From d4bcef3204 on, using a RGBA
texture to hold the data causes the glmemory to have half width
and a scaling of [2, 1]. Using a LA texture solves this problem
however cannot be attached to the framebuffer for copying into
a RGBA texture. Which will be solved by moving to EXT_texture_rg.
https://bugzilla.gnome.org/show_bug.cgi?id=728890