[Bug 5946] text rendering using vsfilter doesn't properly display (affects Flash Pro 8)

http://bugs.winehq.org/show_bug.cgi?id=5946

Niels Martin Hansen  changed:

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--- Comment #12 from Niels Martin Hansen   2009-01-24 10:10:39 ---
I have some experience hacking the VSFilter/TextSub source, and the cause of
this bug is most likely in how Wine stores and returns TrueType text path
outlines in metafile canvases. (Sorry if I use some wrong or inconsistent
terms, I usually don't work much with Windows GDI.)

TextSub (as I believe the rendering engine in VSFilter is called) does its own
rasterisation of text outlines, to be able to add further special effects than
the regular GDI is able of. To retrieve the text outlines, it creates a
metafile canvas and draws text into that, to extract the outlines afterwards.

The relevant code is in CText::CreatePath() in
http://guliverkli.svn.sourceforge.net/viewvc/guliverkli2/src/subtitles/RTS.c...

Two different algorithms are used depending on whether inter-character spacing
is non-zero. This is (part of) the cause of the workaround martino describes
working, although it probably still has to do with a problem in Wine's
implementation of metafile canvases.

In the simple case (as seen by TextSub) where all the text is drawn as a single
path, first BeginPath(hdc) is called, then TextOut(hdc, 0, 0, txt, txtlen) is
called, followed by CloseFigure(hdc) and EndPath(hdc).
After this GetPath(hdc, NULL, NULL, 0) is used to retrieve first the number of
points in the path, then memory is allocated, and finally GetPath(hdc,
mpPathPoints, mpPathTypes, mPathPoints) is used to get the actual points.
I believe it is somewhere here the problem lies. I don't have a machine myself
to test on, but either Wine returns too few points, or it returns them in an
unexpected form, and it seems to be triggered by space characters in the string
to TextOut().
Lastly the path is cleared from the canvas by AbortPath(hdc).

The case where the inter-character spacing is specified to be non-zero, the
same sequence of operations is basically performed for each widecharacter in
the text that should be rendered. The advance for each character is retrieved
with GetTextExtentPoint32W().
The points retrieved for each character in the text are then appended to a list
of all points which are used for further rasterisation. This case where each
character is treated as a separate string works fine, accordint to reports.