Subject: Re: macOS (Cocoa) alpha-background

From: Stefan Kangas <[email-masked]>
Date: Thu, 20 Feb 2025 00:24:20 +0000

-------------------- Start of forwarded message --------------------
From: Jon Rubens <[email-masked]>
Date: Wed, 19 Feb 2025 09:53:42 -0800
Subject: Re: macOS (Cocoa) alpha-background
To: Alan Third <[email-masked]>, Alexander Adolf
<[email-masked]>,
	Eli Zaretskii <[email-masked]>, Rudolf Adamkovič <[email-masked]>,
	[email-masked], [email-masked], [email-masked],
	[email-masked]
diff --git a/src/macfont.m b/src/macfont.m
index 8aba440d196..56c1eb57024 100644
--- a/src/macfont.m
+++ b/src/macfont.m
@@ -2953,9 +2953,14 @@ So we use CTFontDescriptorCreateMatchingFontDescriptor (no
             CG_SET_FILL_COLOR_WITH_FACE_FOREGROUND (context, face);
           else
             CG_SET_FILL_COLOR_WITH_FRAME_CURSOR (context, f);
-        }
+	  CGContextSetAlpha(context, 1);
+	}
       else
-        CG_SET_FILL_COLOR_WITH_FACE_BACKGROUND (context, face);
+	{
+	  CGContextSetAlpha(context, f->alpha_background);
+	  CG_SET_FILL_COLOR_WITH_FACE_BACKGROUND (context, face);
+	}
+      CGContextClearRect(context, background_rect);
       CGContextFillRects (context, &background_rect, 1);
     }
 
@@ -2964,6 +2969,7 @@ So we use CTFontDescriptorCreateMatchingFontDescriptor (no
       CGAffineTransform atfm;
 
       CGContextScaleCTM (context, 1, -1);
+      CGContextSetAlpha(context, 1);
       if (s->hl == DRAW_CURSOR)
         {
           if (face && (NS_FACE_BACKGROUND (face)
diff --git a/src/nsfns.m b/src/nsfns.m
index b0281aac257..37b21e526e7 100644
--- a/src/nsfns.m
+++ b/src/nsfns.m
@@ -301,7 +301,7 @@ Turn the input menu (an NSMenu) into a lisp list for tracking on lisp side.
   struct face *face;
   NSColor *col;
   NSView *view = FRAME_NS_VIEW (f);
-  EmacsCGFloat alpha;
+  EmacsCGFloat alpha = f->alpha_background;
 
   block_input ();
   if (ns_lisp_to_color (arg, &col))
@@ -316,11 +316,10 @@ Turn the input menu (an NSMenu) into a lisp list for tracking on lisp side.
   f->output_data.ns->background_color = col;
 
   FRAME_BACKGROUND_PIXEL (f) = [col unsignedLong];
-  alpha = [col alphaComponent];
 
   if (view != nil)
     {
-      [[view window] setBackgroundColor: col];
+      [[view window] setBackgroundColor: [col colorWithAlphaComponent: alpha]];
 
       if (alpha != (EmacsCGFloat) 1.0)
           [[view window] setOpaque: NO];
@@ -330,10 +329,7 @@ Turn the input menu (an NSMenu) into a lisp list for tracking on lisp side.
       face = FRAME_DEFAULT_FACE (f);
       if (face)
         {
-          col = [NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)];
-          face->background = [[col colorWithAlphaComponent: alpha]
-                               unsignedLong];
-
+          face->background = [col unsignedLong];
           update_face_from_frame_parameter (f, Qbackground_color, arg);
         }
 
@@ -346,6 +342,36 @@ Turn the input menu (an NSMenu) into a lisp list for tracking on lisp side.
   unblock_input ();
 }
 
