GLES 2.0 is a subset of OpenGL, so we allow applications to compile
against LibGL as if it fully supports GLES 2.0.
Additionally, we set the definitions to an integer value of `1` so
applications that check for availability like this...
int main() { return GL_ES_VERSION_2_0; }
...can actually compile. At least ScummVM uses this, and Mesa defines
their constants in the same way:
44b9e11ddb/include/GL/gl.h (L105)
These enums are used to indicate byte-alignment when reading from and
to textures. The `GL_UNPACK_ROW_LENGTH` value was reimplemented to
support overriding the source data row width.
According to the Khronos group, GL enum values are in the spec:
https://www.khronos.org/registry/OpenGL/docs/enums.html
Not adhering to their values will cause issues with projects that ship
their own copy of `gl.h`, such as ScummVM.
This controls how fetched texels are combined with the color that was
produced by a preceding texture unit or with the vertex color if it is
the first texture unit.
Currently only a small subset of possible combine modes is implemented
as required by glquake.
This sets the length of a row for the image to be transferred. This
value is measured in pixels. When a rectangle with a width less than
this value is transferred the remaining pixels of this row are skipped.
Currently just sets the renderer option for what polygon mode we
want the rasterizer to draw in. GLQuake only uses `GL_FRONT_AND_BACK`
with `GL_FILL` )which implies both back and front facing triangles
are to be filled completely by the rasterizer), so keeping this as
a small stub is perfectly fine for now.
This is a very basic implementation of glGetfloatv. It will only give a
result when used with GL_MODELVIEW_MATRIX. In the future
we can update and extend it's functionality.
Textures are now initialized with a nullptr upon generation.
They are only actually created once they are bound to a target.
Currently only the GL_TEXTURE_2D target is supported.
The software rasterizer now allows rendering with or without
a bound TEXTURE_2D.
There is some really wild stuff going on in the OpenGL spec for this..
The Khronos website states that GLsizei is a 32-bit non-negative value
used for sizes, however, some functions such as `glGenTextures` state
that the input `n` could be negative, which implies signage. Most other
implementations of `gl.h` seem to `typedef` this to `int` so we should
too.
