teaching machines

SENG 440: Lecture 20 – Multitouch

Dear students, Today we write an app that solves the problem of choosing of which player goes first in a game. All players place a finger on the phone, and the app chooses one of them randomly. The game is inspired by the commercial app Chwazi. Next lecture we will discuss writing an app that […]

SENG 440: Lecture 19 – Nearby

Dear students, Today we write an app that allows multiple devices to play a single piano using Google’s Nearby API. One device serves as the host, running a third-party MIDI interpreter. (I use FluidSynth.) A client joins the host. The host device plays octave 4, and the client device plays octave 5. Next lecture we […]

Fittin’ Image

How do you fit an image inside a frame such that every pixel is visible and the image isn’t distorted? In CSS, we write object-fit: contain. In an Android ImageView, we use centerInside. But what if you are alone in the wild lands of custom drawing? We must determine the scale factors ourselves. I’ve solved […]

SENG 440: Lecture 18 – Location

Dear students, Today we write an app for hiding and finding messages in geographic locations. Our primary goal is to explore how to acquire and use a device’s location, and this app is just one playful example of the many possible applications that are aware of the user’s place. Next lecture we will discuss communicating […]

SENG 440: Lecture 17 – Gravity Sensor

Dear students, Today we write Lonely Phone, an app that senses when the phone is laid flat and starts ringing to grab the user’s attention. This will be the first time we use the code you wrote outside of class and submitted through the Crowdsource tool. This makes me slightly nervous. When I control the […]


Twoville serves two purposes: to create SVG images that can be used as input to laser and vinyl cutters to create animations To support the second of these, I have been using time blocks to define geometric properties at particular keyframes, and then letting the animation system interpolate between the keyframes. Like this: Here we […]

Polar Graph

A year ago I decided to see if fifth graders could create shapes using polar coordinates. I bet myself that they could if we spent some time first traversing a polar grid, identifying the labels of the rings and the spokes. We didn’t think of them as angles and radii, because those semantics weren’t important […]

SENG 440: Lecture 16 – Camera, Part 2

Dear students, Last time we met we tried something new. I assigned in-class exercises, you worked on them, and that’s all we had time for. We will discuss and implement your solutions today, which will wrap up our work on the Backlog app. I’d like to keep getting you involved in the writing of our […]

Phone Programming

Twoville now supports masking, which means we can subtract shapes from other shapes. Since I’m teaching a course on mobile app programming this semester, phones have been on my mind. Accordingly, here’s one of the first runs of the masking feature: In this code, hole is a container of other shapes that will be subtracted […]