Hiya! I''m doing my part of game creation by doing a remake of the old UFO - Enemy Unknown and so far things are working out quite well. =) I now need a formula for getting the point in 3d space by clicking on a "2D disc shape". Let me explain: I''m using a fixed perspective which can be zoomed in and out, and the earth can be rotated along WorldX,WorldY. - Using fixed perspective, I could probably use some form of sin/cos and hypot(ClickedX-CenterofScreenX,ClickedY-CenterofScreenY) to get a point on the sphere''s surface? Problem is that I cannot really figure this out... what seemed like a easy solution now seem very daunting... :/ I don''t know if I''ve made myself clear about what I need help with, but any help I can get is greatly appreciated!! :D Cheers!

I found a rather cheesy solution.. using opengl´s own Picking/selection system... and then assigning each triangle a nr that is used for identification.

now a "find a point inside a triangle" would be nice... =P

Hi ya!

Thanks for answering, but I''ve already found which triangle is being hit using OpenGL selection.. =)
I would need to find out where inside the triangle the user clicks...

A      /\     /  \         x = clicked point.    /    \   /      \  /     x  \ /__________\B           CA,B,C are known variables. They are also a point in space with its own x,y,z values. 

This should be an issue of standard math.. but I barely made it out of school alive so.. =)

you mean, the cordinates of X(x, y, z)?

hundreds of ways

a way that''s hard to describe, but very efficient, is the barycentric coordinates, or the plucker coordinates. that also returns other useful info, like the ''texture coordinates'' withing that triangle.

if you are not bothered, you can just construct the triangle plane, and do a ray-plane intersection.

both are available here

http://www.realtimerendering.com/int/

Cheers mate!

I´ll look into them right away!