The use of mediump as a specifier in GLSL shaders will have limited
resolution and when used as texture coordinates may become inaccurate
over texture sizes of 1024.
It performs similarly to the existing alpha element however performs
calculations in floating point rather than with small (guint8) integers
so some differences are to be expected.
https://bugzilla.gnome.org/show_bug.cgi?id=794070
