[Bug 60556] New: winex11.drv: per-pixel alpha layered windows show stale or black areas under Xwayland because of the bounding shape

[WineHQ Bugzilla]

http://bugs.winehq.org/show_bug.cgi?id=60556

            Bug ID: 60556
           Summary: winex11.drv: per-pixel alpha layered windows show
                    stale or black areas under Xwayland because of the
                    bounding shape
           Product: Wine
           Version: 11.20
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: winex11.drv
          Assignee: [e-mail]
          Reporter: [e-mail]
  Target Milestone: ---
      Distribution: ---

Autodesk Fusion 360's floating panels (Browser, Comments) are top-level
WS_EX_LAYERED windows with per-pixel alpha
(32-bit ARGB X windows, about 300x1190, mostly transparent below the tree).
After the panel is moved or a design is
opened, part of it shows the panel's old contents and the area the window grew
into stays opaque black. The application
keeps drawing correctly into it. This is not related to Direct3D (unlike bug
60173): there is no swap chain on these
windows.

Environment: Arch Linux, wine 11.20 (Arch package), winex11.drv, Hyprland 0.56
with Xwayland 24.1.14, NVIDIA RTX 5080 with
driver 615.78.

What I observed:

- XGetImage of the panel window returns the correct contents: opaque pixels for
the tree and 0x00000000 below it.
  A screenshot of the same area taken at the same moment shows grey panel and
black instead.
- Drawing an opaque rectangle into the window with XFillRectangle in the lower
area changes neither the screen nor a
  following XGetImage, as expected if that area is outside the window's
bounding shape.

Analysis (from reading dlls/winex11.drv/bitblt.c at wine-11.20 and current
master):

x11drv_surface_flush() sets the window's ShapeBounding from the shape bits
whenever they change (the mask of non
transparent pixels). With Xwayland, what falls outside the bounding shape is no
longer updated in the buffer the
compositor shows, so after the shape shrinks or the window grows those areas
keep old contents or stay black.

For a surface with an alpha channel (ARGB visual) the bounding shape is not
needed to show transparency: the alpha already
does it. It is still useful for input, so that clicks go through transparent
parts. As an experiment, applying the same
mask as ShapeInput instead of ShapeBounding for surfaces created with use_alpha
makes the panels show correctly (I have
not checked yet that clicks go through their transparent part). Windows without
an alpha channel would keep the bounding
shape. I have only tested Hyprland's Xwayland, not a plain X server or other
compositors. I am not attaching that change: it was written with an AI
assistant, which the Developer FAQ does not accept.

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