COS 426:
Computer Graphics
Spring 2018
COS 426:
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COS 426 General | Assignment 3
In this assignment, you will create a raytracer program. You will mainly be working in GLSL, which is the shading language for OpenGL.
This section of the instructions are analogous those of the previous assignments, so by now this should be very familiar.
To get started, download this zip file and unzip it on your computer. Change to the subdirectory
cos426-assign3and run the commandpython -m SimpleHTTPServerwhich will launch a web server on your computer, rooted at this directory. (See previous assignment description about why we do this instead of opening the files directly.)Once you have started the local web server, direct your browser to
http://localhost:8000.Using your favorite text/code editor, edit the file
ls js/student.jsin that directory and fill in your name and NetID. Reload the web page in your browser, and now your information should appear above the image.Driver Setup: Most machines should be ready to go without any additional steps. However, if you are running macOS High Sierra and have an NVIDIA graphics card, there is a bug in the latest built-in graphics drivers that will break this assignment. If you have an affected machine (likely a high end Macbook Pro or iMac from 2014 or earlier), you must do one of the following three things:
If you have any doubts as to whether one of the fixes above has been correctly applied, please come to Kyle's office hours. If it hasn't been patched then correct code will sometimes, but not always, work.
- Install the latest Web Driver directly from NVIDIA. Note that installing this driver will also install the "NVIDIA Driver Manager" for switching between macOS and NVIDIA drivers. Once the driver manager is installed, click the NVIDIA logo in the top right tray and make sure "NVIDIA Web Driver" is selected. This is the recommended option for patching the bug- once you are using the latest web driver, you can be sure the bug isn't affecting you.
- Disable the NVIDIA card, either through the bios or with a tool like gfxCardStatus. This should get the job done, as the integrated intel gpu drivers don't have any issues. However, it is less recommended because it is slower, and Chrome may try to use the discrete card in spite of gfxCardStatus even when passing the --force_integrated_gpu flag. You can check whether the current Chrome window is using the NVIDIA card by navigating to "about:gpu".
- Use a different computer for assignments 3 and 4. :(
index.html?scene=default&width=600&height=400 — this names the scene and sets the dimensions. If you omit the scene name it will use 'default'. The scenes are specified to the json file in the folder scenes/ and the default scene (for example) is created by scenes/default.json. The width and height default to full screen.
The assignment is worth 20 points. The following is a list of features that you may implement. The number in front of the feature corresponds to how many points the feature is worth for the full implementation. Partial or partially-correct solutions will receive partial credit. The features in bold face are required. The other ones are optional. Refer to the examples web page for example output images as well as some implementation hints.
- Ray Intersection - intersect a ray with various shapes:
- (0.0) Plane. This is already implemented as an example.
- (2.0) Triangle. The code can read an obj file as triangle meshes for rendering in the scene by adding
?scene=meshto the URL.- (2.0) Sphere.
- (2.0) Box. (axis aligned)
- (2.0) Cylinder. The code is organized for you as an open cylinder plus two discs that are the end caps.
- (3.0) Cone. Disc is already done (for cylinder) and the open cone is similar to the open cylinder, but this is still quite difficult!
- Lighting and Materials:
- (1.0) Shadows. Cast a single ray to the light.
- (3.0) Soft shadows. Cast multiple rays towards an area around the light position.
- (2.0) Transmission rays. Reflected rays are implemented already (one line in GLSL). For glass-like surfaces, you need to calculate refraction rays based on Snell's law. You may not turn in code using the GLSL built-in refract function.
- (1.0) Checkerboard. Modulate diffuse color by a checkerboard pattern based on spatial position.
- (1.5) Phong material. Add the Phong term in the lighting calculation.
- (1.5) Special material. Add your own, for example incorporate a parametric noise texture (like Perlin noise). Feel free to reuse someone else's GLSL implementation of noise, but list your sources.
- Art and Other - you can implement these features for one point each, and also submit them to the art contest for possible additional point(s):
- (1.0) Scene. Model a scene of your choosing. Be careful that there is a maximum number of triangle faces and increasing this number will slow the program and can also cause the program to fail (depending on your graphics system).
