graphics-drawingcombinators-1.0.2: A functional interface to 2D drawing in OpenGL

Portabilityneeds GADTs and rank n types
MaintainerLuke Palmer <>




Drawing combinators as a functional interface to OpenGL (for 2D drawings only... for now).

This module is intended to be imported qualified, as in:

 import Graphics.DrawingCombinators as Draw

It is recommended that you use this module in combination with SDL; it has not been tested in any other environments. For some reason the GL picking stuff (sample) crashes GHCi, but it works okay compiled.



Basic types

data Image a Source

The type of images.

 [[Image a]] = R2 -> (Color, a)

render :: Image a -> IO ()Source

Draw an Image on the screen in the current OpenGL coordinate system (which, in absense of information, is (-1,-1) in the lower left and (1,1) in the upper right).

clearRender :: Image a -> IO ()Source

Like render, but clears the screen first. This is so you can use this module and pretend that OpenGL doesn't exist at all.


sample :: R2 -> Image a -> IO aSource

Sample the value of the image at a point.

 [[sample p i]] = snd ([[i]] [[p]])


init :: IO ()Source

Perform initialization of the library. This can throw an exception.


The geomertic combinators all return an Image Any. Any is a wrapper around Bool with (False, (||)) as its Monoid. This is so you can use the Monoid instance on Image to automatically get the union of primitives. So:

 circle `mappend` (translate (1,0) %% circle)

Will have the value Any True when either of the circles is sampled. To extract the Bool, use getAny, or pattern match on Any True and Any False instead of True and False.

point :: R2 -> Image AnySource

A single pixel at the specified point.

 [[point p]] r | [[r]] == [[p]] = (one, Any True) 
               | otherwise      = (zero, Any False)

line :: R2 -> R2 -> Image AnySource

A line connecting the two given points.

regularPoly :: Int -> Image AnySource

A regular polygon centered at the origin with n sides.

circle :: Image AnySource

An (imperfect) unit circle centered at the origin. Implemented as:

 circle = regularPoly 24

convexPoly :: [R2] -> Image AnySource

A convex polygon given by the list of points.

(%%) :: Affine -> Image a -> Image aSource

Transform an image by an Affine transformation.

 [[tr % im]] = [[im]] . inverse [[tr]]


data Color Source

Color is defined in the usual computer graphics sense, of a 4 vector containing red, green, blue, and alpha.

The Monoid instance is given by alpha transparency blending, so:

 mempty = Color 1 1 1 1
 mappend c@(Color _ _ _ a) c'@(Color _ _ _ a') = a*c + (1-a)*c'

Where multiplication is componentwise. In the semantcs the values zero and one are used, which are defined as:

 zero = Color 0 0 0 0
 one = Color 1 1 1 1


Color R R R R 


modulate :: Color -> Color -> ColorSource

Modulate two colors by each other.

 modulate (Color r g b a) (Color r' g' b' a') 
           = Color (r*r') (g*g') (b*b') (a*a')

tint :: Color -> Image a -> Image aSource

Tint an image by a color; i.e. modulate the colors of an image by a color.

 [[tint c im]] = first (modulate c) . [[im]]
    where first f (x,y) = (f x, y)

Sprites (images from files)

data Sprite Source

A Sprite represents a bitmap image.

 [[Sprite]] = [-1,1]^2 -> Color

data SpriteScaling Source

Indicate how a non-square image is to be mapped to a sprite.



ScaleMax will set the maximum of the height and width of the image to 1.


ScaleWidth will set the width of the image to 1, and scale the height appropriately.


ScaleHeight will set the height of the image to 1, and scale the width appropriately.

surfaceToSprite :: SpriteScaling -> Surface -> IO SpriteSource

Convert an SDL.Surface to a Sprite.

imageToSprite :: SpriteScaling -> FilePath -> IO SpriteSource

Load an image from a file and create a sprite out of it.

sprite :: Sprite -> Image AnySource

The image of a sprite at the origin.

 [[sprite s]] p | p `elem` [-1,1]^2 = ([[s]] p, Any True) 
                | otherwise         = (zero, Any False)


openFont :: String -> Int -> IO FontSource

Load a TTF font from a file with the given point size (higher numbers mean smoother text but more expensive rendering).

text :: Font -> String -> Image AnySource

The image representing some text rendered with a font. The resulting string will have height 1.