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gator
05-27-2005, 10:37 AM
Does the thickness of points and lines affect picking in any way?

So, for example, if I set a point to glPointSize(1.0), and try to pick it, is there any difference
between a point set at glPointSize(6.0) ? Does making points larger make them easier to pick or not?

Yeah, I tried it, but I don't notice a difference.

Bob
05-28-2005, 04:11 AM
Picking in OpenGL is based on geometry. If an object intersects the clip volume after transformations, a hit is recorded. Line width and point size are rasterization parameters and so does not affect the selection. A hit is only recorded if the geometrical center of the point/line is within the clip volume.

If you want to use selection on thicker points/lines, you should increase the pick region (in gluPickMatrix, for example, the width and height parameters) to the same size as the points/lines you want to pick. Then you can click anywhere on the point/line, and the clip volume will be large anough to always contain the center of the point/line.

gator
05-28-2005, 01:36 PM
Thanks for the explanation. Wasn't too sure about that. :)