Composite Quesiton

[Jonathan Morton]

On Wed, 2010-05-19 at 17:19 +0800, Huang, FrankR wrote:
> I want to know if the black region after SRC is the CLEAR operation?

> If that is so, I want to modify the driver to do the CLEAR outside the
> 20x20 mask region to make the driver does the right SRC operation.

It's not quite the same - it is assuming that the pixels of the source
image that don't actually exist are the all-zeroes vector.  This is the
same vector as for transparency, and is used even if the source image
doesn't have an alpha channel.

For SRC mode this does have the same effect as CLEAR for those pixels,
but for OVER mode it would leave the destination unchanged in that area.
For other operations there are a variety of results, usually one of
these two.

-- 
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From: Jonathan Morton
      jonathan.morton at movial.com