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Shed

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Joined: 6th Feb 2011

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Posted: 6th Feb 2011 20:19

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I searched the forums over and over and have had to resort to this:

How do I detect an intersection efficiently between two lines.

I intend to generalise it to check for collisions between four arrays, describing two sets of lines.

I would love to hear from you guys, as I have been trying to get this to anything except do it by assigning colours, checking the colour of the pixel, and then checking for every pixel on the screen.

xxx

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Sven B

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Joined: 5th Jan 2005

Location: Belgium

Posted: 7th Feb 2011 11:23 Edited at: 7th Feb 2011 11:24

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If it's just checking whether or not they intersect, then this might do the trick:

+ Code Snippet

function LineIntersect(x1, y1, x2, y2, x3, y3, x4, y4)
    `Vectors
    a as double integer
    b as double integer
    c as double integer : `Usually produces large numbers
    x = x1 - x3
    y = y3 - y1
    x1 = x2 - x1
    y1 = y1 - y2
    x2 = x4 - x3
    y2 = y3 - y4
    
    `Calculate coefficients
    a = (x2 * y) - (x * y2)
    b = (x1 * y) - (x * y1)
    c = (x2 * y1) - (x1 * y2)
    
    `Checks
    if a * (a + c) >= 0 then exitfunction 0
    if b * (b + c) >= 0 then exitfunction 0
endfunction 1

I wrote it long ago though. I'm not sure how well it works... If you wish to find the intersection point, then you have to parametrize the line, like in these codes:

http://forum.thegamecreators.com/?m=forum_view&t=99986&b=6

Cheers!
Sven B

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Newcomers DBPro Corner / 2D Line Intersection