[PATCH] New function: color-blend

[PATCH] New function: color-blend

[Joseph Turner]

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Hello!

Here's `color-blend', a function to blend two colors into one.  The
patchset also replaces `vtable--color-blend' with `color-blend'.

Examples of this function being implemented separately in the wild:

https://github.com/alphapapa/prism.el/blob/2fa8eb5a9ca62a548d33befef4517e5d0266eb28/prism.el#L1044
https://oremacs.com/2015/04/28/blending-faces/

Thanks!

Joseph


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From a3a506d4c3bd5d4a9c561e4428b0b5891d96b2ff Mon Sep 17 00:00:00 2001
From: Joseph Turner <joseph@breatheoutbreathe.in>
Date: Fri, 1 Nov 2024 21:58:07 -0700
Subject: [PATCH 1/2] Add color-blend to blend two RGB lists

* lisp/color.el (color-blend): Blend two RGB lists.
* test/lisp/color-tests.el (color-tests-blend): Test color-blend.
* etc/NEWS: Announce color-blend.
---
 etc/NEWS                 |  4 ++++
 lisp/color.el            | 11 +++++++++++
 test/lisp/color-tests.el |  6 ++++++
 3 files changed, 21 insertions(+)

diff --git a/etc/NEWS b/etc/NEWS
index 4aba4b17055..a77e0525dbb 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -685,6 +685,10 @@ single binding syntax, which we'd kept only for backwards compatibility.
 This function natively-compiles all Lisp files in a directory and in its
 sub-directories, recursively, which were not already natively-compiled.
 
+---
+** New function 'color-blend'.
+This function blends two RGB lists into one.
+
 +++
 ** The 'defcustom' ':local' keyword can now be 'permanent-only'.
 This means that the variable's 'permanent-local' property is set to t,
diff --git a/lisp/color.el b/lisp/color.el
index 79dced4e3d7..3828e41755a 100644
--- a/lisp/color.el
+++ b/lisp/color.el
@@ -75,6 +75,17 @@ color-complement
           (- 1.0 (nth 1 color))
           (- 1.0 (nth 2 color)))))
 
+(defun color-blend (a b &optional alpha)
+  "Blend the two colors A and B with ALPHA.
+A and B should be lists (RED GREEN BLUE), where each element is
+between 0.0 and 1.0, inclusive.  ALPHA controls the influence A
+has on the result and should be between 0.0 and 1.0, inclusive."
+  (setq alpha (or alpha 0.5))
+  (let (blend)
+    (dotimes (i 3)
+      (push (+ (* (nth i a) alpha) (* (nth i b) (- 1 alpha))) blend))
+    (nreverse blend)))
+
 (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
diff --git a/test/lisp/color-tests.el b/test/lisp/color-tests.el
index 0f53e4332a4..2f874aa5958 100644
--- a/test/lisp/color-tests.el
+++ b/test/lisp/color-tests.el
@@ -62,6 +62,12 @@ color-tests-complement
   (should (equal (color-complement "#ffffffffffff") '(0.0 0.0 0.0)))
   (should (equal (color-complement "red") '(0.0 1.0 1.0))))
 
+(ert-deftest color-tests-blend ()
+  (should (equal (color-blend '(1.0 0.0 0.0) '(0.0 1.0 0.0)) '(0.5 0.5 0.0)))
+  (should (equal (color-blend '(1.0 1.0 1.0) '(0.0 1.0 0.0)) '(0.5 1.0 0.5)))
+  (should (equal (color-blend '(0.0 0.39215686274509803 0.0) '(0.9607843137254902 0.8705882352941177 0.7019607843137254))
+                 '(0.4803921568627451 0.6313725490196078 0.3509803921568627))))
+
 (ert-deftest color-tests-gradient ()
   (should-not (color-gradient '(0 0 0) '(255 255 255) 0))
   (should
-- 
2.46.0


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From 940d1951548537e07a1fe0ec0acb1858b0af8533 Mon Sep 17 00:00:00 2001
From: Joseph Turner <joseph@breatheoutbreathe.in>
Date: Fri, 1 Nov 2024 22:21:34 -0700
Subject: [PATCH 2/2] Replace vtable--color-blend with color-blend

