Graphics with Gloss

Installing Gloss

Gloss is easily installed using the Cabal tool. Having installed Cabal, one can run cabal install gloss to install Gloss.

Alternatively the package can be built from source, by downloading the source from Hackage or GitHub, and doing the following:

Enter the gloss/gloss-rendering/ directory and do cabal install
Enter the gloss/gloss/ directory and once more do cabal install

Getting something on the screen

In Gloss, one can use the display function to create very simple static graphics.

To use this one needs to first import Graphics.Gloss. Then in the code there should the following:

main :: IO ()
main = display window background drawing

window is of type Display which can be constructed in two ways:

-- Defines window as an actual window with a given name and size
window = InWindow name (width, height) (0,0)

-- Defines window as a fullscreen window
window = FullScreen

Here the last argument (0,0) in InWindow marks the location of the top left corner.

For versions older than 1.11: In older versions of Gloss FullScreen takes another argument which is meant to be the size of the frame that gets drawn on which in turn gets stretched to fullscreen-size, for example: FullScreen (1024,768)

background is of type Color. It defines the background color, so it’s as simple as:

background = white

Then we get to the drawing itself. Drawings can be very complex. How to specify these will be covered elsewhere (one can refer to this for the moment), but it can be as simple as the following circle with a radius of 80:

drawing = Circle 80

Summarizing example

As more or less stated in the documentation on Hackage, getting something on the screen is as easy as:

import Graphics.Gloss

main :: IO ()
main = display window background drawing
    where
      window = InWindow "Nice Window" (200, 200) (0, 0) 
      background = white 
      drawing = Circle 80