Headers should be animated properly

[hmeine]

Currently, the header transition is a little bit buggy: if two frames have overlapping, but not congruent header rects, the new header is first faded in, then the old one is faded out. (This is a workaround for some even more ugly effects that happened due to limited opacity support in the graphics item hierarchy – no transparency groups – and other problems.)

We would like to see a direct blending from old to new header in all cases.

[hmeine]

In the meantime, the rendering has changed, but it still looks bad.

Proper blending still to be done.

[hmeine]

Current status (in try_known_colors branch): headers are represented correctly with alpha, but old header is faded(?) out only after fading in is finished. (Problem is that fading out + fading in != fading from->to.)

[hmeine]

Obviously, proper blending needs a from and a to pixmap. We could achieve that on the level of 'layers', which we have already on two levels:

• in frameItems(), and
• in animatedTransition() (where we effectively move items from the static layers onto animated ones).