CS4451A: Assignment 2

"Hierarchical Coordinate Systems"

Due: September 24th (before class)

Purpose

To become familiar with hierarchical coordinate systems.

Task

Write a Java program using GL4Java that displays a graphical scene containing 7 objects: 1 sphere, 2 cubes and 4 teapots.

The objects should be arranged in a tree layout in the Z=0 plane, with the sphere at the root of the tree (positioned on the positive Y axis), the 2 cubes the next level down (children of the sphere, positioned at Y=0, and +/- X from the sphere), and the 4 teapots at the leaves (two as children of each cube, positioned at negative Y, and +/- X from their parent cube). The objects should be of similar size, and spaced so they are near each other but not overlapping.

A 45 degree field of view perspective projection should be used to view the scene, with the camera on the +Z axis, looking at the origin, far enough away so the entire scene is visible.

Each object should be a different subdued, pastel color; use any colors except yellow and green.

At any time, one of the objects should be "selected"; initially, the sphere should be selected. While an object is selected, it should be bright yellow. The selected objects can be changed using the "n" (next) and "p" (previous) keys. Pressing these keys cycles the selection through the 7 objects.

In addition to selecting an object, the user can put your program in a number of different transformation modes, which are selected by pressing a key: "s" (uniform scale in x, y and z), "x" (rotate around the x axis), "y" (rotate around the y axis) and "z" (rotate around the z axis). You should draw some text in the upper left corner of the window, telling the user what mode they are in.

When the users presses the left mouse button, drags the mouse, and releases it, transformations are applied to the scene as follows:

• all objects have an initial transformation that reflects their layout in a tree.
• the transformation of an object affects that object and all children under it in the tree (ie. objects are specified in the coordinate system of their parent in the tree).
• when the mouse button is pressed, the selected object should change from yellow to green to reflect that it is being transformed.
• the transformation is changed on the selected object only when the button is released.
• while the button is pressed, the object should be transformed when the mouse is moved. In all cases, the magnitude of the transformation is proportional to the distance between the current mouse position and where the mouse was when the button was pressed. You should not change the stored transformation on the object while the button is pressed; rather, you should apply two transformations to the object when the scene is drawn: M1 (the stored transformation) and M2 (the transformation based on the current position of the mouse).
• when the mouse is released, the stored transformation for the object should be updated to reflect the position of the mouse: M1 (the stored transformation) = M1 * M2 (the transformation based on the current mouse position).

  Pressing the "r" key should reset the transformations on all objects to their initial position.

Turn in

Your program should consist of a single java file which should be commented with your name (the name you are registered under!) and GT number. The java file should implement a class "a2" (so the TA can execute it using the command "java a2".) The file should be emailed as an attachment to a single email message to cs4451@cc.gatech.edu.

The time the mail is received will be used to determine whether or not the program is late, so be sure to allow a couple of minutes for the mail system to transmit your file if you are working right up to the deadline.

IMPORTANT: If the TA has to edit your files you will lose points. Similarly, the TA should be able to execute the class "a2", so using any other class as your main class will result in lost points.

Due date

This program is due on or before class on Tuesday, September 24th. This means it must be received by 9:39am EDT on Tuesday to not be considered late.

Additional Instructions

You might want to start with this sample file hw2.java. It sets up some lighting and shows you how to draw a some objects with GLUT.

You are expected to read the OpenGL docuementation to see how to create projects, position the camera, draw text, and manipulate the matrix stacks.

EXTRA CREDIT

There are two extra credit options on this assignment. You may do one or both, and each is worth a possible one point.

1. Add another mode, selected with the "w" key. This moves the camera in the world. Assuming you position your camera N units down the Z axis, you are to move the camera around on a sphere with radius N units. The movement of the mouse should rotate the camera around the sphere in the X and Y direction proportional to the amount you move the mouse in the X and Y direction relative to the position the user clicked. You are expected to computing the new position of the camera on the sphere yourself; do not use the OpenGL transformation to rotate the world and keep the camera still.
2. Use OpenGL picking to select the object to be manipulated with the right mouse button, rather than the "n" and "p" keys.