CAP 201a - Computer Animation I

Lesson 7 - Shapes

Objectives:

This lesson discusses a concept it calls shapes. Objectives important to this lesson:

  1. Types of shapes
  2. Describing the parts of shapes
  3. Editing shapes and shape sub-objects
  4. Modifying 2D shapes to create 3D objects
Concepts:

The lesson begins by telling us that shapes are 2D or 3D objects, that they can be open or closed, and that they have characteristics that help us describe them:

  • a shape may be composed of several splines, called segments
  • a shape may have one or more corners, called vertices (segments are enclosed by vertices)
  • a vertex may be a sharp corner, a smooth curve, a bezier, or a bezier corner

If you have not seen the term before, a bezier is named after a mathematician. In 3DS Max, beziers allow us to use control points to create complex curves. Follow the link above to see an example: click four times in the white space on the screen to set four control points. The Java applet on the page will draw a bezier curve defined by those points. Drag the points to see how their positions affect the curve.

The text reminds us that curves in shapes are approximated on screen by using a number of line segments from one vertex to the next. The number of segments is controlled by the value of Steps in the Interpolation rollout. A smoother line is generated by having more vertices, rather than more steps.

The text describes some shapes as parametric. Think of regular shapes from geometry class, in which the sides are all the same length, angles are all the same number of degrees, etc. When you want a custom shape, you can start with one of these, then do one of two things:

  • Convert the shape to an editable spline. You can convert a shape from its quad menu or from the modifier stack. (Both require a right-click.)
  • If you convert an object to an editable spline, you lose the ability to edit its original object properties. To retain that ability, add Edit Spline to the object's modifier list instead of converting it. This method will give you more flexible control, but makes a larger file.

The first section of the lesson concludes with two operational definitions (page 226):

  • A shape is collection of splines
  • A spline is an open or closed linear or curvilinear element

Sounds like splines can be used to describe anything.

Exercise Notes and Questions

Work through the exercises and turn in your answers to all questions below as part of the homework for this assignment.

Exercise 1: This exercise starts by making a pair of 2D shapes. In it you learn about one function of the Snaps Toggle button: drawing a line that sticks to the vertices of an object.
Question 1: What do you do to set the options for the Snaps Toggle button?
Question 2: In step 24, you are told to close the spline. What does this mean?
Question 3: In step 28, you add an Edit Spline modifier to the star. This gives you three sub-object buttons. What are they? (see step 29)

The lesson continues with new material.

  • You can attach splines to a shape, making them part of it. You can detach splines from a shape that has multiple splines in it.
  • Sub-objects can be moved, rotated, and scaled.
  • You can use the mirror tool to create an opposite edge that matches an existing spline.
  • You can use the outline tool to give thickness to a spline, such as when you want to create matching inside and outside surfaces of a bottle with a defined thickness in between.
  • Segments of a shape can be detached, moved, then reconnected with the connect tool, making a new segments from one open vertex to another.
  • The refine tool can add more vertices to a shape, to allow more editing.

The lesson goes on for several pages about editing vertices.

  • You can delete vertices from a shape.
  • You can weld vertices, combining existing vertices into one. This tool fuses the chosen vertices at a point between them. (Compare this to the connect tool above, that connects two vertices with a new segment.)
  • Use the quad menu to change a vertex from one of the four types (sharp corner, a smooth curve, a bezier, or a bezier corner) to another.
    • a corner vertex is an angle formed by two line segments meeting
    • a smooth vertex is is a curve with no sharp point to it
    • a bezier vertex gives you handles to adjust a curve symmetrically
    • a bezier corner vertex gives you the most control, letting you adjust the a curve asymmetrically
  • Use the fillet tool to round off the corners (vertices) of a shape.
  • Use the chamfer tool to bevel the vertices of a shape. See this lesson on fillets and chamfers in 3DS Max.)
  • The first vertex on a spline is important because the rest of the shape is calculated from it.

Exercise 2: Exercise 2 walks you through a series of steps, using several of the tools above to create an oil drum. Note the use of the bezier vertex, the mirror tool, and the weld tool. When you use the weld tool, notice that you start with two first vertices and wind up with one. This is because the two shapes you are welding become one shape.
Question 4: At the end of the exercise, the can/drum is incomplete. What tool does the text say you will use to complete the object?

Exercise 3: This exercise introduces a helpful idea. You can create a 3D object based on a 2D drawing that you place on the screen. This is a little like the exercise above, but this time you draw the outside edge of a bottle, add bezier corner vertices, and use the outline tool. The edge of the bottle that you draw is a spline, and the text refers to this kind of edge (later) as a profile.
Question 5: The exercise has you change the type of several vertices and modify them. What is the purpose of these steps?

The lesson introduces several more tools, some of which are used in the next exercise.

  • extrude - We have seen this tool before. It adds thickness to a shape.
  • lathe - This tool is used on a shape like the bottle edge created above. It rotates the shape to create a 3D object, as though we had used the shape as a template for a real lathe. You can adjust the axis of rotation to change what the lathe tool will create.
  • bevel - This tool can work like the extrude tool, but it can also modify the edges of shapes.
  • bevel profile - This one is for creating a beveled object from a basic profile spline.
  • sweep - This tool is described briefly, but not used in the next exercise. You might think of its function as the text says: "take a profile and extrudes it along a path". (page 252)

Exercise 4: Exercise 4 demonstrates the lathe tool. In step 5, you are directed to use the Weld Core option.
Question 6: What is the problem that you are solving with the weld core option?
Question 7: The exercise also has you reduce the number of faces in your can object. What action reduces the number most?

Exercise 5: Exercise 5 adds a bevel modifier to a circle with a star cut out of it.

Exercise 6: Exercise 6 uses the bevel profile tool to create a 3D object from a 2D object. It reviews the use of the bezier corner type of vertex.
Question 8: Why is it necessary to create the bullnose before using the bevel profile modifier?

Exercise 7: Exercise 7 uses a sweep modifier to make a wainscoting. This may also be viewed as adding a chair rail to the scene. This exercise clarifies what the author means by extruding a profile along a path.