* lisp/emacs-lisp/vtable.el (vtable--face-color): Use `color-blend'.
(vtable--color-blend): Remove unused function.
---
 lisp/emacs-lisp/vtable.el | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/lisp/emacs-lisp/vtable.el b/lisp/emacs-lisp/vtable.el
index 925961f012c..47eb6e1a7b5 100644
--- a/lisp/emacs-lisp/vtable.el
+++ b/lisp/emacs-lisp/vtable.el
@@ -212,18 +212,12 @@ vtable--face-color
                   (funcall accessor face2)
                 (plist-get face2 slot))))
     (if (and col1 col2)
-        (vtable--color-blend col1 col2)
+        (apply #'color-rgb-to-hex
+               `(,@(color-blend (color-name-to-rgb col1)
+                                (color-name-to-rgb col2))
+                 2))
       (or col1 col2))))
 
-;;; FIXME: This is probably not the right way to blend two colors, is
-;;; it?
-(defun vtable--color-blend (color1 color2)
-  (cl-destructuring-bind (r g b)
-      (mapcar (lambda (n) (* (/ n 2) 255.0))
-              (cl-mapcar #'+ (color-name-to-rgb color1)
-                         (color-name-to-rgb color2)))
-    (format "#%02X%02X%02X" r g b)))
-
 ;;; Interface utility functions.
 
 (defun vtable-current-table ()
-- 
2.46.0

Re: [PATCH] New function: color-blend

[Eli Zaretskii]

> From: Joseph Turner <joseph@breatheoutbreathe.in>
> Date: Fri, 01 Nov 2024 22:29:41 -0700
> 
> Here's `color-blend', a function to blend two colors into one.  The
> patchset also replaces `vtable--color-blend' with `color-blend'.
> 
> Examples of this function being implemented separately in the wild:
> 
> https://github.com/alphapapa/prism.el/blob/2fa8eb5a9ca62a548d33befef4517e5d0266eb28/prism.el#L1044
> https://oremacs.com/2015/04/28/blending-faces/

Thanks.

> +---
> +** New function 'color-blend'.
> +This function blends two RGB lists into one.

This should explain what the function does, in terms that are clear
even to those who are not experts in this area.  AFAIU, "color
blending" has at least two different meanings.

> +(defun color-blend (a b &optional alpha)
> +  "Blend the two colors A and B with ALPHA.
> +A and B should be lists (RED GREEN BLUE), where each element is
> +between 0.0 and 1.0, inclusive.  ALPHA controls the influence A
> +has on the result and should be between 0.0 and 1.0, inclusive."

The doc string should document the return value.  Perhaps an example
of blending will also be a good addition to the doc string.

Re: [PATCH] New function: color-blend

[Yuri Khan]

On Sat, 2 Nov 2024 at 14:03, Joseph Turner <joseph@breatheoutbreathe.in> wrote:

> Here's `color-blend', a function to blend two colors into one.

It would be nice to explicitly mention linear RGB space. Most
users[citation needed] these days are accustomed to colors specified
in sRGB space and naïve conversion dividing by 255 will not give the
desired blends. As an example, linear mixing black (0 0 0) with white
(1 1 1) yields (0.5 0.5 0.5). Naïve scaling will yield #808080 whereas
middle gray is somewhere around #bebebe in sRGB.

Re: [PATCH] New function: color-blend

[Joseph Turner]

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Eli Zaretskii <eliz@gnu.org> writes:

>> From: Joseph Turner <joseph@breatheoutbreathe.in>
>> Date: Fri, 01 Nov 2024 22:29:41 -0700
>> 
>> Here's `color-blend', a function to blend two colors into one.  The
>> patchset also replaces `vtable--color-blend' with `color-blend'.
>> 
>> Examples of this function being implemented separately in the wild:
>> 
>> https://github.com/alphapapa/prism.el/blob/2fa8eb5a9ca62a548d33befef4517e5d0266eb28/prism.el#L1044
>> https://oremacs.com/2015/04/28/blending-faces/
>
> Thanks.
>
>> +---
>> +** New function 'color-blend'.
>> +This function blends two RGB lists into one.
>
> This should explain what the function does, in terms that are clear
> even to those who are not experts in this area.  AFAIU, "color
> blending" has at least two different meanings.
>
>> +(defun color-blend (a b &optional alpha)
>> +  "Blend the two colors A and B with ALPHA.
>> +A and B should be lists (RED GREEN BLUE), where each element is
>> +between 0.0 and 1.0, inclusive.  ALPHA controls the influence A
>> +has on the result and should be between 0.0 and 1.0, inclusive."
>
> The doc string should document the return value.  Perhaps an example
> of blending will also be a good addition to the doc string.

