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[elpa] externals/compat c37b765b9e 1/2: compat-28: Add color-dark-p
From: |
ELPA Syncer |
Subject: |
[elpa] externals/compat c37b765b9e 1/2: compat-28: Add color-dark-p |
Date: |
Tue, 17 Jan 2023 05:57:30 -0500 (EST) |
branch: externals/compat
commit c37b765b9e7f00279cd57d8a8e9f6a79962f6558
Author: Daniel Mendler <mail@daniel-mendler.de>
Commit: Daniel Mendler <mail@daniel-mendler.de>
compat-28: Add color-dark-p
---
NEWS.org | 1 +
compat-28.el | 31 +++++++++++++++++++++++++++++++
compat-tests.el | 6 ++++++
compat.texi | 10 ++++++++--
4 files changed, 46 insertions(+), 2 deletions(-)
diff --git a/NEWS.org b/NEWS.org
index 6335fb2c63..9452ecf8d6 100644
--- a/NEWS.org
+++ b/NEWS.org
@@ -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 dec2d8c0a4..55e0b75d83 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 98c10d4435..cad2b45c29 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 0f8fa1239d..353de31b06 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}.