Rational behind this change is that displayWidth and displayHeight are
X specific API calls in kwinglobals. For the future it's easier to only
rely on functionality which goes through the EffectsHandler API which
allows easier adjustments in KWin core.
displayWidth() and displayHeight() are only used to get the size or the
complete rect of all screens. This is also provided by:
effects->virtualScreenGeometry() or
effects->virtualScreenSize()
REVIEW: 116021
We need to use the varying_in/out variables, the code was a little
bit too modern.
At the same time remove the identity matrix and replace it by mat4(1.0).
Note: the shader should probably go into glsl files as they are not
really generated.
* this effect is way cheaper than blur, don't cache it
* use its own atom
* also pass the matrix in the x property
* remove remnants of the cache
* do just a single pass
* get rid of config ui remnants
* a copy of the blur shader to become a copy of the background contrast effect
* contrastshader actually doing the light modification
* don't expand/shrink the area
