Sv: Sv: Sv: Support for background transparency

["Håkon Flatval" <hkon20@hotmail.com>]

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Thanks for the thorough review!

I have adressed your points in this new patch.

I now run a check on the bit depth of the visual in the x_set_cr_source_with_gc_background function. I'm not too happy about this solution, as it involves two more calls to the X API, but perhaps it is acceptable.

I have primarily considered GTK and Cairo when implementing this. Support for other build configurations do not work currently. It will require additional treatment of e.g. the LUCID libs. I have looked a bit on such builds on the side, but currently have not shaped a plan to finish it.

The preprocessor statements are to ensure nothing else is screwed up when using 32-bit visuals.

Again, I appreciate the feedback.

Best regards,
Håkon

________________________________
Fra: Po Lu <luangruo@yahoo.com>
Sendt: torsdag 20. januar 2022 01:52
Til: Håkon Flatval <hkon20@hotmail.com>
Kopi: Lars Ingebrigtsen <larsi@gnus.org>; emacs-devel@gnu.org <emacs-devel@gnu.org>
Emne: Re: Sv: Sv: Support for background transparency

Håkon Flatval <hkon20@hotmail.com> writes:


> I have attached a final patch. The only changes from the last one is a
> small conflict resolution I did while rebasing today.
>
> Is everything ready to have it merged? And also, how does that happen?
> Is the ball in your court, or does it require action on my end?

I see some problems:

> +  /* This prevents GTK from painting the window's background, which
> +     would interfere with transparent background in some environments */
> +  gtk_widget_set_app_paintable (wtop, TRUE);

This must be under the conditional `!HAVE_PGTK'.

> +#if defined (USE_GTK) && defined (USE_CAIRO)

Why only Cairo?  I see no reason this can't work on non-Cairo
configurations, or Cairo configurations built without GTK.

> +  gui_set_alpha_background,

In this case, please add the frame parameter handler to the rest of the
terminal backends, even if it doesn't do anything:

  - pgtkfns.c
  - nsfns.c
  - w32fns.c
  - haikufns.c

> +                         color.green / 65535.0, color.blue / 65535.0, f->alpha_background);
> +
> +  cairo_set_operator (FRAME_CR_CONTEXT (f), CAIRO_OPERATOR_SOURCE);

Cairo on XCB becomes _very_ slow if this is done and the visual has no
alpha channel, so please make this conditional on both alpha being less
than 1.0 and the display's visual actually having an alpha channel.

Also, I see a hunk that only touches indentation and whitespace.  Please
remove the following whitespace-only change:

> +
>        vinfo = XGetVisualInfo (dpy, VisualIDMask | VisualScreenMask,
>                              &vinfo_template, &n_visuals);
> +
>        if (n_visuals <= 0)
> -     fatal ("Can't get proper X visual info");
> +       fatal ("Can't get proper X visual info");

Aside from that, LGTM.  Thanks.

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diff --git a/src/frame.c b/src/frame.c
index 8aaff949ba..c331cff32b 100644
--- a/src/frame.c
+++ b/src/frame.c
@@ -3907,6 +3907,7 @@ DEFUN ("frame-scale-factor", Fframe_scale_factor, Sframe_scale_factor,
   {"z-group",			SYMBOL_INDEX (Qz_group)},
   {"override-redirect",		SYMBOL_INDEX (Qoverride_redirect)},
   {"no-special-glyphs",		SYMBOL_INDEX (Qno_special_glyphs)},
+  {"alpha-background",          SYMBOL_INDEX (Qalpha_background)},
 #ifdef NS_IMPL_COCOA
   {"ns-appearance",		SYMBOL_INDEX (Qns_appearance)},
   {"ns-transparent-titlebar",	SYMBOL_INDEX (Qns_transparent_titlebar)},
@@ -5024,6 +5025,33 @@ gui_set_alpha (struct frame *f, Lisp_Object arg, Lisp_Object oldval)
     }
 }
 
+void
+gui_set_alpha_background (struct frame *f, Lisp_Object arg, Lisp_Object oldval)
+{
+  double alpha = 1.0;
+
+  if (NILP (arg))
+    alpha = 1.0;
+  else if (FLOATP (arg))
+    {
+      alpha = XFLOAT_DATA (arg);
+      if (! (0 <= alpha && alpha <= 1.0))
+	args_out_of_range (make_float (0.0), make_float (1.0));
+    }
+  else if (FIXNUMP (arg))
+    {
+      EMACS_INT ialpha = XFIXNUM (arg);
+      if (! (0 <= ialpha && ialpha <= 100))
+	args_out_of_range (make_fixnum (0), make_fixnum (100));
+      alpha = ialpha / 100.0;
+    }
+  else
+    wrong_type_argument (Qnumberp, arg);
+
+  f->alpha_background = alpha;
+
+  SET_FRAME_GARBAGED (f);
+}
 
