BSD3 licensed by Andy Gill and Ryan Scott


blank-canvas is a Haskell binding to the complete HTML5 Canvas API. blank-canvas allows Haskell users to write, in Haskell, interactive images onto their web browsers. blank-canvas gives the user a single full-window canvas, and provides many well-documented functions for rendering images.

First Example

{-# LANGUAGE OverloadedStrings #-}
module Main where

import Graphics.Blank                     -- import the blank canvas

main = blankCanvas 3000 $ \ context -> do -- start blank canvas on port 3000
        send context $ do                 -- send commands to this specific context
                lineWidth 10
                strokeStyle "red"
                stroke()                  -- this draws the ink into the canvas

Running this program, and going to http://localhost:3000/ gives


For more details about this example, see Red Line.


Link Notes
Examples Various complete examples of using blank-canvas
Installation How to install blank-canvas
Hackage Current release is 0.5
API Discussion of API, compared with the original JavaScript API
Canvas Examples Transliterated from into Haskell and blank-canvas, with kind permission of Eric Rowell, author of the JavaScript HTML5 Canvas Tutorial.

Other Links


Thank you to Eric Rowell, for allowing blank-canvas to base our Canvas examples on his JavaScript Canvas examples.

The “Haskell” picture is taken by Mandy Lackey, from link <> This picture allows sharing, under the creative commons license.



  • Use base-compat-batteries.



  • Add Semigroup instance for Canvas


  • Fix building with aeson-


API changes

  • The (#) function had its type generalized from a -> (a -> Canvas b) -> Canvas b to a -> (a -> b) -> b. This allows it to be used with font length units.
  • Added more type synonyms (Interval, Degrees, Radians, etc.) to more clearly indicate what functions expect constrained values.
  • showbJS (formerly showJS) and jsStyle now return a text Builder instead of a String. This change was introduced as part of a larger blank-canvas refactoring to increase performance. See the Data.Text.Lazy.Builder module from the text package for more details on how to use Builders.

API additions

  • A new ADT for Fonts has been added in Graphics.Blank.Font that can be used in place of Text. For example, "30pt Calibri" is equivalent to (defFont "Calibri") { fontSize = 30 # pt }.
  • A generalized font function of type CanvasFont canvasFont => canvasFont -> Canvas () was added to Graphics.Blank.Font that can accept a Text or Font argument. The font function in Graphics.Blank remains of type Text -> Canvas ().
  • Added a cursor function to change the browser cursor. Also added the Graphics.Blank.Cursor module containing a generalized cursor function that uses a Cursor ADT instead of Text.
  • Added Bounded, Enum, Eq, Ix, Ord, and Show instances for more data types
  • Added support for more MIME types via the mime-types library


  • Allowed building with base-


  • Require scotty >= 0.10 and kansas-comet >= 0.4


API changes

  • Using Double rather than Float
  • Generalized saveRestore to be polymorphic

API additions

  • Added sync for forcing synchronization between the server and client
  • Added argument specific variants of drawImage and putImageData.
  • Added ADTs for RepeatDirection, Alignment, Baseline, LineEnds, Corner (previous used Text)
  • Use of the colour(sic) package (Text is still allowed)

Bug fixes:

  • Fixed unicode escapes in strings


  • Allow Images to access client-side filesystem
comments powered byDisqus