Alpha map and global alpha


I want to blit a PdOffscreenContext_t masked with an alphamap and
additionally set a global alpha value (fading out the alphamapped context).

Blitting the alphamapped context works and blitting with global alpha
works but I didn’t get the global alpha’ed and alphamapped context to work.

Is there a way to do it with the source and destination multipliers or
do I have to manually multiply the entire alphamap for every global
alpha value?

— Wolfram