Author: tpapp Date: Mon Aug 13 10:00:13 2007 New Revision: 2

Added: introduction.txt Log: added introduction

Added: introduction.txt ============================================================================== --- (empty file) +++ introduction.txt Mon Aug 13 10:00:13 2007 @@ -0,0 +1,52 @@ +Color classes +------------- + +The two main color classes are rgb and hsv, which have slots red, +green, blue and hue, saturation, value respectively. There is also an +rgb class with an alpha channel (slot alpha) called rgba. In the rgb +class, valid slot values are from 0 to 1, while in the hsv class, +saturation and value are in the interval [0,1], but hue is in [0,360). + +You can convert between rgb and hsv using rgb->hsv and hsv->rgb. Note +that for the former, you need to specify what happens when the hue is +undefined (ie the color is gray). By default, the hue of red (0) is +assigned. + +Generic functions which find the appropriate conversion method are +available with names ->rgb and ->hsv. Use these if you want your +functions to handle various different color representations but +eventually you need to work with a single one. + + + +Named colors +------------ + +Named colors, parsed from the X11 colors file, are loaded from +colornames.lisp. As they are constants, names are between +'s. All +named colors are rgb. + + + +Convex combinations +------------------- + +Use hsv-combination or rgb-combination for taking convex combinations +in the respective color space. Note that in the HSV space, you need +to specify the direction on the color wheel, the default is positive. + + +Example session +--------------- + +CL-COLORS> +blue+ +#<RGB red: 0.0d0 green: 0.0d0 blue: 1.0d0> +CL-COLORS> (->hsv +blue+) +#<HSV hue: 240.0d0 saturation: 1.0d0 value: 1.0d0> +CL-COLORS> (rgb-combination +blue+ +green+ 0.5) +#<RGB red: 0.0d0 green: 0.5d0 blue: 0.5d0> +CL-COLORS> (->rgb (hsv-combination (->hsv +blue+) (->hsv +green+) 0.5)) +#<RGB red: 1.0d0 green: 0.0d0 blue: 0.0d0> +CL-COLORS> (->rgb (hsv-combination (->hsv +blue+) (->hsv +green+) 0.5 nil)) +#<RGB red: 0.0d0 green: 1.0d0 blue: 1.0d0> +