Implemented #422 - Possibility to set default window icon for new windows.

src/dlangui/dialogs/dialog.d

@@ -65,7 +65,7 @@ class Dialog : VerticalLayout {
         _caption = caption;
         _parentWindow = parentWindow;
         _flags = flags;
-        _icon = "dlangui-logo1";
+        _icon = "";
     }
 
     /**
@@ -88,9 +88,13 @@ class Dialog : VerticalLayout {
     @property Dialog windowIcon(string iconResourceId) {
         _icon = iconResourceId;
         static if (BACKEND_GUI) {
-            if (_window && _icon)
+            if (_window) {
+                if (_icon.length == 0)
+                    _window.windowIcon = drawableCache.getImage(Platform.instance.defaultWindowIcon);
+                else
                     _window.windowIcon = drawableCache.getImage(_icon);
             }
+        }
         return this;
     }
 
@@ -211,10 +215,7 @@ class Dialog : VerticalLayout {
             if (_initialWidth == 0 && _initialHeight == 0)
                 wflags |= WindowFlag.MeasureSize;
             _window = Platform.instance.createWindow(_caption, _parentWindow, wflags, _initialWidth, _initialHeight);
-            static if (BACKEND_GUI) {
+            windowIcon = _icon;
-                if (_window && _icon)
-                    _window.windowIcon = drawableCache.getImage(_icon);
-            }
             _window.backgroundColor = currentTheme.customColor("dialog_background");
             _window.mainWidget = this;
             _window.show();

src/dlangui/platforms/common/platform.d

@@ -1884,6 +1884,20 @@ class Platform {
         // override and call dispatchThemeChange for all windows
     }
 
+    /// default icon for new created windows
+    private string _defaultWindowIcon = "dlangui-logo1";
+
+    /// sets default icon for new created windows
+    @property void defaultWindowIcon(string newIcon) {
+        _defaultWindowIcon = newIcon;
+    }
+
+    /// gets default icon for new created windows
+    @property string defaultWindowIcon() {
+        return _defaultWindowIcon;
+    }
+
+
 }
 
 /// get current platform object instance

src/dlangui/platforms/sdl/sdlapp.d

@@ -99,6 +99,9 @@ class SDLWindow : Window {
         create(flags);
         _children.reserve(20);
         Log.i(_enableOpengl ? "OpenGL is enabled" : "OpenGL is disabled");
+        
+        if (platform.defaultWindowIcon.length != 0)
+            windowIcon = drawableCache.getImage(platform.defaultWindowIcon);
     }
 
     ~this() {

src/dlangui/platforms/windows/winapp.d

@@ -307,6 +307,9 @@ class Win32Window : Window {
         RECT rect;
         GetWindowRect(_hwnd, &rect);
         handleWindowStateChange(WindowState.unspecified, Rect(rect.left, rect.top, _dx, _dy));
+
+        if (platform.defaultWindowIcon.length != 0)
+            windowIcon = drawableCache.getImage(platform.defaultWindowIcon);
     }
 
     static if (ENABLE_OPENGL) {

src/dlangui/platforms/x11/x11app.d

@@ -373,6 +373,9 @@ class X11Window : DWindow {
         //XFlush(x11display);
 
         handleWindowStateChange(WindowState.unspecified, Rect(0, 0, _dx, _dy));
+
+        if (platform.defaultWindowIcon.length != 0)
+            windowIcon = drawableCache.getImage(platform.defaultWindowIcon);
     }
 
     ~this() {