Question

I have problem with my app. It is developed for both devices. On iPad it works great, but if I run it on iPhone it sucks. It slows down a lot. Note:I use storyboards and same View controllers and delegates for both devices.

Any suggestions?

Is drawRect —- leaking memory

It is iOS 5, On iPhone 3, 3S, 4, and 4S. Everyone is experiencing problems with this.
It draws in response to finger movement.
If I touch the screen, the line I draw falls behind….. and I don’t know why.
On iPad it works great .

maybe but main there could be problem here

- (void)drawRect:(CGRect)rect
{

    CGImageRef cgImage = CGBitmapContextCreateImage(offScreenBuffer);
    UIImage *uiImage = [[UIImage alloc] initWithCGImage:cgImage];

    CGImageRelease(cgImage);

    [uiImage drawInRect:self.bounds];
    [uiImage release];

}

this method is called from touches events …

-(void)drawPoint:(UITouch *)touch {

currentLoc = [[PointLocation alloc] init];

currentLoc.location = [touch locationInView:self];

self.previousPoint = self.point;

self.point = currentLoc;
[self drawToBuffer];

[currentLoc release];
}

and this is draw to buffer….

-(void)drawToBuffer {

CGFloat color[4] = {R,G,B,A};

if (self.previousPoint != nil) {
    CGContextSetRGBStrokeColor(offScreenBuffer, color[0],color[1],color[2],color[3]);

    CGContextBeginPath(offScreenBuffer);
    CGContextSetLineWidth(offScreenBuffer, lane);
    CGContextSetLineCap(offScreenBuffer, kCGLineCapRound);

    CGContextMoveToPoint(offScreenBuffer, previousPoint.location.x, previousPoint.location.y);
    CGContextAddLineToPoint(offScreenBuffer, point.location.x, point.location.y);

    CGContextDrawPath(offScreenBuffer, kCGPathStroke);

}
 [self setNeedsDisplay];
}

but now i really don’t know and have no idea…:(

creating offscreenbuffer
-(CGContextRef)setupBuffer {

CGSize size = self.bounds.size;

CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();

CGContextRef context = CGBitmapContextCreate(NULL, size.width, size.height, 8, size.width*4, colorSpace, kCGImageAlphaPremultipliedLast);


CGColorSpaceRelease(colorSpace);

CGContextTranslateCTM(context, 0, size.height);
CGContextScaleCTM(context, 1.0, -1.0);


return context;

}

Answer 1

You can cut a few corners by drawing the CGImage directly, without the UIImage step, using

CGContextRef context = UIGraphicsGetCurrentContext();
CGContextDrawImage(context, self.bounds, cgImage);

this will probably flip the image vertically, but that can be fixed. It may or may not make a difference, I don’t know what overhead UIImage adds.

As for strange performance differences, you may want to look into the memory alignment of the underlying bitmap. (see the comments for my question regarding offscreenBuffer)

update regarding the code shown in the updated question

The code is not really efficient. For every touch event, you have this happening:

1. a call to -drawPoint:
2. allocation, init, release and dealloc of PointLocation, assignment using setter (self.point = ...)
3. a call to -drawToBuffer
4. setting stroke color/line style/line cap on your offscreen context
5. beginpath, movetopoint, addlinetopoint, drawpath

these may each not take a lot of time, but added together it might just make a difference if you would reduce the complexity. Per item you can try the following:

1. reduce the number of calls, by doing some stuff directly in/from the touch event functions
2. don’t box the CGPoint in an object, but just use two CGPoint ivars instead of properties. So it will look like: lastPoint = currPoint; currPoint = point;, with the rest of the code adapted of course
3. see point 1.
4. if you keep the same CGContext backing throughout the lifecycle of the view, you only need to set these once on initialization. Otherwise, if you do need to switch styles once in a while, use CGContextSaveGState(offscreenBuffer) and CGContextRestoreGState(offscreenBuffer) to see if it is faster

5. there is a neat function for just drawing a simple line: CGContextStrokeLineSegments, which may be faster. Use it like this:

   CGPoint points[2] = { lastPoint, currPoint };
CGContextStrokeLineSegments(offscreenBuffer,points,2);

6. profile/profile/profile: test to see if changes make things faster, by measuring rendering time. At the top: NSDate *tstart = [NSDate date]; and at the bottom NSLog(@"drawRect took %f ms",-[tstart timeIntervalSinceNow]*1000);

You can tackle each of these points individually and check if it still works.

Good luck!