IsItemHovered(), IsWindowHovered(): added flags to enable various and more specific behavior. Will enable improvements for popups/context menus and drag'n drop. (relate ~#439, #1013, #143, #925)

The legacy confusing IsItemRectHovered(), IsWindowRectHovered() can be completely removed now.
Changed IsWindowHovered() behavior with default parameter: it now return false is the window is blocked by a popup.
Demo: Added tests for those two functions.

imgui.h

@@ -80,6 +80,7 @@ typedef int ImGuiColumnsFlags;      // flags: for *Columns*()
 typedef int ImGuiInputTextFlags;    // flags: for InputText*()                  // enum ImGuiInputTextFlags_
 typedef int ImGuiSelectableFlags;   // flags: for Selectable()                  // enum ImGuiSelectableFlags_
 typedef int ImGuiTreeNodeFlags;     // flags: for TreeNode*(), Collapsing*()    // enum ImGuiTreeNodeFlags_
+typedef int ImGuiHoveredFlags;      // flags: for IsItemHovered()               // enum ImGuiHoveredFlags_
 typedef int (*ImGuiTextEditCallback)(ImGuiTextEditCallbackData *data);
 typedef void (*ImGuiSizeConstraintCallback)(ImGuiSizeConstraintCallbackData* data);
 #ifdef _MSC_VER
@@ -414,8 +415,7 @@ namespace ImGui
     IMGUI_API void          StyleColorsClassic(ImGuiStyle* dst = NULL);
 
     // Utilities
-    IMGUI_API bool          IsItemHovered();                                                    // is the last item hovered by mouse (and usable)?
-    IMGUI_API bool          IsItemRectHovered();                                                // is the last item hovered by mouse? even if another item is active or window is blocked by popup while we are hovering this
+    IMGUI_API bool          IsItemHovered(ImGuiHoveredFlags flags = 0);                         // is the last item hovered by mouse (and usable)?
     IMGUI_API bool          IsItemActive();                                                     // is the last item active? (e.g. button being held, text field being edited- items that don't interact will always return false)
     IMGUI_API bool          IsItemClicked(int mouse_button = 0);                                // is the last item clicked? (e.g. button/node just clicked on)
     IMGUI_API bool          IsItemVisible();                                                    // is the last item visible? (aka not out of sight due to clipping/scrolling.)
@@ -426,11 +426,10 @@ namespace ImGui
     IMGUI_API ImVec2        GetItemRectSize();                                                  // "
     IMGUI_API void          SetItemAllowOverlap();                                              // allow last item to be overlapped by a subsequent item. sometimes useful with invisible buttons, selectables, etc. to catch unused area.
     IMGUI_API bool          IsWindowFocused();                                                  // is current window focused
-    IMGUI_API bool          IsWindowHovered();                                                  // is current window hovered and hoverable (not blocked by a popup) (differentiate child windows from each others)
-    IMGUI_API bool          IsWindowRectHovered();                                              // is current window rectangle hovered, disregarding of any consideration of being blocked by a popup. (unlike IsWindowHovered() this will return true even if the window is blocked because of a popup)
+    IMGUI_API bool          IsWindowHovered(ImGuiHoveredFlags flags = 0);                       // is current window hovered (and typically: not blocked by a popup/modal)
     IMGUI_API bool          IsRootWindowFocused();                                              // is current root window focused (root = top-most parent of a child, otherwise self)
     IMGUI_API bool          IsRootWindowOrAnyChildFocused();                                    // is current root window or any of its child (including current window) focused
-    IMGUI_API bool          IsRootWindowOrAnyChildHovered();                                    // is current root window or any of its child (including current window) hovered and hoverable (not blocked by a popup)
+    IMGUI_API bool          IsRootWindowOrAnyChildHovered(ImGuiHoveredFlags flags = 0);         // is current root window or any of its child (including current window) hovered and hoverable (not blocked by a popup)
     IMGUI_API bool          IsAnyWindowHovered();                                               // is mouse hovering any visible window
     IMGUI_API bool          IsRectVisible(const ImVec2& size);                                  // test if rectangle (of given size, starting from cursor position) is visible / not clipped.
     IMGUI_API bool          IsRectVisible(const ImVec2& rect_min, const ImVec2& rect_max);      // test if rectangle (in screen space) is visible / not clipped. to perform coarse clipping on user's side.
@@ -569,6 +568,16 @@ enum ImGuiSelectableFlags_
     ImGuiSelectableFlags_AllowDoubleClick   = 1 << 2    // Generate press events on double clicks too
 };
 
