bug#37385: 27.0.50; Crash on multibyte assertion violation

bug#37385: 27.0.50; Crash on multibyte assertion violation

[Juri Linkov]

Testing the tabs branch helped to expose a bug in master:

In GNU Emacs 27.0.50 (build 6, x86_64-pc-linux-gnu)
 of 2019-09-11 built on localhost
Repository revision: 4d90fadf27ccbb98e0e174304cb4e3008bf364fc
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: Linux Mint 19.1

Configured using:
 'configure --with-x-toolkit=no --enable-checking=yes,glyphs
 --enable-check-lisp-object-type 'CFLAGS=-O0 -g3''

These steps reproduce the crash in master:

0. emacs -Q
1. Eval: (define-key global-map [menu-bar test] '("Test ⮿" keymap))
2. Visit an image file, e.g. etc/images/attach.pbm

#0  0x00005555557a61b8 in terminate_due_to_signal (sig=6, backtrace_limit=2147483647) at emacs.c:374
#1  0x00005555558c7555 in die (msg=0x555555ae73ee "SINGLE_BYTE_CHAR_P (c)", file=0x555555ae4790 "xdisp.c", line=7250) at alloc.c:7256
#2  0x00005555555e9e56 in get_next_display_element (it=0x7fffffff89b0) at xdisp.c:7250
#3  0x000055555562938c in display_string (string=0x0, lisp_string=XIL(0x5555567a0204), face_string=XIL(0), face_string_pos=0, start=0, it=0x7fffffff89b0, field_width=7, precision=0, max_x=674, multibyte=-1) at xdisp.c:25489
#4  0x00005555556239db in display_menu_bar (w=0x5555565cae40) at xdisp.c:23533
#5  0x000055555560d61e in redisplay_window (window=XIL(0x5555565cae45), just_this_one_p=false) at xdisp.c:17821
#6  0x0000555555603b79 in redisplay_window_0 (window=XIL(0x5555565cae45)) at xdisp.c:15116
#7  0x0000555555921b23 in internal_condition_case_1 (bfun=0x555555603b37 <redisplay_window_0>, arg=XIL(0x5555565cae45), handlers=XIL(0x7fffe995aad3), hfun=0x555555603aff <redisplay_window_error>) at eval.c:1379
#8  0x0000555555603ad1 in redisplay_windows (window=XIL(0x5555565cae45)) at xdisp.c:15096
#9  0x00005555556024c2 in redisplay_internal () at xdisp.c:14579
#10 0x00005555555ffea3 in redisplay () at xdisp.c:13806
#11 0x00005555557b7948 in read_char (commandflag=1, map=XIL(0x555556a2aba3), prev_event=XIL(0), used_mouse_menu=0x7fffffffdd25, end_time=0x0) at keyboard.c:2472
#12 0x00005555557c930f in read_key_sequence (keybuf=0x7fffffffdf10, prompt=XIL(0), dont_downcase_last=false, can_return_switch_frame=true, fix_current_buffer=true, prevent_redisplay=false) at keyboard.c:9125
#13 0x00005555557b3d8b in command_loop_1 () at keyboard.c:1345
#14 0x0000555555921a48 in internal_condition_case (bfun=0x5555557b390d <command_loop_1>, handlers=XIL(0x90), hfun=0x5555557b2ed7 <cmd_error>) at eval.c:1355
#15 0x00005555557b34f4 in command_loop_2 (ignore=XIL(0)) at keyboard.c:1091
#16 0x0000555555920ea2 in internal_catch (tag=XIL(0xcdb0), func=0x5555557b34c7 <command_loop_2>, arg=XIL(0)) at eval.c:1116
#17 0x00005555557b3492 in command_loop () at keyboard.c:1070
#18 0x00005555557b29be in recursive_edit_1 () at keyboard.c:714
#19 0x00005555557b2bb6 in Frecursive_edit () at keyboard.c:786
#20 0x00005555557a8acc in main (argc=3, argv=0x7fffffffe368) at emacs.c:2086

An assertion violation is in get_next_display_element:

	  if (! it->multibyte_p && ! ASCII_CHAR_P (c))
	    {
	      eassert (SINGLE_BYTE_CHAR_P (c));

The menu item uses a multibyte char:

  c = 11199 (#o25677, #x2bbf, ?⮿)

But init_iterator sets multibyte_p in the menu-bar window to the
value of enable-multibyte-characters in the current buffer where
enable-multibyte-characters is nil when an image file is visited in
image-mode:

