Overview
This assignment has three parts. First, you will implement Phong
lighting (rather, the OpenGL variant of Phong lighting) of model vertices on the CPU. Then, you will implement a
simple Non-Photorealistic (NPR) rendering technique, namely a "toon shader"
or "cell shader" that simplifies and thresholds the lighting model, and adds
a silhouette edge (see images below). Finally, you will implement both Phong
lighting and toon shading on the GPU.
Your NPR renders might look something like this (from www.paulsprojects.net):
or this (from The Legend of Zelda: The Windwaker):
Required Features
- Implement your own version of OpenGL's lighting model, supporting at least
3 point lights whose colors and location may be controlled independently.
For simplicity you may use the same user-specified RGB color for the light's
ambient, diffuse, and specular coefficients, but all coefficients of the
object must be individually controllable. 30 pts
- Render the silhouette edges of the model. A silhouette edge is any edge shared between a front face and a back face.
30 pts
- Using a single point light, cel-shade the model. Inspired by traditional animation, cel-shading uses one of three colors to render each polygon: a "shadow" color for dark regions, a "lit" color for bright regions, and a "highlight" color for very bright regions. You should be able to rotate the light around the object just like you rotate the camera (use a second mouse button for this). Feel free to define these three colors however you want to give a pleasing effect.
30 pts
- Implement the above lighting and cel-shading as GPU fragment (not
vertex) programs. 30 pts
Getting Started
Some skeleton code is here. This code was
written to be a skeleton for an NPR-only assignment last semester (I added
the glut_printf() function and a couple examples of how to use it). Most of the functions you should have to manipulate for the basic
lighting and NPR
aspects of the assignment should be contained within the student.h and student.cpp files. You
will need to modify other files, but these are a good place to start. Feel free
to modify this skeleton any way you see fit.
Your code should let the user switch between various modes (CPU
lighting, built-in OpenGL lighting, CPU NPR, etc) and control the various
parameters (e.g. the coefficients in the Phong/OpenGL lighting model) with
keyboard and mouse.
To find the silhouette edges, you will need to create a data structure to
represent the polygonal mesh and its connectivity. One simple example
would be an array
of "edges", each of which contains the two vertices which comprise the edge,
and the two triangles which lay on either side. You would then selectively
render the edges which you determine to be silhouettes (as defined above) as
thick lines over top of the previously rendered model. If you want to
explore more sophisticated data structures, look up the winged-edge
and quad-edge representations.
Using the Interface
The interface for the skeleton program
would not win any awards, but will get you started:
- Right-click and drag:
rotates the camera (badly)
- Left-click and drag:
rotates the light source (not implemented)
- Middle-click and drag up/down: changes the current parameter
(only one parameter implemented in skeleton, a uniform scaling of the
wireframe color)
- Up/Down arrows:
zoom in and out (badly)
- 1-5:
Load different
models to view (note: some models may take some time to load)
Sample Assignment
A sample assignment from last year (NPR only) can be found
here.
Extra Credit
Modify your cel-shading code so that triangles
are rendered with an appropriate cross-hatched texture instead of simply being
vertex shaded. You may use the textures provided (xhatch1.bmp-xhatch4.bmp) or
some method of your own. Up to 20 pts
Find a way to make the silhouette edges look more hand-drawn, for example
by making random or wavy lines. Up to 20 pts
There are many other possible cool extra credit projects with NPR
and GPU programming, but check with me before embarking on any of them for
extra credit.
Submission
The usual: write a web page describing what you did, including your entry for the art contest.
Your web page should contain a link to a .zip file that contains ALL of the source code that your TAs will need to build your assignment. It is your responsibility to make sure that the zip file is complete. We are not going to fix compile errors or fill in missing pieces of assignments.
Please e-mail a link to your submission to the TAs. Never, NEVER e-mail the TAs anything except a URL when submitting. In particular, do NOT e-mail your .zip file or any images as attachments.