Calendar is not showing the days

[adrbarros]

I ran some tests with the components I use most, and they seemed to work.
I'd like to know if the calendar isn't displaying the day numbers.
Do I need to do anything else?

• Ubuntu 25.04, Net 8.0

[sancheolz]

Looks like libgdiplus issue. You can try other versions of libgdiplus from Ubuntu repository or from official mono-project.com.

[sancheolz]

Or you can build it from source https://gitlab.winehq.org/mono/libgdiplus if you follow build instructions.

[madewokherd]

I just tested with Mono from Winehq, and I'm seeing the same thing.

[sancheolz]

We are using the libgdiplus at revision https://gitlab.winehq.org/mono/libgdiplus/-/commit/7ad33d8bbb9f39ae4786bb4e1199d30c8c67cd86 with reverted commit https://gitlab.winehq.org/mono/libgdiplus/-/commit/1e6a599d8319e6309f179a29fd920da0bb27d170 . And the calendar is displayed correctly. Could you check with reverted https://gitlab.winehq.org/mono/libgdiplus/-/commit/1e6a599d8319e6309f179a29fd920da0bb27d170 ?

[madewokherd]

We are using the libgdiplus at revision https://gitlab.winehq.org/mono/libgdiplus/-/commit/7ad33d8bbb9f39ae4786bb4e1199d30c8c67cd86 with reverted commit https://gitlab.winehq.org/mono/libgdiplus/-/commit/1e6a599d8319e6309f179a29fd920da0bb27d170 . And the calendar is displayed correctly. Could you check with reverted https://gitlab.winehq.org/mono/libgdiplus/-/commit/1e6a599d8319e6309f179a29fd920da0bb27d170 ?

Revert complains that it's a merge commit.

[madewokherd]

I see no difference with that commit reverted.

[madewokherd]

Tested with Mono on Windows, and it does render there, so I think that confirms a libgdiplus bug.

[madewokherd]

It's specifically the StringFormat.LineLimit flag, set by default in GenericTypographic format, that breaks this. Unsetting that flag on centered_format in the MonthCalendar constructor works around this.

[madewokherd]

That said, I'm not sure libgdiplus's behavior is necessarily wrong here. The date_cell_size calculation is weird, and I don't know that there's any particular reason the height we get from pango or cairo has to match this. (LineLimit will not draw the text if the line's full height doesn't fit in the bounding box it gets.)

I think the solution should be either: stop using the LineLimit flag, or fix the date_cell_size calculation.

We could try to fix the font specs in libgdiplus, but that seems fragile.

[madewokherd]

As for how .NET Core winforms does this: it goes through comctl32. Wine's comctl32 calculates the height as Height+ExternalLeading+InternalLeading given the font metrics. The width is calculated based on the widest day-of-week abbreviation in the current locale.

We could work this out by MeasureString, but this is never going to match what gdi32 does on Windows (even gdiplus.dll on Windows won't match). So then the question is: do we want to keep the existing code to vaguely approximate what Windows does, or accept that it will be different and calculate based on the text rendering engine we have?

[sancheolz]

I think it would be better to fix libgdiplus so that it behaves like gdi32 - this is what is usually expected of it. If this fix leads to regressions in other places, then we will have to take into account the features of the rendering engine already in the WinForms code.

[madewokherd]

It's not the features that are different. It's the sizes of the fonts when scaled by the text rendering engine. We are using a different engine (gdi32 being proprietary) and probably a different font.

gdiplus on Windows does not behave like gdi32. It does all kinds of weird scaling and fudging in order to preserve proportional scaling of text at any cost. So I don't see that this should be a goal of libgdiplus.

I don't think you can ever expect it to get the metrics the same.

[sancheolz]

Than I think we should make fix at Winforms side.

[madewokherd]

Made an MR on Winehq: https://gitlab.winehq.org/mono/mono/-/merge_requests/153

Surprisingly, this seems to naturally produce the hard-coded size in the MonthCalendar constructor. The previous calculation was wrong in that Font.Height isn't enough space for a line of text to "fit" according to libgdiplus.