  /* Are multibyte characters enabled in current_buffer?  */
  it->multibyte_p = !NILP (BVAR (current_buffer, enable_multibyte_characters));

I tried the following fix and it prevents the crash:

diff --git a/src/xdisp.c b/src/xdisp.c
index 94f969f37c..5730145268 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -2984,7 +2984,9 @@ init_iterator (struct it *it, struct window *w,
   it->dp = window_display_table (w);
 
   /* Are multibyte characters enabled in current_buffer?  */
-  it->multibyte_p = !NILP (BVAR (current_buffer, enable_multibyte_characters));
+  it->multibyte_p = WINDOW_MENU_BAR_P (w)
+    || WINDOW_TOOL_BAR_P (w)
+    || !NILP (BVAR (current_buffer, enable_multibyte_characters));
 
   /* Get the position at which the redisplay_end_trigger hook should
      be run, if it is to be run at all.  */
@@ -6864,7 +6866,9 @@ reseat_1 (struct it *it, struct text_pos pos, bool set_stop_p)
   it->method = GET_FROM_BUFFER;
   it->object = it->w->contents;
   it->area = TEXT_AREA;
-  it->multibyte_p = !NILP (BVAR (current_buffer, enable_multibyte_characters));
+  it->multibyte_p = WINDOW_MENU_BAR_P (it->w)
+    || WINDOW_TOOL_BAR_P (it->w)
+    || !NILP (BVAR (current_buffer, enable_multibyte_characters));
   it->sp = 0;
   it->string_from_display_prop_p = false;
   it->string_from_prefix_prop_p = false;

bug#37385: 27.0.50; Crash on multibyte assertion violation

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Date: Wed, 11 Sep 2019 23:24:03 +0300
> 
> Configured using:
>  'configure --with-x-toolkit=no --enable-checking=yes,glyphs
>  --enable-check-lisp-object-type 'CFLAGS=-O0 -g3''
> 
> These steps reproduce the crash in master:
> 
> 0. emacs -Q
> 1. Eval: (define-key global-map [menu-bar test] '("Test ⮿" keymap))
> 2. Visit an image file, e.g. etc/images/attach.pbm
> 
> #0  0x00005555557a61b8 in terminate_due_to_signal (sig=6, backtrace_limit=2147483647) at emacs.c:374
> #1  0x00005555558c7555 in die (msg=0x555555ae73ee "SINGLE_BYTE_CHAR_P (c)", file=0x555555ae4790 "xdisp.c", line=7250) at alloc.c:7256
> #2  0x00005555555e9e56 in get_next_display_element (it=0x7fffffff89b0) at xdisp.c:7250
> #3  0x000055555562938c in display_string (string=0x0, lisp_string=XIL(0x5555567a0204), face_string=XIL(0), face_string_pos=0, start=0, it=0x7fffffff89b0, field_width=7, precision=0, max_x=674, multibyte=-1) at xdisp.c:25489
> [...]
> An assertion violation is in get_next_display_element:
> 
> 	  if (! it->multibyte_p && ! ASCII_CHAR_P (c))
> 	    {
> 	      eassert (SINGLE_BYTE_CHAR_P (c));
> 
> The menu item uses a multibyte char:
> 
>   c = 11199 (#o25677, #x2bbf, ?⮿)
> 
> But init_iterator sets multibyte_p in the menu-bar window to the
> value of enable-multibyte-characters in the current buffer where
> enable-multibyte-characters is nil when an image file is visited in
> image-mode:
> 
>   /* Are multibyte characters enabled in current_buffer?  */
>   it->multibyte_p = !NILP (BVAR (current_buffer, enable_multibyte_characters));
> 
> I tried the following fix and it prevents the crash:

Thanks, but this is a backward-incompatible change on too low a level.
It is a long-standing "convention" in Emacs that Lisp strings rendered
as part of, or in relation to, unibyte buffers are assumed unibyte by
default, and I don't want to change that -- who knows how many places
in the code rely on this implicit assumption?

Also, the change in reseat_1 looks unnecessary, as I'd be surprised if
that function was called in your use case (reseat_1 is used only when
displaying buffers, not strings).

Please try an alternative patch below.  (I don't have access to an X
build without a toolkit, so I cannot test this myself.)

Stepping a notch back, I cannot say I like this "non-ASCII art"
implementation for tabs.  It has two annoying problems:

  . it looks unprofessional on GUI frames
  . it requires you to determine whether the frame/font used for the
    menu can display this character, which is not easy

Why not use an image of a plus sign on GUI frames, and a simple ASCII
"+" on TTY frames and frames that have no image support?  I think the
result will be much better.

