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Say we bind vertex attribute locations to the same values on two programs. Is it correct to use the same vertex array object to draw with these two programs?
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No. You can bind a VBO before you bind a VAO, and fill the VBO with data using glBufferData() . A VBO is essentially just a dumb data container. But any kind of vertex attribute setup tracked in the VAO can only be done after the VAO is bound.
A Vertex Array Object (VAO) is an OpenGL Object that stores all of the state needed to supply vertex data (with one minor exception noted below). It stores the format of the vertex data as well as the Buffer Objects (see below) providing the vertex data arrays.
A Vertex Array Object (VAO) is an object which contains one or more Vertex Buffer Objects and is designed to store the information for a complete rendered object. In our example this is a diamond consisting of four vertices as well as a color for each vertex.
Define "correct."
If two program objects use compatible attribute locations, then they use the same attribute locations. VAOs work off of attribute locations, so a VAO that works with one will work with another. So this will work.
In general, it is a matter of performance whether you actually take advantage of this. It's generally a good idea to avoid changing vertex array state, but it's not clear how important this is relative to other state changes. You're changing programs anyway, so not changing VAOs when you change programs will at worst be no slower and can lead to significant performance increases.
However, it is not clear how much work you should do to minimize vertex array state changes. If you can pack models into the same buffer objects with the same format, you can render all of them without VAO changing using functions like glDrawArrays or glDrawElementsBaseVertex.
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