Let's continue our exploration by comparing the top sections of the Editable Mesh and Editable Poly panels.
Note the differences in the sub-object selection modes. Both Editable Mesh and Editable Poly have Vertex, Edge, Polygon and Element modes. But Editable Mesh has a Face mode that is missing in Editable Poly, and Editable Poly has a Border mode that isn't found in Editable Mesh.
These two screenshots reflect the state of each panel in the Polygon sub-object mode, and their differences get to the heart of the distinction between the two types of objects. The Editable Poly panel indicates that no "Polygons" are selected, while the Editable Mesh panel says that no "Faces" are selected (even though we are not in Face sub-object mode). Note, also, how the Editable Mesh panel contains a checkbox to "Ignore Visible Edges" and a Planar Threshold spinner. Finally, the Editable Mesh (but not the Editable Poly) panel permits you to display normals. Each one of the points is worth understanding completely if one takes modeling seriously in MAX.
The word "Face" in MAX always refers to triangles. As in the previous lesson, an Editable Mesh cube in on the left and an otherwise identical Editable Poly object in on the right (in green). When the Edges Only option is turned off in the Display Properties panel, we see the Invisible Edges as dotted lines on the Editable Mesh object, but not on the Editable Poly object. As we noted in the previous lesson, even though the Editable Poly object is triangulated under the surface, the concept of Visible and Invisible edges does not apply.
Let's consider Polygon selection in Editable Mesh. In Polygon selection mode, I click anywhere on the top quad on the cube and it's selected. But notice how the panel informs me that "2 Faces" have been selected. The Polygon unit in Editable Mesh is essentially a way of selecting groups of triangles.
To qualify as a Polygon in Editable Mesh, triangles must be coplanar within the limit set on the Planar Threshold spinner, and must be joined at Invisible Edges. Here, the two triangles are absolutely coplanar, as all four vertices are on the same plane. If I were to move one of the vertices so that the two triangle break along their diagonal at more than 20 degrees (the value I set on the spinner), each triangle would be selectable only as a separate Polygon. Make sure you test this idea yourself, because it's a little subtle.
If I select the Invisible edge on the top face and make it Visible, I can only select one of the two Faces while in Polygon mode (regardless of the fact that they are co-planar).
I can override this rule by checking the "Ignore Visible Edges" box. Now both Faces are selectable together as a Polygon simply because they are co-planar, even though they are divided by a Visible diagonal edge.
But just checking this box doesn't mean that Visible edges are ignored for reasons other than selection. For example, the top quad will be treated as two triangles for subdivision with the Mesh Smooth modifier.
If all this is confusing you, you are perfectly normal. This mish-mash of rules has always made it very difficult to work with quads and n-gons in MAX, and is the reason why long-time MAX practitioners should be looking over the Editable Poly alternative very seriously.
The selection of Polygons in Editable Poly couldn't be more straightforward. There is no issue of planarity or Invisible edges. The underlying organization of Polygons into triangles is hidden from you (unless you choose to get involved). Click on any of the four quads, and you've selected a quad. How revolutionary!
Having eliminating the confusing distinction between a Face and Polygon, you make two triangular Polygons by simply creating a new edge (in the Edge mode) between two of the vertices. It's as simple as drawing a line between them.
Back in Polygon mode, the new triangles are selectable as Polygons, just as the quads are. Much simpler!
Before leaving the subject of Polygon sub-object selection mode, we should consider the issue of normals. A normal (for our purposes) is a ray that is perpendicular to the plane of the polygon. This ray is used to indicate the renderable side of the polygon. The concept of a perpendicular ray only makes sense for polygons that are perfectly planar. Triangles are, inherently, perfectly planar. Thus in Editable Mesh, it makes sense to be able to display the normals for the Faces in selected Polygons.
We can then flip the direction of the normals of the selected Faces so they point in, instead of out. The next image can be confusing to read, but note that although the top quad is not rendering, it still exists and its two normals are pointing downward.
Editable Poly takes a simplified approach that makes sense in the overwhelming majority of cases. Normals cannot be displayed, nor can you flip the normals of selected polygons. You can only flip all the normals of a mesh Element as a group. An Element is a group of contiguous (connected) Polygons. Thus you must go into Element sub-object mode first. In the case of our cube, there is only a single Element to select, compromised of the entire mesh.
After flipping all the normals together, we see the inside surfaces of the cube.