 /**
  * gui_set_no_special_glyphs:
@@ -6100,6 +6128,7 @@ syms_of_frame (void)
 #endif
 
   DEFSYM (Qalpha, "alpha");
+  DEFSYM (Qalpha_background, "alpha-background");
   DEFSYM (Qauto_lower, "auto-lower");
   DEFSYM (Qauto_raise, "auto-raise");
   DEFSYM (Qborder_color, "border-color");
diff --git a/src/frame.h b/src/frame.h
index cb2f58e261..5d5f2122fb 100644
--- a/src/frame.h
+++ b/src/frame.h
@@ -637,6 +637,9 @@ #define EMACS_FRAME_H
      Negative values mean not to change alpha.  */
   double alpha[2];
 
+  /* Background opacity */
+  double alpha_background;
+
   /* Exponent for gamma correction of colors.  1/(VIEWING_GAMMA *
      SCREEN_GAMMA) where viewing_gamma is 0.4545 and SCREEN_GAMMA is a
      frame parameter.  0 means don't do gamma correction.  */
@@ -1669,6 +1672,7 @@ #define EMACS_CLASS "Emacs"
 extern long gui_figure_window_size (struct frame *, Lisp_Object, bool, bool);
 
 extern void gui_set_alpha (struct frame *, Lisp_Object, Lisp_Object);
+extern void gui_set_alpha_background (struct frame *, Lisp_Object, Lisp_Object);
 extern void gui_set_no_special_glyphs (struct frame *, Lisp_Object, Lisp_Object);
 
 extern void validate_x_resource_name (void);
diff --git a/src/gtkutil.c b/src/gtkutil.c
index 3cb8cd1533..bd34999630 100644
--- a/src/gtkutil.c
+++ b/src/gtkutil.c
@@ -1467,6 +1467,10 @@ xg_create_frame_widgets (struct frame *f)
     }
   wtop = gtk_window_new (type);
   gtk_widget_add_events (wtop, GDK_ALL_EVENTS_MASK);
+
+  /* This prevents GTK from painting the window's background, which
+     would interfere with transparent background in some environments */
+  gtk_widget_set_app_paintable (wtop, TRUE);
 #endif
 
   /* gtk_window_set_has_resize_grip is a Gtk+ 3.0 function but Ubuntu
@@ -1587,6 +1591,15 @@ xg_create_frame_widgets (struct frame *f)
 #endif
                          | GDK_VISIBILITY_NOTIFY_MASK);
 
+  GdkScreen *screen = gtk_widget_get_screen (wtop);
+
+  if (x_get_bit_depth (f) == 32)
+    {
+      GdkVisual *visual = gdk_screen_get_rgba_visual (screen);
+      gtk_widget_set_visual (wtop, visual);
+      gtk_widget_set_visual (wfixed, visual);
+    }
+
 #ifndef HAVE_PGTK
   /* Must realize the windows so the X window gets created.  It is used
      by callers of this function.  */
@@ -1651,7 +1664,6 @@ xg_create_frame_widgets (struct frame *f)
 #endif
 
   {
-    GdkScreen *screen = gtk_widget_get_screen (wtop);
     GtkSettings *gs = gtk_settings_get_for_screen (screen);
     /* Only connect this signal once per screen.  */
     if (! g_signal_handler_find (G_OBJECT (gs),
diff --git a/src/haikufns.c b/src/haikufns.c
index 58a2e1d464..7117296a73 100644
--- a/src/haikufns.c
+++ b/src/haikufns.c
@@ -2609,7 +2609,8 @@ DEFUN ("haiku-frame-restack", Fhaiku_frame_restack, Shaiku_frame_restack, 2, 3,
     haiku_set_no_accept_focus,
     NULL, /* set z group */
     haiku_set_override_redirect,
-    gui_set_no_special_glyphs
+    gui_set_no_special_glyphs,
+    gui_set_alpha_background,
   };
 
