Data.Colour

Datatypes for representing the human perception of colour. Includes common operations for blending and compositing colours. The most common way of creating colours is either by name (see Data.Colour.Names) or by giving an sRGB triple (see Data.Colour.SRGB).

Methods of specifying Colours can be found in

• Data.Colour.SRGB
• Data.Colour.SRGB.Linear
• Data.Colour.CIE

Colours can be specified in a generic Data.Colour.RGBSpace.RGBSpace by using

• Data.Colour.RGBSpace

Colour type

data Colour a

This type represents the human preception of colour. The a parameter is a numeric type used internally for the representation.

The Monoid instance allows one to add colours, but beware that adding colours can take you out of gamut. Consider using blend whenever possible.

Instances

ColourOps Colour

AffineSpace Colour

Eq a => Eq (Colour a)

(Fractional a, Read a) => Read (Colour a)

Fractional a => Show (Colour a)

Num a => Monoid (Colour a)

colourConvert :: (Fractional b, Real a) => Colour a -> Colour b

Change the type used to represent the colour coordinates.

data AlphaColour a

This type represents a Colour that may be semi-transparent.

The Monoid instance allows you to composite colours.

x `mappend` y == x `over` y

To get the (pre-multiplied) colour channel of an AlphaColour c, simply composite c over black.

c `over` (mempty :: Colour a)

Instances

ColourOps AlphaColour

AffineSpace AlphaColour

Eq a => Eq (AlphaColour a)

(Fractional a, Read a) => Read (AlphaColour a)

Fractional a => Show (AlphaColour a)

Num a => Monoid (AlphaColour a)

AlphaColour forms a monoid with over and transparent.

opaque :: Num a => Colour a -> AlphaColour a

Creates an opaque AlphaColour from a Colour.

withOpacity :: Num a => Colour a -> a -> AlphaColour a

Creates an AlphaColour from a Colour with a given opacity.

c `withOpacity` o == dissolve o (opaque c) 

transparent :: Num a => AlphaColour a

This AlphaColour is entirely transparent and has no associated colour channel.

alphaColourConvert :: (Fractional b, Real a) => AlphaColour a -> AlphaColour b

Change the type used to represent the colour coordinates.

alphaChannel :: AlphaColour a -> a

Returns the opacity of an AlphaColour.

Colour operations

These operations allow combine and modify existing colours

class AffineSpace f where

Methods

affineCombo :: Num a => [(a, f a)] -> f a -> f a

Compute a affine Combination (weighted-average) of points. The last parameter will get the remaining weight. e.g.

affineCombo [(0.2,a), (0.3,b)] c == 0.2*a + 0.3*b + 0.4*c

Weights can be negative, or greater than 1.0; however, be aware that non-convex combinations may lead to out of gamut colours.

Instances

AffineSpace Chromaticity

AffineSpace AlphaColour

AffineSpace Colour

blend :: (Num a, AffineSpace f) => a -> f a -> f a -> f a

Compute the weighted average of two points. e.g.

blend 0.4 a b = 0.4*a + 0.6*b

The weight can be negative, or greater than 1.0; however, be aware that non-convex combinations may lead to out of gamut colours.

class ColourOps f where

Methods

over :: Num a => AlphaColour a -> f a -> f a

c1 `over` c2 returns the Colour created by compositing the AlphaColour c1 over c2, which may be either a Colour or AlphaColour.

darken :: Num a => a -> f a -> f a

darken s c blends a colour with black without changing it's opacity.

For Colour, darken s c = blend s c mempty

Instances

ColourOps AlphaColour

ColourOps Colour

dissolve :: Num a => a -> AlphaColour a -> AlphaColour a

Returns an AlphaColour more transparent by a factor of o.

atop :: Fractional a => AlphaColour a -> AlphaColour a -> AlphaColour a

c1 `atop` c2 returns the AlphaColour produced by covering the portion of c2 visible by c1. The resulting alpha channel is always the same as the alpha channel of c2.

c1 `atop` (opaque c2) == c1 `over` (opaque c2)
AlphaChannel (c1 `atop` c2) == AlphaChannel c2