+enum ImGuiHoveredFlags_
+{
+    ImGuiHoveredFlags_Default                       = 0,        // Return true if directly over the item/window, not obstructed by another window, not obstructed by an active popup or modal blocking inputs under them.
+    ImGuiHoveredFlags_AllowWhenBlockedByPopup       = 1 << 0,   // Return true even if a popup window is normally blocking access to this item/window
+    //ImGuiHoveredFlags_AllowWhenBlockedByModal     = 1 << 1,   // Return true even if a modal popup window is normally blocking access to this item/window. FIXME-TODO: Unavailable yet.
+    ImGuiHoveredFlags_AllowWhenBlockedByActiveItem  = 1 << 2,   // Return true even if an active item is blocking access to this item/window
+    ImGuiHoveredFlags_AllowWhenOverlapped           = 1 << 3,   // Return true even if the position is overlapped by another window
+    ImGuiHoveredFlags_RectOnly                      = ImGuiHoveredFlags_AllowWhenBlockedByPopup | ImGuiHoveredFlags_AllowWhenBlockedByActiveItem | ImGuiHoveredFlags_AllowWhenOverlapped
+};
+
 // User fill ImGuiIO.KeyMap[] array with indices into the ImGuiIO.KeysDown[512] array
 enum ImGuiKey_
 {
@@ -881,10 +890,10 @@ namespace ImGui
     bool                    Begin(const char* name, bool* p_open, const ImVec2& size_on_first_use, float bg_alpha_override = -1.0f, ImGuiWindowFlags flags = 0); // OBSOLETE 1.52+. use SetNextWindowSize() instead if you want to set a window size.
     static inline void      AlignFirstTextHeightToWidgets() { AlignTextToFramePadding(); }     // OBSOLETE 1.52+
     static inline void      SetNextWindowPosCenter(ImGuiCond cond = 0) { SetNextWindowPos(ImVec2(GetIO().DisplaySize.x * 0.5f, GetIO().DisplaySize.y * 0.5f), cond, ImVec2(0.5f, 0.5f)); } // OBSOLETE 1.52+
-    static inline bool      IsItemHoveredRect() { return IsItemRectHovered(); }                // OBSOLETE 1.51+
+    static inline bool      IsItemHoveredRect() { return IsItemHovered(ImGuiHoveredFlags_RectOnly); } // OBSOLETE 1.51+
     static inline bool      IsPosHoveringAnyWindow(const ImVec2&) { IM_ASSERT(0); return false; } // OBSOLETE 1.51+. This was partly broken. You probably wanted to use ImGui::GetIO().WantCaptureMouse instead.
     static inline bool      IsMouseHoveringAnyWindow() { return IsAnyWindowHovered(); }        // OBSOLETE 1.51+
-    static inline bool      IsMouseHoveringWindow() { return IsWindowRectHovered(); }          // OBSOLETE 1.51+
+    static inline bool      IsMouseHoveringWindow() { return IsWindowHovered(ImGuiHoveredFlags_AllowWhenBlockedByPopup | ImGuiHoveredFlags_AllowWhenBlockedByActiveItem); } // OBSOLETE 1.51+
     static inline bool      CollapsingHeader(const char* label, const char* str_id, bool framed = true, bool default_open = false) { (void)str_id; (void)framed; ImGuiTreeNodeFlags default_open_flags = 1 << 5; return CollapsingHeader(label, (default_open ? default_open_flags : 0)); } // OBSOLETE 1.49+
     static inline ImFont*   GetWindowFont() { return GetFont(); }                              // OBSOLETE 1.48+
     static inline float     GetWindowFontSize() { return GetFontSize(); }                      // OBSOLETE 1.48+