Add a macro to switch between white and blacvk lines

Polyhedron/demo/Polyhedron/Plugins/Display/Display_property_plugin.cpp

@@ -29,6 +29,9 @@
 #define ARBITRARY_DBL_MIN 1.0E-30
 #define ARBITRARY_DBL_MAX 1.0E+30
 
+// Define this and resources/heat_intensity_shader.f will draw black instead of white lines.
+// #define HEAT_METHOD_BLACK_LINES
+
 //Item for heat values
 typedef CGAL::Three::Triangle_container Tri;
 typedef CGAL::Three::Viewer_interface VI;

Polyhedron/demo/Polyhedron/resources/heat_intensity_shader.f

@@ -76,9 +76,11 @@ void main(void) {
     h = h - floor(h);
     h = (1./(1.+exp(-100.*(h-.55)))) + (1./(1.+exp(-100.*(-h+.45))));
     h = 1.-h;
-    
-    c = h*vec3(1.,1.,1.) + (1.-h)*c;
-    
+#ifdef HEAT_METHOD_BLACK_LINES
+      c = h*vec3(0.,0.,0.) + (1.-h)*c;
+#else
+      c = h*vec3(1.,1.,1.) + (1.-h)*c;
+#endif
     out_color.rgb = c;
     out_color.a = alpha;
   }