chipmunkcore

chipmunkcore is a low-level wrapper around the Chipmunk2d rigid body physics simulation library.

There are many low-level functions available, but currently it’s probably best to use the limited functionality available through the simple R6 class provided - ChipmunkBasic

chipmunkcore is just the simulator. To render the positions of bodies in the simulation you’ll need to use ggplot2, cairocore or something else

Read the online documentation here

Pre-requisites

You’ll need to install the Chipmunk2d library on your system.

I only know how to do this on macOS where you can do

brew install chipmunk

If you know how to install this library on other systems, and subsequently compile this package, please let me know by filing an issue, or pinging me on twitter

Installation

After installing the Chipmunk2d C library, you can install this package from GitHub with:

# install.package('remotes')
remotes::install_github('coolbutuseless/chipmunkcore')

ToDo

Add other shapes besides circles
Add constraints
Expose more of the underlying C library

Galton Board

For full code, see the vignette

A simple simulation

library(chipmunkcore)
library(ggplot2)
set.seed(1)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Initialize a simulation space
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cm <- Chipmunk$new()

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Add fixed segments
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cm$add_segment(-20, 10, -5, 0)
cm$add_segment( 20, 10,  5, 0)

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Fetch all the segments. Use for plotting
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
segments_df <- cm$get_segments()

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Add some bodies. Currently only circular bodies supported
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
for (i in 1:10) {
  cm$add_body(
    x = runif(1, -20, 20), 
    y = runif(1,  10, 50),
    vx = 10 * rnorm(1),
    vy = 10 * rnorm(1)
  )
}

#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
# Get the current positions of the bodies. as a data.frame
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
bodies <- cm$get_bodies()
bodies



for (frame in 1:45) {
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # Advance the simulation
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  cm$advance(5)
  
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # Get the bodies in their new locations
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  bodies <- cm$get_bodies()
  
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  # Plot everything
  #~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  p <- ggplot(bodies) + 
    geom_point(aes(x, y, colour = as.factor(idx)), size = 4, na.rm=TRUE) + 
    geom_segment(data = segments_df, aes(x = x1, y = y1, xend = x2, yend = y2)) + 
    coord_fixed() + 
    # theme_void() + 
    theme_minimal() + 
    xlim(-20, 20) + 
    ylim(-10, 50) + 
    theme(legend.position = 'none')
  
  ggsave(sprintf("man/figures/png/%04i.png", frame), p, width = 6, height = 6)
}

Acknowledgements

R Core for developing and maintaining the language.
CRAN maintainers, for patiently shepherding packages onto CRAN and maintaining the repository

Introducing 'chipmunkcore' - a wrapper for the chipmunk2d physics simulation c library