Window: Shrink close button hit-testing region when it covers an abno…

…rmally high portion of the window visible area (e.g. when window is collapsed and moved in a corner)to facilitate moving the window away. (#3825)

docs/CHANGELOG.txt

@@ -45,6 +45,8 @@ Other Changes:
 
 - DragScalar: Fixed crash when using DragScalar() directly (not via common wrapper like DragFloat() etc.)
   with ImGuiSliderFlags_AlwaysClamp + only one of either p_min or p_max set. (#3824) [@harry75369]
+- Window: Shrink close button hit-testing region when it covers an abnormally high portion of the window visible
+  area (e.g. when window is collapsed + moved in a corner) to facilitate moving the window away. (#3825)
 - ImDrawList: AddCircle, AddCircleFilled(): Tweaked default segment count calculation to honor MaxError
   with more accuracy. Made default segment count always even for better looking result. (#3808) [@thedmd]
 - ImDrawList: AddCircle, AddCircleFilled(): New default for style.

imgui_internal.h

@@ -448,6 +448,7 @@ struct IMGUI_API ImRect
     ImVec2      GetSize() const                     { return ImVec2(Max.x - Min.x, Max.y - Min.y); }
     float       GetWidth() const                    { return Max.x - Min.x; }
     float       GetHeight() const                   { return Max.y - Min.y; }
+    float       GetArea() const                     { return (Max.x - Min.x) * (Max.y - Min.y); }
     ImVec2      GetTL() const                       { return Min; }                   // Top-left
     ImVec2      GetTR() const                       { return ImVec2(Max.x, Min.y); }  // Top-right
     ImVec2      GetBL() const                       { return ImVec2(Min.x, Max.y); }  // Bottom-left

imgui_widgets.cpp

@@ -782,22 +782,30 @@ bool ImGui::ArrowButton(const char* str_id, ImGuiDir dir)
 }
 
 // Button to close a window
-bool ImGui::CloseButton(ImGuiID id, const ImVec2& pos)//, float size)
+bool ImGui::CloseButton(ImGuiID id, const ImVec2& pos)
 {
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = g.CurrentWindow;
 
-    // We intentionally allow interaction when clipped so that a mechanical Alt,Right,Validate sequence close a window.
-    // (this isn't the regular behavior of buttons, but it doesn't affect the user much because navigation tends to keep items visible).
+    // Tweak 1: Shrink hit-testing area if button covers an abnormally large proportion of the visible region. That's in order to facilitate moving the window away. (#3825)
+    // This may better be applied as a general hit-rect reduction mechanism for all widgets to ensure the area to move window is always accessible?
     const ImRect bb(pos, pos + ImVec2(g.FontSize, g.FontSize) + g.Style.FramePadding * 2.0f);
-    bool is_clipped = !ItemAdd(bb, id);
+    ImRect bb_interact = bb;
+    const float area_to_visible_ratio = window->OuterRectClipped.GetArea() / bb.GetArea();
+    if (area_to_visible_ratio < 1.5f)
+        bb_interact.Expand(ImFloor(bb_interact.GetSize() * -0.25f));
+
+    // Tweak 2: We intentionally allow interaction when clipped so that a mechanical Alt,Right,Activate sequence can always close a window.
+    // (this isn't the regular behavior of buttons, but it doesn't affect the user much because navigation tends to keep items visible).
+    bool is_clipped = !ItemAdd(bb_interact, id);
 
     bool hovered, held;
-    bool pressed = ButtonBehavior(bb, id, &hovered, &held);
+    bool pressed = ButtonBehavior(bb_interact, id, &hovered, &held);
     if (is_clipped)
         return pressed;
 
     // Render
+    // FIXME: Clarify this mess
     ImU32 col = GetColorU32(held ? ImGuiCol_ButtonActive : ImGuiCol_ButtonHovered);
     ImVec2 center = bb.GetCenter();
     if (hovered)