wobbly-bars

A little physics-related toy, written in Rust using rust_minifb

© 2017 William Eustace, MIT licensed (see licence)

The initial version of this app, which displays a series of coloured bars on a screen which are modelled as viscously damped mass-spring oscillators, was a couple of hours' work: an afternoon has since been spent splitting the "physics engine" onto a separate thread. When the cursor is above (in the y-axis on screen) or over them, and the mouse button is pressed, a force is applied upwards on them; when it moves away or the button is released, they bounce back again.

Screenshot of wobbly-bars in action.

I strongly recommend building in release mode (run cargo build --release and use the executable in ./target/release). There is a very dramatic performance improvement.

The frame rate of the physics engine can be changed by altering the constant PHYSICS_UPDATE_TIME (line 16), which is the minimum update period of the physics engine (if it has time to spare after a cycle, it will make sure this much time has elapsed in total before it starts the next).

The size of the window can be changed by altering WIDTH and HEIGHT on lines 12 and 14.

To change the behaviour of the bars, bearing in mind that all rates are per timestep of the physics engine (I know...):

• ACC_RATE is the acceleration rate of a bar towards the top of the screen when the user hovers over the bar
• SPRING_RATE is the spring constant (in very convoluted units, given it takes mass and timestep into account - not spring constant in the conventional sense) of the 'spring' pulling the bar downwards
• DAMPING is the non-dimensional viscous damping coefficient.
• CENTRE_HEIGHT is the equilibrium (and initial) height of the bars`
• The bars can have their colours etc. altered in the rather messy manual instantiation to be found from line 80 onwards; if ever I get round to it, I might make this nicer!

Don't forget to rebuild after making these changes!