MultiSelect+TreeNode: default open behavior is OpenOnDoubleClick + OpenOnArrow when used in a multi-select context without any OpenOnXXX flags set. (#7850)

docs/CHANGELOG.txt

@@ -43,8 +43,10 @@ Breaking changes:
 
 Other changes:
 
-- MultiSelect, TreeNode, Drag and Drop: fixed an issue where carrying a drag and drop
+- MultiSelect+TreeNode+Drag and Drop: fixed an issue where carrying a drag and drop
   payload over an already open tree node would incorrectly select it. (#7850)
+- MultiSelect+TreeNode: default open behavior is OpenOnDoubleClick + OpenOnArrow
+  when used in a multi-select context without any OpenOnXXX flags set. (#7850)
 - Backends: GLFW: added ImGui_ImplGlfw_Sleep() helper function because GLFW does not
   provide a way to do a portable sleep. (#7844)
 - Examples: GLFW (all), SDL2 (all), SDL3 (all), Win32+OpenGL3: rework examples main loop

imgui.h

@@ -1177,8 +1177,8 @@ enum ImGuiTreeNodeFlags_
     ImGuiTreeNodeFlags_NoTreePushOnOpen     = 1 << 3,   // Don't do a TreePush() when open (e.g. for CollapsingHeader) = no extra indent nor pushing on ID stack
     ImGuiTreeNodeFlags_NoAutoOpenOnLog      = 1 << 4,   // Don't automatically and temporarily open node when Logging is active (by default logging will automatically open tree nodes)
     ImGuiTreeNodeFlags_DefaultOpen          = 1 << 5,   // Default node to be open
-    ImGuiTreeNodeFlags_OpenOnDoubleClick    = 1 << 6,   // Need double-click to open node
-    ImGuiTreeNodeFlags_OpenOnArrow          = 1 << 7,   // Only open when clicking on the arrow part. If ImGuiTreeNodeFlags_OpenOnDoubleClick is also set, single-click arrow or double-click all box to open.
+    ImGuiTreeNodeFlags_OpenOnDoubleClick    = 1 << 6,   // Open on double-click instead of simple click (default for multi-select unless any _OpenOnXXX behavior is set explicitly). Both behaviors may be combined.
+    ImGuiTreeNodeFlags_OpenOnArrow          = 1 << 7,   // Open when clicking on the arrow part (default for multi-select unless any _OpenOnXXX behavior is set explicitly). Both behaviors may be combined.
     ImGuiTreeNodeFlags_Leaf                 = 1 << 8,   // No collapsing, no arrow (use as a convenience for leaf nodes).
     ImGuiTreeNodeFlags_Bullet               = 1 << 9,   // Display a bullet instead of arrow. IMPORTANT: node can still be marked open/close if you don't set the _Leaf flag!
     ImGuiTreeNodeFlags_FramePadding         = 1 << 10,  // Use FramePadding (even for an unframed text node) to vertically align text baseline to regular widget height. Equivalent to calling AlignTextToFramePadding() before the node.

imgui_internal.h

@@ -970,6 +970,7 @@ enum ImGuiTreeNodeFlagsPrivate_
 {
     ImGuiTreeNodeFlags_ClipLabelForTrailingButton = 1 << 28,// FIXME-WIP: Hard-coded for CollapsingHeader()
     ImGuiTreeNodeFlags_UpsideDownArrow            = 1 << 29,// FIXME-WIP: Turn Down arrow into an Up arrow, but reversed trees (#6517)
+    ImGuiTreeNodeFlags_OpenOnMask_                = ImGuiTreeNodeFlags_OpenOnDoubleClick | ImGuiTreeNodeFlags_OpenOnArrow,
 };
 
 enum ImGuiSeparatorFlags_

imgui_widgets.cpp

@@ -6475,6 +6475,10 @@ bool ImGui::TreeNodeBehavior(ImGuiID id, ImGuiTreeNodeFlags flags, const char* l
     const float arrow_hit_x2 = (text_pos.x - text_offset_x) + (g.FontSize + padding.x * 2.0f) + style.TouchExtraPadding.x;
     const bool is_mouse_x_over_arrow = (g.IO.MousePos.x >= arrow_hit_x1 && g.IO.MousePos.x < arrow_hit_x2);
 
+    const bool is_multi_select = (g.LastItemData.InFlags & ImGuiItemFlags_IsMultiSelect) != 0;
+    if (is_multi_select) // We absolutely need to distinguish open vs select so _OpenOnArrow comes by default
+        flags |= (flags & ImGuiTreeNodeFlags_OpenOnMask_) == 0 ? ImGuiTreeNodeFlags_OpenOnArrow | ImGuiTreeNodeFlags_OpenOnDoubleClick : ImGuiTreeNodeFlags_OpenOnArrow;
+
     // Open behaviors can be altered with the _OpenOnArrow and _OnOnDoubleClick flags.
     // Some alteration have subtle effects (e.g. toggle on MouseUp vs MouseDown events) due to requirements for multi-selection and drag and drop support.
     // - Single-click on label = Toggle on MouseUp (default, when _OpenOnArrow=0)
@@ -6495,16 +6499,12 @@ bool ImGui::TreeNodeBehavior(ImGuiID id, ImGuiTreeNodeFlags flags, const char* l
     const bool was_selected = selected;
 
     // Multi-selection support (header)
-    const bool is_multi_select = (g.LastItemData.InFlags & ImGuiItemFlags_IsMultiSelect) != 0;
     if (is_multi_select)
     {
         // Handle multi-select + alter button flags for it
         MultiSelectItemHeader(id, &selected, &button_flags);
         if (is_mouse_x_over_arrow)
             button_flags = (button_flags | ImGuiButtonFlags_PressedOnClick) & ~ImGuiButtonFlags_PressedOnClickRelease;
-
-        // We absolutely need to distinguish open vs select so comes by default
-        flags |= ImGuiTreeNodeFlags_OpenOnArrow;
     }
     else
     {
@@ -6519,12 +6519,12 @@ bool ImGui::TreeNodeBehavior(ImGuiID id, ImGuiTreeNodeFlags flags, const char* l
     {
         if (pressed && g.DragDropHoldJustPressedId != id)
         {
-            if ((flags & (ImGuiTreeNodeFlags_OpenOnArrow | ImGuiTreeNodeFlags_OpenOnDoubleClick)) == 0 || (g.NavActivateId == id && !is_multi_select))
-                toggled = true;
+            if ((flags & ImGuiTreeNodeFlags_OpenOnMask_) == 0 || (g.NavActivateId == id && !is_multi_select))
+                toggled = true; // Single click
             if (flags & ImGuiTreeNodeFlags_OpenOnArrow)
                 toggled |= is_mouse_x_over_arrow && !g.NavDisableMouseHover; // Lightweight equivalent of IsMouseHoveringRect() since ButtonBehavior() already did the job
             if ((flags & ImGuiTreeNodeFlags_OpenOnDoubleClick) && g.IO.MouseClickedCount[0] == 2)
-                toggled = true;
+                toggled = true; // Double click
         }
         else if (pressed && g.DragDropHoldJustPressedId == id)
         {