gl_common: use texelFetch

This relieves us from the need to normalize texture coordinates.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

new backend: ignore window tranparency info from the backend

Doing this forces compton to blur every windows' background.

However, doing this can be beneficial, we will figure out a way
to do this properly in the future.

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

Stop debug mode from being used without the new backends

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

new backend: handle --use-damage

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>