- (1.0) Animation. Animate the scene somehow (you can access the uniform variable "frame" in the fragment shader). To enable this feature you need to add "?animated=1" to the URL. The code base does not save animations, but you can simply provide a link in your submission file and we can see the result. Also, if you really want to save a movie, use screen grab software like quicktime.
The plane intersection method is already implemented for you as an example. By implementing all the required features (in bold), you get 13 points. Full credit for this assignment is 20 points, so to complement the required features you may choose from the optional features listed above and participate in the art contest (which yields one point for participation and two for winning). Your final score is based on the following factors:
Final score will be rounded to the nearest 0.5. The formula in javascript is:
- r: your score on the required features (up to R = 13 points)
- n: your score on the non-required features (value diminishes when n > N = 7) .
- a: your participation in the art contest (1 point for participating, 1.5 for being selected for gallery, 2 for winning). You can make use of
customFilter()- d: diminishing return factor (d = 3/4 in this assignment)
Math.round((Math.min(R, r) + Math.min(N, n) + d * (1 - Math.pow(d, Math.max(n - N, 0))) / (1 - d) + a) * 2.0) / 2.0
Score Calculator:
my score on the required features my score on the non-required features my score on the art contest total score
How to Program the Shaders
Before getting started with coding, make sure the downloaded code works on your Computer/OS/Browser. When you launch the raytracer you should see red-green-blue walls and a white floor and you should be able to move around with the mouse. In order to get this relatively advanced functionality out of the graphics engine, unfortunately, we are working in a relatively new software interface, and there are variations among browsers and operating systems. It may require some experimentation to find a computer/browser combination that works for you. If you cannot find a good development combination on your own computer, try a cluster computer. We have tested heavily on Chrome and Firefox on MacOS and these seem to work well.To implement the features listed above, you only need to edit the files
shaders/fragmentShader.glsl. For the raytracer, you may also wish to take a look at or try to edit the scenes filescenes/*.jsonbecause it helps create your own scenes. You are welcome to look at any of the other files, but it should not be necessary.Except for adding a scene in javascript, the coding is entirely in GLSL. It is a powerful language, but tricky to debug. So we recommend making small, incremental changes to the code as you edit, reloading the page often. A compiler error in the shader code will pop up as an alert in javascript.
For some tips on GLSL see the FAQ below and the precept slide.
Submitting
You should submit your solution via CS dropbox here. The submitted zip file should preserve the directory structure of the skeleton code we provided in the zip file above.
The
writeup.htmlfile should be an HTML document demonstrating the effects of the features you have implemented and would like scored. For some features (e.g., sharpen), you can simply show the input and output of your program. (No need to show inputs for the default images in the images folder.) However, for features that take an input parameter (e.g., blur), you should provide a series of images showing at least two settings of the input parameter to demonstrate that your code is working properly.You should start from the the example
writeup.htmlprovided. At the top of that file are a list of features that you might implement, linking to the section where you talk about them. Please remove any features that you do not implement, but otherwise leave this header section in tact. As in previous assignments, When you include an image, also include a link to theindexURL that creates that image. To save space, please submit images inpngformat.Note that you are expected to use good programming style at all times, including meaningful variable names, a comment or three describing what the code is doing, etc. Partial credit may not be assigned for code without comments. We have mostly tried to conform to the idiomatic JS style conventions.
Hints
As in the last assignment:
- Do the simplest operations first! Note, however, there are some dependencies, for example you need to handle mesh traversal before the other analysis and filtering operations.
- Look at the example page.
- Post a message to Piazza if you have questions.
- Take note of the late policy and the collaboration policy.
FAQ
Here are some answers to frequently asked questions. Check back here occasionally, as we may add FAQs to this list:
What browsers are supported?
The code has been pretty heavily tested on Chrome and Firefox runing on MacOSX. It is possible it will not work on some configurations. We have seen some problems in safari. If you load the page and see black from the outset, try a different browser or a different computer.Where can I learn more about GLSL?
There are many resources online, including these: