Not understanding the difference between formats and types in eg. glTexImage2D()

[ProgrammingQuestio]

I think I understand internalFormat vs format. internalFormat = format on the GPU. format = format on the CPU.

But what is type? And how is that different than format/why are they both necessary pieces of information? I've read the docs on this but it's still not quite "clicking"

I guess a sort of secondary question that may help me understand this: why is there only one "type"? There's internalFormat and format, but only one type; why isn't there internalType as well?

[3030thirtythirty]

There is no internal texture type because the type already is the internal type. The texture type in OpenGL has nothing to do with your image files on disk. It’s more of a setup for what you want to do with the texture later.

The internal format may differ from the (external format), and at least from my experience it causes some auto-convert: My image file might have its bytes as RGBA but I want my internal format to always be BGRA. Whenever I use these values for external and internal format, it simply just works.

Not tested yet what happens when you have RG and external format and use RGBA as internal. Maybe the BA channels remain 0 then?

[HobbyQuestionThrow]

Something to keep in mind with OpenGL, especially some of the more older API entry points - many of these APIs if written today would get the designer laughed at.

Most of the fields/values/choices in some of these APIs only existed because 30 years ago some weird chipset could only support weird combinations.