OpenGL Scene Graph Animated Lamp

This is a Java program involves using OpenGL 3.x to render a 3D scene, which contains an animated lamp. The scene graph was using in the modelling process, and the animation controls are implemented for the hierarchical model — the lamp.

The project is my previous coursework in the masters study period.

Demo

Click the link to view the project demo.

From the demo, the animation of lamp in the video demo is not smooth, and the lamp jumped strangely sometimes. Note that it is due to system recording and would not happen when consuming the project locally.

---

Scene and Scene Graph

The scene includes:

• A plot of floor.
• A wall.
• A piece of an outside scene that could be seen through the window on the wall (the moving texture outside the window is fog).
• A lamp with a light bulb, which is positioned on the tabletop.
• A table located on the floor under the window on the wall.
• Three other objects (not including the lamp) on the table.
• Two global static lights.
• A virtual camera for viewing and controlling.

These objects are made of primitive objects only — basic triangles, cubes and spheres, and they are modelled either by linear modelling method (modelling objects directly without using scene graph) or hierarchical modelling method (scene graph), which are categorised as the table below:

Object	Modelling Method
Floor	Linear Modelling Method (modelling objects directly without using scene graph)
Outside Scene
The Book on the Table
The Globe on the Table
The Mobile Phone on the Table
Global Light 1
Global Light 2
Viewing Camera
The Lamp on the Table	Hierarchical Modelling Method (Scene Graph)
The Light Bulb in the Lamp
Table
Wall

Example: Lamp

The angle-poise lamp is a hierarchical model, which is made up of the four basic parts:

• A base.
• A lower arm.
• An upper arm.
• A head which contains a protruding light bulb.

Every part of lamp connects at joints, so we can specify the model by giving all joint angles and positions. The lower arm can rotate about the base, the upper arm can rotate about the lower arm, and the head can rotate about the upper arm. The light bulb shines in the same direction that the head is pointing in. Imagine the lamp is standing on a tabletop in a room looking out of a window. The lamp can also jump around the tabletop.

In terms of code set up the scene graph, we are using Object-Oriented Design to construct scene graph nodes to represent, record and manipulate the hierarchical relationship in an 3D object in Java.

The diagram below shows the class structure for an SGNode (Scene Graph Node). The link from an SGNode to itself is an indicator that this is a recursive structure. In fact, an SGNode contains an ArrayList of child nodes, each of which is an SGNode.

Three other classes extend SGNode: a ModelNode contains a reference to a Model instance; a NameNode is used solely to make the scene graph hierarchy clearer by allowing nodes that contain nothing but a String to represent their name; and a TransformNode is used to represent a transformation (a Mat4 (transformation matrix) instance) to be applied to its children in the scene graph.

Comparing this structure to the scene graph of lamp, we have a mixture of NameNodes (lamp base, lamp lower arm, lamp head joint, etc), ModelNodes (cube and sphere) and TransformNodes (lamp base rotate, lamp upper joint z rotate, lamp tail y rotate, etc). This is reflected in the code in Program Listing below. SGNode contains a method called addChild() which is used to build the scene graph. I've used indentation in the program code to make the hierarchy clearer, although some may argue that it makes the code a little more difficult to read. It's personal choice.

0 Name: lamp root
1   Name: lamp transform
2       Name: lamp base scale
3           Name: lamp base
4               Name: lamp base 1
4               Name: lamp base rotate
5                   Name: lamp base 2
2       Name: lamp joint scale
3           Name: lamp lower joint
4               Name: lamp lower joint translate
5                   Name: lamp lower joint y rotate
6                       Name: lamp lower joint z rotate
7                           Name: lamp lower joint
7                           Name: lamp lower arm
8                               Name: lamp arm scale
9                                   Name: lamp lower arm translate
10                                      Name: lamp lower arm
8                               Name: lamp upper joint translate
9                                   Name: lamp upper joint y rotate
10                                      Name: lamp upper joint z rotate
11                                          Name: lamp upper joint
12                                              Name: lamp upper joint
12                                              Name: lamp upper arm
13                                                  Name: lamp upper arm translate
14                                                      Name: lamp upper arm
13                                                  Name: lamp head joint translate
14                                                      Name: lamp head joint y rotate
15                                                          Name: lamp head joint z rotate
16                                                              Name: lamp head joint
17                                                                  Name: lamp head joint self scale
18                                                                      Name: lamp head joint
17                                                                  Name: lamp head translate
18                                                                      Name: lamp head y rotate
19                                                                          Name: lamp head z rotate
20                                                                              Name: lamp head
21                                                                                  Name: lamp head self scale
22                                                                                      Name: lamp head
18                                                                      Name: lamp head transform
19                                                                          Name: lamp head back
20                                                                              Name: lamp head back
17                                                                  Name: lamp head ear left transform
18                                                                      Name: lamp head ear left
19                                                                          Name: lamp head ear left
17                                                                  Name: lamp head ear right transform
18                                                                      Name: lamp head ear right
19                                                                          Name: lamp head ear right
9                                   Name: lamp tail x rotate
10                                      Name: lamp tail y rotate
11                                          Name: lamp tail z rotate
12                                              Name: lamp tail
13                                                  Name: lamp tail transform
14                                                      Name: lamp tail

The visualised scene graph of the lamp is shown below:

---

Set Up Guide

Embed JOGL in the project

you will need to download the JOGL version 3.x files that are relevant for your computer and operating system. When you use your own Windows PC, you can set up permanent environment variables. You need administrator privileges to do this. Once the environment variables are set up, you can open a command window at any time and the environment variables are automatically associated with it. This means you can immediately compile and run your Java and JOGL programs.

Compile and Run

The main class of the project called Anilamp.java. To begin with, you need to compile the project using the following command in the terminal:

javac Anilamp.java

Then, use the following command to start the project:

java Anilamp

It could take approximate 10 seconds to popup the window and get the scene rendered since it needs to load the scene graph and textures.

---

Interaction

• There are control buttons on the window bottom. You might not be able to see them as the resolution of the window might be larger than the device screen. In this case, please maximise the window.
• The lamp can change different poses plausibly by pressing the "Random Pose" button.
• Every time the lamp jumps, by pressing the "Jump" button, it will reset its pose at first, then jumping to a random place.
• The buttons, "Random Pose" and "Jump", will be disabled for about 2 seconds after the previous action of the lamp has completed.
• Please wait for the lamp to complete the jump (back in the table and restore the initial pose), then press the "Random Pose" or "Jump" button again, or the lamp will change the direction incorrectly in the next time.
• The lamp can avoid intersecting other three objects on the table when jumping.
• There are three buttons that enable users to switch on/off two global lights and the light bulb.
• The program contains classes for Keyboard input and Mouse input, each of which can set attributes in the Camera class based on user input. Holding down the left button and moving the mouse will move the direction that the camera is looking in. The A and Z keys can be used to move in and out of the scene in the direction the camera is looking in. The arrow keys can be used to move up, down, left and right.

---

Limitations

• Shadow and ray-trace are not implemented in the project.
• Spotlight does not track correctly with some random poses — the direction Vec3 value was used a magic number for convenience rather than calculating from the subtraction between the position of lamp head and the light bulb.

---

License and Copyright

• Some classes are implemented by Dr. Steve Maddock.
• This project has MIT licence.
• The copyright of texture images states in the *.txt file in the textures folder.