LibGUI: Simplify Dialog::ScreenPosition and allow Dialogs to opt out

These options were created 2 years ago but the only use cases thus far
are for Center and CenterWithinParent, so let's chuck the rest for now.

Adds a new DoNotPosition option to opt out of automatic centering and
a ScreenPosition setter and getter for configuration before exec()

Userland/Libraries/LibGUI/Dialog.cpp

@@ -6,7 +6,6 @@
  */
 
 #include <LibCore/EventLoop.h>
-#include <LibGUI/Desktop.h>
 #include <LibGUI/Dialog.h>
 #include <LibGUI/Event.h>
 #include <LibGfx/Palette.h>
@@ -25,83 +24,21 @@ Dialog::ExecResult Dialog::exec()
     VERIFY(!m_event_loop);
     m_event_loop = make<Core::EventLoop>();
 
-    auto desktop_rect = Desktop::the().rect();
-    auto window_rect = rect();
-
-    auto top_align = [](Gfx::Rect<int>& rect) { rect.set_y(32); };
-    auto bottom_align = [this, desktop_rect](Gfx::Rect<int>& rect) { rect.set_y(desktop_rect.height() - Desktop::the().taskbar_height() - height() - 12); };
-
-    auto left_align = [](Gfx::Rect<int>& rect) { rect.set_x(12); };
-    auto right_align = [this, desktop_rect](Gfx::Rect<int>& rect) { rect.set_x(desktop_rect.width() - width() - 12); };
-
     switch (m_screen_position) {
+    case ScreenPosition::DoNotPosition:
+        break;
     case ScreenPosition::CenterWithinParent:
-        if (parent() && is<Window>(parent())) {
-            auto& parent_window = *static_cast<Window*>(parent());
-            if (parent_window.is_visible()) {
-                // Check the dialog's position against the Desktop's rect and reposition it to be entirely visible.
-                // If the dialog is larger than the desktop's rect just center it.
-                window_rect.center_within(parent_window.rect());
-                if (window_rect.size().width() < desktop_rect.size().width() && window_rect.size().height() < desktop_rect.size().height()) {
-                    auto taskbar_top_y = desktop_rect.bottom() - Desktop::the().taskbar_height();
-                    auto palette = GUI::Application::the()->palette();
-                    auto border_thickness = palette.window_border_thickness();
-                    auto top_border_title_thickness = border_thickness + palette.window_title_height();
-                    if (window_rect.top() < top_border_title_thickness) {
-                        window_rect.set_y(top_border_title_thickness);
-                    }
-                    if (window_rect.right() + border_thickness > desktop_rect.right()) {
-                        window_rect.translate_by((window_rect.right() + border_thickness - desktop_rect.right()) * -1, 0);
-                    }
-                    if (window_rect.bottom() + border_thickness > taskbar_top_y) {
-                        window_rect.translate_by(0, (window_rect.bottom() + border_thickness - taskbar_top_y) * -1);
-                    }
-                    if (window_rect.left() - border_thickness < 0) {
-                        window_rect.set_x(0 + border_thickness);
-                    }
-                }
-                break;
-            }
+        if (auto parent = find_parent_window(); parent && parent->is_visible()) {
+            center_within(*parent);
+            constrain_to_desktop();
+            break;
         }
-        [[fallthrough]]; // Fall back to `Center` if parent window is invalid or not visible
+        [[fallthrough]];
     case ScreenPosition::Center:
-        window_rect.center_within(desktop_rect);
-        break;
-    case ScreenPosition::CenterLeft:
-        left_align(window_rect);
-        window_rect.center_vertically_within(desktop_rect);
-        break;
-    case ScreenPosition::CenterRight:
-        right_align(window_rect);
-        window_rect.center_vertically_within(desktop_rect);
-        break;
-    case ScreenPosition::TopLeft:
-        left_align(window_rect);
-        top_align(window_rect);
-        break;
-    case ScreenPosition::TopCenter:
-        window_rect.center_horizontally_within(desktop_rect);
-        top_align(window_rect);
-        break;
-    case ScreenPosition::TopRight:
-        right_align(window_rect);
-        top_align(window_rect);
-        break;
-    case ScreenPosition::BottomLeft:
-        left_align(window_rect);
-        bottom_align(window_rect);
-        break;
-    case ScreenPosition::BottomCenter:
-        window_rect.center_horizontally_within(desktop_rect);
-        bottom_align(window_rect);
-        break;
-    case ScreenPosition::BottomRight:
-        right_align(window_rect);
-        bottom_align(window_rect);
+        center_on_screen();
         break;
     }
 
-    set_rect(window_rect);
     show();
     auto result = m_event_loop->exec();
     m_event_loop = nullptr;

Userland/Libraries/LibGUI/Dialog.h

@@ -22,20 +22,11 @@ public:
         Yes = 3,
         No = 4,
     };
-    enum class ScreenPosition {
-        CenterWithinParent = 0,
-
-        Center = 1,
-        CenterLeft = 2,
-        CenterRight = 3,
-
-        TopLeft = 4,
-        TopCenter = 5,
-        TopRight = 6,
 
-        BottomLeft = 7,
-        BottomCenter = 8,
-        BottomRight = 9,
+    enum class ScreenPosition {
+        DoNotPosition,
+        CenterWithinParent,
+        Center,
     };
 
     virtual ~Dialog() override = default;
@@ -45,6 +36,9 @@ public:
     ExecResult result() const { return m_result; }
     void done(ExecResult);
 
+    ScreenPosition screen_position() const { return m_screen_position; }
+    void set_screen_position(ScreenPosition position) { m_screen_position = position; }
+
     virtual void event(Core::Event&) override;
 
     virtual void close() override;