EECS 487 PA2: Scene, Camera, Lights!

Overview

In this assignment you will work on a simple model/scene viewer view3D that uses a simplified X3D scene graph as well as two simple programmable shaders. The provided view3D parses as input a scene description file in the X3D format, partially constructs a scene graph with various X3D nodes, and passes the scene to the renderer. The full X3D file format is described in the X3D Specification. Most of your tasks will be modifying the source file scene.cpp. Look for words YOUR CODE HERE to locate where to work. You will also modify the GLSL vertex and fragment shader files: phong.vs along with phong.fs, and interesting.vs along with interesting.fs.

You're not required to read most of the X3D documentation reference herein. Actually, you may find it more helpful to simply read the class definitions in scene.h and glace over the provided code in scene.cpp relevant to the class of interest. The one exception is the X3D Lighting Specification referenced below, which you do need to read carefully.

The provided code has been tested to compile under Linux, Mac OS X, and Windows. However, CAEN Linux workstations do not have great graphics drivers and the programmable GPU shaders will not work there. If you have a Linux machine with good drivers you can use the Makefile provided. I haven't been able to get shader support to work with Cygwin/X under Windows 7. If you manage to get it to work, please let me know. For further help with the support code, please see details below.

Graded tasks overview (100 points total)

1. Implement rendering of a Cylinder node modifying X3Cylinder::Render() function. (5 pts)
2. Implement simple camera navigation ("examine mode") by writing a couple of X3Viewpoint methods. (25 pts)
3. Implement proper modeling Transformation sequence by modifying X3Transform::Render() function. (10 pts)
4. Setup Point Lights by modifying X3PointLight::SetupLights() and X3Transform::SetupLights() functions. (10 pts)
5. Setup the Material properties by modifying X3Material::Render() function. (5 pts)
6. Compute the normals and render the IndexedFaceSet (mesh) node, modifying methods of X3IndexedFaceSet::Render() and X3IndexedFaceSet::Add(). (15 pts)
7. Implement per-vertex Gouraud shading that matches the fixed-function per-vertex rendering (modify gouraud.vs). (10 pts)
8. Implement Phong and Blinn-Phong variants of per-fragment shading (phong.vs, phong.fs, and blinn.fs) (10 pts)
9. Implement some interesting shader (modify interesting.vs and interesting.fs). (10 pts)

Implementation details

Cylinder rendering

Modify the X3Cylinder::Render() function to render Cylinders using all the provided data fields of the cylinder node. It may help to look at how the same function is implemented for the Cone primitive. After you're done with this task, your view3D should be able to display 01-cylinder.x3d.

Camera examine mode

The simple X3D viewer and parser included with the project does not include a camera class. All the viewing information is stored within the X3Viewpoint node. The gaze center ("lookAt" coordinates) of the camera is assumed to be the origin of the camera coordinate frame. The location of the camera itself is stored in the position_ member of X3Viewpoint, in camera coordinates. The camera coordinate frame is initialized to coincide with the world coordinate frame and the camera is initialy placed on the positive z-axis of the world coordinates (equivalentlly, the w-axis of the camera coordinates), with the gaze vector pointing towards the origin. The up_ member of the X3Viewpoint class helps you keep track of the camera's up direction, which we assumed to be the same as the v-axis of the camera coordinate frame and initialy coincides with the positive y-axis of the world coordinates.

You will need to implement dollying in and out (mapped to dragging the mouse up and down with the right button pressed— FYI, vanilla GLUT doesn't support the mouse wheel). You will also need to implement camera tracking along the latitude and longitude of a spherical space around the origin of the camera coordinate frame (a.k.a. arcball or trackball camera). After each viewing transform (each call to display()), the camera is always at lat/lon (0, 0) in the camera coordinate frame, with its gaze towards the origin (of the camera coordinate frame, which coincides with the origin of the world coordinate frame). Dragging the mouse left and right with the left button pressed causes the camera to track along the equator. Dragging the mouse up and down with the left button pressed causes the camera to track along its longitude. In the figure below assume the mouse is dragged from point 'a' to point 'b' on the screen. You need to translate this linear movement of the mouse into a rotation of the camera on the sphere around the origin.

