement refCount to 1 and leak...
}