Recursive alpha maps (where one picture's alpha map is set to a
picture with an external alpha map) would be all fine and dandy,
except for the case where the client constructs a loop. Detecting this
case when setting the alpha map values would be difficult as any time
an alpha map is set, the server would have to check for the looping
case.
Instead, a far simpler fix is to simply disallow recursive alpha maps
in the rendering code, the Render spec is ambiguous in this area and
allows us to to ignore the recursive case.
Signed-off-by: Keith Packard <keithp@keithp.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>
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