CODEWITHSUNDEEP
opengl
Maik Klein
Maik Klein

Reputation: 16148

Deprecated OpenGL functions

I am currently learning OpenGL via the 5th Superbible. It teaches you the core profile. But I am really confused.

I know that khronos removed the fixed function pipeline in 3.3 and declared some functions as deprecated. But the Superbible now just replaces those deprecated functions with their own functions.

Why should khronos remove something like glRotate or the matrixstack just so that I have to use 3rd party libraries (or my own) instead of the official ones?

Maybe the superbible is flawed?

Upvotes: 2

Views: 841

Answers (2)

didierc
didierc

Reputation: 14730

Khronos removed these functions from the core profiles, but they are still available in the compatibility ones. The main reason is one of performance:

In most applications nowadays, the amount of information which must be passed back and forth between the renderer and the application is magnitude larger than ten years ago. So the ARB came up with the buffers (vertex arrays and vertex buffer objects) to maximize the use of the bandwidth available between the main system and the rendering hardware. However, if you start using the VBO mechanism to transfert data, then most of the legacy functions become useless.

That said, besides the need to support legacy applications, which is a sufficient reason for a compatibility profile, I think that this API is still useful for learning purpose.

As for your main question, the above is only valid for the full fledged version of OpenGL, not the ES one, which doesn't support the old primitives, and in this context an emulation layer is necessary.

Upvotes: 3

Martin Beckett
Martin Beckett

Reputation: 96119

glRotate() etc was removed because internally openGL deals with the matrices so it is a cleaner design to just have you supply the matrices directly.

Almost all openGL apps of any complexity are going to be doing a bunch of other matrix stuff anyway and will have their own matrix classes it's easier for openGL to just take the result rather than insist on creating them from a bunch of rotate/translate/scale calls.

They could have supplied their own matrix classes - but there are a lot of 3rd party libs you can use. One of openGL's policies (failings) is that it does rely on 3rd party libs to do anything outside the actual graphics. So beginner programs are a tricky mix of GLUT, GLEW, SDL, etc to get anything on the screen - while DirectX has everything out of the box.

Upvotes: 6

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