Re: Sv: Sv: Sv: Support for background transparency

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

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> BTW, this parameter should be set during frame creation

I have put `gui_default_parameter` calls in the relevant *fns-files.
I ended up putting it in wherever the 'alpha' frame parameter is set.

> The resource and class names should then be documented under
> (emacs)Table of Resources in the user manual.

I've added it with a very brief description. I noticed that the alpha
frame parameter is not mentioned there, although it is also accessible
through an X resource. I took the liberty to add it there, also with a
very brief explanation. Do tell if it should be left for another commit.

I also notice that it would be very handy with some link to the lispref
describing the frame parameters from these sections, but I don't suppose
that's easily doable.


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diff --git a/doc/emacs/xresources.texi b/doc/emacs/xresources.texi
index ccf7e35eee..e2a1948637 100644
--- a/doc/emacs/xresources.texi
+++ b/doc/emacs/xresources.texi
@@ -149,6 +149,14 @@ Table of Resources
 is the case.
 
 @table @asis
+@item @code{alpha} (class @code{Alpha})
+Frame transparency. A value between 0 (full transparency) and 100
+(no transparency).
+
+@item @code{alphaBackground} (class @code{AlphaBackground})
+Background transparency. A value between 0 (full background
+transparency) and 0 (no background transparency).
+
 @item @code{background} (class @code{Background})
 Background color (@pxref{Colors}).
 
diff --git a/doc/lispref/frames.texi b/doc/lispref/frames.texi
index 2eeb8b7ed7..16748ac922 100644
--- a/doc/lispref/frames.texi
+++ b/doc/lispref/frames.texi
@@ -2433,6 +2433,16 @@ Font and Color Parameters
 
 Some window systems do not support the @code{alpha} parameter for child
 frames (@pxref{Child Frames}).
+
+@vindex alpha-background@r{, a frame parameter}
+@item alpha-background
+@cindex opacity, frame
+@cindex transparency, frame
+Sets the background transparency of the frame.  Unlike the @code{alpha}
+frame parameter, this only controls the transparency of the background
+while keeping foreground elements such as text fully opaque.  It
+should be an integer between 0 and 100, where 0 means
+completely transparent and 100 means completely opaque (default).
 @end table
 
 The following frame parameters are semi-obsolete in that they are
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 eb14856062..19dd04523e 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 (FRAME_DISPLAY_INFO (f)->n_planes == 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..0e0cffea72 100644
--- a/src/haikufns.c
+++ b/src/haikufns.c
@@ -830,6 +830,8 @@ #define ASSIGN_CURSOR(cursor, be_cursor) \
 			 RES_TYPE_NUMBER);
   gui_default_parameter (f, parms, Qalpha, Qnil,
 			 "alpha", "Alpha", RES_TYPE_NUMBER);
+  gui_default_parameter (f, parms, Qalpha_background, Qnil,
+                         "alphaBackground", "AlphaBackground", RES_TYPE_NUMBER);
   gui_default_parameter (f, parms, Qfullscreen, Qnil,
 			 "fullscreen", "Fullscreen", RES_TYPE_SYMBOL);
 
@@ -1043,6 +1045,8 @@ haiku_create_tip_frame (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,
+                         "alphaBackground", "AlphaBackground", RES_TYPE_NUMBER);
 
   initial_setup_back_buffer (f);
 
@@ -2609,7 +2613,8 @@ 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..467e56ece4 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,
@@ -1436,6 +1437,8 @@ Turn the input menu (an NSMenu) into a lisp list for tracking on lisp side.
                          RES_TYPE_NUMBER);
   gui_default_parameter (f, parms, Qalpha, Qnil,
                          "alpha", "Alpha", RES_TYPE_NUMBER);
+  gui_default_parameter (f, parms, Qalpha_background, Qnil,
+                         "alphaBackground", "AlphaBackground", RES_TYPE_NUMBER);
   gui_default_parameter (f, parms, Qfullscreen, Qnil,
                          "fullscreen", "Fullscreen", RES_TYPE_SYMBOL);
 
diff --git a/src/pgtkfns.c b/src/pgtkfns.c
index 9c37c04810..5980b31d6e 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,
 };
 
