diff options
| -rw-r--r-- | NEWS.org | 1 | ||||
| -rw-r--r-- | compat-28.el | 31 | ||||
| -rw-r--r-- | compat-tests.el | 6 | ||||
| -rw-r--r-- | compat.texi | 10 |
4 files changed, 46 insertions, 2 deletions
@@ -4,6 +4,7 @@ - compat-27: Add ~date-ordinal-to-time~. - compat-27: Add ~make-decoded-time~. +- compat-28: Add ~color-dark-p~. * Release of "Compat" Version 29.1.2.0 diff --git a/compat-28.el b/compat-28.el index dec2d8c..55e0b75 100644 --- a/compat-28.el +++ b/compat-28.el @@ -635,6 +635,37 @@ is included in the return value." default))) ": ")) +;;;; Defined in faces.el + +(compat-defvar color-luminance-dark-limit 0.325 ;; <compat-tests:color-dark-p> + "The relative luminance below which a color is considered \"dark\". +A \"dark\" color in this sense provides better contrast with white +than with black; see `color-dark-p'. +This value was determined experimentally." + :constant t) + +(compat-defun color-dark-p (rgb) ;; <compat-tests:color-dark-p> + "Whether RGB is more readable against white than black. +RGB is a 3-element list (R G B), each component in the range [0,1]. +This predicate can be used both for determining a suitable (black or white) +contrast color with RGB as background and as foreground." + (unless (<= 0 (apply #'min rgb) (apply #'max rgb) 1) + (error "RGB components %S not in [0,1]" rgb)) + ;; Compute the relative luminance after gamma-correcting (assuming sRGB), + ;; and compare to a cut-off value determined experimentally. + ;; See https://en.wikipedia.org/wiki/Relative_luminance for details. + (let* ((sr (nth 0 rgb)) + (sg (nth 1 rgb)) + (sb (nth 2 rgb)) + ;; Gamma-correct the RGB components to linear values. + ;; Use the power 2.2 as an approximation to sRGB gamma; + ;; it should be good enough for the purpose of this function. + (r (expt sr 2.2)) + (g (expt sg 2.2)) + (b (expt sb 2.2)) + (y (+ (* r 0.2126) (* g 0.7152) (* b 0.0722)))) + (< y color-luminance-dark-limit))) + ;;;; Defined in windows.el (compat-defun count-windows (&optional minibuf all-frames) ;; <compat-tests:count-windows> diff --git a/compat-tests.el b/compat-tests.el index 98c10d4..cad2b45 100644 --- a/compat-tests.el +++ b/compat-tests.el @@ -2263,6 +2263,12 @@ (goto-char (point-max)) (should-not (text-property-search-backward 'non-existant)))) +(ert-deftest color-dark-p () + (should (color-dark-p '(0 0 0))) + (should (color-dark-p '(0.5 0.5 0.5))) + (should-not (color-dark-p '(0.5 0.7 0.5))) + (should-not (color-dark-p '(1 1 1 )))) + (ert-deftest color-values-from-color-spec () ;; #RGB notation (should-equal '(0 0 0) (color-values-from-color-spec "#000")) diff --git a/compat.texi b/compat.texi index 0f8fa12..353de31 100644 --- a/compat.texi +++ b/compat.texi @@ -1776,6 +1776,14 @@ environment variable and @var{value} is that variable's value. @xref{System Environment,System Environment,,elisp}. @end defmac +@c based on lisp/faces.el +@defun color-dark-p rgb +Whether @var{rgb} is more readable against white than black. @var{rgb} +is a 3-element list (R G B), each component in the range [0,1]. This +predicate can be used both for determining a suitable (black or white) +contrast color with RGB as background and as foreground. +@end defun + @c based on src/xfaces.c @defun color-values-from-color-spec spec Convert the textual color specification @var{spec} to a color triple @@ -1970,8 +1978,6 @@ The function @code{split-string-shell-command}. @item The function @code{string-limit}. @item -The function @code{color-dark-p}. -@item The function @code{innermost-minibuffer-p}. @item The function @code{max-mini-window-lines}. |