-static void fghDrawGeometrySolid(GLfloat *vertices, GLfloat *normals, GLubyte *vertIdxs, GLsizei numVertices, GLsizei numEdgePerFace)
+/**
+ * Draw the geometric shape with filled triangles
+ *
+ * - If the shape is naturally triangulated (numEdgePerFace==3), each
+ * vertex+normal pair is used only once, so no vertex indices.
+ *
+ * - If the shape was triangulated (DECOMPOSE_TO_TRIANGLE), some
+ * vertex+normal pairs are reused, so use vertex indices.
+ */
+static void fghDrawGeometrySolid(GLfloat *vertices, GLfloat *normals, GLubyte *vertIdxs,
+ GLsizei numVertices, GLsizei numVertIdxs)