Lag while drawing in ios7

问题:

I am having an app in which I am doing some sketching on a view.

So far, it was working fine until I installed ios7.

My app uses touches moved method for recognizing the change of a movement. But when I draw a line, touches method gets called but line doesn't get updated until I touch ends in ios7.

So there is a slight lag in drawing.

It works fine on ios6 and on ios7 simulator but when i test it on a real ios7 device, there is a lag in drawing algorithm.

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
if (!isImageSelection) {

            mouseSwiped = NO;
            UITouch *touch = [touches anyObject];

            if ( [touch view] != baseview) {

                lastPoint2 = [touch locationInView:self.viewDrawing2];
            }
        }
    }

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

          //  NSLog(@"in image selection==%d touch moved   ",isImageSelection );

            mouseSwiped = YES;

            UITouch *touch = [touches anyObject];
            // if (([touch view] != btnInkColor) || ([touch view] != btnPenSize)  || ([touch view] != baseview)) {
            if ( [touch view] != baseview) {

                CGPoint currentPoint = [touch locationInView:self.viewDrawing];



                if(isEraser) {
                    // [[NSUserDefaults standardUserDefaults] floatForKey:@"strokeValue"];
                    UIGraphicsBeginImageContext(self.viewDrawing.frame.size);
                    [imgDrawing.image drawInRect:CGRectMake(0, 0, self.viewDrawing.frame.size.width, self.viewDrawing.frame.size.height)];
                    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
                    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), stroke);
                    //uncommented by prerak
                        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);

                    CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);
                    CGContextBeginPath(UIGraphicsGetCurrentContext());
                    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
                    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
                    CGContextStrokePath(UIGraphicsGetCurrentContext());
                    imgDrawing.image = UIGraphicsGetImageFromCurrentImageContext();
                    UIGraphicsEndImageContext();
                } else {
                    float strokeT= [[NSUserDefaults standardUserDefaults] floatForKey:@"strokeValue"];
                    //   NSLog(@"strokeT=%f",strokeT);
                    UIGraphicsBeginImageContext(self.viewDrawing.frame.size);
                    [imgDrawing.image drawInRect:CGRectMake(0, 0, self.viewDrawing.frame.size.width, self.viewDrawing.frame.size.height)];
                    //   NSLog(@"STROKE %f",stroke);
                    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), strokeT);
                    CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeCopy);
                    float redT=[[NSUserDefaults standardUserDefaults] floatForKey:@"redvalue"];
                    float greenT= [[NSUserDefaults standardUserDefaults] floatForKey:@"greenvalue"];
                    float blueT= [[NSUserDefaults standardUserDefaults] floatForKey:@"bluevalue"];

                    //   NSLog(@"red=%f",redT);
                    //   NSLog(@"green=%f",greenT);
                    //   NSLog(@"blue=%f",blueT);

                    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), redT, greenT, blueT, 1.0);
                    CGContextSetRGBFillColor(UIGraphicsGetCurrentContext(), redT, greenT, blueT, 1.0);

                    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
                    CGContextSetLineJoin(UIGraphicsGetCurrentContext(), kCGLineJoinRound);
                    CGContextBeginPath(UIGraphicsGetCurrentContext());
                    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
                    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
                    CGContextStrokePath(UIGraphicsGetCurrentContext());
                    imgDrawing.image = UIGraphicsGetImageFromCurrentImageContext();
                    UIGraphicsEndImageContext();
                }
                lastPoint = currentPoint;
            }
        }
    }

- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
  UITouch *touch = [touches anyObject];