Thanks.

diff --git a/src/xdisp.c b/src/xdisp.c
index 94f969f..d342da5 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -12994,7 +12994,8 @@ redisplay_tool_bar (struct frame *f)
 
   /* Build a string that represents the contents of the tool-bar.  */
   build_desired_tool_bar_string (f);
-  reseat_to_string (&it, NULL, f->desired_tool_bar_string, 0, 0, 0, -1);
+  reseat_to_string (&it, NULL, f->desired_tool_bar_string,
+		    0, 0, 0, STRING_MULTIBYTE (f->desired_tool_bar_string));
   /* FIXME: This should be controlled by a user option.  But it
      doesn't make sense to have an R2L tool bar if the menu bar cannot
      be drawn also R2L, and making the menu bar R2L is tricky due
@@ -23531,7 +23532,7 @@ display_menu_bar (struct window *w)
       /* Display the item, pad with one space.  */
       if (it.current_x < it.last_visible_x)
 	display_string (NULL, string, Qnil, 0, 0, &it,
-			SCHARS (string) + 1, 0, 0, -1);
+			SCHARS (string) + 1, 0, 0, STRING_MULTIBYTE (string));
     }
 
   /* Fill out the line with spaces.  */

Using images in tabs (was: bug#37385: 27.0.50; Crash on multibyte assertion violation)

[Juri Linkov]

[-- Attachment #1: Type: text/plain, Size: 765 bytes --]

> Stepping a notch back, I cannot say I like this "non-ASCII art"
> implementation for tabs.  It has two annoying problems:
>
>   . it looks unprofessional on GUI frames
>   . it requires you to determine whether the frame/font used for the
>     menu can display this character, which is not easy
>
> Why not use an image of a plus sign on GUI frames, and a simple ASCII
> "+" on TTY frames and frames that have no image support?  I think the
> result will be much better.

The biggest advantage of using “Unicode art” is its scalability for free,
i.e. scalable fonts keep the size of the character used in the close button
proportional to the font size of text in tabs.

I tried a small image with small font size and the result is not bad:


[-- Attachment #2: small_font.png --]
[-- Type: image/png, Size: 2916 bytes --]

[-- Attachment #3: Type: text/plain, Size: 57 bytes --]


But a small image with big font size looks too clumsy:


[-- Attachment #4: large_font.png --]
[-- Type: image/png, Size: 5037 bytes --]

[-- Attachment #5: Type: text/plain, Size: 409 bytes --]


I don't know if the patch to vertically center line content
recently sent here by Jesse, could improve the look to align
the button image to the center of the text line in tabs.

Another advantage of “Unicode art” is that on moving the mouse over the
close button the foreground color of its Unicode text changes to red
simply by using mouse-face.  I don't know how to do the same with images:


[-- Attachment #6: close_red.png --]
[-- Type: image/png, Size: 7317 bytes --]

bug#37385: 27.0.50; Crash on multibyte assertion violation

[Juri Linkov]

>> I tried the following fix and it prevents the crash:
>
> Thanks, but this is a backward-incompatible change on too low a level.
> It is a long-standing "convention" in Emacs that Lisp strings rendered
> as part of, or in relation to, unibyte buffers are assumed unibyte by
> default, and I don't want to change that -- who knows how many places
> in the code rely on this implicit assumption?
>
> Also, the change in reseat_1 looks unnecessary, as I'd be surprised if
> that function was called in your use case (reseat_1 is used only when
> displaying buffers, not strings).
>
> Please try an alternative patch below.  (I don't have access to an X
> build without a toolkit, so I cannot test this myself.)

Thanks for the proper fix.  I tried and it works without problems.
Also I found third place (in addition to two places in your patch)
where STRING_MULTIBYTE could be used for reseat_to_string.  Is the
following change needed as well?

diff --git a/src/xdisp.c b/src/xdisp.c
index 9f999c7903..af6faf9d34 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -13804,7 +13812,8 @@ tool_bar_height (struct frame *f, int *n_rows, bool pixelwise)
   temp_row->reversed_p = false;
   it.first_visible_x = 0;
   it.last_visible_x = WINDOW_PIXEL_WIDTH (w);
-  reseat_to_string (&it, NULL, f->desired_tool_bar_string, 0, 0, 0, -1);
+  reseat_to_string (&it, NULL, f->desired_tool_bar_string,
+                    0, 0, 0, STRING_MULTIBYTE (f->desired_tool_bar_string));
   it.paragraph_embedding = L2R;
 
   while (!ITERATOR_AT_END_P (&it))

Re: Using images in tabs (was: bug#37385: 27.0.50; Crash on multibyte assertion violation)

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: emacs-devel@gnu.org
> Date: Fri, 13 Sep 2019 00:18:37 +0300
> 
> The biggest advantage of using “Unicode art” is its scalability for free,
> i.e. scalable fonts keep the size of the character used in the close button
> proportional to the font size of text in tabs.

