CODEWITHSUNDEEP
iphoneiosobjective-cipad
ios_dev
ios_dev

Reputation: 113

Multicolor line drawing

I am creating a drawing app. One of the features is multicolour line drawing. It should work like user touch up the screen and leads on it drawing a line. Colour of the line changes smoothly. Like that http://www.examples.pavelgatilov.com/Screen%20Shot%202013-09-22%20at%208.37.42%20PM.png

I tried several approaches, but haven't been lucky.

My line drawing method is below:

- (void) drawLineFrom:(CGPoint)from to:(CGPoint)to width:(CGFloat)width
{
self.drawColor = toolColor;
UIGraphicsBeginImageContext(self.frame.size);
CGContextRef ctx = UIGraphicsGetCurrentContext();
CGContextScaleCTM(ctx, 1.0f, -1.0f);
CGContextTranslateCTM(ctx, 0.0f, -self.frame.size.height);
if (drawImage != nil) {
    CGRect rect = CGRectMake(0.0f, 0.0f, self.frame.size.width, self.frame.size.height);
    CGContextDrawImage(ctx, rect, drawImage.CGImage);
}
CGContextSetLineCap(ctx, kCGLineCapRound);
CGContextSetLineWidth(ctx, width);
CGContextSetStrokeColorWithColor(ctx, self.drawColor.CGColor);
CGContextMoveToPoint(ctx, from.x, from.y);
CGContextAddLineToPoint(ctx, to.x, to.y);
CGContextStrokePath(ctx);
CGContextFlush(ctx);
drawImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
drawLayer.contents = (id)drawImage.CGImage;
}

Thanks for your help

Upvotes: 0

Views: 119

Answers (1)

Wain
Wain

Reputation: 119041

Depending on exactly what colours, how they change and what effect you want / what happens with turns in the line, you may want to look at some combination of:

  • CGContextDrawLinearGradient with masking to the users drawn path.
  • colorWithPatternImage:
  • CGContextDrawLinearGradient drawn behind another layer and drawing transparency into the top layer with kCGBlendModeClear

Upvotes: 2

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