All supported pixel formats have a specific "mapping" of CPU data to
textures. This function determines the number and the formats of these
textures. Moving it to a helper will be useful for some hardware decode
interop backends, since they all need similar things.
GL_LUMINANCE_ALPHA is the only reason why per-plane swizzles exist.
Remove per-plane swizzles (again), and regrettably handle them as
special cases (again). Carry along the logical texture format (called
gl_format in some parts of the code, including the new one).
We also don't need a use_integer flag, since the new gl_format member
implies whether it's an integer texture. (Yes, the there are separate
logical GL formats for integer textures. This aspect of the OpenGL API
is hysteric at best.)
This should change nothing about actual rendering logic and GL API
usage.
Some of these checks became pointless after dropping ES 2.0 support for
extended filtering.
GL_EXT_texture_rg is part of core in ES 3.0, and we already check for
this version, so testing for the extension is redundant.
GL_OES_texture_half_float_linear is also always available, at least as
far as our needs go.
The functionality we need from GL_EXT_color_buffer_half_float is always
available in ES 3.2, and we explicitly check for ES 3.2, so reject this
extension if the ES version is new enough.
This merges all knowledge about texture format into a central table.
Most of the work done here is actually identifying which formats exactly
are supported by OpenGL(ES) under which circumstances, and keeping this
information in the format table in a somewhat declarative way. (Although
only to the extend needed by mpv.) In particular, ES and float formats
are a horrible mess.
Again this is a big refactor that might cause regression on "obscure"
configurations.
