How would I create a composition that is transparent, such that
it can be used as an overlay to a regular cocoa app? By default,
the background looks like it should be transparent, but shows up
all black.
In QuickTime, the background of the composition is always painted
black, but the alpha channel is valid (it's actually transparent
black, so you can composite with it).
In other environments (QCRenderer or QCView), the background is not
painted black.
You can achieve transparency with a QCView if:
- the composition properly paints its background with a color with an
alpha component different than 1.0
- the alpha component of the erase color of the QCView is different
than 1.0
