tdf#101026 Create more correct replacement control vector

Change-Id: I909adaab3dca3c1bac4331b164343cdbc1205df2
Reviewed-on: https://gerrit.libreoffice.org/27365
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Reviewed-by: Armin Le Grand <Armin.Le.Grand@cib.de>

3 files changed, 16 insertions, 13 deletions

diff --git a/vcl/headless/svpgdi.cxx b/vcl/headless/svpgdi.cxx
index 7482a68da7dc..af26bd13bbc5 100644
--- a/vcl/headless/svpgdi.cxx
+++ b/vcl/headless/svpgdi.cxx
@@ -651,14 +651,16 @@ static void AddPolygonToPath(cairo_t* cr, const basegfx::B2DPolygon& rPolygon, b
 
             // tdf#99165 if the control points are 'empty', create the mathematical
             // correct replacement ones to avoid problems with the graphical sub-system
-            if(aCP1.equal(aLast))
+            // tdf#101026 The 1st attempt to create a mathematically correct replacement control
+            // vector was wrong. Best alternative is one as close as possible which means short.
+            if (aCP1.equal(aLast))
             {
-                aCP1 = aLast + ((aCP2 - aLast) * 0.3);
+                aCP1 = aLast + ((aCP2 - aLast) * 0.0005);
             }
 
             if(aCP2.equal(aPoint))
             {
-                aCP2 = aPoint + ((aCP1 - aPoint) * 0.3);
+                aCP2 = aPoint + ((aCP1 - aPoint) * 0.0005);
             }
 
             cairo_curve_to(cr, aCP1.getX(), aCP1.getY(), aCP2.getX(), aCP2.getY(),
diff --git a/vcl/unx/generic/gdi/salgdi.cxx b/vcl/unx/generic/gdi/salgdi.cxx
index 66c9e6248bbc..72daa7165bc3 100644
--- a/vcl/unx/generic/gdi/salgdi.cxx
+++ b/vcl/unx/generic/gdi/salgdi.cxx
@@ -825,14 +825,16 @@ bool X11SalGraphics::drawPolyLine(
                     // miter graphics (and maybe others) when empty control points
                     // are used, so fallback to the mathematical 'default' control
                     // points in that case
-                    if(aStart.equal(aCP1))
+                    // tdf#101026 The 1st attempt to create a mathematically correct replacement control
+                    // vector was wrong. Best alternative is one as close as possible which means short.
+                    if (aStart.equal(aCP1))
                     {
-                        aCP1 = aStart + ((aCP2 - aStart) * 0.3);
+                        aCP1 = aStart + ((aCP2 - aStart) * 0.0005);
                     }
 
                     if(aEnd.equal(aCP2))
                     {
-                        aCP2 = aEnd + ((aCP1 - aEnd) * 0.3);
+                        aCP2 = aEnd + ((aCP1 - aEnd) * 0.0005);
                     }
 
                     cairo_curve_to(cr,
diff --git a/vcl/win/gdi/gdiimpl.cxx b/vcl/win/gdi/gdiimpl.cxx
index 09c63f554799..996822259d01 100644
--- a/vcl/win/gdi/gdiimpl.cxx
+++ b/vcl/win/gdi/gdiimpl.cxx
@@ -1925,19 +1925,18 @@ void impAddB2DPolygonToGDIPlusGraphicsPathReal(
                     // tdf#99165 MS Gdiplus cannot handle creating correct extra geometry for fat lines
                     // with LineCap or LineJoin when a bezier segment starts or ends trivial, e.g. has
                     // no 1st or 2nd control point, despite that these are mathematicaly correct definitions
-                    // (basegfx can handle that). To solve, create replacement vectors to thre resp. next
-                    // control point with 1/3rd of length (the default control vector for these cases).
-                    // Only one of this can happen here, else the is(Next|Prev)ControlPointUsed wopuld have
-                    // both been false.
+                    // (basegfx can handle that).
                     // Caution: This error (and it's correction) might be necessary for other graphical
-                    // sub-systems in a similar way
+                    // sub-systems in a similar way.
+                    // tdf#101026 The 1st attempt to create a mathematically correct replacement control
+                    // vector was wrong. Best alternative is one as close as possible which means short.
                     if(!b1stControlPointUsed)
                     {
-                        aCa = aCurr + ((aCb - aCurr) * 0.3);
+                        aCa = aCurr + ((aCb - aCurr) * 0.0005);
                     }
                     else if(!b2ndControlPointUsed)
                     {
-                        aCb = aNext + ((aCa - aNext) * 0.3);
+                        aCb = aNext + ((aCa - aNext) * 0.0005);
                     }
 
                     rGraphicsPath.AddBezier(