> From: Yuri Khan <yuri.v.khan@gmail.com>
> Subject: Re: [PATCH] New function: color-blend
> To: Joseph Turner <joseph@breatheoutbreathe.in>
> Cc: Emacs Devel Mailing List <emacs-devel@gnu.org>
> Date: Sat, 2 Nov 2024 18:26:57 +0700 (6 hours, 32 minutes, 20 seconds ago)
> Flags: seen, personal
> Maildir: /joseph-breatheoutbreathein/INBOX

> On Sat, 2 Nov 2024 at 14:03, Joseph Turner <joseph@breatheoutbreathe.in> wrote:

> > Here's `color-blend', a function to blend two colors into one.

> It would be nice to explicitly mention linear RGB space. Most
> users[citation needed] these days are accustomed to colors specified
> in sRGB space and naïve conversion dividing by 255 will not give the
> desired blends. As an example, linear mixing black (0 0 0) with white
> (1 1 1) yields (0.5 0.5 0.5). Naïve scaling will yield #808080 whereas
> middle gray is somewhere around #bebebe in sRGB.

Thanks for the feedback!  Please see the attached revised patch.


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From 8c3e96583b6c8248251c026edc730f6ff0b050d4 Mon Sep 17 00:00:00 2001
From: Joseph Turner <joseph@breatheoutbreathe.in>
Date: Fri, 1 Nov 2024 21:58:07 -0700
Subject: [PATCH 1/2] Add color-blend to blend two RGB lists

* lisp/color.el (color-blend): Blend two RGB lists.
* test/lisp/color-tests.el (color-tests-blend): Test color-blend.
* etc/NEWS: Announce color-blend.
---
 etc/NEWS                 |  5 +++++
 lisp/color.el            | 16 ++++++++++++++++
 test/lisp/color-tests.el |  6 ++++++
 3 files changed, 27 insertions(+)

diff --git a/etc/NEWS b/etc/NEWS
index 4aba4b17055..434732dfccf 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -685,6 +685,11 @@ single binding syntax, which we'd kept only for backwards compatibility.
 This function natively-compiles all Lisp files in a directory and in its
 sub-directories, recursively, which were not already natively-compiled.
 
+---
+** New function 'color-blend'.
+This function takes two RGB lists and optional ALPHA and returns an RGB
+list whose elements are blended in linear space proportional to ALPHA.
+
 +++
 ** The 'defcustom' ':local' keyword can now be 'permanent-only'.
 This means that the variable's 'permanent-local' property is set to t,
diff --git a/lisp/color.el b/lisp/color.el
index 79dced4e3d7..155b0dd54ca 100644
--- a/lisp/color.el
+++ b/lisp/color.el
@@ -75,6 +75,22 @@ color-complement
           (- 1.0 (nth 1 color))
           (- 1.0 (nth 2 color)))))
 
+(defun color-blend (a b &optional alpha)
+  "Blend the two colors A and B in linear space with ALPHA.
+A and B should be lists (RED GREEN BLUE), where each element is
+between 0.0 and 1.0, inclusive.  ALPHA controls the influence A
+has on the result and should be between 0.0 and 1.0, inclusive.
+
+For instance:
+
+   (color-blend '(1 0.5 1) '(0 0 0) 0.75)
+      => (0.75 0.375 0.75)"
+  (setq alpha (or alpha 0.5))
+  (let (blend)
+    (dotimes (i 3)
+      (push (+ (* (nth i a) alpha) (* (nth i b) (- 1 alpha))) blend))
+    (nreverse blend)))
+
 (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
diff --git a/test/lisp/color-tests.el b/test/lisp/color-tests.el
index 0f53e4332a4..2f874aa5958 100644
--- a/test/lisp/color-tests.el
+++ b/test/lisp/color-tests.el
@@ -62,6 +62,12 @@ color-tests-complement
   (should (equal (color-complement "#ffffffffffff") '(0.0 0.0 0.0)))
   (should (equal (color-complement "red") '(0.0 1.0 1.0))))
 
