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

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
}