GL setting of identity matrices

[hendu]

All GL performance guides say that when you want to reset a matrix, you use glLoadIdentity instead of uploading your own identity matrix.

In Irr currently, only the texture matrices do this, the other matrices upload their own.


Why is this?

[hybrid]

Well, where would you assume to find the identity matrix? Or do you say that one should always first call LoadIdentity first?

[hendu]

It would call the isIdentity method, just like is done for the texture matrices, see line COpenGLDriver.cpp:980 in current svn.

I mean, if one calls setTransform(ETS_WORLD, IdentityMatrix), irr spends time uploading its own identity matrix instead of calling the faster glLoadIdentity. But if setting a texture matrix instead, it detects it's an identity matrix and correctly uses the faster function.

[hybrid]

The reason is that for texture matrices, about 99.9% will be identity, but for transformation, only 0.1% will be. So a check will be probably counter productive, as it will almost always fail and cost a few cycles each time.

[hendu]

Then maybe add a setTransformIdentity call, only taking the target matrix as a parameter?