fix line width in DrawPolyLine() with matrix (tdf#132498)

For backends that do the object-to-device coordinates transformation
directly, it's necessary to also convert the size of line width.
But simply multiplying it with the matrix can also rotate the line
width "vector", making it e.g. negative. So don't use just the X
coordinate, use vector length for the transformation, which is ok.
In fact it doesn't even make sense to treat width as a vector, because
a width simply is not a vector (and for this reason it's also not
actually used).

Change-Id: I1241c9cb29155df105170d568a879ebc32b11a5f
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/93203
Reviewed-by: Tomaž Vajngerl <quikee@gmail.com>
Tested-by: Jenkins

1 files changed, 9 insertions, 10 deletions

diff --git a/vcl/headless/svpgdi.cxx b/vcl/headless/svpgdi.cxx
index b5649b093e31..fadf641fd290 100644
--- a/vcl/headless/svpgdi.cxx
+++ b/vcl/headless/svpgdi.cxx
@@ -1092,7 +1092,7 @@ void SvpSalGraphics::drawPolyLine(sal_uInt32 nPoints, const SalPoint* pPtAry)
         basegfx::B2DHomMatrix(),
         aPoly,
         0.0,
-        basegfx::B2DVector(1.0, 1.0),
+        1.0,
         nullptr, // MM01
         basegfx::B2DLineJoin::Miter,
         css::drawing::LineCap_BUTT,
@@ -1456,7 +1456,7 @@ bool SvpSalGraphics::drawPolyLine(
     const basegfx::B2DHomMatrix& rObjectToDevice,
     const basegfx::B2DPolygon& rPolyLine,
     double fTransparency,
-    const basegfx::B2DVector& rLineWidth,
+    double fLineWidth,
     const std::vector< double >* pStroke, // MM01
     basegfx::B2DLineJoin eLineJoin,
     css::drawing::LineCap eLineCap,
@@ -1488,7 +1488,7 @@ bool SvpSalGraphics::drawPolyLine(
             rObjectToDevice,
             rPolyLine,
             fTransparency,
-            rLineWidth,
+            fLineWidth,
             pStroke, // MM01
             eLineJoin,
             eLineCap,
@@ -1508,7 +1508,7 @@ bool SvpSalGraphics::drawPolyLine(
     const basegfx::B2DHomMatrix& rObjectToDevice,
     const basegfx::B2DPolygon& rPolyLine,
     double fTransparency,
-    const basegfx::B2DVector& rLineWidth,
+    double fLineWidth,
     const std::vector< double >* pStroke, // MM01
     basegfx::B2DLineJoin eLineJoin,
     css::drawing::LineCap eLineCap,
@@ -1522,21 +1522,20 @@ bool SvpSalGraphics::drawPolyLine(
     }
 
     // need to check/handle LineWidth when ObjectToDevice transformation is used
-    basegfx::B2DVector aLineWidth(rLineWidth);
     const bool bObjectToDeviceIsIdentity(rObjectToDevice.isIdentity());
 
     // tdf#124848 calculate-back logical LineWidth for a hairline
     // since this implementation hands over the transformation to
     // the graphic sub-system
-    if(aLineWidth.equalZero())
+    if(fLineWidth == 0)
     {
-        aLineWidth = basegfx::B2DVector(1.0, 1.0);
+        fLineWidth = 1.0;
 
         if(!bObjectToDeviceIsIdentity)
         {
             basegfx::B2DHomMatrix aObjectToDeviceInv(rObjectToDevice);
             aObjectToDeviceInv.invert();
-            aLineWidth = aObjectToDeviceInv * aLineWidth;
+            fLineWidth = (aObjectToDeviceInv * basegfx::B2DVector(fLineWidth, 0)).getLength();
         }
     }
 
@@ -1617,7 +1616,7 @@ bool SvpSalGraphics::drawPolyLine(
 
     cairo_set_line_join(cr, eCairoLineJoin);
     cairo_set_line_cap(cr, eCairoLineCap);
-    cairo_set_line_width(cr, aLineWidth.getX());
+    cairo_set_line_width(cr, fLineWidth);
     cairo_set_miter_limit(cr, fMiterLimit);
 
     // try to access buffered data
@@ -1654,7 +1653,7 @@ bool SvpSalGraphics::drawPolyLine(
 
     // check for basegfx::B2DLineJoin::NONE to react accordingly
     const bool bNoJoin((basegfx::B2DLineJoin::NONE == eLineJoin
-        && basegfx::fTools::more(aLineWidth.getX(), 0.0)));
+        && basegfx::fTools::more(fLineWidth, 0.0)));
 
     if(pSystemDependentData_CairoPath)
     {