        //if (([touch view] != btnInkColor) || ([touch view] != btnPenSize) || ([touch view] != baseview)) {
        if ( [touch view] != baseview) {

            if (!isImageSelection) {

                if(!mouseSwiped) {
                    if (isEraser) {
                        UIGraphicsBeginImageContext(self.viewDrawing.frame.size);
                        [imgDrawing.image drawInRect:CGRectMake(0, 0, self.viewDrawing.frame.size.width, self.viewDrawing.frame.size.height)];
                        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
                        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), stroke);
                        // CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);
                        CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeClear);
                        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
                        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
                        CGContextStrokePath(UIGraphicsGetCurrentContext());
                        CGContextFlush(UIGraphicsGetCurrentContext());
                        imgDrawing.image = UIGraphicsGetImageFromCurrentImageContext();
                        UIGraphicsEndImageContext();
                    } else {
                        UIGraphicsBeginImageContext(self.viewDrawing.frame.size);
                        [imgDrawing.image drawInRect:CGRectMake(0, 0, self.viewDrawing.frame.size.width, self.viewDrawing.frame.size.height)];

                        CGContextSetLineWidth(UIGraphicsGetCurrentContext(), stroke);
                        CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeCopy);

                        CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);
                        CGContextSetRGBFillColor(UIGraphicsGetCurrentContext(), red, green, blue, 1.0);

                        CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
                        CGContextSetLineJoin(UIGraphicsGetCurrentContext(), kCGLineJoinRound);
                        CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
                        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
                        CGContextStrokePath(UIGraphicsGetCurrentContext());
                        CGContextFlush(UIGraphicsGetCurrentContext());
                        imgDrawing.image = UIGraphicsGetImageFromCurrentImageContext();
                        UIGraphicsEndImageContext();
                    }
                }
            }
        }
    }
}

How can i solve this?

回答1:

To find a instant solution, Replace this line

 mainImage.image = UIGraphicsGetImageFromContext(UIGraphicsGetCurrentContext());

with

[mainImage performSelectorInBackground:@selector(setImage:) withObject:UIGraphicsGetImageFromCurrentImageContext()];

If you need an elaborate and accurate solution try to replace the MoveTo with CGMutablepath . Hope this helps.

回答2:

we have solved this problem using dispatch_async(dispatch_get_main_queue(), ^{)}; block in touchMoved method like this :

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

        dispatch_async(dispatch_get_main_queue(), ^{
        mouseSwiped = YES;
        UITouch *touch = [touches anyObject];
        if(touch.view==self.vwSwipePage)
        {
            return;
        }
        if(flagIsEraser)
        {
            CGPoint currentPoint;
            if(flagActiveViewPage)
            {

                currentPoint = [touch locationInView:self.mainImage];
                UIGraphicsBeginImageContext(self.mainImage.frame.size);
                [self.mainImage.image drawInRect:CGRectMake(0, 0, self.mainImage.frame.size.width, self.mainImage.frame.size.height)];
            }
            else
            {
                currentPoint = [touch locationInView:self.mainImage1];
                UIGraphicsBeginImageContext(self.mainImage1.frame.size);
                [self.mainImage1.image drawInRect:CGRectMake(0, 0, self.mainImage1.frame.size.width, self.mainImage1.frame.size.height)];
            }

            //clear using circle brush........
            CGContextRef context = UIGraphicsGetCurrentContext();
            CGContextSetLineCap(context, kCGLineCapRound);
            CGContextSetLineWidth(context,20);
            CGContextSetBlendMode(context, kCGBlendModeClear);
            CGContextSetStrokeColorWithColor(context, [[UIColor clearColor] CGColor]);
            CGContextBeginPath(context);
            CGContextMoveToPoint(context, lastPoint.x, lastPoint.y);
            CGContextAddLineToPoint(context, currentPoint.x, currentPoint.y);
            CGContextStrokePath(context);
            CGContextFlush(context);
            if(flagActiveViewPage)
                self.mainImage.image = UIGraphicsGetImageFromCurrentImageContext();
            else
                self.mainImage1.image = UIGraphicsGetImageFromCurrentImageContext();

            UIGraphicsEndImageContext();
            lastPoint = currentPoint;

        }
    });
    }

May this will Help u to solve ur problem.

Thanks

回答3:

Here's listed same code with same problem on ios7 https://stackoverflow.com/questions/18198129/ios-7-making-my-apps-drawing-algorithm-lag people suggest moving drawing logic into drawRect: