Should I prefer glMapBufferRange over glMapBuffer?

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The documentation for glMapBuffer says it can only use the enum access specifiers of GL_READ_ONLY, GL_WRITE_ONLY, or GL_READ_WRITE.

The documentation for glMapBufferRange says it uses bitflag access specifiers instead, which include a way to persistently map the buffer with GL_MAP_PERSISTENT_BIT.

I want to map the buffer persistently, so should I just always use glMapBufferRange even though I want to map the entire buffer? I haven't seen anyone point out this rather important distinction between the two functions, so I was wondering if glMapBufferRange is a total and complete replacement for glMapBuffer, or if I should be prepared to use both in certain situations?

(I guess I'm just confused because, given the naming, I would think only the sub-range would be the difference between the two calls.)

opengl-3 opengl c++
1 Answers

glMapBufferRange was first introduced in OpenGL 3. OpenGL has evolved to provide more control to developers while keeping backwards compatibility as much as possible. So glMapBuffer remained unchanged, and glMapBufferRange introduced the explicitness that developers wanted (not only the subrange part, but also other bits).

glMapBufferRange reminds me of the options that are available nowadays in Vulkan (i.e cache invalidation and explicit synchronization). For some use cases, you might get better performance using the right flags with the new function. If you don't use any of the optional flags, the behaviour should be equivalent to the old function (except for the subrange part).

I think I would always use glMapBufferRange as it can do everything that the other does. Plus you can tweak for performance later on. Just my humble opinion :)

user_17543220
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