How to draw lines in iOS platform - ios

Question

I am using apps like bamboo book and paper, in iPad, the experience is really good, how is it work? which technology does it used when draw lines or curves on screen?

Answer 1

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
mouseSwiped = NO;
UITouch *touch = [touches anyObject];
if ([touch tapCount] == 2) {
//self.imageView.image = nil;
return;
}
lastPoint = [touch locationInView:self.view];
lastPoint.y -= 20;
}
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
mouseSwiped = YES;
UITouch *touch = [touches anyObject];
CGPoint currentPoint = [touch locationInView:self.view];
currentPoint.y -= 20;
CGFloat components[3];
[self getRGBComponents:components forColor:self.colorView.backgroundColor];
NSLog(#"%f %f %f", components[0], components[1], components[2]);
UIGraphicsBeginImageContext(self.view.frame.size);
[self.imageView.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 10.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), components[0], components[1], components[2],5.0);
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextSetBlendMode(UIGraphicsGetCurrentContext(), kCGBlendModeNormal);
CGContextStrokePath(UIGraphicsGetCurrentContext());
self.imageView.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
lastPoint = currentPoint;
mouseMoved++;
if (mouseMoved == 10) {
mouseMoved = 0;
}
}
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
UITouch *touch = [touches anyObject];
if ([touch tapCount] == 2) {
//self.imageView.image = nil;
return;
}
if(!mouseSwiped) {
CGFloat components[3];
[self getRGBComponents:components forColor:self.colorView.backgroundColor];
NSLog(#"%f %f %f", components[0], components[1], components[2]);
UIGraphicsBeginImageContext(self.view.frame.size);
[self.imageView.image drawInRect:CGRectMake(0, 0, self.view.frame.size.width, self.view.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), components[0], components[1], components[2], 5.0);
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
CGContextFlush(UIGraphicsGetCurrentContext());
self.imageView.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}
}
Also check following link
http://www.techotopia.com/index.php/An_iOS_4_iPhone_Graphics_Drawing_Tutorial_using_Quartz_2D
https://stackoverflow.com/questions/6449661/drawing-2d-images-on-iphone-tutorials
http://mobile.tutsplus.com/tutorials/iphone/ios-sdk_freehand-drawing/
http://www.raywenderlich.com/18840/how-to-make-a-simple-drawing-app-with-uikit