fix issues with transparent configs on es2gears
If es2gears gets a framebuffer config with an alpha channel, two things go wrong:
- We mark the region as opaque, even though we clear to tranparent black instead of opaque black
- We modulate the entire color with the light-factor, instead of just the RGB components.
While it could also be argued that the gears maybe should clear with an opaque black instead of a transparent black, it kinda looks cool when rendered correct to me, so I would love it if this would work anyway
An alternative could be to clear to 50% black instead, which maybe gets us the best of both worlds, and also matches what weston's "simple-egl" demo does. In either case, that can be fixed separately if anyone cares enough.