tdf#99244 opengl: miter limit for poly lines

(cherry picked from commit ea6196f0a51d1bf4cd722468406dcc8c64c7435c)

also includes commit cb4015bb28dd7430efaaa523d04a155eb7e46305

Change-Id: I1c363a8f1d21bbacab0c5785544aa8becfe39363
Reviewed-on: https://gerrit.libreoffice.org/24072
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>

1 files changed, 13 insertions, 0 deletions

diff --git a/vcl/opengl/gdiimpl.cxx b/vcl/opengl/gdiimpl.cxx
index d3d6392bf96c..0c107da49abc 100644
--- a/vcl/opengl/gdiimpl.cxx
+++ b/vcl/opengl/gdiimpl.cxx
@@ -682,6 +682,8 @@ inline glm::vec2 normalize(const glm::vec2& vector)
     return vector;
 }
 
+SAL_CONSTEXPR float constMiterMinimumAngle = 15.0f;
+
 } // end anonymous namespace
 
 void OpenGLSalGraphicsImpl::DrawLineCap(float x1, float y1, float x2, float y2, css::drawing::LineCap eLineCap, float fLineWidth)
@@ -864,6 +866,17 @@ void OpenGLSalGraphicsImpl::DrawPolyLine(const basegfx::B2DPolygon& rPolygon, fl
 
             if (eLineJoin == basegfx::B2DLineJoin::Miter)
             {
+                float angle = std::atan2(previousLineVector.x * nextLineVector.y - previousLineVector.y * nextLineVector.x,
+                                         previousLineVector.x * nextLineVector.x + previousLineVector.y * nextLineVector.y);
+
+                angle = (F_PI - std::fabs(angle)) / F_PI180;
+
+                if (angle < constMiterMinimumAngle)
+                    eLineJoin = basegfx::B2DLineJoin::Bevel;
+            }
+
+            if (eLineJoin == basegfx::B2DLineJoin::Miter)
+            {
                 // With miter join we calculate the extrusion vector by adding normals of
                 // previous and next line segment. The vector shows the way but we also
                 // need the length (otherwise the line will be deformed). Length factor is