 
@@ -1667,6 +1668,8 @@ #define INSTALL_CURSOR(FIELD, NAME) \
 			 RES_TYPE_NUMBER);
   gui_default_parameter (f, parms, Qalpha, Qnil,
 			 "alpha", "Alpha", RES_TYPE_NUMBER);
+  gui_default_parameter (f, parms, Qalpha, Qnil,
+                         "alphaBackground", "AlphaBackground", RES_TYPE_NUMBER);
 
   if (!NILP (parent_frame))
     {
@@ -2936,6 +2939,8 @@ x_create_tip_frame (struct pgtk_display_info *dpyinfo, Lisp_Object parms, struct
                          "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,
+                         "alphaBackground", "AlphaBackground", RES_TYPE_NUMBER);
 
   /* Add `tooltip' frame parameter's default value. */
   if (NILP (Fframe_parameter (frame, Qtooltip)))
diff --git a/src/w32fns.c b/src/w32fns.c
index 37f9b813c6..39c4d47d02 100644
--- a/src/w32fns.c
+++ b/src/w32fns.c
@@ -6018,6 +6018,8 @@ DEFUN ("x-create-frame", Fx_create_frame, Sx_create_frame,
                          NULL, NULL, RES_TYPE_BOOLEAN);
   gui_default_parameter (f, parameters, Qno_special_glyphs, Qnil,
                          NULL, NULL, RES_TYPE_BOOLEAN);
+  gui_default_parameter (f, parameters, Qalpha_background, Qnil,
+                         "alphaBackground", "AlphaBackground", RES_TYPE_NUMBER);
 
   /* Process alpha here (Bug#16619).  On XP this fails with child
      frames.  For `no-focus-on-map' frames delay processing of alpha
@@ -6155,6 +6157,9 @@ DEFUN ("x-create-frame", Fx_create_frame, Sx_create_frame,
   gui_default_parameter (f, parameters, Qz_group, Qnil,
                          NULL, NULL, RES_TYPE_SYMBOL);
 
+  gui_default_parameter (f, parameters, Qalpha_background, Qnil,
+                         "alphaBackground", "AlphaBackground", RES_TYPE_NUMBER);
+
   /* Make the window appear on the frame and enable display, unless
      the caller says not to.  However, with explicit parent, Emacs
      cannot control visibility, so don't try.  */
@@ -7089,6 +7094,8 @@ w32_create_tip_frame (struct w32_display_info *dpyinfo, Lisp_Object parms)
   /* Process alpha here (Bug#17344).  */
   gui_default_parameter (f, parms, Qalpha, Qnil,
                          "alpha", "Alpha", RES_TYPE_NUMBER);
+  gui_default_parameter (f, parms, Qalpha_background, Qnil,
+                         "alphaBackground", "AlphaBackground", RES_TYPE_NUMBER);
 
   /* Add `tooltip' frame parameter's default value. */
   if (NILP (Fframe_parameter (frame, Qtooltip)))
@@ -10436,6 +10443,7 @@ 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 33d8d98e70..303f9b0770 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -4591,6 +4591,8 @@ 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,
+                         "alphaBackground", "AlphaBackground", RES_TYPE_NUMBER);
 
   if (!NILP (parent_frame))
     {
@@ -6364,10 +6366,29 @@ 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)
@@ -7225,6 +7246,8 @@ 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,
+                         "alphaBackground", "AlphaBackground", RES_TYPE_NUMBER);
 
   /* Add `tooltip' frame parameter's default value. */
   if (NILP (Fframe_parameter (frame, Qtooltip)))
@@ -8553,6 +8576,7 @@ 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 bf611db6bc..51c320771a 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -858,12 +858,27 @@ 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 = FRAME_DISPLAY_INFO (f)->n_planes;
+
+  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;
@@ -1302,6 +1317,29 @@ 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)
 {
@@ -1882,9 +1920,9 @@ 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);
@@ -2185,12 +2223,7 @@ 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);
 }