[Bug 60464] New: Direct2D collinear joins extend a stroked open path past its endpoint

[WineHQ Bugzilla]

http://bugs.winehq.org/show_bug.cgi?id=60464

            Bug ID: 60464
           Summary: Direct2D collinear joins extend a stroked open path
                    past its endpoint
           Product: Wine
           Version: 11.17
          Hardware: x86-64
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: d2d
          Assignee: [e-mail]
          Reporter: [e-mail]
  Target Milestone: ---
      Distribution: ---

Created attachment 82289
  --> http://bugs.winehq.org/attachment.cgi?id=82289
pedigree-line-join-probe.c — standalone C pixel reproducer (AI-assisted)

A collinear intermediate vertex causes a Direct2D stroked open path to extend
well beyond its endpoint. This produces extra tails on connectors in RootsMagic
11's Pedigree and Family views.

The attached standalone C reproducer requires no RootsMagic installation or
database. It creates a 64x64 DXGI surface at 192 DPI and draws a 1.5-DIP black
stroke on a gray background. It compares:
1. A single segment from (2,16) to (8,16).
2. The same path with an intermediate vertex at (6,16).

Expected: both paths leave the pixel at x=25 DIP (device pixel x=50, y=32)
gray.
Actual: the single-segment control leaves it gray, but the collinear path makes
it black.

Test environment: Linux Mint 22.3, x86_64; 32-bit D3D11/Direct2D; Wine 11.17
Direct2D sources used with this project's Wine 11.0 loader/runtime; Vulkan
renderer; 192 DPI. This was a local mixed-version runtime, not a complete stock
Wine 11.17 installation. We have not verified the latest unmodified Wine
release or run this probe on native Windows.

Build:
i686-w64-mingw32-gcc -std=c99 -O2 -Wall -Werror pedigree-line-join-probe.c -o
probe.exe -ld2d1 -ld3d11 -ldxguid -luuid -lole32

Run:
WINEPREFIX=/path/to/test-prefix
WINEDLLOVERRIDES='d2d1,dwrite=b;d3d11,d3d10core,dxgi=b'
WINE_D3D_CONFIG=renderer=vulkan WINEDEBUG=-all wine probe.exe

Recorded results: without the local join fix, the control sampled inside=0,
beyond=128, while the collinear case sampled inside=0, beyond=0 (exit 1). With
the local join fix both cases sampled inside=0, beyond=128 (exit 0).

Investigation points to d2d_geometry_outline_add_join() in
dlls/d2d1/geometry.c. The straight-through vertex takes the ccw == 0 branch,
which creates join vertices 25 units away. A local proof-of-concept skips the
join when ccw == 0 and the normalized tangent dot product is negative,
retaining the reversal case. This corrected the pixel probe and the visible
connector tails in both application views. This is a diagnosis to review, not a
claim of a fully validated upstream fix.

This report and standalone reproducer were prepared with AI assistance.

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