Question

Given a list of points that form a simple 2d polygon oriented in 3d space and a normal for that polygon, what is a good way to determine which points are specific ‘corner’ points?

For example, which point is at the lower left, or the lower right, or the top most point? The polygon may be oriented in any 3d orientation, so I’m pretty sure I need to do something with the normal, but I’m having trouble getting the math right.

Thanks!

Answer 1

Are you looking for a bounding box?

I’m not sure the normal has anything to do with what you are asking.

To get a Bounding box, keep 4 variables: MinX, MaxX, MinY, MaxY

Then loop through all of your points, checking the X values against MaxX and MinX, and your Y values against MaxY and MinY, updating them as needed.

When looping is complete, your box is defined as MinX,MinY as the upper left, MinX, MaxY as upper right, and so on…

Response to your comment:

If you want your box after a projection, what you need is to get the ‘transformed’ points. Then apply bounding box loop as stated above.

Transformed usually implies 2D screen coordinates after a projection(scene render) but it could also mean the 2D points on any plane that you projected on to.