CODEWITHSUNDEEP
c++openglglfwglad
haxen
haxen

Reputation: 43

Are OpenGL functions actually context-specific?

I know that I must pass glfwGetProcAddress function to gladLoadGLLoader function after context was initialized. GLFW documentation says that this function returns the address of the specified function for the CURRENT context. Based on this information, if I want to draw something on another context, I must type

glfwMakeContextCurrent(*window*)
gladLoadGLLoader((GLADloadproc)glfwGetProcAddress)

each time I want to change drawing context. However, it is enough to simply change the context with glfwMakeContextCurrent function. Documentation also remarks

The address of a given function is not guaranteed to be the same between contexts.

But it seems like returned addresses are the actually same between contexts (In windows, at least). The question is, what is true way to do this, in order to achieve stable and portable behaviour?

Upvotes: 4

Views: 665

Answers (1)

Nicol Bolas
Nicol Bolas

Reputation: 474376

Technically yes: function pointers retrieved from an OpenGL context are valid only for that specific context. However, for most practical purposes, you can ignore this. If two contexts can share objects, then they almost certainly share function pointers.

If you want to account for those cases where function pointers can't be shared across contexts, the best option is to write a loader specifically for dealing with that eventuality. You could for example modify GLAD to put OpenGL functions in a struct and then load the functions into different structs for different contexts.

Upvotes: 4

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