[REBOL] Re: Face Transparency?
From: rotenca:telvia:it at: 18-Nov-2002 18:10
"Previously the effect pipeline had an undocumented side effect, that
if the face was transparent and did not have an image, the effects
would not apply to the face, but rather to the background behind the
face. This would allow you to create faces that act as filters.
Because of the implied transparency caused by alpha channels, this
side effect no longer exists, i.e. an effect always applies to the
image itself, never to the background. You can still create faces
that act as filters, but you need to tell the system about that.
The effect keyword for that is "merge". It can appear anywhere in
an effect block, but will most commonly appear at the beginning.
What "merge" does is merge the image currently in the pipeline
with the background behind the face, using alpha-based compositing.
The result is then used as the current pipeline image. If there
is no current image then just the background itself is used.
For instance, if you previously used [colorize 255.0.0] to colorize
the background behind a face red you now have to use [merge colorize