Cross fading with previous pixmap is achieved by referencing the old
window pixmap. WindowPaintData has a cross-fade-factor which interpolates
between 0.0 (completely old pixmap) to 1.0 (completely new pixmap).
If a cross fading factor is set and a previous pixmap is valid this one
is rendered on top of the current pixmap with opacity adjusted. This
results in a smoother fading.
To simplify the setup the AnimationEffect is extended and also takes care
about correctly (un)referencing the previous window pixmap. The maximize
effect is adjusted to make use of this new capabilities.
Unfortunately this setup has a huge problem with the case that the window
decoration gets smaller (e.g. from normal to maximized state). In this
situation it can happen that the old window is rendered with parts outside
the content resulting in video garbage being shown. To prevent this a set
of new WindowQuads is generated with normalized texture coordinates in
the safe area which contains real content.
For OpenGL2Window a PreviousContentLeaf is added which is only set up in
case the crass fading factor is set.
REVIEW: 110578
941c02a60f