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日期:2020-12-02 11:19

CS 135: Assignment 3: Fun with WebXR

In this assignment, you will gain experience in basic WebXR development in a web browser.

The lab is due in 2 weeks. This is the final lab; for the remaining lab sessions this quarter,

please use the time to work on your final projects.

Due date

Tuesday lab: Dec. 1, 2020 @ 11:59PM

Thursday lab: Dec. 3, 2020 @ 11:59PM

Important Notes:

1. Read all submission instructions carefully, and submit all required documents.

2. The WebXR Documentation

(https://developer.mozilla.org/en-US/docs/Web/API/WebXR_Device_API) and samples

(https://immersive-web.github.io/webxr-samples/) are good sources of

information/examples.

3. Check Slack for any bugs, updates, or important information for this programming

assignment.

Part 1: Setup

In this lab, you will be experimenting with WebXR. WebXR provides APIs to render VR/AR

content from a browser, using WebGL under the hood. WebXR allows access to VR/AR input

controllers, if you have them, but for this lab, we will be using a hardware emulator and work

entirely in the browser.

To do this, you will need to install a few things:

● A recent version of Google Chrome (79+ should be enough, tested on 86). Once you

have done this, you can visit the WebXR sample page

<https://immersive-web.github.io/webxr-samples/>, and you should see a green

checkmark at the top showing that your browser supports WebXR.

● WebXR API emulator to emulate VR hardware:

<https://chrome.google.com/webstore/detail/webxr-api-emulator/mjddjgeghkdijejnciaefnk

jmkafnnje/>

● Your favorite web server. The easiest way is probably to run a local web server in your

browser using the “Web Server for Chrome” browser extension:

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<https://chrome.google.com/webstore/detail/web-server-for-chrome/ofhbbkphhbklhfoeikj

pcbhemlocgigb/>

Now save and extract the lab files (http://www.cs.ucr.edu/~jiasi/webxr_lab.zip) onto your local

web server. If you’re using “Web Server for Chrome”, configure the extension to host the lab

files folder.

When you open “index.html” (or whatever localhost Web Server for Chrome is set to), you

should see a scene with 3 cubes. Click “Enter VR” on the right button to see the view from each

eye.

Next open up the WebXR emulator from Chrome menu > More Tools > Developer Tools >

WebXR tab. You should have a display similar to that shown below (you may wish to re-arrange

the layout):

2

There are several important parts of the screen:

● Top third of the screen: The WebXR application.

● Middle third of the screen: The emulated VR hardware. Please select “Oculus Quest”

in the drop-down menu for this lab. Play around with the headset and controllers to

rotate and translate them (first click = translation controls, second click = rotation

controls). On the right, you can see the position and rotation of the headset and

controllers. There are “Select button” and “Squeeze button” controls for each of the

controllers.

● Bottom third of the screen: The console where you can view debug messages.

Play around with the default app to get familiar with it. The default behavior is:

● Select: When you press and de-press the “Select button” while interacting with a cube ,

its size and color should change.

● Squeeze: When you press, move the controller, and de-press the “Squeeze button”

while interacting with a cube, the cube should follow the controller’s position and also

change color and size. There may be a slight change in the cube’s position when you

first press the button; that is normal.

Great, now you’re all set up! Let’s move on to the fun part!

3

Part 2

You will mainly modify the index.html file for this lab. Open it up and get familiar with the

Javascript content. There are comments sprinkled throughout to help you understand. The

WebXR documentation linked in “Important Notes” above can also help.

One thing you may wish to know is that each controller has a ray emanating from it, pointing in a

straight line. This ray has both an origin and a direction in world space, and is already visualized

for you in the default app. For more information, see the documentation.

Example of a ray emanating from a controller

For debugging, you can use commands like “console.log("variable name " +

variable);” to print things into the WebXR console.

A) The default behavior of the app is that once the “Squeeze button” is de-pressed, the cube

goes back to its original position. Modify the code so that the cube stays at its current position

when the button is de-pressed. In other words, you can now drag and drop the cubes anywhere

you want in the scene.

Hint: Modify the onSqueezeEnd function and comment out the unnecessary lines.

B) Next, modify the code so that if the “select button” did not result in a cube changing color/size

(i.e., the hit test failed), then a new cube is created somewhere along the raycast from the

controller, in a color of your choosing. In other words, you can create new cubes at arbitrary

locations in the scene.

Hints: Add the necessary code to the onSelectStart function to create the new box. There is

an addBox helper function that may be handy. You can get an idea from onXRFrame on how to

get the origin and direction of the targetRayPose emanating from the controller.

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Example: new red cubes created surrounding the center green cube.

C) Finally, modify the code so that when any two cubes are within 0.25 m of each other, they

1

both change color to white. For example, if I grab one cube using the “squeeze button” and drag

it on top of another cube, they should both turn white instantly. A cube should keep its white

color even if it moves away. If the “select” button is pushed on a white cube, a new random

color is selected. This should work for both the original cubes and the new cubes you created.

Hints: Add the necessary code to the onXRFrame function to detect the intersection and change

the color. There are some useful vector manipulation helper functions (e.g., length) in

js/third-party/gl-matrix/src/gl-matrix/vec3.js. The boxes array contains a list of the

current cubes in the scene. onSelect and onSqueeze have examples of how to change the box

color.

Example: The three cubes in the middle intersected with each other, so they turned white.

1 As long as the cubes’ “position” attributes are within 0.25 m, you can trigger the color change. You do

NOT need to do anything fancier, for example determining if the cube faces are within 0.25 m of each

other.

5

Grading Rubric

Submission Instructions

1. Create a zip file containing the following items:

a. The index.html file you modified for this lab.

b. A README.txt file containing any special instructions or notes you think are

relevant for evaluating your assignment.

2. Name the file by separating NetIDs with underscores- _cs135vr_HW3.zip. EXAMPLE: If

steve1 and anna2 worked together, the file should be called

steve1_anna2_cs135vr_HW3.zip

3. Only one team member should submit the zip.

Materials from The Immersive Web Community Group

<https://github.com/immersive-web/webxr-samples> is gratefully acknowledged.

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Name Points Description

Part 1

Setup 0 Download and install necessary browser and browser

extensions, test basic WebXR app. No points.

Part 2

Cube positions 10 Cubes remain where you put them after “squeeze button”

is depressed

New cube 10 A new cube is created along the controller’s raycast if

“select button” does not interact with an existing cube

Cube intersection 10 Intersection of two cubes within 0.25 m detected

Color change 5 Cubes turn white upon intersection

Total 35


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