I agree that using characters is easier in several senses, but I think
the results will be much better if we don't.  E.g., what do you do if
the font doesn't support that character, and how do you determine that
in the first place?

> I tried a small image with small font size and the result is not bad:
> 
> But a small image with big font size looks too clumsy:

Since Emacs 27 now supports native image scaling, you could use that
to scale the image to the appropriate size.  Alternatively, you could
let users customize its size if needed: after all, changing the size
of tab headers is something that should be relatively rare.

> I don't know if the patch to vertically center line content
> recently sent here by Jesse, could improve the look to align
> the button image to the center of the text line in tabs.

The image used should be centered to begin with.  You could also try
playing with :ascent property of images.

> Another advantage of “Unicode art” is that on moving the mouse over the
> close button the foreground color of its Unicode text changes to red
> simply by using mouse-face.  I don't know how to do the same with images:

The same way we do it with tool-bar buttons, I'd say.  The code for
that is already in the display engine, you just need to reuse it.  Or
am I missing something?

bug#37385: 27.0.50; Crash on multibyte assertion violation

[Eli Zaretskii]

> From: Juri Linkov <juri@linkov.net>
> Cc: 37385@debbugs.gnu.org
> Date: Fri, 13 Sep 2019 00:30:11 +0300
> 
> Thanks for the proper fix.  I tried and it works without problems.
> Also I found third place (in addition to two places in your patch)
> where STRING_MULTIBYTE could be used for reseat_to_string.  Is the
> following change needed as well?

Yes, thanks.  I installed all of them, and I'm closing this bug
report.

Re: Using images in tabs

[Juri Linkov]

[-- Attachment #1: Type: text/plain, Size: 435 bytes --]

>> I don't know if the patch to vertically center line content
>> recently sent here by Jesse, could improve the look to align
>> the button image to the center of the text line in tabs.
>
> The image used should be centered to begin with.  You could also try
> playing with :ascent property of images.

Thanks for the hint.  Using :ascent property with the center value
on images solved the issue, so now tabs are more nice-looking:


[-- Attachment #2: tab-bar-image-buttons.png --]
[-- Type: image/png, Size: 11748 bytes --]

Re: Using images in tabs

[Yuri Khan]

On Mon, 16 Sep 2019 at 05:12, Juri Linkov <juri@linkov.net> wrote:
>
> >> I don't know if the patch to vertically center line content
> >> recently sent here by Jesse, could improve the look to align
> >> the button image to the center of the text line in tabs.
> >
> > The image used should be centered to begin with.  You could also try
> > playing with :ascent property of images.
>
> Thanks for the hint.  Using :ascent property with the center value
> on images solved the issue, so now tabs are more nice-looking:

Do images also play nice with HiDPI?

Re: Using images in tabs

[Eli Zaretskii]

On September 16, 2019 7:15:12 AM GMT+03:00, Yuri Khan <yuri.v.khan@gmail.com> wrote:
> On Mon, 16 Sep 2019 at 05:12, Juri Linkov <juri@linkov.net> wrote:
> >
> > >> I don't know if the patch to vertically center line content
> > >> recently sent here by Jesse, could improve the look to align
> > >> the button image to the center of the text line in tabs.
> > >
> > > The image used should be centered to begin with.  You could also
> try
> > > playing with :ascent property of images.
> >
> > Thanks for the hint.  Using :ascent property with the center value
> > on images solved the issue, so now tabs are more nice-looking:
> 
> Do images also play nice with HiDPI?

If they don't, we need to fix that (and then it is a problem that affects more than just ghis feature).  But using characters instead is not the solution.

Re: Using images in tabs

[Juri Linkov]

>> >> I don't know if the patch to vertically center line content
>> >> recently sent here by Jesse, could improve the look to align
>> >> the button image to the center of the text line in tabs.
>> >
>> > The image used should be centered to begin with.  You could also try
>> > playing with :ascent property of images.
>>
>> Thanks for the hint.  Using :ascent property with the center value
>> on images solved the issue, so now tabs are more nice-looking:
>
> Do images also play nice with HiDPI?

