Starting From Scratch: Making Your Own Polygons

Although it is certainly faster to make objects from a spline with an extrusion, a revolution, a skin, or a four-sided patch, and it is easier to make polygons from a primitive polygon object, you can draw your very own polygons, one point at a time. We'll cover this method first, on the theory that you must crawl before you learn to walk. A firm understanding of polygon terminology and practice in creating polygons will certainly serve you well as you go forward.

To recap from Chapter 6, "The Model Shop-All About Modeling," a polygon is a geometric construct composed of at least three vertices positioned in space and connected by straight line segments called edges. Each polygon has a front face and a back face, indicated by which direction the polygon normal is pointing (see Figure 7.8).

Figure 7.8 Polygon basics.

The Draw->Polygon Command

The Draw->Polygon command in the Model module is the place to start drawing your first polygon (see Figure 7.9). The Draw command doesn't just draw single polygons; it starts by creating a new polygonal mesh object, visible in the Schematic view. You can then attach additional polygons to the first one, sharing vertices and edges.

Because Softimage attempts to keep polygons within the same mesh consistent in their normal orientation, the direction you draw a polygon is important. The default method is to draw polygons counterclockwise. After the first polygon is placed and confirmed, the command automatically changes to the Attach mode.

Figure 7.9 The Draw->Polygon menu cell.

With Draw->Polygon active, you can click in any View window and hold down the mouse button to place the first vertex. It's a good idea to draw polygons in an orthographic view instead of the Perspective view, because you can keep the polygons planar. You can place additional vertices with the left mouse button, or add vertices between existing ones with the middle mouse button. You can add as many points as you wish to the polygon, but it's a good idea to keep the number of points in a polygon under 255. When you are done with the polygon, click the right mouse button to end the Polygon Add mode and enter the Polygon Attach mode (see Figure 7.10).

Figure 7.10 Drawing and attaching new polygons.

In the Polygon Attach mode (also found by itself in the Polygon->Polygon command), you must pick two existing vertices on the polygon to define the shared edge between the old polygon and the new one. You then add additional vertices that belong only to the new polygon, by clicking in space with the left mouse button.

If you select the first two vertices for the shared edge in a way that would lead to the new and old polygons having different normal orientations, Softimage gives you an error message in the status line and makes you re-pick. This refusal to allow bad polygons seems like a hassle, but it prevents rendering and redraw problems later.

When you are done with the new polygon, click the middle mouse button to accept it as done and add another. Use the right mouse button to end the mode. In this manner, you can add one polygon to another, carefully defining the shape of the object.

Adding and Removing Vertices

What if you have a polygon already made that needs to be subdivided to create more detail? You can add more vertices to any polygon, in places where additional edges would help you create more polygonal detail. Then you can add edges to subdivide the polygon into two smaller ones, and further subdivide those smaller polygons as needed. This is the process most often used to create polygonal detail for faces, fingers, and musculature on low-poly characters.

You add vertices with the Polygon->Vertex command, found in the Model module. Clicking the left mouse button adds a vertex to an edge at the spot under your mouse pointer. If you click an edge with the middle mouse button, the vertex is added at the exact center of the edge, which makes it easy to keep lines straight when adding polygonal detail for buildings, and so on (see Figure 7.11).

Figure 7.11 A polygon with some added vertices in the middle of edges.

To remove vertices that are no longer needed, click the offending point with the right mouse button. If the vertex is redundant, it simply goes away, but if there are other edges defined by that vertex, the edges go away as well, and so will the polygons that rely on those edges, leaving a hole in your model. Be careful.

Adding and Removing Edges

After adding vertices to a polygon, you can connect them with an edge to subdivide the one previous polygon into two. Simply choose the Polygon->Edge command (see Figure 7.12), pick the first vertex, and then the second. Softimage adds an edge (see Figure 7.13), unless the operation creates adjacent polygons with different normal orientations. In this case, the error message "Bad edge orientation" appears in the Status Bar and you must pick the vertices in the opposite order.

Figure 7.12 The Polygon->Edge menu cell.

Figure 7.13 The polygon from Figure 7.11 with edges added between the new vertices.

Edges can only be added within a single polygon. This means that if the vertices you want to connect belong to different polygons, you cannot add an edge. You have to find an edge between the two vertices and add an intermediate vertex, making two more edges to connect the points. Using the middle mouse button allows you to connect a series of vertices with shared edges. The right mouse button removes edges, which removes the polygons dependent on that edge, and may create a hole in your model.