How to draw straight lines by touch in iphone using a UItouch or Rubber band style drawing

Question

I am new to iPhone development,

I am making an application in which i am trying to make a line that is straight so that it doesn't has any irregular curves it must be smooth

I have used core graphics but it doesn't seem to be working.

Screen shot I Just want to make these lines drawn in red color with UITouch to be straight.

Should I go for openGl?

If yes, how can i implement.

  drawImage = [[UIImageView alloc] initWithImage:nil];
drawImage.frame = viewField.frame;
[self.view addSubview:drawImage];
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {

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

if ([touch tapCount] == 2) {
    drawImage.image = nil;
    return;
}

lastPoint = [touch locationInView:viewField];
//lastPoint.y = 20;

}


- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
mouseSwiped = YES;
UITouch *touch = [touches anyObject];    
CGPoint currentPoint = [touch locationInView:viewField];
//currentPoint.y -= 20; // only for 'kCGLineCapRound'
UIGraphicsBeginImageContext(viewField.frame.size);
//Albert Renshaw - Apps4Life
[drawImage.image drawInRect:CGRectMake(0, 0, drawImage.frame.size.width, drawImage.frame.size.height)]; //originally self.frame.size.width, self.frame.size.height)];
CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound); //kCGLineCapSquare, kCGLineCapButt, kCGLineCapRound
CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0); // for size
CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0); //values for R, G, B, and Alpha
CGContextBeginPath(UIGraphicsGetCurrentContext());
CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), currentPoint.x, currentPoint.y);
CGContextStrokePath(UIGraphicsGetCurrentContext());
drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();

lastPoint = currentPoint;    
   }

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

  UITouch *touch = [touches anyObject];

  if ([touch tapCount] == 2) {
    drawImage.image = nil;
    return;
  }
  if(!mouseSwiped) {
    //if color == green
    UIGraphicsBeginImageContext(viewField.frame.size);
    [drawImage.image drawInRect:CGRectMake(0, 0, drawImage.frame.size.width,   drawImage.frame.size.height)]; //originally self.frame.size.width, self.frame.size.height)];
    CGContextSetLineCap(UIGraphicsGetCurrentContext(), kCGLineCapRound);   //kCGLineCapSquare, kCGLineCapButt, kCGLineCapRound
    CGContextSetLineWidth(UIGraphicsGetCurrentContext(), 5.0);
    CGContextSetRGBStrokeColor(UIGraphicsGetCurrentContext(), 1.0, 0.0, 0.0, 1.0);
    CGContextMoveToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
    CGContextAddLineToPoint(UIGraphicsGetCurrentContext(), lastPoint.x, lastPoint.y);
    CGContextStrokePath(UIGraphicsGetCurrentContext());
    CGContextFlush(UIGraphicsGetCurrentContext());
    drawImage.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
   }
   }

Thanks in Advance !

Answer 1

Judging by the image you posted, I suggest you change your approach. Start drawing by double clicking. Then tap (= touchesStarted and touchesEnded, not touchesMoved) on every single edge point in your polygon. Draw a straight line between those points as you go along. End the polygon by Double Clicking. You could decide to close you path automatically if the end point is close enough to the start point.