feat: EColLayer according to flow direction

particle-track-and-trace/src/main.cpp

@@ -35,7 +35,7 @@ int main() {
   l->setDt(DT);
 
   unique_ptr<Program> program = make_unique<Program>(DT);
-  program->addLayer(new BackgroundImage(dataPath + "/map_661-661.png"));
+  program->addLayer(new BackgroundImage(dataPath + "/map_qgis_1035.png"));
   // program->addLayer(new EGlyphLayer(uvGrid));
   program->addLayer(new EColLayer(uvGrid));
   program->addLayer(l);