Modeling transformation hierarchy

The scene graph represents the scene as a directed acyclic graph (it is not a simple tree since some nodes can be reused multiple times) and the traversal of this graph is performed when the scene is rendered. Grouping nodes such as X3Scene, Group, and Transform traverse their children so that each child renders itself. The Transform node adds the ability to specify the transformation between the child coordinate system and the parent coordinate system so that children can be specified with respect to their parent nodes. Implement X3Transform::Render() following the inline instructions. The inline comments pretty much give you the solution to this task, so think of it as a chance to practice your knowledge of OpenGL API calling conventions (10 lines). Practice and drill. The reward though is that you can now view 03-bikeframe.x3d, 03-desklamp.x3d, and 03-desktop.x3d.

Lighting setup

We will support only point lights in view3D. We will assume each point light effects the whole scene, and therefore a separate pass is needed to setup light positions and other light parameters before the scene is rendered. Each point light can be located anywhere in the scenegraph. A light attached to a child node is transformed by the modeling transformation of the child's parent(s), allowing a light to be "attached" to a particular object.

The X3Scene::SetupLights() method recursively calls the SetupLights method of children nodes down the scenegraph hierarchy. Each node's SetupLights should be implemented very similar to the node's Render method. Implement the X3Transform::SetupLights() method to do this for X3Transform node (10 lines). Then in the X3PointLight::SetupLights() method set up OpenGL lighting parameters for PointLight to match the X3D Lighting Specification (9 lines, you need to read this lighting specification). In our simplified viewer we have no fog and no spot light, so ignore those parameters. Be careful to match X3D lighting parameters onto OpenGL's parameters. If no lights are specified within the X3D file, a default light is added to the scene (in display()). Make sure to assign properties to the light with the proper id: GL_LIGHT0 + light_index. You can now see the effect of lighting on 03-bikeframe.x3d, and 03-desktop.x3d. But to really put a shine on the surfaces, you need to finish the next task.

Material setup

You set up the Material properties of your surface inside the X3Material::Render() method (6 lines). Lights are setup once before rendering the whole scene whereas materials vary from node to node. Be careful to match X3D material properties onto OpenGL's material properties, for instance, shininess in X3D gets multiplied by 128, so check that the resulting colors and intensities are what you intended. Now you can view 00-cone.x3d, 00-cube.x3d, 01-cylinder.x3d, 03-desklamp.x3d, 03-bikeframe.x3d, and 03-desktop.x3d in their glorious colors.

Computation of mesh normals and mesh rendering

IndexedFaceSet represents a polygonal mesh node in the form of a list of vertex indices. Each entry in the vertex index list refers to an entry in the list of vertex coordinates. Our simplified X3D parser supports only triangle and quad meshes. From an X3D file, the parser extracts two separate lists: one of quads and the other of triangles (see the X3IndexedFaceSet class and the comments in X3IndexedFaceSet::Add()). The parser also assumes only coordinates are given (no normals or colors, for example). In order to compute lighting, you need to compute a normal for each vertex. The normal of a vertex is the average of the normals of the polygons sharing the vertex. To compute the normal of a vertex, you need to first compute the normal for each polygon. Each vertex then accumulates the normal computed for each of its incident polygon. After all the polygons have been processed, average out the normals of the vertices by normalizing them. Vertex normal computation is to be done in the X3IndexedFaceSet::Add() method.

You will also need to implement mesh rendering within the X3IndexedFaceSet::Render() method. For each triangle, draw triples of vertices in a loop within the GL_TRIANGLES rendering mode. Remember to specify glNormal() before each call to glVertex(). Similarly for quads. Review your X3Cylinder::Render() for an example, but specify a separate normal for each vertex. Once you are done with this task you will be able to display the famous graphics teapot model, 04-teapot.x3d but check out the 04-coolcube.x3d! Other files you can now view are: 04-eight.x3d, 04-fish.x3d, and 04-torch.x3d. A few of the models provided have non-planar surfaces in their indexed face sets. This will cause them to have a small number of polygons missing, such as 04-fish.x3d having a small hole in its cheek. This is caused by view3D supporting only a subset of X3D, e.g., we throw away the provided normals and colors and we only recognize triangles and quads. You don't have to fix the holes.

