Reducing Polygons Through the Modifier Stack

The scene now consists of two objects that make up the main portion of the house. There should be 48 total faces in the scene, as can be verified by checking File Ø Summary Info. That’s a relatively low polygon count for a house, but let’s reduce this total even more. The total of 48 might not seem to be much, but one of the main things to remember about modeling for games is to keep the overhead of any unnecessary polygons to an absolute minimum (or none). Since the house we are creating is not going to dance around in our final scene (it will just sit on the ground like a real house), we can eliminate some polygons that the viewer will never see: namely, the bottoms of both house pieces, and the inside end of HouseShape01.

Since game engines typically do not read the MAX modifier stack, the object’s stack will need to be collapsed before the model is brought into the game. Because collapsing the stack makes further modifications to the base object impossible (such as changing the amount of the previously applied Extrude modifier), we will take the extra steps necessary to preserve the stack. These extra steps will make certain that you do not perform any “irreversible” edits to the base object (until the very end). This will, perhaps, create a modifier stack that is more extensive than you might be used to, but you will be able to go back into the stack and adjust the parameters throughout the object’s creation history. This will be explained in further detail shortly.

	NOTE If you want to start from here, you can open the file House01.max on the CD.

1.  Select HouseShape01 and rotate the perspective viewport so you are looking at the bottom of the home.

2.  From the Modify tab, apply a Mesh Select modifier.

3.  Enter the Polygon sub-object level of the Mesh Select modifier by using the drop-down list or the Selection icons.

4.  Click the bottom face of the selected object. It will become highlighted in red.

5.  While still in Sub-Object level and with the bottom of the house selected, apply a DeleteMesh modifier. You will notice the floor of the house disappear. You should now have something like Figure 4.19.

Understanding this combination of a Mesh Select followed by DeleteMesh modifier is crucial to understanding the modifier stack for the purpose of this exercise. To eliminate the bottom of the house, we could obviously have collapsed the extruded piece to the editable mesh level and then deleted the bottom face at the Sub-Object level. The problem with this method is that this would permanently delete the face and, if saved and reloaded, this scene would no longer be able to access the deleted face. Because the DeleteMesh modifier was applied when a polygon was selected at the Sub-Object level of the previous (Mesh Select) modifier, only that active polygon was removed. Read the previous sentence again slowly.

FIGURE 4.19  Perspective view of the house from underneath

Furthermore, since a modifier performed the deletion, the user has the option of going back into the stack and editing the Mesh Select (to change what is selected for deletion) or removing the DeleteMesh (thus returning the face). Before any further house-creation, we will temporarily alter the modifier stack, attempting to clear up any confusion.

6.  Edit Ø Hold. You will shortly want to resume building the house from this point.

7.  Verify that you still have HouseShape01 selected. In the Modifier Stack rollout, use the drop-down list to go back one step to the Mesh Select modifier. Do not remove the DeleteMesh modifier.

Notice that the bottom geometry miraculously returns. The Sub-Object level of the Mesh Select should still be active, with Polygon as the type.

8.  In the perspective viewport, click the front face of the house. It will become red when selected.

9. Activate the Show End Result button in the modifier stack. Now the DeleteMesh modifier affects the newly selected face.

	NOTE Show End Result maintains your location in the modifier stack at Mesh Select, but attempts to show the results of the entire list of cumulative modifiers of the stack in the viewports. This is part of the fundamental functionality of the modifier stack and should be understood to take full advantage of MAX.

With the Show End Result still active and while still in Sub-Object mode, try clicking different faces of the object and notice that the face chosen is “passed up” the stack to the DeleteMesh modifier (and removed from view). Also try holding down the Ctrl key while selecting faces; this allows you to pass multiple sub-object selections up to the DeleteMesh modifier. Also, if you now toggle the yellow Sub-Object button off, you will see the entire front section of the house disappear. This is because, in effect, you are selecting no part of the object with the Mesh Select modifier. Hence, the following DeleteMesh modifier removes the entire object from the viewports. While this is the case, you must remember that this is non-destructive, and you can return the house section by once again turning on the Sub-Object level.

10.  To return to the task at hand, go to the Edit menu and select Fetch. Click Yes when asked if it is OK to fetch.

11.  Select HouseShape02.

12.  Apply a Mesh Select modifier.

13.  Select the Polygon Sub-Object level and choose the bottom face of the object as you did previously with HouseShape01.

14.  While still in sub-object mode, apply a DeleteMesh modifier.

It will appear as though the house is transparent in some areas and missing many more faces than the two affected by the current pair of DeleteMesh modifiers. This is because we are looking at the wrong side of the polygons. The normals of the faces that appear to be missing are on the other side of the house, when considered from our current viewpoint.

15.  Select Arc Rotate Selected from the Viewport Navigation controls and return to a bird’s-eye view of the house in the Perspective viewport. From above, it should (still) resemble Figure 4.18.

There is still a polygon on the back of HouseShape01 (inside the house) that will never be seen. It is directly beneath the centerline of HouseShape02, and can be seen from under and behind the house.

16  .With the Arc Rotate tool still active in the perspective viewport, get behind and beneath the house pieces.

17.  Select HouseShape01.

18.  Apply a Mesh Select modifier.

19.  At the Polygon sub-object level, select the polygon that is inside the house.

20.  While still in Sub-Object mode and with the polygon selected, apply another DeleteMesh modifier. From below and behind, the perspective viewport should look like Figure 4.20.

FIGURE 4.20  From behind, you can tell where the house is missing polygons.

© 2000, Frol (selection, edition, publication)