Encountered the following problem:
Where to boot, right after the login, the lower portion of the screen (about 1/4, and always the same width) or black (rare), or a set of colored dots (most often), or "cutting" of the desktop last session. Occurs in homes and offices (Radeon HD4770 and NVIDIA GeForce 7300 + Linux sabayon 3.0.0-sabayon) When started with a live-DVD (7 or 8 ) such that the same situation.
In addition to this house after a certain time after power collapse OpenGL. It looks like blinking elements of windows on a black background. Or their partial drawing followed by the mouse cursor.
Heal is obtained as follows: Settings -> System Settings -> Desktop Effects ->In addition:
Engine converted to a value XRender, apply the changes, return back, read about the collapse of the engine OpenGL and apply the changes.
It began on the drivers version 11.12, at the time tried the driver 12.1 with AMD's website. Now updated driver to 12.1 from the repository. The situation has not changed.