How I can I make smoke and fire look like it coming from behind a building or through a window?
Masking lets you block out portions of the added effects so
that you can make the effects look like they are coming from behind
structures, through windows, or otherwise blocked by other elements in
the scene. For example, if there is a lamppost directly in front of
you (and on the background image), you can mask out any smoke you put
on the picture in the area of the lamppost. Then the smoke that is
“behind” the lamppost will be blocked out, making it appear that the
lamppost is in front of the smoke. Watch this video to see how to mask
the roof line, to make smoke look like it is coming from the roof or
from the opposite side of the building.