 void
diff --git a/src/nsfns.m b/src/nsfns.m
index 11132a294a..a4f3f091fc 100644
--- a/src/nsfns.m
+++ b/src/nsfns.m
@@ -1004,6 +1004,7 @@ Turn the input menu (an NSMenu) into a lisp list for tracking on lisp side.
   ns_set_z_group,
   0, /* x_set_override_redirect */
   gui_set_no_special_glyphs,
+  gui_set_alpha_background,
 #ifdef NS_IMPL_COCOA
   ns_set_appearance,
   ns_set_transparent_titlebar,
diff --git a/src/pgtkfns.c b/src/pgtkfns.c
index 9c37c04810..b46429379e 100644
--- a/src/pgtkfns.c
+++ b/src/pgtkfns.c
@@ -1043,6 +1043,7 @@ frames (each of which corresponds to one page).  Each frame should be
   x_set_z_group,
   x_set_override_redirect,
   gui_set_no_special_glyphs,
+  gui_set_alpha_background,
 };
 
 
diff --git a/src/w32fns.c b/src/w32fns.c
index 37f9b813c6..a360faefa8 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -10436,6 +10436,7 @@ w32_get_resource (const char *key, const char *name, LPDWORD lpdwtype)
   w32_set_z_group,
   0, /* x_set_override_redirect */
   gui_set_no_special_glyphs,
+  gui_set_alpha_background,
 };
 
 void
diff --git a/src/xfns.c b/src/xfns.c
index a1435d5351..fca2badb79 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -4569,6 +4569,8 @@ DEFUN ("x-create-frame", Fx_create_frame, Sx_create_frame,
                          RES_TYPE_NUMBER);
   gui_default_parameter (f, parms, Qalpha, Qnil,
                          "alpha", "Alpha", RES_TYPE_NUMBER);
+  gui_default_parameter (f, parms, Qalpha_background, Qnil,
+			 "alpha_background", "AlphaBackground", RES_TYPE_NUMBER);
 
   if (!NILP (parent_frame))
     {
@@ -6342,10 +6344,29 @@ select_visual (struct x_display_info *dpyinfo)
       int n_visuals;
       XVisualInfo *vinfo, vinfo_template;
 
-      dpyinfo->visual = DefaultVisualOfScreen (screen);
+      vinfo_template.screen = XScreenNumberOfScreen (screen);
+
+#if defined (USE_GTK) && defined (USE_CAIRO)
+      /* First attempt to use 32-bit visual if available */
+
+      vinfo_template.depth = 32;
+
+      vinfo = XGetVisualInfo (dpy, VisualScreenMask | VisualDepthMask,
+			      &vinfo_template, &n_visuals);
 
+      if (n_visuals > 0)
+	{
+	  dpyinfo->n_planes = vinfo->depth;
+	  dpyinfo->visual = vinfo->visual;
+	  XFree (vinfo);
+	  return;
+	}
+
+#endif // defined (USE_GTK) && defined (USE_CAIRO)
+
+      /* 32-bit visual not available, fallback to default visual */
+      dpyinfo->visual = DefaultVisualOfScreen (screen);
       vinfo_template.visualid = XVisualIDFromVisual (dpyinfo->visual);
-      vinfo_template.screen = XScreenNumberOfScreen (screen);
       vinfo = XGetVisualInfo (dpy, VisualIDMask | VisualScreenMask,
 			      &vinfo_template, &n_visuals);
       if (n_visuals <= 0)
@@ -7203,6 +7224,8 @@ x_create_tip_frame (struct x_display_info *dpyinfo, Lisp_Object parms)
                          "cursorType", "CursorType", RES_TYPE_SYMBOL);
   gui_default_parameter (f, parms, Qalpha, Qnil,
                          "alpha", "Alpha", RES_TYPE_NUMBER);
+  gui_default_parameter (f, parms, Qalpha_background, Qnil,
+			 "alpha_background", "AlphaBackground", RES_TYPE_NUMBER);
 
   /* Add `tooltip' frame parameter's default value. */
   if (NILP (Fframe_parameter (frame, Qtooltip)))
@@ -8531,6 +8554,7 @@ DEFUN ("x-gtk-debug", Fx_gtk_debug, Sx_gtk_debug, 1, 1, 0,
   x_set_z_group,
   x_set_override_redirect,
   gui_set_no_special_glyphs,
+  gui_set_alpha_background,
 };
 
 void
diff --git a/src/xterm.c b/src/xterm.c
index 5adbf210be..507dae670e 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -836,12 +836,24 @@ x_set_cr_source_with_gc_background (struct frame *f, GC gc)
 {
   XGCValues xgcv;
   XColor color;
+  unsigned int depth;
 
