commit d5ffb72e00e528796c07d51b3ed9d7a28ad12668
author Patrick Luby <guibmacdev@gmail.com> Fri Apr 26 20:25:03 2024 -0400
committer Christian Lohmaier <lohmaier+LibreOffice@googlemail.com> Thu May 16 19:56:34 2024 +0200
tree f1001c65f2adb36252677c65b968b471ee2bcded
parent ed4316d109841c31de49493092d82b40259e818a

tdf#153306 prevent subpixel shifting of X coordinate

HACK: for some unknown reason, if the X coordinate of the
path's bounds is more than 1024, SkBlendMode::kExclusion will
shift by about a half a pixel to the right with Skia/Metal on
a Retina display. Weirdly, if the same polygon is repeatedly
drawn, the total shift is cumulative so if the drawn polygon
is more than a few pixels wide, the blinking cursor in Writer
will exhibit this bug but only for one thin vertical slice at
a time. Apparently, shifting drawing a very tiny amount to
the left seems to be enough to quell this runaway cumulative
X coordinate shift.

Change-Id: Ic1ac8a390df51c4aa1cc3183590dce72059af6b6
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/166766
Reviewed-by: Patrick Luby <guibomacdev@gmail.com>
Tested-by: Jenkins
(cherry picked from commit 05d3a99aa687ee4e1706f9403651379b7ebdad89)
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/166722
Reviewed-by: Christian Lohmaier <lohmaier+LibreOffice@googlemail.com>

vcl/skia/gdiimpl.cxx

diff --git a/vcl/skia/gdiimpl.cxx b/vcl/skia/gdiimpl.cxx
index f4ad57f..5a04a08 100644
--- a/vcl/skia/gdiimpl.cxx
+++ b/vcl/skia/gdiimpl.cxx
@@ -1490,6 +1490,26 @@ void SkiaSalGraphicsImpl::invert(basegfx::B2DPolygon const& rPoly, SalInvert eFl
            aPaint.setShader(
                aBitmap.makeShader(SkTileMode::kRepeat, SkTileMode::kRepeat, SkSamplingOptions()));
        }

#ifdef SK_METAL
        // tdf#153306 prevent subpixel shifting of X coordinate
        // HACK: for some unknown reason, if the X coordinate of the
        // path's bounds is more than 1024, SkBlendMode::kExclusion will
        // shift by about a half a pixel to the right with Skia/Metal on
        // a Retina display. Weirdly, if the same polygon is repeatedly
        // drawn, the total shift is cumulative so if the drawn polygon
        // is more than a few pixels wide, the blinking cursor in Writer
        // will exhibit this bug but only for one thin vertical slice at
        // a time. Apparently, shifting drawing a very tiny amount to
        // the left seems to be enough to quell this runaway cumulative
        // X coordinate shift.
        if (isGPU())
        {
            SkMatrix aMatrix;
            aMatrix.set(SkMatrix::kMTransX, -0.001);
            getDrawCanvas()->concat(aMatrix);
        }
#endif
    }
    getDrawCanvas()->drawPath(aPath, aPaint);
    postDraw();