Just for the hell of it (to learn), im writting my own code to represent the "scene". This implies a parent/child treeish relationship in which every object has a local transformation that represents its location and rotation relative to its parent's base (coordinate system). So the rendering in opengl would go something like... each object in turn (parent first, and then all its children) push their transformations to the transformation stack (so each object's final transformation is the combination of the tranformations of all its ancestors, in the right order), then draws itself and then pops the transformation after its last child is done. All that would be done at the time i want to do a "render". The problem is that i also need to have all that spatial representation for other things, like collition detection, mouse pointer picking, ai, etc. Maybe all this is calculated many times before any render occurs. For example, at some moment during the "update(elapsedtime);" of an object, it needs to know it's world coordinates, not just the local ones. So what should be done? Am i supposed to make all those matrix multiplications for each object myself, keep a copy of the whole transformation stack up to that point, use them for whatever game logic i need, and then just load them into OpenGL (without using the stack, it would mean calculating twise, right?) for drawing? What does everyone else do? I'd appreciate any suggestions or ideas. If i didn't explain my doubt enough, please tell me and i'll try harder to explain myself. please help :) Thanks a lot in advance.

Quote:Original post by ElPeque2
The problem is that i also need to have all that spatial representation for other things, like collition detection, mouse pointer picking, ai, etc. Maybe all this is calculated many times before any render occurs.

For example, at some moment during the "update(elapsedtime);" of an object, it needs to know it's world coordinates, not just the local ones.

So what should be done? Am i supposed to make all those matrix multiplications for each object myself, keep a copy of the whole transformation stack up to that point, use them for whatever game logic i need, and then just load them into OpenGL (without using the stack, it would mean calculating twise, right?) for drawing?

What does everyone else do?

Yes, a few transforms are definetly needed.
Static data is obviously pre-transformed once while for dynamic working on low-detail model usually suffices.

Don't even think at transforming the vertices yourself and then fetch to GL. Besides the fact this would generate a ton of dynamic data (better to re-compute everything on the GPU again) you stand no chance of beating vertex transform performance (let alone the vertex shader issues)!

great. thanks for your time :)