artemp/trac2github — Issue #675: set_rectangle_alpha2() doesn't blend alpha correctly
Author: artemp
Created: 2011-10-09 20:46:33+00:00
State: open
Labels: Symbolizers

If I render a RasterSymbolizer using opacity < 1.0, mapnik pre-multiplies the other channels by the alpha when blending it into the destination image.

This means if you have a RasterSymbolizer with a white image and 50% opacity, it will come out grey in the output.