GLSL shaders

These last three tasks will be done in GLSL. Before starting this part of the assignment, you may want to review the GLSL syntax in the lecture slides on Programmable Shaders. The provided support code reads and compiles shader files. The shader files must be in the same folder from where view3D is run (if you're using an IDE, this could be where the project file is). The program compiles the shaders into GPU-executable program objects. The code in shaders.cpp performs these tasks. You are encouraged to read it to see how it traps errors and notifies the user of failed compilation and linkage. You can mix and match compatible vertex and fragment shaders. By default, the program uses OpenGL fixed-function pipeline.

Next implement per-pixel shading. Most of the work will be done in the fragment shader phong.fs, but the vertex shader phong.vs must first prepare the per-vertex attributes. Unlike with the vertex shader, the final color in the fragment shader must be assigned to the vector gl_FragColor.rgb. Compute the per-pixel shading using the original Phong algorithm. View the effect of your Phong shaders on 01-cylinder.x3d, 04-coolcube.x3d, 03-desktop.x3d, and 04-torch.x3d

To implement the Blinn-Phong variant of per-pixel lighting, copy your phong.fs to blinn.fs and make the slight Blinn-Phong modification (view3D will quietly reuse your phong.vs as vertex shader). Now view 04-torch.x3d and 03-desktop.x3d again and marvel at the difference such a slight modification to the formula can achieve. Below are the screenshots for 03-desktop.x3d with Phong and Blinn-Phong shading respectively.

The "interesting" shader task is an open-ended task and you can implement any nice or weird looking shader. Examples of interesting shaders may include the brick procedural texture or some cartoonish looking textures (note that the provided interesting.[vf]s already implements some simple cartoon shading so you need to come up with something a bit more interesting). Be original; do not simply take some random dot product, multiply by 4, take the square root, and convert to rods per hogshead. Think it through and make sure to explain and understand the choices that you made.

Download the assignment archive from /afs/umich.edu/class/eecs487/f15/FILES/pa2.tgz.

The program view3D should be called with one command-line argument—the name of the X3D scene file. We have included some in the scenes sub folder—there are many other on the web, and some graphics packages can export to X3D.

The following keyboard shortcuts are defined for view3D (you may bind other operations to keys in view3D.cpp:kbd(), but do not change these predefined keys):

• 'q' or ESC: quits the program
• '@': resets the camera
• 'p': activates the per-pixel Phong shaders.
• 'b': activates the per-pixel Blinn-Phong shaders.
• 'i': activates the interesting shaders.
• 'n': disables shaders (default, no shader, fixed-function pipeline mode).

The provided code must be linked with the Expat XML Parser library, in addition to the usual OpenGL, GLU, and GLUT libraries. On Linux and Windows platforms, the code must further be linked with GLEW, the OpenGL Extension Wrangler. Please see the course note on how to install and use GLEW and Expat, which also covers other IDE-related topics such as how to specify command line options, add header file search path, and link against external libraries and dynamically linked libraries. The use of expat should be completely transparent to you and you don't need to study it. Your code must not require other external libraries or include files other than the ones listed in this spec.

Submission Guidelines

As with PA1, to incorporate publicly available code in your solution is considered cheating in this course. To pass off the implementation of an algorithm as that of another is also considered cheating. For example, if the assignment asks you to implement sort using heap sort and you turn in a working program that uses insertion sort in place of the heap sort, it will be considered cheating. If you can not implement a required algorithm, you must inform the teaching staff when turning in your assignment, e.g., by documenting it in your writeup.

Test the compilation!
Code that does not compile will be heavily penalized.

1. Your platform and its version - Linux, Mac OS X, or Windows.
   
2. Anything about your implementation that is noteworthy.
3. Feedback on the assignment.
4. Name the file writeup-uniqname.txt.
   For example, the person with uniqname tarukmakto would create writeup-tarukmakto.txt.

Do remove all printf()'s or cout's and cerr's you've added for debugging purposes.

General

The General Advice section from PA1 applies. Please review it if you haven't read it or would like to refresh your memory.