I don't know, I'm using HiDPI and see no problems.  But maybe if
someone prefers Double HiDPI with huge scaling, then we could provide
larger images.  Is it possible to detect such scaling in Emacs?

Re: Using images in tabs

[Lars Ingebrigtsen]

Juri Linkov <juri@linkov.net> writes:

> I don't know, I'm using HiDPI and see no problems.  But maybe if
> someone prefers Double HiDPI with huge scaling, then we could provide
> larger images.  Is it possible to detect such scaling in Emacs?

xg_get_scale and friends?  (For gtk-ish Emacsen.)

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Re: Using images in tabs

[Clément Pit-Claudel]

On 2019-09-16 16:51, Juri Linkov wrote:
>>>>> I don't know if the patch to vertically center line content
>>>>> recently sent here by Jesse, could improve the look to align
>>>>> the button image to the center of the text line in tabs.
>>>>
>>>> The image used should be centered to begin with.  You could also try
>>>> playing with :ascent property of images.
>>>
>>> Thanks for the hint.  Using :ascent property with the center value
>>> on images solved the issue, so now tabs are more nice-looking:
>>
>> Do images also play nice with HiDPI?
> 
> I don't know, I'm using HiDPI and see no problems.  But maybe if
> someone prefers Double HiDPI with huge scaling, then we could provide
> larger images.  Is it possible to detect such scaling in Emacs?

Would using SVG be an option? I use SVG (with a fallback) in my packages when I support the tool-bar, and it works nicely wrt scaling.

Re: Using images in tabs

[Eli Zaretskii]

> From: Clément Pit-Claudel <cpitclaudel@gmail.com>
> Date: Mon, 16 Sep 2019 18:49:22 -0400
> 
> Would using SVG be an option? I use SVG (with a fallback) in my packages when I support the tool-bar, and it works nicely wrt scaling.

I think we should support any image format that Emacs can support,
including SVG.  Emacs can be built with SVG support, but without PNG
or other formats, and it still should be functional.  And I think if
SVG is supported, we should indeed prefer it.

Re: Using images in tabs

[Juri Linkov]

>> I don't know, I'm using HiDPI and see no problems.  But maybe if
>> someone prefers Double HiDPI with huge scaling, then we could provide
>> larger images.  Is it possible to detect such scaling in Emacs?
>
> xg_get_scale and friends?  (For gtk-ish Emacsen.)

Maybe xg_get_scale should be exposed to Lisp, then find-image
could use it to choose a suitable image specification among e.g.

etc/images/icons/hicolor/16x16/
etc/images/icons/hicolor/24x24/
etc/images/icons/hicolor/32x32/
etc/images/icons/hicolor/48x48/
etc/images/icons/hicolor/128x128/
etc/images/icons/hicolor/scalable/

Similar subdirs could be added to other images as well
because this problem exists for other features, e.g. for
subtree arrows in customization buffers, tool-bar icons, etc.

Re: Using images in tabs

[Juri Linkov]

>>> Do images also play nice with HiDPI?
>>
>> I don't know, I'm using HiDPI and see no problems.  But maybe if
>> someone prefers Double HiDPI with huge scaling, then we could provide
>> larger images.  Is it possible to detect such scaling in Emacs?
>
> Would using SVG be an option? I use SVG (with a fallback) in my
> packages when I support the tool-bar, and it works nicely wrt scaling.

Indeed, like there is etc/images/icons/hicolor/scalable/ we could
also add SVG versions in addition to existing .pbm and .xpm files,
and prefer SVG when the build supports SVG format.

Re: Using images in tabs

[Robert Pluim]

>>>>> On Tue, 17 Sep 2019 23:33:21 +0300, Juri Linkov <juri@linkov.net> said:

    >>> I don't know, I'm using HiDPI and see no problems.  But maybe if
    >>> someone prefers Double HiDPI with huge scaling, then we could provide
    >>> larger images.  Is it possible to detect such scaling in Emacs?
    >> 
    >> xg_get_scale and friends?  (For gtk-ish Emacsen.)

    Juri> Maybe xg_get_scale should be exposed to Lisp, then find-image
    Juri> could use it to choose a suitable image specification among e.g.

I donʼt think lisp should know about the scaling, it should work
tranparently, which to me implies that images that can be scaled
should be used.

