Why the responds is slow as stroke PNG images with UItouch?

Question

I used below code to stroke PNG with finger move. There has 2 UIImage View. One locates at background to put background image there. The other one is clear UIImage view to stroke PNG images on top of it.

  -(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
   {
       for (UITouch * touch in touches) {

          currentPoint = [touch locationInView:self.view];
          lastPoint = [touch previousLocationInView:self.view];

    //set up array to make space between PNG images
          if (ABS(currentPoint.x-lastPoint.x)>16
               || ABS(currentPoint.y - lastPoint.y) > 13) {

              [brushLocations addObject:[NSValue valueWithCGPoint:currentPoint]];


      }
        [self drawingWithArray];

 }

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

         [brushLocations removeAllObjects];//reset


     }


 -(void)drawingWithArray{



     UIGraphicsBeginImageContext(self.view.frame.size);
     [drawImage.image drawInRect:CGRectMake(0, 0, drawImage.frame.size.width,    drawImage.frame.size.height)];

     for (int i=0; i<[brushLocations count]; i++) {

 CGPoint center =[[brushLocations objectAtIndex:i]CGPointValue];


    // bokehImage is UIImage 

         bokehImage=[bokehImgArray objectAtIndex: i%[bokehImgArray count]];

 /// the PNG images are not semi-transparent, even set the alpha is 0.5??

         [bokehImage drawAtPoint:center blendMode:kCGBlendModeOverlay alpha:0.5f];

//drawImage is uiimage view on top of background image view for stroke PNG images.
     drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
     UIGraphicsEndImageContext();

}

Now, I got problem is the respond is slow. The PNG images didn’t display immediately while finger move on device (IPad4).

Also, the PNG images are not semi-transparent. I suppose that the function of “drawAtPoint .. blendMode .. alpha “ can make images to be semi-transparent (set 0.5 alpha).

Answer 1

Yes, something like this should work:

-(void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
    for (UITouch * touch in touches) {
        currentPoint = [touch locationInView:self.view];
        lastPoint = [touch previousLocationInView:self.view];
        //set up array to make space between PNG images
        if (ABS(currentPoint.x-lastPoint.x)>16
            || ABS(currentPoint.y - lastPoint.y) > 13) {
            [brushLocations addObject:[NSValue valueWithCGPoint:currentPoint]];
        }
//        [self drawingWithArray]; // don't call draw routine during touch handler
         [self setNeedsDisplay]; // queue the redraw instead
    }
}

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
// Not needed here
//    [brushLocations removeAllObjects];//reset
}

//-(void)drawingWithArray
- (void)drawRect:(CGRect)rect
{
    // CGContext is already set when drawRect is called
//    UIGraphicsBeginImageContext(self.view.frame.size);
//    [drawImage.image drawInRect:CGRectMake(0, 0, drawImage.frame.size.width, drawImage.frame.size.height)];
    [drawImage.image drawInRect:rect];
    for (int i=0; i<[brushLocations count]; i++) {
        CGPoint center =[[brushLocations objectAtIndex:i]CGPointValue];
        // bokehImage is UIImage
        bokehImage=[bokehImgArray objectAtIndex: i%[bokehImgArray count]];
        // the PNG images are not semi-transparent, even set the alpha is 0.5??
        [bokehImage drawAtPoint:center blendMode:kCGBlendModeOverlay alpha:0.5f];
        //drawImage is uiimage view on top of background image view for stroke PNG images.
        drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
//        UIGraphicsEndImageContext();
    }
    [brushLocations removeAllObjects];//reset
}