+static void
+ns_set_alpha_background (struct frame *f, Lisp_Object arg, Lisp_Object oldval)
+{
+  NSView *view = FRAME_NS_VIEW (f);
+  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;
+  [[view window] setBackgroundColor: [f->output_data.ns->background_color colorWithAlphaComponent: alpha]];
+
+  recompute_basic_faces (f);
+  SET_FRAME_GARBAGED (f);
+}
 
 static void
 ns_set_cursor_color (struct frame *f, Lisp_Object arg, Lisp_Object oldval)
@@ -1065,7 +1091,7 @@ 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,
+  ns_set_alpha_background,
   NULL,
 #ifdef NS_IMPL_COCOA
   ns_set_appearance,
diff --git a/src/nsfont.m b/src/nsfont.m
index 1205fbe5263..9da964956e1 100644
--- a/src/nsfont.m
+++ b/src/nsfont.m
@@ -1185,7 +1185,7 @@ is false when (FROM > 0 || TO < S->nchars).  */
 	{
 	  if (s->hl != DRAW_CURSOR)
 	    [(NS_FACE_BACKGROUND (face) != 0
-	      ? [NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)]
+	      ? [[NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)] colorWithAlphaComponent: s->f->alpha_background]
 	      : FRAME_BACKGROUND_COLOR (s->f)) set];
 	  else
 	    [FRAME_CURSOR_COLOR (s->f) set];
diff --git a/src/nsterm.m b/src/nsterm.m
index 518b38658d1..bda3a12172f 100644
--- a/src/nsterm.m
+++ b/src/nsterm.m
@@ -2618,8 +2618,9 @@ Hide the window (X11 semantics)
 
   block_input ();
   ns_focus (f, &r, 1);
-  [[NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND
-			    (FACE_FROM_ID (f, DEFAULT_FACE_ID))] set];
+  [[[NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND
+				 (FACE_FROM_ID (f, DEFAULT_FACE_ID))]
+                                 colorWithAlphaComponent: f->alpha_background] set];
   NSRectFill (r);
   ns_unfocus (f);
 
@@ -2647,7 +2648,7 @@ Hide the window (X11 semantics)
 
   r = NSIntersectionRect (r, [view frame]);
   ns_focus (f, &r, 1);
-  [[NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)] set];
+  [[[NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)] colorWithAlphaComponent: f->alpha_background] set];
 
   NSRectFill (r);
 
@@ -2751,7 +2752,7 @@ Hide the window (X11 semantics)
         return;
 
       ns_focus (f, NULL, 1);
-      [[NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)] set];
+      [[[NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)] colorWithAlphaComponent: f->alpha_background] set];
       NSRectFill (NSMakeRect (0, margin, width, border));
       NSRectFill (NSMakeRect (0, 0, border, height));
       NSRectFill (NSMakeRect (0, margin, width, border));
@@ -2802,7 +2803,7 @@ Hide the window (X11 semantics)
           NSRect r = NSMakeRect (0, y, FRAME_PIXEL_WIDTH (f), height);
           ns_focus (f, &r, 1);
 
-          [[NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)] set];
+          [[[NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)] colorWithAlphaComponent: f->alpha_background] set];
           NSRectFill (NSMakeRect (0, y, width, height));
           NSRectFill (NSMakeRect (FRAME_PIXEL_WIDTH (f) - width,
                                   y, width, height));
@@ -2966,8 +2967,7 @@ Hide the window (X11 semantics)
   if (! NSIsEmptyRect (clearRect))
     {
       NSTRACE_RECT ("clearRect", clearRect);
-
-      [[NSColor colorWithUnsignedLong:face->background] set];
+      [[[NSColor colorWithUnsignedLong:face->background] colorWithAlphaComponent: f->alpha_background] set];
       NSRectFill (clearRect);
     }
 
@@ -2998,7 +2998,7 @@ Hide the window (X11 semantics)
       else
         bm_color = f->output_data.ns->cursor_color;
 
-      [bm_color set];
+      [[bm_color colorWithAlphaComponent:f->alpha_background] set];
       [bmp fill];
 
