The merge fade merges the two frames before drawing them to the framebuffer.
This makes a smooth transition between areas with partly transparent pixels or
areas in later frames becoming trasparent. This is set as the default on the
"glow" theme.
Some of the plugins (well, the glow plugin) would be a lot more
versatile if they could be reused for multiple splashes with different
images.
This commit splits boot splashes into two parts, the plugin engine which
does all the dirty work, and the theme which says which plugin to use
and optionally how the plugin should work (using plugin specific
key/value pairs)
