Introduce method to draw background ob IngameWindows

Some windows need to draw a custom background where all controls, borders etc. are on top.
In the observation window this is the map view which should seemlessly blend
with all controls.

This fixes a regression of 700945f
where the controls of the observation window got hidden behind the map view.

Fixes #1787

Author: Flamefire

libs/s25main/ingameWindows/IngameWindow.cpp

@@ -423,9 +423,7 @@ void IngameWindow::Draw_()
     // Client area
     if(!isMinimized_)
     {
-        if(background)
-            background->DrawPart(Rect(GetPos() + DrawPoint(contentOffset), GetIwSize()));
-
+        DrawBackground();
         Window::Draw_();
         DrawContent();
     }
@@ -435,6 +433,12 @@ void IngameWindow::Draw_()
     bottomBorderSideImg->DrawFull(GetPos() + GetSize() - bottomBorderSideImg->GetSize());
 }
 
+void IngameWindow::DrawBackground()
+{
+    if(background)
+        background->DrawPart(Rect(GetPos() + DrawPoint(contentOffset), GetIwSize()));
+}
+
 void IngameWindow::MoveToCenter()
 {
     SetPos(DrawPoint(VIDEODRIVER.GetRenderSize() - GetSize()) / 2);

libs/s25main/ingameWindows/IngameWindow.h

@@ -104,6 +104,8 @@ class IngameWindow : public Window
 
 protected:
     void Draw_() final;
+    /// Called when not minimized before drawing the frame
+    virtual void DrawBackground();
     /// Called when not minimized after the frame and background have been drawn
     virtual void DrawContent() {}
 

libs/s25main/ingameWindows/iwObservate.cpp

@@ -179,7 +179,7 @@ void iwObservate::Msg_Timer(const unsigned ctrl_id)
     }
 }
 
-void iwObservate::DrawContent()
+void iwObservate::DrawBackground()
 {
     if(GetPos() != lastWindowPos)
     {

libs/s25main/ingameWindows/iwObservate.h

@@ -37,7 +37,7 @@ class iwObservate : public IngameWindow
     iwObservate(GameWorldView& gwv, MapPoint selectedPt);
 
 private:
-    void DrawContent() override;
+    void DrawBackground() override;
     void Msg_ButtonClick(unsigned ctrl_id) override;
     bool Msg_MouseMove(const MouseCoords& mc) override;
     bool Msg_RightDown(const MouseCoords& mc) override;