Graphics.HGL

A simple graphics library.

Documentation

The Haskell Graphics Library is designed to give the programmer access to most interesting parts of the Win32 Graphics Device Interface and X11 library without exposing the programmer to the pain and anguish usually associated with using these interfaces.

To give you a taste of what the library looks like, here is the obligatory "Hello World" program:

 module Main where

 import Graphics.HGL

 main :: IO ()
 main = runGraphics $
	withWindow_ "Hello World Window" (300, 200) $ \ w -> do
	drawInWindow w $ text (100, 100) "Hello World"
	drawInWindow w $ ellipse (100, 80) (200, 180)
	getKey w

Here's what each function does:

• runGraphics (defined in Graphics.HGL.Run) runs a graphical action in an appropriate environment. All the other functions of the library should be used inside runGraphics.
• withWindow_ runs an action using a new Window, specifying the window title and size (300 pixels wide and 200 high). The window is closed when the action finishes.
• drawInWindow draws a Graphic (an abstract representation of a picture) on a Window.
• text creates a Graphic consisting of a string at the specified position.
• ellipse creates a Graphic consisting of an ellipse fitting inside a rectangle defined by the two points. These and other functions for defining, combining and modifying pictures are in Graphics.HGL.Draw.
• getKey waits for the user to press (and release) a key. (This is necessary here to prevent the window from closing before you have a chance to read what's on the screen.)

The library is broken up into several pieces.

module Graphics.HGL.Units

module Graphics.HGL.Run

module Graphics.HGL.Window

module Graphics.HGL.Draw

module Graphics.HGL.Key

module Graphics.HGL.Utils

The module Graphics.HGL.Utils defines a number of convenience functions in terms of more primitive functions defined by other modules. For example,

• withWindow_ is defined using openWindowEx and closeWindow (from Graphics.HGL.Window).
• getKey is defined using getWindowEvent, which waits for a range of user interface events.
• Instead of drawing several Graphic objects sequentially as in the above example, you can combine them into a single Graphic object using overGraphic.