Fix for PlgBlt, the XFORM matrix was calculated incorrectly

Alexander Almaleh sashoalm at gmail.com
Thu May 22 01:25:12 CDT 2014


Hi, Michael

On Thu, May 22, 2014 at 4:56 AM, Michael Mc Donnell <michael at mcdonnell.dk>wrote:

> 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.
>

OK, I'll try to write a unit test. I found this tutorial -
https://www.winehq.org/docs/winedev-guide/testing, is it the correct thing
to read?


> 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.
>

The trouble is I don't quite remember the exact steps I took 5 years ago to
come up with the new formula. However, I do remember I came up to it by
solving a system of linear equations. Since XFORM matrix is applied to each
point, I took 3-4 measurements of how points are transformed by PlgBlt, and
then used that to make equations of the type applyXFORM(xSrc) = xDest. By
solving the equations for the XFORM matrix, I came up with the correct
formula I need to get the XFORM matrix from the input variables. I used an
online linear equation solver, so there's no human error.

I'll try to recreate the steps, maybe it'll be easier to just explain them.
I'll look into making automated tests, too.
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