Discard lines behind camera when processing grease penicl line art

Source/gpla/LineArtParser.cpp

@@ -157,6 +157,10 @@ std::vector<Line> LineArtParser::generateFrame(juce::Array <juce::var> objects,
                 double rotatedY2 = end.x * allMatrices[i][4] + end.y * allMatrices[i][5] + end.z * allMatrices[i][6] + allMatrices[i][7];
                 double rotatedZ2 = end.x * allMatrices[i][8] + end.y * allMatrices[i][9] + end.z * allMatrices[i][10] + allMatrices[i][11];
 
+                // I think this discards every line with a vertex behind the camera? Needs more testing.
+                // - DJ_Level_3
+                if (rotatedZ < 0 && rotatedZ2 < 0) {
+
                     double x = rotatedX * focalLength / rotatedZ;
                     double y = rotatedY * focalLength / rotatedZ;
 
@@ -167,5 +171,6 @@ std::vector<Line> LineArtParser::generateFrame(juce::Array <juce::var> objects,
                 }
             }
         }
+    }
     return frame;
 }