out was simply not initialized if the source and destination
were the same. The COW flag is required here to separate input
and output properly. Also, the source & destination pointers
were badly calculated and could overflow.
Instead of using memcpy this filter was supposed to use the
blend functions. This patch also fixes that.
In order to make this filter actually useful (think text reflection
on a flat surface), more information needs to be passed to the Lua
script, such as the text ascent, descent, etc...
26e74c4219