opengl: shader based polyline rendering - fixes tdf#97137 for OGL

Adds native opengl polyline rendering to draw polylines, line joins
and line caps as triangle strips. The vertex shader allows for the
dynamic line width by calculating the correct vertex posiitons,
and the fragment shader is used for anti-aliasing.

(cherry picked from commit d18ad8a7fb3257001a5045e11f3f770a48a7fa69)

Change-Id: If7982c828cae1fae59c57194c8ac77e5ad7f1d26
Reviewed-on: https://gerrit.libreoffice.org/22706
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: László Németh <nemeth@numbertext.org>
Reviewed-by: Tor Lillqvist <tml@collabora.com>
Tested-by: Tor Lillqvist <tml@collabora.com>

1 files changed, 29 insertions, 0 deletions

diff --git a/basegfx/source/polygon/b2dlinegeometry.cxx b/basegfx/source/polygon/b2dlinegeometry.cxx
index c259fef49504..a3095caa05f0 100644
--- a/basegfx/source/polygon/b2dlinegeometry.cxx
+++ b/basegfx/source/polygon/b2dlinegeometry.cxx
@@ -779,6 +779,35 @@ namespace basegfx
 
     namespace tools
     {
+        B2DPolygon polygonSubdivide(const B2DPolygon& rCandidate, double fMaxAllowedAngle, double fMaxPartOfEdge)
+        {
+            if(fMaxAllowedAngle > F_PI2)
+            {
+                fMaxAllowedAngle = F_PI2;
+            }
+            else if(fMaxAllowedAngle < 0.01 * F_PI2)
+            {
+                fMaxAllowedAngle = 0.01 * F_PI2;
+            }
+
+            if(fMaxPartOfEdge > 1.0)
+            {
+                fMaxPartOfEdge = 1.0;
+            }
+            else if(fMaxPartOfEdge < 0.01)
+            {
+                fMaxPartOfEdge = 0.01;
+            }
+
+            B2DPolygon aCandidate(rCandidate);
+            const double fMaxCos(cos(fMaxAllowedAngle));
+
+            aCandidate.removeDoublePoints();
+            aCandidate = subdivideToSimple(aCandidate, fMaxCos * fMaxCos, fMaxPartOfEdge * fMaxPartOfEdge);
+
+            return aCandidate;
+        }
+
         B2DPolyPolygon createAreaGeometry(
             const B2DPolygon& rCandidate,
             double fHalfLineWidth,