Fix conic point identification in the path renderer.

The numeric value of FT_CURVE_TAG_CONIC is 0, so the translation
to local ControlType failed when testing

  if (fttag & FT_CURVE_TAG_CONIC) { ... }

Replaced the translation with a more robust approach.

This wasn't readily apparent using the fonts embedded in VTK, as those
fonts consist entirely of linear and cubic curves.

Also fixed this functiont to use the pen_[xy] variables, which account
for kerning.

Change-Id: Ibcd7d28365ecad22d62073dc8bbf89405478f791

Author: David C. Lonie

Rendering/FreeType/vtkFreeTypeTools.cxx

@@ -1964,22 +1964,31 @@ bool vtkFreeTypeTools::RenderCharacter(CharType character, int &x, int &y,
         FT_Vector ftvec = outline->points[point];
         char fttag = outline->tags[point];
         controlType tag = FIRST_POINT;
-        if (fttag & FT_CURVE_TAG_ON)
-          {
-          tag = ON_POINT;
-          }
-        else if (fttag & FT_CURVE_TAG_CUBIC)
-          {
-          tag = CUBIC_POINT;
-          }
-        else if (fttag & FT_CURVE_TAG_CONIC)
+
+        // Mask the tag and convert to our known-good control types:
+        // (0x3 mask is because these values often have trailing garbage --
+        // see note above controlType enum).
+        switch (fttag & 0x3)
           {
-          tag = CONIC_POINT;
+          case (FT_CURVE_TAG_ON & 0x3): // 0b01
+            tag = ON_POINT;
+            break;
+          case (FT_CURVE_TAG_CUBIC & 0x3): // 0b11
+            tag = CUBIC_POINT;
+            break;
+          case (FT_CURVE_TAG_CONIC & 0x3): // 0b00
+            tag = CONIC_POINT;
+            break;
+          default:
+            vtkWarningMacro("Invalid control code returned from FreeType: "
+                            << static_cast<int>(fttag) << " (masked: "
+                            << static_cast<int>(fttag & 0x3));
+            return false;
           }
 
         double vec[2];
-        vec[0] = ftvec.x / 64.0 + x;
-        vec[1] = ftvec.y / 64.0 + y;
+        vec[0] = ftvec.x / 64.0 + pen_x;
+        vec[1] = ftvec.y / 64.0 + pen_y;
 
         // Handle the first point here, unless it is a CONIC point, in which
         // case the switches below handle it.