| Safe Haskell | Safe-Inferred |
|---|---|
| Language | Haskell98 |
Data.Colour
Description
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
Colours can be specified in a generic
RGBSpace
by using
Synopsis
- data Colour a
- colourConvert :: ( Fractional b, Real a) => Colour a -> Colour b
- black :: Num a => Colour a
- data AlphaColour a
- opaque :: Num a => Colour a -> AlphaColour a
- withOpacity :: Num a => Colour a -> a -> AlphaColour a
- transparent :: Num a => AlphaColour a
- alphaColourConvert :: ( Fractional b, Real a) => AlphaColour a -> AlphaColour b
- alphaChannel :: AlphaColour a -> a
-
class
AffineSpace
f
where
- affineCombo :: Num a => [(a, f a)] -> f a -> f a
- blend :: ( Num a, AffineSpace f) => a -> f a -> f a -> f a
-
class
ColourOps
f
where
- over :: Num a => AlphaColour a -> f a -> f a
- darken :: Num a => a -> f a -> f a
- dissolve :: Num a => a -> AlphaColour a -> AlphaColour a
- atop :: Fractional a => AlphaColour a -> AlphaColour a -> AlphaColour a
Interfacing with Other Libraries' Colour Spaces
Executive summary: Always use
Data.Colour.SRGB
when interfacing with
other libraries.
Use
toSRGB24
/
sRGB24
when
interfacing with libraries wanting
Word8
per channel.
Use
toSRGB
/
sRGB
when
interfacing with libraries wanting
Double
or
Float
per channel.
Interfacing with the colour for other libraries, such as cairo ( http://www.haskell.org/gtk2hs/archives/category/cairo/ ) and OpenGL ( http://hackage.haskell.org/cgi-bin/hackage-scripts/package/OpenGL ), can be a challenge because these libraries often do not use colour spaces in a consistent way. The problem is that these libraries work in a device dependent colour space and give no indication what the colour space is. For most devices this colours space is implicitly the non-linear sRGB space. However, to make matters worse, these libraries also do their compositing and blending in the device colour space. Blending and compositing ought to be done in a linear colour space, but since the device space is typically non-linear sRGB, these libraries typically produce colour blends that are too dark.
(Note that
Data.Colour
is a device
independent
colour space, and
produces correct blends.
e.g. compare
toSRGB (blend 0.5 lime red)
with
RGB 0.5 0.5 0
)
Because these other colour libraries can only blend in device colour spaces, they are fundamentally broken and there is no "right" way to interface with them. For most libraries, the best one can do is assume they are working with an sRGB colour space and doing incorrect blends. In these cases use Data.Colour.SRGB to convert to and from the colour coordinates. This is the best advice for interfacing with cairo.
When using OpenGL, the choice is less clear. Again, OpenGL usually does blending in the device colour space. However, because blending is an important part of proper shading, one may want to consider that OpenGL is working in a linear colour space, and the resulting rasters are improperly displayed. This is born out by the fact that OpenGL extensions that support sRGB do so by converting sRGB input/output to linear colour coordinates for processing by OpenGL.
The best way to use OpenGL, is to use proper sRGB surfaces for textures and rendering. These surfaces will automatically convert to and from OpenGL's linear colour space. In this case, use Data.Colour.SRGB.Linear to interface OpenGL's linear colour space.
If not using proper surfaces with OpenGL, then you have a choice between having OpenGL do improper blending or improper display If you are using OpenGL for 3D shading, I recommend using Data.Colour.SRGB.Linear (thus choosing improper OpenGL display). If you are not using OpenGL for 3D shading, I recommend using Data.Colour.SRGB (thus choosing improper OpenGL blending).
Colour type
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 Source # | |
| AffineSpace Colour Source # | |
|
Defined in Data.Colour.Internal |
|
| Eq a => Eq ( Colour a) Source # | |
| ( Fractional a, Read a) => Read ( Colour a) Source # | |
| ( Fractional a, Show a) => Show ( Colour a) Source # | |
| Num a => Semigroup ( Colour a) Source # | |
| Num a => Monoid ( Colour a) Source # | |
colourConvert :: ( Fractional b, Real a) => Colour a -> Colour b Source #
Change the type used to represent the colour coordinates.
data AlphaColour a Source #
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` black
Instances
opaque :: Num a => Colour a -> AlphaColour a Source #
Creates an opaque
AlphaColour
from a
Colour
.
withOpacity :: Num a => Colour a -> a -> AlphaColour a Source #
Creates an
AlphaColour
from a
Colour
with a given opacity.
c `withOpacity` o == dissolve o (opaque c)
transparent :: Num a => AlphaColour a Source #
This
AlphaColour
is entirely transparent and has no associated
colour channel.
alphaColourConvert :: ( Fractional b, Real a) => AlphaColour a -> AlphaColour b Source #
Change the type used to represent the colour coordinates.
alphaChannel :: AlphaColour a -> a Source #
Returns the opacity of an
AlphaColour
.
Colour operations
These operations allow combine and modify existing colours
class AffineSpace f where Source #
Methods
affineCombo :: Num a => [(a, f a)] -> f a -> f a Source #
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 + 0.5*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 Source # | |
|
Defined in Data.Colour.CIE Methods affineCombo :: Num a => [(a, Chromaticity a)] -> Chromaticity a -> Chromaticity a Source # |
|
| AffineSpace AlphaColour Source # | |
|
Defined in Data.Colour.Internal Methods affineCombo :: Num a => [(a, AlphaColour a)] -> AlphaColour a -> AlphaColour a Source # |
|
| AffineSpace Colour Source # | |
|
Defined in Data.Colour.Internal |
|
blend :: ( Num a, AffineSpace f) => a -> f a -> f a -> f a Source #
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 Source #
Methods
over :: Num a => AlphaColour a -> f a -> f a Source #
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 Source #
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 Source # | |
|
Defined in Data.Colour.Internal Methods over :: Num a => AlphaColour a -> AlphaColour a -> AlphaColour a Source # darken :: Num a => a -> AlphaColour a -> AlphaColour a Source # |
|
| ColourOps Colour Source # | |
dissolve :: Num a => a -> AlphaColour a -> AlphaColour a Source #
Returns an
AlphaColour
more transparent by a factor of
o
.
atop :: Fractional a => AlphaColour a -> AlphaColour a -> AlphaColour a Source #
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
Orphan instances
| ( Fractional a, Read a) => Read ( AlphaColour a) Source # | |
|
Methods readsPrec :: Int -> ReadS ( AlphaColour a) Source # readList :: ReadS [ AlphaColour a] Source # readPrec :: ReadPrec ( AlphaColour a) Source # readListPrec :: ReadPrec [ AlphaColour a] Source # |
|
| ( Fractional a, Read a) => Read ( Colour a) Source # | |
| ( Fractional a, Show a, Eq a) => Show ( AlphaColour a) Source # | |
| ( Fractional a, Show a) => Show ( Colour a) Source # | |