In this assignment you will write a scene modeler using Inventor. After
the last assignment, you are probably really tired of typing in vertex
coordinates by hand. With this program you will be able to create, write,
read and modify complex scenes using a graphical user interface. Inventor
gives you (among many other facilities) easy ways to create, modify, save
and restore, and render a hierarchical scene graph. Using your program,
you will be able to instantiate primitive objects (cubes, cones, cylinders,
and spheres) group these objects, move them around, apply material properties,
and interactively explore the scene that you create.
Assignment 3: Scene Maker
Due 10/29/98 11:59pm
To learn all about Inventor, read The Inventor Mentor, which can
be accessed online through Insight, or can be purchased at the bookstore.
We suggest reading the material for the required features, implement them,
and then, for each optional feature that you choose to implement, read
the related chapter. In general, you can skip the sections marked Advanced.
For the required features you will need:
For the optional features:
While you're reading the book, you may wish to try out some of the examples,
make a few changes and see how they work. All of the examples from the
book are available in the directory:
Chapter 3 - you can skip SoLevelOfDetail
Chapter 5 - only the SoMaterial node and the Transformation sections
Chapter 15 - only the part about Manipulators
You may also wish to have a look at some of the example models in the directory:
These models can be viewed with several programs, each of which has different
features (gview is most like the program you will create):
Now that you have some understanding of how Inventor scene graphs work,
sit down and design a reasonable organization of your scene graph. You
may want to make simplifying assumptions. Some possibilities:
It is very important that you do this design step BEFORE you start coding.
Think about all the behavior of your program (what happens when you paste
objects? what happens when you ungroup? how many nodes can affect a certain
object (transformation, material, texture, rotationXYZ for animation, etc)
Can nodes be shared? Sharing is nice, but it is very easy to introduce
bugs if you use it. ) It will be very hard (and very error-prone) to change
the underlying assuptions about your scene graph after implementing a good
part of the code.
All objects correspond to a subtree: you have a separator root, the first
child will always be a transform node, possibly followed by a material
node, with the shape node (or group node) the last child
All objects have a transformation node and a material node present
The first level of the graph has only "utility" nodes (Camera, Selection,
Required Features (10 points):
Rapidapp UI: a viewer, menus for load/save, new object, etc.
Be able to create objects (cubes, spheres, cylinders, cones) and position,
scale, and rotate them in 3-space.
Select single objects / multiple objects. When one object is selected you
should show some object properties (name, world coordinates of bounding
box center, bounding box dimensions). Selected objects should be highlighted.
Names: all your objects should have names. Newly created objects should
get default names (eg. cube1, cube2, sphere1 , group1, ...) and the user
should have the option to change current names.
Group several objects to create a new one. Ungrouping should do something
sensible with the properties (eg. if the whole group was green and the
individual parts did not have materials, after ungrouping each part should
Transform (move, rotate, scale) the selected object.
Edit the material for the selected objects (you should be able to change
the material for several selected objects at the same time).
Write/read the scene graph to/from a file. It is ok to be able to read
only the files that you produced, but you should reject other files gracefully.
Cut, copy, paste.
Implement a traversal function that visits your scene graph and writes
an indented tree of the object names. This is useful for debugging your
Turn in an inventor file that represents a scene similar to the one you
created for the previous assignment.
(1) Don't forget the art contest.
(1) Be able to load an arbitrary Inventor scene graph and treat it as an
object. If it is a scene that you created it should be inserted as a new
group object (which you could later ungroup).
(1) Render a frame using the current camera and save the image to disk.You
may wish to use an off-screen buffer.
(1) Undo / Redo.
(1) Unlimited Undo / Redo.
(1) Apply textures to objects.
(1) Dialog allowing user to specify texture parameters (like texture transform
(1) Be able to record a set of camera positions.
(1) Interpolation between camera positions.
(1) Make a fly-by movie of a scene by saving frames for each interpolated
(1) Allow shared instancing in your scene graph. When the user tries to change the property of an object that appears in several instances, ask if just the instance that was selected is to be changed, or if all instances should be changed at the same time.
(1) Be able to produce VRML 2.0 files (using available IV->VRML1.0->VRML2.0 converters)
In your writeup.html, have a link to the VRML model that you have put on your web page.
(1) Be able to produce VRML 2.0 files directly from your code (without using any 3rd party converter)
(2) Snap to 3D grid: when you move/scale an object, the center/ top/ bottom
(let the user chose) of the bounding box should be aligned with the grid.
(2) Objects with simple animations (eg. rotation around some axis, swing
between 2 positions, etc.)
(3) Have a separate window showing a graphical representation of your scene
(2) Be able to edit it the scene graph in the other window (like gview
(5) Create a cool 3D interactive game, e.g. 3D pong or 3D break-out.
(?) Any other feature you can think of.
Inventor uses ROW vectors to represent points (as opposed to GL
and the rest of the graphics world who use COLUMN vectors). This means
that to transform a point, you multiply vector * matrix (the matrix goes
on the right, not on the left as in GL). Also when descending the scene
graph, transformations are accumulated by multiplying with the new matrix
on the left. So ... when in doubt, transpose!
Inventor doesn't particularly like you to modify its scene graph while
it's traversing it. If you want to do anything useful from an EventCallback
node, all the immediate children of all the ancestors of the callback node
have to be unaffected. To ensure this, you could place the EventCallback
node as the last child on the first level of the graph, and have
all object subtrees have their roots on levels>1.
Use LOTS of assertions, particularly when typecasting objects. Inventor
will happily core-dump (without giving you a reason) when you typecast
a class to an incompatible type. We will penalize programs that core-dump
without giving a reason, so ASSERTIONS ARE YOUR FRIENDS.
All the Inventor classes have man pages. Run xman and view the Inventor
section for a list of all the classes.
To render a frame into memory, use SoOffscreenRenderer. If you submit a
movie, use 10 frames/ second and JPEG compression to keep the file size
low. DO NOT submit rgb files.
To keep the set of camera positions in the graph, you might use a SoSwitch
gview is your friend when you want to try out different types of nodes
( say you want to experiment with manipulators ... )