Is it important to call glDisableVertexAttribArray()?

Question

I'm not entirely clear on the scope of enabling vertex attrib arrays. I've got several different shader programs with differing numbers of vertex attributes. Are glEnableVertexAttribArray calls local to a shader program, or global?

Right now I'm enabling vertex attrib arrays when I create the shader program, and never disabling them, and all seems to work, but it seems like I'm possibly supposed to enable/disable them right before/after draw calls. Is there an impact to this?

(I'm in WebGL, as it happens, so we're really talking about gl.enableVertexAttribArray and gl.disableVertexAttribArray. I'll note also that the orange book, OpenGL Shading Language, is quite uninformative about these calls.)

Answer 1

The state of which Vertex Attribute Arrays are enabled can be either bound to a Vertex Array Object (VAO), or be global.

If you're using VAOs, then you should not disable attribute arrays, as they are encapsulated in the VAO.

However for global vertex attribute array enabled state you should disable them, because if they're left enabled OpenGL will try to read from arrays, which may be bound to a invalid pointer, which may either crash your program if the pointer is to client address space, or raise a OpenGL error if it points out of the limits of a bound Vertex Buffer Object.