Quote:Original post by cgrant
The pipeline requires the data to be as such for processing..i.e internally it makes the assumption that stuff are in a right handed coordinate system. Not directly related, but APIs have to make certain assumptions, ex. that is why by default vertices in GL have to be specified counter-clockwise...thats just the way it is.

Ah, this is exactly what I'm getting at. Do you know which part of the pipeline requires a right handed system? I've searched all over for this info, but all I can find is "OpenGL is right handed", "DirectX is left handed".

The difference I see is actually in projection computation (as was already mentioned above). If you choose the view local x and y directions for spanning the view plane, and let stuff at less depth cover stuff at greater depth, then choosing whether depth increases with increasing local z or else increases with decreasing local z makes the difference. The former method would be LHS, and the latter one RHS.

Quote:Original post by Daaark

Quote:Original post by GaryNas
I've searched all over for this info, but all I can find is "OpenGL is right handed", "DirectX is left handed".

That's all you can find, because that's the entirety of it. There's nothing more to say about it.

I'm not sure it's quite that simple.

I said this same thing in another recent thread, but as far as I can tell, Direct3D/DirectX is no more left-handed than it is right-handed. It works fine with both left- and right-handed systems (as far as I can tell, at least), and the DX math library includes transform functions for each handedness.

Why Direct3D is thought of as being left-handed, I'm not sure, but I suspect it may be historical. Maybe someone else can shed some light on this.

My guess is that OpenGL can be used with a left-handed system just as easily as Direct3D can be used with a right-handed system (as was suggested previously). I haven't actually tried this myself though, so I can't say for sure.

If that's true though, then I would think that the only thing that makes OpenGL 'right-handed' is the few convenience functions that build transforms for which handedness matters (gluLookAt, gluPerspective, etc.). If you take these out of the picture (e.g. by using glLoad/MultMatrix, or by using the programmable pipeline), then I'm not sure that OpenGL can be said to have an inherent handedness.

So to get back to the original question, my guess is that the only thing that makes OpenGL 'right-handed' is a few convenience functions that you can easily do without, and that in fact are no longer even included as part of the API. (I could be overlooking something though.)

Quote:Original post by szecs
Maybe I will tell a totally dumb thing, but I'm a bit tired.
I think that makes openGL right-handed, is that if you don't apply any transformations (identity as model-view and projection), a model made and viewed in a left handed editor would appear mirrored in onenGL in the said conditions.

Some one please clarify this.

I don't think that's right; if the projection matrix is identity, I don't think the visual output will be anything meaningful (in the general case, at least).

Quote:Original post by jyk
I said this same thing in another recent thread, but as far as I can tell, Direct3D/DirectX is no more left-handed than it is right-handed.

You may be thinking about row mayor vs column mayor notation, but anyway in order to use the opposite handedness multiply your matrices by/or use this as your identity matrix:

 [ 1  0  0  0 ][ 0  1  0  0 ][ 0  0 -1  0 ][ 0  0  0  1 ]