How to draw free hand line smoothly in objective c?

Question

I hav used uigraphics cgcontext to draw line on touch...but my line is not smooth I mean edges is not smooth so can anybody suggest me how to draw smooth line..?? Here my code what i used to draw line:

/* touchesBegan */
UITouch *touch = [touches anyObject];
lastPoint = [touch locationInView:imagevw];

/* touchesMoved */

CGFloat width = [mySlider value];
UIGraphicsBeginImageContext(imagevw.frame.size);
[imagevw.image drawInRect:CGRectMake(0, 0, imagevw.frame.size.width,imagevw.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), width);
UITouch *touch = [touches anyObject];
mouseSwiped = YES;  
    CGPoint currentPoint = [touch locationInView:imagevw];
    CGContextBeginPath(UIGraphicsGetCurrentContext());
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
    CGContextStrokePath(UIGraphicsGetCurrentContext());
    imagevw.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
lastPoint = currentPoint;





/*  touchesEnded */
/* same here */ 
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
        CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);`

This is my code and i can draw line free hand but it is not that smooth showing pixels i mean edges not smooth

score 5 · Accepted Answer · edited May 23 '17 at 10:30

This code posted by kyoji works perfectly. You can read the question here:

    CGPoint midPoint(CGPoint p1, CGPoint p2)
{

    return CGPointMake((p1.x + p2.x) * 0.5, (p1.y + p2.y) * 0.5);

}

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

    UITouch *touch = [touches anyObject];

    previousPoint1 = [touch previousLocationInView:self];
    previousPoint2 = [touch previousLocationInView:self];
    currentPoint = [touch locationInView:self];

}

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

    UITouch *touch = [touches anyObject];

    previousPoint2 = previousPoint1;
    previousPoint1 = [touch previousLocationInView:self];
    currentPoint = [touch locationInView:self];


    // calculate mid point
    CGPoint mid1 = midPoint(previousPoint1, previousPoint2); 
    CGPoint mid2 = midPoint(currentPoint, previousPoint1);

    UIGraphicsBeginImageContext(self.imageView.frame.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    [self.imageView.image drawInRect:CGRectMake(0, 0, self.imageView.frame.size.width, self.imageView.frame.size.height)];

    CGContextMoveToPoint(context, mid1.x, mid1.y);
    // Use QuadCurve is the key
    CGContextAddQuadCurveToPoint(context, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y); 

    CGContextSetLineCap(context, kCGLineCapRound);
    CGContextSetLineWidth(context, 2.0);
    CGContextSetRGBStrokeColor(context, 1.0, 0.0, 0.0, 1.0);
    CGContextStrokePath(context);

    self.imageView.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

}

I have tried this still this is not that smooth.... if you know any other can you please send me, if any sample code it will be very helpfull. thanks in advanc.. — Sandhya Shettigar, Jun 20 '12 at 06:06

score 1 · Answer 2 · answered Aug 03 '13 at 11:55

is not fluid and smooth using points.. You should use NSBeziePath...

it took 3000 lines but is very smooth, as "bamboo" tool.

The correct approach is using a Bezier path that:

records every drawings
is used to draw effectively on view
you should compute on-fly anchor point for bezier path while tracking (you do NOT draw the touch-point of events)
You can even record and save it.

score 1 · Answer 3 · answered Aug 03 '13 at 12:51

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{   
    UITouch *touch = [touches anyObject];
    pointCurrent = [touch locationInView:self.view];
}

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{   
    UITouch *touch = [touches anyObject];
    CGPoint pointNext = [touch locationInView:self.view];
    UIGraphicsBeginImageContext(img.frame.size);
    [img.image drawInRect:CGRectMake(0, 0, img.frame.size.width, img.frame.size.height)];
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 2.0);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), pointCurrent.x, pointCurrent.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), pointNext.x, pointNext.y);
    CGContextStrokePath(UIGraphicsGetCurrentContext());
    img.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    pointCurrent = pointNext;
}

How to draw free hand line smoothly in objective c?

3 Answers3