They are never used in practice, which makes all of our flag
handling effectively dead code. Also, APIs such as KMS don't
provide a good way to deal with the flags. Let's just fail the
DMA-BUF import when clients provide flags.
texcoord is a vector of coordinates, with the first member being the X
axis value and the second member being the Y axis value. It makes more
sense to use the accessors with the same names.
By using the same vertex shader and adding alpha to the fragment shader
for external textures we can:
- use alpha blending
- have wlr_gles2_render_texture_with_matrix work with
the GL_TEXTURE_EXTERNAL_OES. So far this failed
since we passed in alpha which was unknown by fragment_src_external