+(ert-deftest color-tests-blend ()
+  (should (equal (color-blend '(1.0 0.0 0.0) '(0.0 1.0 0.0)) '(0.5 0.5 0.0)))
+  (should (equal (color-blend '(1.0 1.0 1.0) '(0.0 1.0 0.0)) '(0.5 1.0 0.5)))
+  (should (equal (color-blend '(0.0 0.39215686274509803 0.0) '(0.9607843137254902 0.8705882352941177 0.7019607843137254))
+                 '(0.4803921568627451 0.6313725490196078 0.3509803921568627))))
+
 (ert-deftest color-tests-gradient ()
   (should-not (color-gradient '(0 0 0) '(255 255 255) 0))
   (should
-- 
2.46.0


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From abbd1210755f466d40f8167792200bcda306d7d7 Mon Sep 17 00:00:00 2001
From: Joseph Turner <joseph@breatheoutbreathe.in>
Date: Fri, 1 Nov 2024 22:21:34 -0700
Subject: [PATCH 2/2] Replace vtable--color-blend with color-blend

* lisp/emacs-lisp/vtable.el (vtable--face-color): Use `color-blend'.
(vtable--color-blend): Remove unused function.
---
 lisp/emacs-lisp/vtable.el | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/lisp/emacs-lisp/vtable.el b/lisp/emacs-lisp/vtable.el
index 925961f012c..47eb6e1a7b5 100644
--- a/lisp/emacs-lisp/vtable.el
+++ b/lisp/emacs-lisp/vtable.el
@@ -212,18 +212,12 @@ vtable--face-color
                   (funcall accessor face2)
                 (plist-get face2 slot))))
     (if (and col1 col2)
-        (vtable--color-blend col1 col2)
+        (apply #'color-rgb-to-hex
+               `(,@(color-blend (color-name-to-rgb col1)
+                                (color-name-to-rgb col2))
+                 2))
       (or col1 col2))))
 
-;;; FIXME: This is probably not the right way to blend two colors, is
-;;; it?
-(defun vtable--color-blend (color1 color2)
-  (cl-destructuring-bind (r g b)
-      (mapcar (lambda (n) (* (/ n 2) 255.0))
-              (cl-mapcar #'+ (color-name-to-rgb color1)
-                         (color-name-to-rgb color2)))
-    (format "#%02X%02X%02X" r g b)))
-
 ;;; Interface utility functions.
 
 (defun vtable-current-table ()
-- 
2.46.0

Re: [PATCH] New function: color-blend

[Eli Zaretskii]

> From: Joseph Turner <joseph@breatheoutbreathe.in>
> Cc: emacs-devel@gnu.org
> Date: Sat, 02 Nov 2024 11:00:46 -0700
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> From: Joseph Turner <joseph@breatheoutbreathe.in>
> >> Date: Fri, 01 Nov 2024 22:29:41 -0700
> >> 
> >> Here's `color-blend', a function to blend two colors into one.  The
> >> patchset also replaces `vtable--color-blend' with `color-blend'.
> >> 
> >> Examples of this function being implemented separately in the wild:
> >> 
> >> https://github.com/alphapapa/prism.el/blob/2fa8eb5a9ca62a548d33befef4517e5d0266eb28/prism.el#L1044
> >> https://oremacs.com/2015/04/28/blending-faces/
> >
> > Thanks.
> >
> >> +---
> >> +** New function 'color-blend'.
> >> +This function blends two RGB lists into one.
> >
> > This should explain what the function does, in terms that are clear
> > even to those who are not experts in this area.  AFAIU, "color
> > blending" has at least two different meanings.
> >
> >> +(defun color-blend (a b &optional alpha)
> >> +  "Blend the two colors A and B with ALPHA.
> >> +A and B should be lists (RED GREEN BLUE), where each element is
> >> +between 0.0 and 1.0, inclusive.  ALPHA controls the influence A
> >> +has on the result and should be between 0.0 and 1.0, inclusive."
> >
> > The doc string should document the return value.  Perhaps an example
> > of blending will also be a good addition to the doc string.
> 
> > From: Yuri Khan <yuri.v.khan@gmail.com>
> > Subject: Re: [PATCH] New function: color-blend
> > To: Joseph Turner <joseph@breatheoutbreathe.in>
> > Cc: Emacs Devel Mailing List <emacs-devel@gnu.org>
> > Date: Sat, 2 Nov 2024 18:26:57 +0700 (6 hours, 32 minutes, 20 seconds ago)
> > Flags: seen, personal
> > Maildir: /joseph-breatheoutbreathein/INBOX
> 
> > On Sat, 2 Nov 2024 at 14:03, Joseph Turner <joseph@breatheoutbreathe.in> wrote:
> 
> > > Here's `color-blend', a function to blend two colors into one.
> 
> > It would be nice to explicitly mention linear RGB space. Most
> > users[citation needed] these days are accustomed to colors specified
> > in sRGB space and naïve conversion dividing by 255 will not give the
> > desired blends. As an example, linear mixing black (0 0 0) with white
> > (1 1 1) yields (0.5 0.5 0.5). Naïve scaling will yield #808080 whereas
> > middle gray is somewhere around #bebebe in sRGB.
> 
> Thanks for the feedback!  Please see the attached revised patch.

