Graphics.DrawingCombinators

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.

Documentation

module Graphics.DrawingCombinators.Affine

Basic types

data Image a

The type of images.

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

Instances

Functor Image

Applicative Image

Monoid m => Monoid (Image m)

render :: Image a -> IO ()

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 ()

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

Selection

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

Sample the value of the image at a point.

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

Initialization

init :: IO ()

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

Geometry

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 Any

A single pixel at the specified point.

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

line :: R2 -> R2 -> Image Any

A line connecting the two given points.

regularPoly :: Int -> Image Any

A regular polygon centered at the origin with n sides.

circle :: Image Any

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

 circle = regularPoly 24

convexPoly :: [R2] -> Image Any

A convex polygon given by the list of points.

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

Transform an image by an Affine transformation.

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

Colors

data Color

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

Constructors

Color R R R R

Instances

Monoid Color

modulate :: Color -> Color -> Color

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 a

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

A Sprite represents a bitmap image.

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

data SpriteScaling

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

Constructors

ScaleMax

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

ScaleWidth

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

ScaleHeight

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

surfaceToSprite :: SpriteScaling -> Surface -> IO Sprite

Convert an SDL.Surface to a Sprite.

imageToSprite :: SpriteScaling -> FilePath -> IO Sprite

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

sprite :: Sprite -> Image Any

The image of a sprite at the origin.

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

Text

data Font

openFont :: String -> Int -> IO Font

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 Any

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