Revision as of 21:49, 25 October 2013

Project 4: Light and Shade

This project is on OpenGL lighting and shading, and includes GLSL shader programs.

This project is due on Friday, November 1st at 1:30pm. It will be discussed in Center Hall 105 on Monday, October 28th at 3:00pm.

Note that GLSL shaders, which are needed for part 2 of the assignment, will be covered in class on Tuesday, October 22nd.

1. Mouse Control (20 Points)

Start by reviving your application from assignment 2: you will need to be able to display the cube, as well as the following three 3D models into your application and display them at reasonable sizes (screen filling). The function keys should switch between the models.

These are the models you need to be able to load, you will have to unzip them to get at the OBJ files. Note that some of them are different files than before, as we now need files with normals. The OBJ reader we gave you in project 2 already parses normals.

• Dragon (same as before)
• Bunny (new)
• Head (new)

You are welcome but not required to support the keyboard commands from assignment 2 to move around the models. However, you will need to add mouse control, which will allow rotating the model about the center of your OpenGL window, as well as scaling the model up and down. The left mouse button should be used for rotation, the right mouse button should zoom in and out when the mouse is moved up or down while it is pressed.

This video shows how the trackball-like rotation should work. We provide sample code for the trackball rotation. You will need to adapt it to the syntax of your matrix and vector classes and get it to work within your application.

To access the mouse x and y coordinates, you will need to use GLUT's callback functions glutMouseFunc(), which gets called when you press a mouse button, and glutMotionFunc(), which gets called constantly while you hold the button down and move the mouse. Note that successive trackball rotations must build on previous ones; at no point should the model snap back to a previous or default position.

2. OpenGL Lighting and Shading (40 points)

Write classes to manage light and material properties (Light and Material). As a starting point, refer to the relevant sections in Chapter 5 of the OpenGL Programming Guide, as well as the OpenGL Lighting FAQ.

Associate material properties with each of the four 3D model files: two of them should be shiny, and the other two should be shiny and diffuse - you choose which. Use colors other than white. (10 points)

Create three light sources: one directional light, one point light and one spot light. The spot light should always point towards the center of the OpenGL window. Give them initial positions and colors. Each of them must have a different position and color. The spot light should have a spot width narrow enough so that it only illuminates a small part of the surface of the models. Toggle each of them on and off with one of the number keys: 1, 2, and 3. Rotate those light sources which are on with the 3D model.

Add a freeze mode for the 3D model and toggle it with the 'm' key: when it is enabled, the model will not respond to mouse control commands and instead stay in its last orientation and size. In this mode only the enabled light sources rotate and zoom in and out.

Notes:

• OpenGL multiplies light position and direction with the Modelview matrix when they are set. Therefore, you need to modify the Modelview matrix with your mouse control routines to rotate the light sources, independently for each light source.
• To ascertain that the normals of your 3D models will survive zoom operations correctly, you should use the following OpenGL command: glEnable(GL_NORMALIZE).
• By default, OpenGL uses a simplified model for the calculation of the highlights. For a more realistic model add this command to your code: glLightModelf(GL_LIGHT_MODEL_LOCAL_VIEWER, GL_TRUE).

3. GLSL Shader Programs (40 Points)

Imagine that each of your light sources has a force field, which attracts or repulses the vertices of your geometry, and shifts their color.

• The directional light should repulse the vertices, and shift their color towards red.
• The point light should repulse the vertices as well, and shift their color towards green.
• The spot light should attract the vertices, but only if they fall within its spot, and shift their color towards blue.

In each case, the attraction or repulsion should happen in the direction of the light (using the light vector), and should attenuate with the square distance from the light source, so that the vertices on the side of the object facing the light move more than those away from it. Note that the directional light does not have a position, so that you will have to calculate the amount of repulsion based on whether the light hits the polygons from the front or back (done by comparing the surface normals to the incoming light vector). Implement this effect as a GLSL vertex shader.

The color shift should be done by about 10%, it must be strong enough so that it is obvious. The color shift must happen on a per pixel basis, which means that you will need to implement it as a GLSL fragment shader.

You will need to demonstrate the described effect for the 3D objects you used in the prior homework projects: specifically: cube, sphere, teddy, bunny, cow, and teapot. Be sure to make your objects big enough that they almost fill the OpenGL window, either by using your code from project 2, or by using fixed scale factors.

For Windows and Linux users, in order to use OpenGL extensions, you should download GLee and add the glee.h and glee.c files to your project files, or tell the linker to link with the GLee library (glee.lib or glee.dll for Windows, or libglee.a/libglee.so for Linux). OSX users will not need GLee, as OpenGL extensions are available by default.

We provide a sample shader class and three sample combinations of vertex and fragment shaders for you to familiarize yourself with GLSL shader programming. For this exercise, extend the diffuse_shading shader to implement the desired effects.

If the respective light is off, the attraction/repulsion and color shifting effects need to stop.

You will get points for the following things:

• At least one attraction or repulsion effect ( 10 points).
• At least one color shifting effect (10 points).
• The effect of the directional light works correctly (5 points).
• The effect of the point light works correctly (5 points).
• The effect of the spot light works correctly (5 points).
• Each of the 6 3D models needs to work with the shaders and you will need to be able to switch between the models with the keyboard. The models need to be big enough to roughly fill the OpenGL window. (5 points)

Notes

• While most CSE lab computers do, some older computers or simpler graphics cards do not support GLSL. Be aware that this might be a problem with your personal computer.
• You only need to create vertex shaders, no fragment shaders are necessary. But you are welcome to do the color shift

Here are a few URLs with tutorials on how to write GLSL shader code.

• Lighthouse3D GLSL tutorials
• Clockworkcoders GLSL tutorials
• GLSL quick reference
• GLSL reference documentation

4. Extra Credit (10 Points)

Under construction.