Fix for PlgBlt, the XFORM matrix was calculated incorrectly

[Alexander Almaleh]

Ok. Btw, I have some other things on my head now, so it might be a week or
two before I come back to this.


On Fri, May 23, 2014 at 1:35 AM, Michael Mc Donnell <michael at mcdonnell.dk>wrote:

> Hi Alexander
>
> On Thu, May 22, 2014 at 2:25 AM, Alexander Almaleh <sashoalm at gmail.com>wrote:
>>
>> 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?
>>
>
> Yes that is 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.
>>
>
> Sounds good. Like you are saying, figuring out the formulas again would be
> a good idea. The current code does not explain where the formulas are
> coming from. Adding that as comments in your patch would make it easier to
> verify than the current code.
>
> Michael
>
>
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