Thanks, installed on master.

(I needed a few followup changes, as it looks like you ignored
byte-compilation warnings...)

Re: [PATCH] New function: color-blend

[Joseph Turner]

Eli Zaretskii <eliz@gnu.org> writes:

>> From: Joseph Turner <joseph@breatheoutbreathe.in>
>> Cc: emacs-devel@gnu.org
>> Date: Sat, 02 Nov 2024 11:00:46 -0700
>> 
>> Eli Zaretskii <eliz@gnu.org> writes:
>> 
>> >> From: Joseph Turner <joseph@breatheoutbreathe.in>
>> >> Date: Fri, 01 Nov 2024 22:29:41 -0700
>> >> 
>> >> Here's `color-blend', a function to blend two colors into one.  The
>> >> patchset also replaces `vtable--color-blend' with `color-blend'.
>> >> 
>> >> Examples of this function being implemented separately in the wild:
>> >> 
>> >> https://github.com/alphapapa/prism.el/blob/2fa8eb5a9ca62a548d33befef4517e5d0266eb28/prism.el#L1044
>> >> https://oremacs.com/2015/04/28/blending-faces/
>> >
>> > Thanks.
>> >
>> >> +---
>> >> +** New function 'color-blend'.
>> >> +This function blends two RGB lists into one.
>> >
>> > This should explain what the function does, in terms that are clear
>> > even to those who are not experts in this area.  AFAIU, "color
>> > blending" has at least two different meanings.
>> >
>> >> +(defun color-blend (a b &optional alpha)
>> >> +  "Blend the two colors A and B with ALPHA.
>> >> +A and B should be lists (RED GREEN BLUE), where each element is
>> >> +between 0.0 and 1.0, inclusive.  ALPHA controls the influence A
>> >> +has on the result and should be between 0.0 and 1.0, inclusive."
>> >
>> > The doc string should document the return value.  Perhaps an example
>> > of blending will also be a good addition to the doc string.
>> 
>> > From: Yuri Khan <yuri.v.khan@gmail.com>
>> > Subject: Re: [PATCH] New function: color-blend
>> > To: Joseph Turner <joseph@breatheoutbreathe.in>
>> > Cc: Emacs Devel Mailing List <emacs-devel@gnu.org>
>> > Date: Sat, 2 Nov 2024 18:26:57 +0700 (6 hours, 32 minutes, 20 seconds ago)
>> > Flags: seen, personal
>> > Maildir: /joseph-breatheoutbreathein/INBOX
>> 
>> > On Sat, 2 Nov 2024 at 14:03, Joseph Turner <joseph@breatheoutbreathe.in> wrote:
>> 
>> > > Here's `color-blend', a function to blend two colors into one.
>> 
>> > It would be nice to explicitly mention linear RGB space. Most
>> > users[citation needed] these days are accustomed to colors specified
>> > in sRGB space and naïve conversion dividing by 255 will not give the
>> > desired blends. As an example, linear mixing black (0 0 0) with white
>> > (1 1 1) yields (0.5 0.5 0.5). Naïve scaling will yield #808080 whereas
>> > middle gray is somewhere around #bebebe in sRGB.
>> 
>> Thanks for the feedback!  Please see the attached revised patch.
>
> Thanks, installed on master.
>
> (I needed a few followup changes, as it looks like you ignored
> byte-compilation warnings...)

Thank you!  I see the changes you made, and I'll byte compile before
submitting patches next time.

Joseph