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).
7.8 Polygon basics.
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
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.
7.9 The Draw->Polygon menu cell.
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).
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
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
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.
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
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.
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.
7.12 The Polygon->Edge menu cell.
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.