Writing direct coloring algorithms

Direct coloring algorithms directly output a color instead of an index value. This is done by assigning 

a value to the 

#color

 predefined symbol instead of to 

#index

.

To compute this color, you can use color expressions, color variables, and color arithmetic. The 

following arithmetic operations are available:

Returns a color where each component is the sum of the respective components 

c1 + c2

from c1 and c2. So, red(c1 + c2) is equal to red(c1) + red(c2).

Subtracts the color components in c2 from the respective color components in c1. 

c1   c2

So, red(c1   c2) is equal to red(c1)   red(c2).

Multiplies each component of c with a float value. So, red(c * f) is equal to red(c) * 

c * f

f. Note: the float value must be at the righthand side of the * operator.

c / f

Divides each component of c by a float value. So, red(c / f) is equal to red(c) / f.

For example, to calculate the average of two colors, use (c1 + c2) / 2. Be aware of the fact that the 

alpha value is treated just like the other components. So, c / 2 will not only darken a color, it will 

also make it more transparent.

The following conversion functions are available:

G     

rgb

G     

rgba

G     

hsl

G     

hsla

G     

red

G     

green

G     

blue

G     

hue

G     

sat

G     

lum

G     

alpha

There are some functions for blending and retrieving gradient colors:

G     

gradient

G     

blend

G     

compose

There are also functions to reproduce all layer merge modes. They are called mergeX, where X 

stands for the name of the merge mode. See 

Merging functions

.

You can use color 

parameters

 to let user specify a color. You can also use special user functions that 

allow a user to select a merge mode. See 

Parameter blocks

.

Next: 

Global sections

See Also

Writing coloring algorithms

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