Adding some convenience functions to color.el

Adding some convenience functions to color.el

[Yilkal Argaw]

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Hi
Today I was messing around with some theme that  made use of color.el and I
noticed some functions that might be of use could be added to color.el to
help with the conditionally assigning setting some colors based on
lightness or darkness of some other color. I wondered if it might be useful
to other users and if it might be worth adding it to color.el. I

diff --git a/lisp/color.el b/lisp/color.el
index f68cf5e6b17..3740c3d5a7c 100644
--- a/lisp/color.el
+++ b/lisp/color.el
@@ -119,6 +119,18 @@ inclusive."
        (color-hue-to-rgb m1 m2 H)
        (color-hue-to-rgb m1 m2 (mod (- H (/ 3.0)) 1))))))

+(defun color-name-to-hsl (color)
+ "Convert COLOR to HSL."
+  (apply #'color-rgb-to-hsl (color-name-to-rgb color)))
+
+(defun color-name-light-p (color)
+   "Return non-nil if COLOR is on the lighter side."
+  (when color (>= (caddr (color-name-to-hsl color) 0.5))))
+
+(defun color-name-dark-p (color)
+  "Return non-nil if COLOR is on the darker side."
+  (when color (not (color-name-light-p color))))
+
 (defun color-complement-hex (color)
   "Return the color that is the complement of COLOR, in hexadecimal
format."
   (apply 'color-rgb-to-hex (color-complement color)))


With Regards
Yilkal Argaw

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Re: Adding some convenience functions to color.el

[Philip Kaludercic]

Yilkal Argaw <yilkalargawworkneh@gmail.com> writes:

> Hi
> Today I was messing around with some theme that  made use of color.el and I
> noticed some functions that might be of use could be added to color.el to
> help with the conditionally assigning setting some colors based on
> lightness or darkness of some other color. I wondered if it might be useful
> to other users and if it might be worth adding it to color.el. I
>
> diff --git a/lisp/color.el b/lisp/color.el
> index f68cf5e6b17..3740c3d5a7c 100644
> --- a/lisp/color.el
> +++ b/lisp/color.el
> @@ -119,6 +119,18 @@ inclusive."
>         (color-hue-to-rgb m1 m2 H)
>         (color-hue-to-rgb m1 m2 (mod (- H (/ 3.0)) 1))))))
>
> +(defun color-name-to-hsl (color)
> + "Convert COLOR to HSL."

I think it would make sense to mention what COLOR is.  Or at least call
it COLOR-NAME.

> +  (apply #'color-rgb-to-hsl (color-name-to-rgb color)))
> +
> +(defun color-name-light-p (color)
> +   "Return non-nil if COLOR is on the lighter side."
> +  (when color (>= (caddr (color-name-to-hsl color) 0.5))))

IMO using `and' is better if you are interested the return value of an
expression, while `when' is usually more indicative of a side-effect (on
my first reading of this assumption had me confused to the point of the
function).

But setting that aside, why should someone pass nil to this function?

> +
> +(defun color-name-dark-p (color)
> +  "Return non-nil if COLOR is on the darker side."
> +  (when color (not (color-name-light-p color))))
> +
>  (defun color-complement-hex (color)
>    "Return the color that is the complement of COLOR, in hexadecimal
> format."
>    (apply 'color-rgb-to-hex (color-complement color)))

This is useful!

Could you prepare a patch and update etc/NEWS?  It seems that the other
color functions are not documented in the Emacs Lisp manual.

>
> With Regards
> Yilkal Argaw

Re: Adding some convenience functions to color.el

[Eli Zaretskii]

> From: Yilkal Argaw <yilkalargawworkneh@gmail.com>
> Date: Fri, 9 Jun 2023 02:57:41 +0300
> 
> Today I was messing around with some theme that  made use of color.el and I noticed some functions
> that might be of use could be added to color.el to help with the conditionally assigning setting some
> colors based on lightness or darkness of some other color. I wondered if it might be useful to other
> users and if it might be worth adding it to color.el. I 

We already have color-dark-p (and color-name-to-rgb to complement it),
so I'm not sure I understand the rationale for these functions.  Can
you explain more why you needed them?

Re: Adding some convenience functions to color.el

[Yilkal Argaw]

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  > From: Eli Zaretskii <eliz@gnu.org>
  > We already have color-dark-p (and color-name-to-rgb to complement it),
   > so I'm not sure I understand the rationale for these functions.  Can
   > you explain more why you needed them?

Sorry I totally missed color-dark-p. I did not check faces.el and
color-dark-p was in faces.el.
Having color-name-to-hsl is just a convenience function to make it easier
when working in some
color spaces. Because some operations are easier in certain color spaces.


On Fri, Jun 9, 2023 at 9:55 AM Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Yilkal Argaw <yilkalargawworkneh@gmail.com>
> > Date: Fri, 9 Jun 2023 02:57:41 +0300
> >
> > Today I was messing around with some theme that  made use of color.el
> and I noticed some functions
> > that might be of use could be added to color.el to help with the
> conditionally assigning setting some
> > colors based on lightness or darkness of some other color. I wondered if
> it might be useful to other
> > users and if it might be worth adding it to color.el. I
>
> We already have color-dark-p (and color-name-to-rgb to complement it),
> so I'm not sure I understand the rationale for these functions.  Can
> you explain more why you needed them?
>

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Re: Adding some convenience functions to color.el

[Eli Zaretskii]

> From: Yilkal Argaw <yilkalargawworkneh@gmail.com>
> Date: Fri, 9 Jun 2023 10:26:57 +0300
> Cc: emacs-devel@gnu.org
> 
>   > From: Eli Zaretskii <eliz@gnu.org>
>   > We already have color-dark-p (and color-name-to-rgb to complement it),
>    > so I'm not sure I understand the rationale for these functions.  Can
>    > you explain more why you needed them? 
> 
> Sorry I totally missed color-dark-p. I did not check faces.el and color-dark-p was in faces.el.

They are now documented in the ELisp manual.

> Having color-name-to-hsl is just a convenience function to make it easier when working in some
> color spaces. Because some operations are easier in certain color spaces.

color.el already provides color-rgb-to-hsl and color-hsl-to-rgb, so
you should be able to easily work in the HSL space, and still call
functions that accept RGB arguments.

IMO, we already have a large and rich collection of color-related
functions, so adding more will run the risk to increase confusion and
produce inconsistencies.  (E.g., your proposed color-name-dark-p uses
a threshold for dark vs light colors that is different from what we
use in color-dark-p.)