TreeNode: Reworded code for ImGuiTreeNodeFlags_OpenOnArrow (follow up to f79b2d6c) to make it lightweight. Should be a no-op from user's point of view. Will facilitate using the arrow hovering information in the hot path. (#2886)

imgui_widgets.cpp

@@ -5287,13 +5287,15 @@ bool ImGui::TreeNodeBehavior(ImGuiID id, ImGuiTreeNodeFlags flags, const char* l
     {
         if (pressed)
         {
-            const float arrow_x1 = text_pos.x - text_offset_x;
-            const float arrow_x2 = arrow_x1 + g.FontSize + padding.x * 2.0f;
-            toggled = !(flags & (ImGuiTreeNodeFlags_OpenOnArrow | ImGuiTreeNodeFlags_OpenOnDoubleClick)) || (g.NavActivateId == id);
+            const float hit_padding_x = style.TouchExtraPadding.x;
+            const float arrow_hit_x1 = (text_pos.x - text_offset_x) - hit_padding_x;
+            const float arrow_hit_x2 = (text_pos.x - text_offset_x) + (g.FontSize + padding.x * 2.0f) + hit_padding_x;
             if (flags & ImGuiTreeNodeFlags_OpenOnArrow)
-                toggled |= IsMouseHoveringRect(ImVec2(arrow_x1, interact_bb.Min.y), ImVec2(arrow_x2, interact_bb.Max.y)) && (!g.NavDisableMouseHover);
-            if (flags & ImGuiTreeNodeFlags_OpenOnDoubleClick)
-                toggled |= g.IO.MouseDoubleClicked[0];
+                toggled |= (g.IO.MousePos.x >= arrow_hit_x1 && g.IO.MousePos.x < arrow_hit_x2) && (!g.NavDisableMouseHover); // Lightweight equivalent of IsMouseHoveringRect() since ButtonBehavior() already did the job
+            if ((flags & (ImGuiTreeNodeFlags_OpenOnArrow | ImGuiTreeNodeFlags_OpenOnDoubleClick)) == 0 || (g.NavActivateId == id))
+                toggled = true;
+            if ((flags & ImGuiTreeNodeFlags_OpenOnDoubleClick) && g.IO.MouseDoubleClicked[0])
+                toggled = true;
             if (g.DragDropActive && is_open) // When using Drag and Drop "hold to open" we keep the node highlighted after opening, but never close it again.
                 toggled = false;
         }