Drag and Drop: added ImGuiDragDropFlags_AcceptDrawAsHovered. (#8632)

Not calling SetHoveredId() in that path, does not seem necessary.

docs/CHANGELOG.txt

@@ -94,9 +94,12 @@ Other Changes:
   triggered by some widgets e.g. Checkbox(), Selectable() and many others, which
   cleared ActiveId at the same time as editing. (#9028)
   Note that IsItemDeactivatedAfterEdit() was not affected, only IsItemEdited).
-- Style, Drag and Drop: added ImGuiCol_DragDropTargetBg, style.DragDropTargetRounding,
-  style.DragDropTargetBorderSize and style.DragDropTargetPadding to configure
-  the drop target highlight. (#9056) [@aaronkirkham]
+- Drag and Drop:
+  - Added ImGuiDragDropFlags_AcceptDrawAsHovered to make accepting item render
+    as hovered, which can allow using e.g. Button() as drop target. (#8632)
+  - Style: added ImGuiCol_DragDropTargetBg, style.DragDropTargetRounding,
+    style.DragDropTargetBorderSize and style.DragDropTargetPadding to configure
+    the drop target highlight. (#9056) [@aaronkirkham]
 - Demo: About Box: emit infos to convey when IM_ASSERT() macro is disabled,
   - so users don't miss out on programming errors being reported.
   - so it is included in config/build info submitted in new GitHub Issues.

imgui.h

@@ -1484,6 +1484,7 @@ enum ImGuiDragDropFlags_
     ImGuiDragDropFlags_AcceptBeforeDelivery         = 1 << 10,  // AcceptDragDropPayload() will returns true even before the mouse button is released. You can then call IsDelivery() to test if the payload needs to be delivered.
     ImGuiDragDropFlags_AcceptNoDrawDefaultRect      = 1 << 11,  // Do not draw the default highlight rectangle when hovering over target.
     ImGuiDragDropFlags_AcceptNoPreviewTooltip       = 1 << 12,  // Request hiding the BeginDragDropSource tooltip from the BeginDragDropTarget site.
+    ImGuiDragDropFlags_AcceptDrawAsHovered          = 1 << 13,  // Accepting item will render as if hovered. Useful for e.g. a Button() used as a drop target.
     ImGuiDragDropFlags_AcceptPeekOnly               = ImGuiDragDropFlags_AcceptBeforeDelivery | ImGuiDragDropFlags_AcceptNoDrawDefaultRect, // For peeking ahead and inspecting the payload before delivery.
 
 #ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS

imgui_widgets.cpp

@@ -574,8 +574,9 @@ bool ImGui::ButtonBehavior(const ImRect& bb, ImGuiID id, bool* out_hovered, bool
 
     // Special mode for Drag and Drop used by openables (tree nodes, tabs etc.)
     // where holding the button pressed for a long time while drag a payload item triggers the button.
-    if (g.DragDropActive && (flags & ImGuiButtonFlags_PressedOnDragDropHold) && !(g.DragDropSourceFlags & ImGuiDragDropFlags_SourceNoHoldToOpenOthers))
-        if (IsItemHovered(ImGuiHoveredFlags_AllowWhenBlockedByActiveItem))
+    if (g.DragDropActive)
+    {
+        if ((flags & ImGuiButtonFlags_PressedOnDragDropHold) && !(g.DragDropSourceFlags & ImGuiDragDropFlags_SourceNoHoldToOpenOthers) && IsItemHovered(ImGuiHoveredFlags_AllowWhenBlockedByActiveItem))
         {
             hovered = true;
             SetHoveredID(id);
@@ -586,6 +587,9 @@ bool ImGui::ButtonBehavior(const ImRect& bb, ImGuiID id, bool* out_hovered, bool
                 FocusWindow(window);
             }
         }
+        if (g.DragDropAcceptIdPrev == id && (g.DragDropAcceptFlagsPrev & ImGuiDragDropFlags_AcceptDrawAsHovered))
+            hovered = true;
+    }
 
     if (flatten_hovered_children)
         g.HoveredWindow = backup_hovered_window;