bug#65042: 30.0.50; alpha-background doesn't effect background of stipple in emacs 30.0.50 pgtk

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Felix <felix.dick@web.de> writes:

> Po Lu <luangruo@yahoo.com> writes:
>
>> Felix <felix.dick@web.de> writes:
>>
>>> Po Lu <luangruo@yahoo.com> writes:
>>>
>>>> Felix <felix.dick@web.de> writes:
>>>>
>>>>> The background of stipple stays opaque with alpha-background parameter
>>>>> set for transparency.
>>>>> This came up in the use of the new package 'indent-bars'.
>>>>> The github issue: https://github.com/jdtsmith/indent-bars/issues/8
>>>>> I tested this with 'emacs -Q' only enabling the needed packages (compat
>>>>> and indent-bars).
>>>>
>>>> Thanks.  Do stipples start displaying adequately with this change?
>>>>
>>> No it doesn't.
>>> But it gives weird artifacts (doubling the character one
>>> line above or something like that)
>>
>> How about this?
>>
>> diff --git a/src/pgtkterm.c b/src/pgtkterm.c
>> index 9c1fc7bef4e..a7c687d811d 100644
>> --- a/src/pgtkterm.c
>> +++ b/src/pgtkterm.c
>> @@ -1328,14 +1328,17 @@ fill_background_by_face (struct frame *f, struct face *face, int x, int y,
>>  			 int width, int height)
>>  {
>>    cairo_t *cr = pgtk_begin_cr_clip (f);
>> +  double r, g, b, a;
>>
>> +  cairo_set_operator (cr, CAIRO_OPERATOR_SOURCE);
>>    cairo_rectangle (cr, x, y, width, height);
>>    cairo_clip (cr);
>>
>> -  double r = ((face->background >> 16) & 0xff) / 255.0;
>> -  double g = ((face->background >> 8) & 0xff) / 255.0;
>> -  double b = ((face->background >> 0) & 0xff) / 255.0;
>> -  cairo_set_source_rgb (cr, r, g, b);
>> +  r = ((face->background >> 16) & 0xff) / 255.0;
>> +  g = ((face->background >> 8) & 0xff) / 255.0;
>> +  b = ((face->background >> 0) & 0xff) / 255.0;
>> +  a = f->alpha_background;
>> +  cairo_set_source_rgba (cr, r, g, b, a);
>>    cairo_paint (cr);
>>
>>    if (face->stipple != 0)
>> @@ -1343,10 +1346,10 @@ fill_background_by_face (struct frame *f, struct face *face, int x, int y,
>>        cairo_pattern_t *mask
>>  	= FRAME_DISPLAY_INFO (f)->bitmaps[face->stipple - 1].pattern;
>>
>> -      double r = ((face->foreground >> 16) & 0xff) / 255.0;
>> -      double g = ((face->foreground >> 8) & 0xff) / 255.0;
>> -      double b = ((face->foreground >> 0) & 0xff) / 255.0;
>> -      cairo_set_source_rgb (cr, r, g, b);
>> +      r = ((face->foreground >> 16) & 0xff) / 255.0;
>> +      g = ((face->foreground >> 8) & 0xff) / 255.0;
>> +      b = ((face->foreground >> 0) & 0xff) / 255.0;
>> +      cairo_set_source_rgba (cr, r, g, b, a);
>>        cairo_mask (cr, mask);
>>      }
>>
>
> This time it works,
> Thanks for this, and thanks your work on Emacs in general!

OK, thanks.  Eli, should this reach Emacs 29.2, or is it too involved
for the release branch?