Failing VCL complextext rendering unit test on Windows

[Jan-Marek Glogowski]

Am 24.03.2017 um 12:32 schrieb Khaled Hosny:
> On Fri, Mar 24, 2017 at 11:29:52AM +0100, Jan-Marek Glogowski wrote:
>> Hi everyone,
>>
>> when running
>>
>> $ /opt/lo/bin/make-4.2.1-msvc -C vcl CppunitTest_vcl_complextext
>>
>> on Windows 7, KVM QXL GUI via Spice I get the following failures:
> […] 
>> All height values are the same, just the width and x-offsets change.
> 
> Hmm, might be related to Windows font rendering settings, AFAIK Windows
> disables anti-aliasing for rdesktop (and I guess this what Spice uses)

No. Spice is a protocol (https://www.spice-space.org/) and has it's own
graphic driver (QXL). I don't know how rdesktop and Spice work in
detail, but my guess is it's different. QXL is more in line with the
vmware and virtualbox video drivers, which allow to resize the viewers
window and adapt the VMs graphic output size.

Originally I thought it may be an off-by-one problem in the QXL driver,
but then I saw all the different glyph calculation and gave up on this idea.

> and different font rendering strategy can result in different glyph
> widths. Only bounding box is affected since we still use Windows API
> for it (unlike glyph widths for layout).
> 
>> From the documentation, the provided matrix to the function is the
>> identity matrix, which just leaves some room for different HDC.
>>
>> AFAIK HDC is driver dependent (whatever driver is used for SSH) and so
>> I'm not sure this is fixable at all.
>>
>> So I propose disabling it also on Windows.
> 
> I suppose we have no way to change the font settings during the testing,
> so disabling this part of the test would be the simplest. Alternatively
> we can add some tolerance to the test (a pixel or two?) but no idea how.

No idea, if possible.
https://gerrit.libreoffice.org/#/c/35647/ fixes the problem for me.

Do you remember, if there were many different results on Linux tinderboxes?
Because your commit message mentioned them as the reason to run the test
only on Windows and Mac.

> Regards,
Jan-Marek