It's not just unused, it's also wrong.
We are reading from the buffer when reallocating the vertex buffer
and memcpy()ing the old into the new buffer - at that point we read from
it.
Some maps are used for read only and do not require uploading contents
back to the GPU afterwards. In other cases, we can often upload less than
the fully allocated buffer size.
Don't try to use all those fancy GL features like glMapBuffer() and
such. Just malloc() some buffer memory and glBufferSubData() it later.
That works everywhere and is faster than (almost?) any combination of
fancy new buffer APIs. And yes I'm frustrated because I played with
those flags and none of them were better than this.
Doubles the framerate on my discrete AMD GPU.
This heaves over an inital chunk of code from the Vulkan renderer to
execute shaders.
The only shader that exists for now is a shader that draws a single
texture.
We use that to replace the blit op we were doing before.
