drawinglayer: avoid AA for hairline polygons built from hori/vert lines only

For one, it seems this was the intention already since commit
85c70f37b56299f6fa02312c0fb73cc55af084ef (CWS-TOOLING: integrate CWS
aw063, 2009-03-04): "suppress AntiAliasing for pure horizontal or
vertical lines".

For another, this fixes the TileCacheTests::testTileWireIDHandling()
testcase in online.git, which assumes that the indicators at the corners
of the Writer body frame (paragraph marks hidden / default case) can be
painted multiple times, producing pixel-by-pixel matching results. But
in reality AA breaks that assumption, and we know these indicators are
never diagonal lines.

Change-Id: Ib74f823165799991296b64cee58ec106dbdcedcf
Reviewed-on: https://gerrit.libreoffice.org/72000
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>
Tested-by: Jenkins

2 files changed, 20 insertions, 0 deletions

diff --git a/drawinglayer/source/processor2d/vclpixelprocessor2d.cxx b/drawinglayer/source/processor2d/vclpixelprocessor2d.cxx
index 03012fb5d35a..db65dc3de4bb 100644
--- a/drawinglayer/source/processor2d/vclpixelprocessor2d.cxx
+++ b/drawinglayer/source/processor2d/vclpixelprocessor2d.cxx
@@ -140,6 +140,16 @@ namespace drawinglayer
             mpOutputDevice->SetLineColor(Color(aLineColor));
             //aLocalPolygon.transform(maCurrentTransformation);
 
+            if (getOptionsDrawinglayer().IsAntiAliasing() && getOptionsDrawinglayer().IsSnapHorVerLinesToDiscrete())
+            {
+                if (basegfx::utils::containsOnlyHorizontalOrVerticalLines(rLocalPolygon))
+                {
+                    // DrawPolyLineDirect() only works in AA mode, but pure horizontal or vertical
+                    // lines are better with AA off.
+                    return false;
+                }
+            }
+
             // try drawing; if it did not work, use standard fallback
             return mpOutputDevice->DrawPolyLineDirect(
                 maCurrentTransformation,
diff --git a/drawinglayer/source/processor2d/vclprocessor2d.cxx b/drawinglayer/source/processor2d/vclprocessor2d.cxx
index 361f7a5bd5a3..335e30a56ce9 100644
--- a/drawinglayer/source/processor2d/vclprocessor2d.cxx
+++ b/drawinglayer/source/processor2d/vclprocessor2d.cxx
@@ -331,6 +331,7 @@ namespace drawinglayer
             basegfx::B2DPolygon aLocalPolygon(rPolygonCandidate.getB2DPolygon());
             aLocalPolygon.transform(maCurrentTransformation);
 
+            bool bDisableAA = false;
             if(bPixelBased && getOptionsDrawinglayer().IsAntiAliasing() && getOptionsDrawinglayer().IsSnapHorVerLinesToDiscrete())
             {
                 // #i98289#
@@ -339,9 +340,18 @@ namespace drawinglayer
                 // not-AntiAliased such lines look more pleasing to the eye (e.g. 2D chart content). This
                 // NEEDS to be done in discrete coordinates, so only useful for pixel based rendering.
                 aLocalPolygon = basegfx::utils::snapPointsOfHorizontalOrVerticalEdges(aLocalPolygon);
+
+                // Also disable AA, snap would leave the start/end of lines still anti-aliased when
+                // their coordinates are provided in logic units.
+                bDisableAA = basegfx::utils::containsOnlyHorizontalOrVerticalLines(aLocalPolygon);
             }
 
+            const AntialiasingFlags nOriginalAA(mpOutputDevice->GetAntialiasing());
+            if (bDisableAA && (nOriginalAA & AntialiasingFlags::EnableB2dDraw))
+                mpOutputDevice->SetAntialiasing(nOriginalAA & ~AntialiasingFlags::EnableB2dDraw);
             mpOutputDevice->DrawPolyLine(aLocalPolygon, 0.0);
+            if (bDisableAA && (nOriginalAA & AntialiasingFlags::EnableB2dDraw))
+                mpOutputDevice->SetAntialiasing(mpOutputDevice->GetAntialiasing() | AntialiasingFlags::EnableB2dDraw);
         }
 
         // direct draw of transformed BitmapEx primitive