put the controls panel in the corner and let it step around the build bar

src/ui/ControlsPanel.h

@@ -38,11 +38,13 @@ public:
     // selection.
     ControlsPanel(const GameWorldView* view, QWidget* parent = nullptr);
 
-    // Confines the panel to the given band of the game world view: it left-aligns
-    // within it and sits on its bottom edge. The band is the world view less the strip
-    // the build button bar occupies, so the two never overlap and the bar never has to
-    // move (REQ-UI-CONTROLS-PANEL, REQ-UI-BUILD-BAR).
-    void anchorTo(const QRect& bandRect);
+    // Places the panel in the bottom-left corner of the game world view. It shares the
+    // bottom edge with the build button bar rather than clearing its strip, the bar
+    // being centered and sized to its buttons and so usually leaving the left free; it
+    // rises above the bar only when the two would otherwise overlap. `buildBarRect` is
+    // the bar's current geometry in the same coordinates, or a null rect when there is
+    // none to avoid (REQ-UI-CONTROLS-PANEL, REQ-UI-BUILD-BAR).
+    void anchorTo(const QRect& worldRect, const QRect& buildBarRect);
 
 protected:
     // Clicking the heading collapses and expands the panel (REQ-UI-CONTROLS-PANEL).
@@ -77,7 +79,8 @@ private:
     // command (REQ-UI-CONTROLS-PANEL).
     bool m_collapsed = false;
 
-    // The band the panel confines itself to, in the coordinates of its parent; null
-    // until the owner has anchored it for the first time.
-    QRect m_bandRect;
+    // The world view the panel sits in, and the build button bar it steps around, both
+    // in the coordinates of its parent. Null until the owner has anchored it.
+    QRect m_worldRect;
+    QRect m_buildBarRect;
 };