Enables blurring in the title screen.

Shadowm figured out why blurring didn't work properly in the title screen
and created a proof-of-concept patch. This patch is heavily based upon
that patch.

changelog

@@ -24,6 +24,7 @@ Version 1.11.9+dev:
      ability to copy the report to clipboard.
    * Fixed bug #21584: Properly redraw the minimap when the minimap is
      resized.
+   * Fixed: Enable blurring in the title screen.
  * WML engine:
    * WML loading phase errors are reported to stderr in a new indented format.
    * Implemented [true] and [false] ConditionalWML tags, which describe a

data/gui/default/widget/panel_title_screen.cfg

@@ -19,14 +19,13 @@
 
 			[draw]
 
-# Blurring doesn't work yet, keeps adding
-#				[pre_commit]
-#
-#					[blur]
-#						depth = 1
-#					[/blur]
-#
-#				[/pre_commit]
+				[pre_commit]
+
+					[blur]
+						depth = 1
+					[/blur]
+
+				[/pre_commit]
 
 				[image]
 					name = "dialogs/translucent54-border-topleft.png"

src/gui/auxiliary/canvas.cpp

@@ -30,6 +30,7 @@
 #include "gui/widgets/helper.hpp"
 #include "../../text.hpp"
 #include "utils/foreach.tpp"
+#include "video.hpp"
 #include "wml_exception.hpp"
 
 namespace gui2
@@ -1475,7 +1476,12 @@ void tcanvas::blit(surface& surf, SDL_Rect rect)
 	draw();
 
 	if(blur_depth_) {
-		if(is_neutral(surf)) {
+		/*
+		 * If the surf is the video surface the blurring seems to stack, this
+		 * can be seen in the title screen. So also use the not 32 bpp method
+		 * for this situation.
+		 */
+		if(surf != get_video_surface() && is_neutral(surf)) {
 			blur_surface(surf, rect, blur_depth_);
 		} else {
 			// Can't directly blur the surface if not 32 bpp.