       [bmp release];
@@ -3719,7 +3719,7 @@ Function modeled after x_draw_glyph_string_box ().
   if (s->face->box == FACE_SIMPLE_BOX && s->face->box_color)
     {
       ns_draw_box (r, abs (hthickness), abs (vthickness),
-                   [NSColor colorWithUnsignedLong:face->box_color],
+                   [[NSColor colorWithUnsignedLong:face->box_color] colorWithAlphaComponent: s->f->alpha_background],
                    left_p, right_p);
     }
   else
@@ -3757,8 +3757,10 @@ Function modeled after x_draw_glyph_string_box ().
             {
               if (s->hl != DRAW_CURSOR)
                 [(NS_FACE_BACKGROUND (face) != 0
-                  ? [NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)]
+		  ? [[NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)]
+		      colorWithAlphaComponent: s->f->alpha_background]
                   : FRAME_BACKGROUND_COLOR (s->f)) set];
+
               else if (face && (NS_FACE_BACKGROUND (face)
                                 == [(NSColor *) FRAME_CURSOR_COLOR (s->f)
                                                 unsignedLong]))
@@ -3902,7 +3904,7 @@ Function modeled after x_draw_glyph_string_box ().
      otherwise, since we composite the image under NS (instead of mucking
      with its background color), we must clear just the image area.  */
 
-  [[NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)] set];
+  [[[NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND (face)] colorWithAlphaComponent: s->f->alpha_background] set];
 
   if (bg_height > s->slice.height || s->img->hmargin || s->img->vmargin
       || s->img->mask || s->img->pixmap == 0 || s->width != s->background_width)
@@ -3972,7 +3974,7 @@ Function modeled after x_draw_glyph_string_box ().
   if (s->hl == DRAW_CURSOR)
     {
       [FRAME_CURSOR_COLOR (s->f) set];
-      tdCol = [NSColor colorWithUnsignedLong: NS_FACE_BACKGROUND (face)];
+      tdCol = [[NSColor colorWithUnsignedLong: NS_FACE_BACKGROUND (face)] colorWithAlphaComponent: s->f->alpha_background];
     }
   else
     tdCol = [NSColor colorWithUnsignedLong: NS_FACE_FOREGROUND (face)];
@@ -4066,10 +4068,10 @@ Function modeled after x_draw_glyph_string_box ().
 		face = FACE_FROM_ID (s->f, MOUSE_FACE_ID);
 	      prepare_face_for_display (s->f, face);
 
-	      [[NSColor colorWithUnsignedLong: face->background] set];
+	      [[[NSColor colorWithUnsignedLong: face->background] colorWithAlphaComponent: s->f->alpha_background] set];
 	    }
 	  else
-	    [[NSColor colorWithUnsignedLong: s->face->background] set];
+	    [[[NSColor colorWithUnsignedLong: s->face->background] colorWithAlphaComponent: s->f->alpha_background] set];
 	  NSRectFill (NSMakeRect (x, y, w, h));
 	}
     }
@@ -4095,7 +4097,7 @@ Function modeled after x_draw_glyph_string_box ().
 	  if (s->hl == DRAW_CURSOR)
 	    [FRAME_CURSOR_COLOR (s->f) set];
 	  else
-	    [[NSColor colorWithUnsignedLong: s->face->background] set];
+	    [[[NSColor colorWithUnsignedLong: s->face->background] colorWithAlphaComponent: s->f->alpha_background] set];
 
 	  NSRectFill (NSMakeRect (x, s->y, background_width, s->height));
 	}
@@ -8436,8 +8438,8 @@ - (void)toggleFullScreen: (id)sender
         }
 
       [w setContentView:[fw contentView]];
-      [w setBackgroundColor: col];
-      if ([col alphaComponent] != (EmacsCGFloat) 1.0)
+      [w setBackgroundColor: [col colorWithAlphaComponent: f->alpha_background]];
+      if (f->alpha_background != (EmacsCGFloat) 1.0)
         [w setOpaque: NO];
 
       f->border_width = [w borderWidth];
@@ -9172,9 +9174,9 @@ - (instancetype) initWithEmacsFrame: (struct frame *) f
       f->border_width = [self borderWidth];
 
       col = [NSColor colorWithUnsignedLong:NS_FACE_BACKGROUND
-                                     (FACE_FROM_ID (f, DEFAULT_FACE_ID))];
-      [self setBackgroundColor:col];
-      if ([col alphaComponent] != (EmacsCGFloat) 1.0)
+		      (FACE_FROM_ID (f, DEFAULT_FACE_ID))];
+      [self setBackgroundColor:[col colorWithAlphaComponent:f->alpha_background]];
+      if (f->alpha_background != (EmacsCGFloat) 1.0)
         [self setOpaque:NO];
 
       /* toolbar support */