Question

I’m starting study opengl, and im tring to make a 3d chess like, but i cant figureout, how i can know where i have clicked in the “table” to make the proper animations, any advice ?

Answer 1

This is called “3D picking”. You have to translate screen coordinates into world coordinates. From there, do a ray/collision object (bounding box?) intersection test. If they intersect, that’s where the user clicked.

You’ll have to do a little bit more than this to solve the depth-order problem, like finding the first time to intersection of each object, then selecting the one with the lowest (positive) time.

If you google for “3D picking” you might find what you are looking for.

Here is a tutorial:
http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=32

Note that this is not specific to any shape of bounding object, be it a bounding box, a polygon, a curve, etc. You just have to figure out the math for the intersection test for each type of object you want to support.

Edit:

I didn’t read that tutorial before I linked it, I just figured NEHE is where all the cool kids learn OpenGL (admittedly ten years ago…).

Here is something from the OpenGL FAQ about picking:

http://www.opengl.org/resources/faq/technical/selection.htm