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POHit-testing line segments
 

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  1. POHit-testing line segments
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    <p>1) I have a list of line segments (defined by their two endpoints and a width.)<br> 2) These line segments are drawn in a panel.<br> 3) When my mouse moves (Panel.MouseMove event), I loop over the list of line segments.<br> 4) Foreach:</p> <pre><code> gPath.Reset(); Pen Pen = new Pen(Color.White, 20); gPath.AddLine(P1, P2); return gPath.IsOutlineVisible(cursorPos, Pen); </code></pre> <p>5) If I get true, then I know my cursor is hovering over the current line segment. </p> <p>This works fine for about... 300 lines or so. When I reach 1,000 my program slows to a halt (profiling shows that it's caused by IsOutlineVisible). So, is there any way I could increase performance of my hit-testing algorithm? I don't know how efficient IsOutlineVisible is, so I don't want to implement any optimizations that the method already uses. Any ideas?</p> <p><strong>EDIT:</strong><br> After digging into my data I noticed some of the lines were extremely large. For example:<br> endpoint1 = (16000, -16000)<br> endpoint2 = (5041448, -32868734)</p> <p>(yes, one of the coordinates is in the negative tens of millions...)</p> <p>I verified that hit-testing against just one such line segment is enough to bring my program to a halt, (IsOutlineVisible takes 2-3 seconds to do the test, and the test is run whenever the cursor moves...).</p> <p>I should have tested this more thoroughly before posting. Thanks to all that responded (a 2d spatial index is a great suggestion if I end-up handling thousands of lines). </p> <p>p.s. If anyone knows why a large line-segment is that big a problem for IsOutlineVisible, that would be great.</p>
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    1. COYou may want to have a look at [My Example](http://stackoverflow.com/a/15469477/643085) of a very similar thing using current, relevant .Net Windows UI technologies. It includes some interesting functionalities such as line selection and highlight.
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      1. USFederico Berasategui
    2. COthanks, but I'm currently using winforms.
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