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We have a situation in which user will be drawing many lines on the screen and we need to find out the crossing lines and get intersection point.

Is there any way to achieve this in iPhone using cocoa-touch ? Please show a direction and if possible code sample would be gr8 for me as I am stuck for this since last 2 days.

Please help.

Janak Nirmal
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1 Answers1

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As I see it, this is purely mathematics.

When the user touches the screen (and moving around with his finger) you will get some coordinates. Based on the current touch place (x,y) and the previous one, you can consider to be a line. Store each line inside an array.

Now when a new touch takes place, check whether this new line (current touch coordinates and previous ones) cross any other line from your array.

I don't remember what is the formula to check this intersection, but after a quick search, I found this, maybe will help.

CristiC
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  • We have thought in that way but when user swipe fast we are not able to get all the coordinates. And link I visited but it seems for straight lines, isn't it ? In my case user can draw curves too like that. – Janak Nirmal Jun 10 '11 at 13:06
  • Using touchesMoved you will get all the touches even if the swipe is fast. And curve lines eventually are also made up from several points. And 2 points will make a line. – CristiC Jun 10 '11 at 13:35
  • Weird, I tried this code and not seeing all the coordinates if I swipe fast. UITouch *touch = [touches anyObject]; CGPoint currentTouch = [touch locationInView:self.view]; NSLog(@"x->%f y->%f",currentTouch.x,currentTouch.y); Please check and let me know if I am doing any mistake. – Janak Nirmal Jun 10 '11 at 13:50