color: add color-gradient function

Signed-off-by: Julien Danjou <julien@danjou.info>

diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 414175e..10c658e 100644 (file)
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,7 @@
+2011-02-01  Julien Danjou  <julien@danjou.info>
+
+       * color.el (color-gradient): Add a color-gradient function.
+

 2011-02-01  Lars Ingebrigtsen  <larsi@gnus.org>
 
        * shr.el (shr-render-td): Only do colours at the final rendering.
 2011-02-01  Lars Ingebrigtsen  <larsi@gnus.org>
 
        * shr.el (shr-render-td): Only do colours at the final rendering.

diff --git a/lisp/color.el b/lisp/color.el
index 5c95fff..3874e33 100644 (file)
--- a/lisp/color.el
+++ b/lisp/color.el
@@ -47,6 +47,20 @@ RED GREEN BLUE must be values between 0 and 1 inclusively."
           (- 1.0 (cadr color))
           (- 1.0 (caddr color)))))
 
           (- 1.0 (cadr color))
           (- 1.0 (caddr color)))))
 

+(defun color-gradient (start stop step-number)
+  "Return a list with STEP-NUMBER colors from START to STOP.
+The color list builds a color gradient starting at color START to
+color STOP. It does not include the START and STOP color in the
+resulting list."
+  (loop for i from 1 to step-number
+        with red-step = (/ (- (car stop) (car start)) (1+ step-number))
+        with green-step = (/ (- (cadr stop) (cadr start)) (1+ step-number))
+        with blue-step = (/ (- (caddr stop) (caddr start)) (1+ step-number))
+        collect (list
+                 (+ (car start) (* i red-step))
+                 (+ (cadr start) (* i green-step))
+                 (+ (caddr start) (* i blue-step)))))
+

 (defun color-complement-hex (color)
   "Return the color that is the complement of COLOR, in hexadecimal format."
   (apply 'color-rgb->hex (color-complement color)))
 (defun color-complement-hex (color)
   "Return the color that is the complement of COLOR, in hexadecimal format."
   (apply 'color-rgb->hex (color-complement color)))