M.S. Project Proposal: Tinker Toys Online

Andrew Robbins
5/21/96

The goal of this project is to create an interactive computer graphics teaching aid that will help students understand the transformations that are used to manipulate and view three-dimensional graphical objects.

Tinker Toys Online will be an on-line model of the tinker toys that are commonly used to aid in understanding three-dimensional graphics transforms. It will be implemented as a java applet and reside on a web page that will also reference HTML user guides. This will increase the potential audience and minimize the issues of access to the application software, platform inter-operability and dependence on previously loaded software libraries.

There will always be a place in the world for a student bending a paper clip into a three-dimensional (x, y, z) axis and saying "Now if I rotate the tennis ball in my left hand around the x-axis for 30 degrees...", but the web page, used by itself or in conjunction with its physical counterparts, will provide a deeper understanding of how the transformation is accomplished. What it looses in physical immediacy, it makes up for by allowing the student to examine how the object is transformed and how various views are created.

Relevant information such as the World and View Reference Coordinate systems, viewing parameters, and vertex coordinates of the model will be presented. The student will be able to manipulate the model and view objects and examine the resulting transform matrices and their effects. In addition to graphical control of objects, the project will allow the user to specifically set the translate value, rotate angle or scale percentage by typing them in. A professor may use this feature to create a directed study assignment in which a set of questions leads the student through a predetermined scenario.

Deliverables

There will be four major deliverables:

• An informative teaching aid, implemented as a java applet.
• Written user and technical documentation. The HTML user guides, java class api definitions (in the standard java format used by Sun), and formal project write-up will also be available on-line.
• Extendable object classes. The project will be designed using an object-oriented methodology and may serve as a platform for further development.
• Java code. The project will be implemented in well-documented, clearly written java code that other students may use as an introduction to the language. The source code will be available on-line along with the documentation.

Functionality

The applet will consist of four main windows, described below. Each window will be created as an external frame and may be manipulated independently while the browser is used to display HTML user guides.

• Object Control Window
  • The Object Control Window may be thought of as the main window. It is displayed throughout the life of the applet and contains three panels and a message display bar.
    • The World Panel will show a "Bird's eye view" of all the objects as they sit in world space.
    • The View Window Panel will show what is visible in the View Window using the current viewing parameter settings.
    • The Operation Panel is used to select the desired operation and method of control when moving objects.
    • The Message Bar will display messages and information about the objects.
  • The following objects may be viewed and modified:
    • the (x, y, z) World-Coordinate (WC) System
    • the (u, v, n) Viewing-Reference Coordinate (VRC) System
    • the View Window
    • the Front and Back Clipping Planes
    • the PRP (Projection Reference Point)
    • and the Model, a house
  • Objects may be translated, rotated about any axis, and scaled. Rotation and scaling may be done with respect to the WC origin or the object's center. Objects may be moved graphically with the mouse or by specifying the transformation in a pop up window.
  • The view of the world as seen in the World Panel may be manipulated by rotating the World-Coordinate System. Shortcut options will be provided to quickly jump to any of the orthogonal views (straight ahead, side and top).
  • The Model will be displayed as a wire frame object that may be viewed in the View Window Panel using either a parallel or perspective projection. The view will be clipped using the Front and Back Clipping Planes, but no back-face removal will be done.
  • Objects that have been moved will be able to be backed-up to their former location(s) and/or orientation(s) one step at a time.
  • A Reset option may be used to return all objects to their initial position.
• Matrix Window
  • The Matrix Window will display the contents of the transformation matrices that are used to move an object and generate the views displayed in the World and View Window Panels.
  • Three types of matrices can be displayed:
    • Object transformation matrices. If an object is selected by clicking on one of its vertices in the World Panel, that object's last transformation matrix will be displayed.
    • The View-Orientation Matrix, which transforms from WC to VRC.
    • The Shear-Parallel Matrix, which generates the parallel projection view of a VRC point and adjusts for an off-center PRP.
  • Matrices will be displayed both visually (4 x 4 array of numbers) and textually
    (ie. "Matrix T = translate by (dx = 5, dy = 6, dz = 0)").
  • Composite matrices will be displayed such that their sub-matrices may be viewed and applied individually. For example, the composite matrix that scales an object that has been rotated is made up of sub-matrices that translate the object's center to the WC origin, return it to its original alignment (which has been changed by the rotation), scale it, return it to its current alignment and translate its center back to its current position. Once the scale has been completed, the user may back the object up and then apply the sub-matrices one at a time to see how the scale operation is implemented.
  • The Matrix Window's contents will change dynamically as the mouse is used to select objects in the World and View Window Panels.
• View Control Window
  • The View Control Window is used to modify the following view parameters:
    • VRP: View Reference Point (shown in WC)
    • VPN: View Plane Normal vector (shown in WC)
    • VUP: View-Up vector (shown in WC)
    • PRP: Projection Reference Point (shown in VRC)
    • View Window min: the View Window minimum point (shown in VRC)
    • View window max: the View Window maximum point (shown in VRC)
    • F clip: the Front Clipping Distance (shown in VRC)
    • B clip: the Back Clipping Distance (shown in VRC)
• Vertex Window
  • The Vertex Window will display a specific vertex of the model and show how the various transformation matrices affect that vertex.
  • The vertex that is presented will change if the student clicks on another vertex of the the model in the World or View Window Panel.

Project Committee

• Nan Schaller - chairperson
• Larry Coon - reading member
• Peter Anderson

Current Timeline

• Proposal finalized: 5/17/96
• Java code completed: 5/24/96
• HTML user guides completed: 5/24/96
• Formal write-up complete: 7/1/96
• Project defense: 7/20/96