This library features a number of utility functions for drawing simple 2d graphics on a canvas, including features for running simple user-interactive apps that display such canvas. A small DSL for drawing using turtle graphics is included.

Features for loading a canvas from an image file and saving canvas to .png are included. They should work out of the box on Windows, but on Linux and MacOS they require the user to have SDL2 installed locally.

The library, which is based on SDL2, is portable, in the sense that applications built using the library can execute on Linux, macOS, and Windows using .NET6.0.

The library is intended to be built (and consumed) as a NuGet package.

The library API is available in the file canvas.fsi.

Make an F# script, say example.fsx and make a NuGet reference:

#r "nuget:DIKU.Canvas";;

Or, if you want a specific version:

#r "nuget:DIKU.Canvas, 1.0.1";;

Make an new directory, say mycanvasapp, in that directory start a F# "Console App" project with the command:

dotnet new console -lang "F#"

(This will give you both a Program.fs file and a mycanvasapp.fsproj file.)

Add a reference to the DIKU.Canvas package with the command:

dotnet add package DIKU.Canvas

Edit Program.fs to have the content:

let draw width height =
    let canvas = Canvas.create width height
    Canvas.setFillBox canvas Canvas.blue (0,0) (width, height)
    canvas

do Canvas.runSimpleApp "Hello from F#" 400 400 draw

Run your app with the command:

dotnet run

This should result in a window with a blue background.

A number of examples are available in the examples folder.

The best show-cases for using the library are

• examples/color_boxes.fsx
• examples/keyboard_example.fsx
• examples/spiral.fsx
• examples/turtle.fsx (eventually)

Note that it is not all the examples in the examples directory that have been ported to the current version of the Canvas library.

If you want to build the library and NuGet package yourself, you will need the .NET6.0 SDK and development versions of SDL2 and SDL2_image for your platform.

First install .NET 6 for your platform.

Then install SDL2 and SDL2_image:

• On macOS with homebrew:

  brew install sdl2 sdl2_image
  

• On Debian and Ubuntu:

  apt install libsdl2-dev libdl2-image-dev
  

• On Arch (and probably Manjaro), sdl2 is available in extra:

  sudo pacman -S sdl2 sdl2_image
  

• On Windows you need SDL2.dll and SDL2_image.dll in a search path available to dotnet. The .dll's in the lib/ folder should be sufficient for building. (Better instructions are a welcome contribution if anyone builds on Windows)

Finally, compile the library:

dotnet build

And pack it into a NuGet package:

dotnet pack

The package will be available in bin/Debug/Canvas.X.y.z.nupkg.

Start by creating a directory to use as a local NuGet repository. Add it to the NuGet sources list:

dotnet nuget add source /full/path/to/the/directory

Ensure the repository was added with:

dotnet nuget list source

Place Canvas.X.y.z.nupkg in the local repository. Now clear the nuget cache:

dotnet nuget locals all -c

Test that everything worked with dotnet fsi

dotnet fsi
>#r "nuget:DIKU.Canvas";;
>open Canvas;;

Canvas is now available to use in projects through NuGet, both in the interpreter and in projects with e.g. .fsproj files.

MIT license

Copyright 2018-2021 - Martin Elsman

Copyright 2022-2023 - Ken Friis Larsen

The following individuals have contributed to the DIKU.Canvas (previosly ImgUtil) library:

• Ken Friis Larsen
• Martin Elsman
• Mads Dyrvig Obitsø Thomsen
• Jon Sporring
• Jan Rolandsen
• Chris Pritchard (original SDL P/Invoke)