TreeNode: The collapsing arrow accepts click even if modifier keys are being held, facilitating interactions with multi-select patterns. (#2886, #1896, #1861)

docs/CHANGELOG.txt

@@ -66,6 +66,8 @@ Other Changes:
 - ColorPicker: Fixed SV triangle gradient to block (broken in 1.73). (#2864, #2711). [@lewa-j]
 - TreeNode: Fixed combination of ImGuiTreeNodeFlags_SpanFullWidth and ImGuiTreeNodeFlags_OpenOnArrow
   incorrectly locating the arrow hit position to the left of the frame. (#2451, #2438, #1897)
+- TreeNode: The collapsing arrow accepts click even if modifier keys are being held, facilitating
+  interactions with multi-select patterns. (#2886, #1896, #1861)
 - DragScalar, SliderScalar, InputScalar: Added p_ prefix to parameter that are pointers to the data
   to clarify how they are used, and more comments redirecting to the demo code. (#2844)
 - Misc: Optimized storage of window settings data (reducing allocation count).

imgui_internal.h

@@ -365,7 +365,7 @@ enum ImGuiButtonFlags_
     ImGuiButtonFlags_DontClosePopups        = 1 << 7,   // disable automatically closing parent popup on press // [UNUSED]
     ImGuiButtonFlags_Disabled               = 1 << 8,   // disable interactions
     ImGuiButtonFlags_AlignTextBaseLine      = 1 << 9,   // vertically align button to match text baseline - ButtonEx() only // FIXME: Should be removed and handled by SmallButton(), not possible currently because of DC.CursorPosPrevLine
-    ImGuiButtonFlags_NoKeyModifiers         = 1 << 10,  // disable interaction if a key modifier is held
+    ImGuiButtonFlags_NoKeyModifiers         = 1 << 10,  // disable mouse interaction if a key modifier is held
     ImGuiButtonFlags_NoHoldingActiveID      = 1 << 11,  // don't set ActiveId while holding the mouse (ImGuiButtonFlags_PressedOnClick only)
     ImGuiButtonFlags_PressedOnDragDropHold  = 1 << 12,  // press when held into while we are drag and dropping another item (used by e.g. tree nodes, collapsing headers)
     ImGuiButtonFlags_NoNavFocus             = 1 << 13,  // don't override navigation focus when activated

imgui_widgets.cpp

@@ -5269,7 +5269,7 @@ bool ImGui::TreeNodeBehavior(ImGuiID id, ImGuiTreeNodeFlags flags, const char* l
     // - OpenOnDoubleClick .............. double-click anywhere to open
     // - OpenOnArrow .................... single-click on arrow to open
     // - OpenOnDoubleClick|OpenOnArrow .. single-click on arrow or double-click anywhere to open
-    ImGuiButtonFlags button_flags = ImGuiButtonFlags_NoKeyModifiers;
+    ImGuiButtonFlags button_flags = 0;
     if (flags & ImGuiTreeNodeFlags_AllowItemOverlap)
         button_flags |= ImGuiButtonFlags_AllowItemOverlap;
     if (flags & ImGuiTreeNodeFlags_OpenOnDoubleClick)
@@ -5277,6 +5277,15 @@ bool ImGui::TreeNodeBehavior(ImGuiID id, ImGuiTreeNodeFlags flags, const char* l
     if (!is_leaf)
         button_flags |= ImGuiButtonFlags_PressedOnDragDropHold;
 
+    // We allow clicking on the arrow section with keyboard modifiers held, in order to easily 
+    // allow browsing a tree while preserving selection with code implementing multi-selection patterns.
+    // When clicking on the rest of the tree node we always disallow keyboard modifiers.
+    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 (window != g.HoveredWindow || !(g.IO.MousePos.x >= arrow_hit_x1 && g.IO.MousePos.x < arrow_hit_x2))
+        button_flags |= ImGuiButtonFlags_NoKeyModifiers;
+    
     bool selected = (flags & ImGuiTreeNodeFlags_Selected) != 0;
     const bool was_selected = selected;
 
@@ -5287,13 +5296,10 @@ bool ImGui::TreeNodeBehavior(ImGuiID id, ImGuiTreeNodeFlags flags, const char* l
     {
         if (pressed)
         {
-            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 |= (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_OpenOnArrow)
+                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_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.