Robert

Re: Using images in tabs

[Lars Ingebrigtsen]

Juri Linkov <juri@linkov.net> writes:

> Maybe xg_get_scale should be exposed to Lisp, then find-image
> could use it to choose a suitable image specification among e.g.
>
> etc/images/icons/hicolor/16x16/
> etc/images/icons/hicolor/24x24/
> etc/images/icons/hicolor/32x32/
> etc/images/icons/hicolor/48x48/
> etc/images/icons/hicolor/128x128/
> etc/images/icons/hicolor/scalable/
>
> Similar subdirs could be added to other images as well
> because this problem exists for other features, e.g. for
> subtree arrows in customization buffers, tool-bar icons, etc.

Yup.  Emacs currently auto-scales images using this very er ad-hoc method:

(defun image-compute-scaling-factor (scaling)
[...]
   ((eq scaling 'auto)
    (let ((width (/ (float (window-width nil t)) (window-width))))
      ;; If we assume that a typical character is 10 pixels in width,
      ;; then we should scale all images according to how wide they
      ;; are.  But don't scale images down.
      (if (< width 10)
          1
        (/ (float width) 10))))


-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Re: Using images in tabs

[Juri Linkov]

[-- Attachment #1: Type: text/plain, Size: 502 bytes --]

>> etc/images/icons/hicolor/scalable/
>>
>> Similar subdirs could be added to other images as well
>> because this problem exists for other features, e.g. for
>> subtree arrows in customization buffers, tool-bar icons, etc.
>
> Yup.  Emacs currently auto-scales images using this very er ad-hoc method:
>
> (defun image-compute-scaling-factor (scaling)
> [...]

Meanwhile I tried to scale svg, and the result is not great.
Scaling up makes the image blurred, and scaling down makes the
image smeared.


[-- Attachment #2: close.png --]
[-- Type: image/png, Size: 5847 bytes --]

[-- Attachment #3: Type: text/plain, Size: 873 bytes --]


This is unexpected since svg is supposed to be scalable.

Another problem is that svg background is not transparent -
it takes the background color from the default face.
Like on the screenshot above, the unscaled image
in the buffer has the default brown background, and transparent
svg button on the grey tab-bar takes the same background.

PS: Tried out with this code:

  (defvar tab-bar-button-close
    (let ((svg (svg-create 33 33 :stroke-width 3 :stroke-color "black" :fill-color "none")))
      (svg-circle svg 16 16 12)
      (svg-line svg 10 10 22 22)
      (svg-line svg 10 22 22 10)
      (propertize "x"
                  'display (svg-image svg
                                      :max-width 9 :max-height 9
                                      :margin '(2 . 0)
                                      :ascent 'center)))
    "Button for closing the tab.")

Re: Using images in tabs

[Lars Ingebrigtsen]

Juri Linkov <juri@linkov.net> writes:

> Meanwhile I tried to scale svg, and the result is not great.
> Scaling up makes the image blurred, and scaling down makes the
> image smeared.

Emacs calls the svg library which generates a bunch of pixels that we
then tell X (or whatever) to scale.  This is always going to be blurry.

Instead if you want to scale svg properly, you have to give a :scaling
of 1 (and not :max-width etc) and then somehow instruct the svg library
to render it at whatever size you want to.  Perhaps altering the XML is
the easiest...

> Another problem is that svg background is not transparent -
> it takes the background color from the default face.

The backgrounds are transparent, but we render it towards some
background or other.

-- 
(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

Re: Using images in tabs

[Alan Third]

On Thu, Sep 19, 2019 at 03:47:12PM +0200, Lars Ingebrigtsen wrote:
> Juri Linkov <juri@linkov.net> writes:
> 
> > Meanwhile I tried to scale svg, and the result is not great.
> > Scaling up makes the image blurred, and scaling down makes the
> > image smeared.
> 
> Emacs calls the svg library which generates a bunch of pixels that we
> then tell X (or whatever) to scale.  This is always going to be blurry.
> 
> Instead if you want to scale svg properly, you have to give a :scaling
> of 1 (and not :max-width etc) and then somehow instruct the svg library
> to render it at whatever size you want to.  Perhaps altering the XML is
> the easiest...

Librsvg appears to be designed to use Cairo to do any resizing for it.
IIRC librsvg does provide a way to change the DPI, but it’s
deprecated.

I’m curious if it would be possible to use Cairo in a toolkit
independent way to resize and render SVG files. The alternative, I
suppose, would be to find a different SVG library.
-- 
Alan Third