Fix for PlgBlt, the XFORM matrix was calculated incorrectly

[Michael Mc Donnell]

Hi Alexander

On Tue, May 20, 2014 at 1:39 PM, Alexander Almaleh <sashoalm at gmail.com>
wrote:
> I had tried to submit a patch for that 5 years ago, but couldn't figure
out
> how to make a patch/test it, and eventually gave up and forgot about it.
But
> recently I remembered about it, and now I want to try again.

The easiest way to get your patches accepted, in my experience, is to write
an automated test. That way it is easier for everyone to verify that your
patch is doing the right thing. We will be able to run it on the Wine
Testbot and see it working.

It might be difficult in your case though. Wine does usually not include
big test files so you would probably have to write some code that draws a
test image. The test image needs to be easy to verify in code if it has
been transformed correctly. You might be able to draw a filled rectangle in
one hdc and a filled parallelogram in another. Transform the filled
rectangle using PlgBlt and then compare it to the parallelogram. I have not
thought it all the way through so it might not work :-)

It seems like there are no automated bitblt tests in the wine source tree.
The first step would be to add a file bitblt.c in /dlls/gdi32/tests/ and
then add it to the Makefile.in file in that directory. My first commit to
Wine [1] added a new test file brsfolder.c to shell32.

You might be able to get your patch in without the automated test, but I
think you need to explain clearly what was wrong with the old code and what
you are doing instead. A few more simplified examples that test other cases
in your bug report might also help.

Best of luck,
Michael Mc Donnell

[1]
http://source.winehq.org/git/wine.git/?a=commit;h=5c715b46f4312a2e76aa14499e09edad2af42e20
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