   XGetGCValues (FRAME_X_DISPLAY (f), gc, GCBackground, &xgcv);
   color.pixel = xgcv.background;
+
   x_query_colors (f, &color, 1);
-  cairo_set_source_rgb (FRAME_CR_CONTEXT (f), color.red / 65535.0,
-			color.green / 65535.0, color.blue / 65535.0);
+
+  depth = x_get_bit_depth (f);
+
+  if (f->alpha_background < 1.0 && depth == 32) {
+    cairo_set_source_rgba (FRAME_CR_CONTEXT (f), color.red / 65535.0,
+                           color.green / 65535.0, color.blue / 65535.0, f->alpha_background);
+
+    cairo_set_operator (FRAME_CR_CONTEXT (f), CAIRO_OPERATOR_SOURCE);
+  } else {
+    cairo_set_source_rgb (FRAME_CR_CONTEXT (f), color.red / 65535.0,
+                          color.green / 65535.0, color.blue / 65535.0);
+  }
 }
 
 static const cairo_user_data_key_t xlib_surface_key, saved_drawable_key;
@@ -1254,6 +1266,29 @@ x_fill_rectangle (struct frame *f, GC gc, int x, int y, int width, int height)
 #endif
 }
 
+
+static void
+x_clear_rectangle (struct frame *f, GC gc, int x, int y, int width, int height)
+{
+#ifdef USE_CAIRO
+  cairo_t *cr;
+
+  cr = x_begin_cr_clip (f, gc);
+  x_set_cr_source_with_gc_background (f, gc);
+  cairo_rectangle (cr, x, y, width, height);
+  cairo_fill (cr);
+  x_end_cr_clip (f);
+#else
+  XGCValues xgcv;
+  Display *dpy = FRAME_X_DISPLAY (f);
+  XGetGCValues (dpy, gc, GCBackground | GCForeground, &xgcv);
+  XSetForeground (dpy, gc, xgcv.background);
+  XFillRectangle (dpy, FRAME_X_DRAWABLE (f),
+		  gc, x, y, width, height);
+  XSetForeground (dpy, gc, xgcv.foreground);
+#endif
+}
+
 static void
 x_draw_rectangle (struct frame *f, GC gc, int x, int y, int width, int height)
 {
@@ -1830,9 +1865,9 @@ x_draw_fringe_bitmap (struct window *w, struct glyph_row *row, struct draw_fring
       if (face->stipple)
 	XSetFillStyle (display, face->gc, FillOpaqueStippled);
       else
-	XSetForeground (display, face->gc, face->background);
+	XSetBackground (display, face->gc, face->background);
 
-      x_fill_rectangle (f, face->gc, p->bx, p->by, p->nx, p->ny);
+      x_clear_rectangle (f, face->gc, p->bx, p->by, p->nx, p->ny);
 
       if (!face->stipple)
 	XSetForeground (display, face->gc, face->foreground);
@@ -2133,12 +2168,7 @@ x_compute_glyph_string_overhangs (struct glyph_string *s)
 static void
 x_clear_glyph_string_rect (struct glyph_string *s, int x, int y, int w, int h)
 {
-  Display *display = FRAME_X_DISPLAY (s->f);
-  XGCValues xgcv;
-  XGetGCValues (display, s->gc, GCForeground | GCBackground, &xgcv);
-  XSetForeground (display, s->gc, xgcv.background);
-  x_fill_rectangle (s->f, s->gc, x, y, w, h);
-  XSetForeground (display, s->gc, xgcv.foreground);
+  x_clear_rectangle (s->f, s->gc, x, y, w, h);
 }
 
 
@@ -4019,6 +4049,27 @@ x_get_scale_factor(Display *disp, int *scale_x, int *scale_y)
     }
 }
 
+unsigned int
+x_get_bit_depth (struct frame *f)
+{
+  Visual *visual = FRAME_X_VISUAL (f);
+  VisualID visual_id = XVisualIDFromVisual (visual);
+
+  XVisualInfo vinfo_template;
+  vinfo_template.visualid = visual_id;
+
+  int num_items;
+
+  XVisualInfo *visual_infos = XGetVisualInfo (FRAME_X_DISPLAY (f),
+					      VisualIDMask,
+					      &vinfo_template,
+					      &num_items);
+
+  eassert (num_items > 0);
+
+  return visual_infos[0].depth;
+}
+
 /*
    Draw a wavy line under S. The wave fills wave_height pixels from y0.
 
diff --git a/src/xterm.h b/src/xterm.h
index 26b2851590..7899d4f264 100644
--- a/src/xterm.h
+++ b/src/xterm.h
@@ -1155,6 +1155,7 @@ #define SELECTION_EVENT_TIME(eventp)	\
 typedef void (*x_special_error_handler)(Display *, XErrorEvent *, char *,
 					void *);
 
+extern unsigned int x_get_bit_depth (struct frame *f);
 extern bool x_text_icon (struct frame *, const char *);
 extern void x_catch_errors (Display *);
 extern void x_catch_errors_with_handler (Display *, x_special_error_handler,