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Index › Programming Questions & Help › Syntax Questions › click-select a line

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click-select a line? (Read 733 times)

jbmaxwell

click-select a line?
May 18^th, 2007, 6:07pm

I'm working on a GUI design, and I'm wondering how one might go about allowing a user to select a line by clicking on it? I've thought maybe of calculating little "bounding boxes" between each point, but that seems really tedious and calculation-heavy. The big hitch is that the line will be on top of another object, so the ability to accurately determine when a mouse-click is actually *on* the line is pretty important.

Any thoughts? This is done pretty reguarly in drawing programs, and the like, so I'm sure it's not a huge deal... but it would be nice to avoid re-inventing the wheel!

J.

davbol

Re: click-select a line?
Reply #1 - May 18^th, 2007, 8:52pm

You'll almost certainly need to calc a distance for all lines, then compare and find the smallest, and verify that it falls within some selection tolerance distance. Why? Especially for non-orthogonal lines, the mouse will hardly ever truly be "on" the line in a mathematical sense, even when over one of the lit pixels from the rasterization.

How do you store your lines? As two-point segments? If so, then this is what you need:
http://local.wasp.uwa.edu.au/~pbourke/geometry/pointline/
(if stored in some other form, either substitute in if you have the math, or google until you find it in the proper form)

jbmaxwell

Re: click-select a line?
Reply #2 - May 18^th, 2007, 9:23pm

davbol wrote on May 18^th, 2007, 8:52pm:

You'll almost certainly need to calc a distance for all lines, then compare and find the smallest, and verify that it falls within some selection tolerance distance. Why Especially for non-orthogonal lines, the mouse will hardly ever truly be "on" the line in a mathematical sense, even when over one of the lit pixels from the rasterization.

How do you store your lines As two-point segments If so, then this is what you need:
http://local.wasp.uwa.edu.au/~pbourke/geometry/pointline/
(if stored in some other form, either substitute in if you have the math, or google until you find it in the proper form)

Great. Thanks for this. These will actually generally be hand-drawn lines, so they should have a lot of point data. I had thought it might be possible, in this case, to interpolate a point between the two closest points. Anyway, I'll take a more detailed look at your link.

cheers,

J.

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