These same magic constants were used in all cases, so move them into a
common place.
While we are touching all these lines, also change from the four floats
into a vec4. This allows further clean-up in the next patch.
This makes the code easier to read.
Behavior and results are unchanged.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>