ios paint application overwriting paint strokes

Question

I'm creating a paint application but if stroke one line one color and if stroke another line crossing the previous stroke the first stroke change color to the second color enter image description here

Here is the code I'm using to paint:

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

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

    [self touchesMoved:touches withEvent:event];
}

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

    CGPoint point = [touch locationInView:self];

    /* check if the point is farther than min dist from previous */
    CGFloat dx = point.x - currentPoint.x;
    CGFloat dy = point.y - currentPoint.y;

    if ((dx * dx + dy * dy) < kPointMinDistanceSquared) {
        return;
    }

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

    CGPoint mid1 = midPoint(previousPoint1, previousPoint2);
    CGPoint mid2 = midPoint(currentPoint, previousPoint1);
    CGMutablePathRef subpath = CGPathCreateMutable();
    CGPathMoveToPoint(subpath, NULL, mid1.x, mid1.y);
    CGPathAddQuadCurveToPoint(subpath, NULL, previousPoint1.x, previousPoint1.y, mid2.x, mid2.y);
    CGRect bounds = CGPathGetBoundingBox(subpath);

    CGPathAddPath(path, NULL, subpath);
    CGPathRelease(subpath);

    CGRect drawBox = bounds;
    drawBox.origin.x -= self.lineWidth * 2.0;
    drawBox.origin.y -= self.lineWidth * 2.0;
    drawBox.size.width += self.lineWidth * 4.0;
    drawBox.size.height += self.lineWidth * 4.0;

    [self setNeedsDisplayInRect:drawBox];
}

- (void)drawRect:(CGRect)rect {

    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextAddPath(context, path);
    CGContextSetLineCap(context, kCGLineCapRound);
    CGContextSetLineWidth(context, self.lineWidth);
    CGContextSetStrokeColorWithColor(context, self.lineColor.CGColor);

    CGContextStrokePath(context);


    self.empty = NO;
}

Any of you knows what I'm doing wrong or how can I keep each stroke independent one from each other ?

I'll really appreciate your help.

Looks like you need to use kCGBlend... options on your paths. — CodaFi, Oct 21 '12 at 06:25

score 0 · Answer 1 · answered Oct 22 '12 at 01:18

I think what you need to do is to start a new path when you change color. Don't just keep adding new subpaths with the new color to the same path that had the old color.

You will need to store for each path the color it should be rendered and then loop over your paths in the drawRect method.

ios paint application overwriting paint strokes

1 Answers1