Add ImGuiTreeNodeFlags_NoFrameOuterPadding flag

imgui.h

@@ -1309,13 +1309,14 @@ enum ImGuiTreeNodeFlags_
     ImGuiTreeNodeFlags_LabelSpanAllColumns  = 1 << 15,  // Label will span all columns of its container table
     //ImGuiTreeNodeFlags_NoScrollOnOpen     = 1 << 16,  // FIXME: TODO: Disable automatic scroll on TreePop() if node got just open and contents is not visible
     ImGuiTreeNodeFlags_NavLeftJumpsToParent = 1 << 17,  // Nav: left arrow moves back to parent. This is processed in TreePop() when there's an unfulfilled Left nav request remaining.
+    ImGuiTreeNodeFlags_NoFrameOuterPadding  = 1 << 18,  // Don't apply outer padding on the header's frame so that it aligns with the contents.
     ImGuiTreeNodeFlags_CollapsingHeader     = ImGuiTreeNodeFlags_Framed | ImGuiTreeNodeFlags_NoTreePushOnOpen | ImGuiTreeNodeFlags_NoAutoOpenOnLog,
 
     // [EXPERIMENTAL] Draw lines connecting TreeNode hierarchy. Discuss in GitHub issue #2920.
     // Default value is pulled from style.TreeLinesFlags. May be overridden in TreeNode calls.
-    ImGuiTreeNodeFlags_DrawLinesNone        = 1 << 18,  // No lines drawn
-    ImGuiTreeNodeFlags_DrawLinesFull        = 1 << 19,  // Horizontal lines to child nodes. Vertical line drawn down to TreePop() position: cover full contents. Faster (for large trees).
-    ImGuiTreeNodeFlags_DrawLinesToNodes     = 1 << 20,  // Horizontal lines to child nodes. Vertical line drawn down to bottom-most child node. Slower (for large trees).
+    ImGuiTreeNodeFlags_DrawLinesNone        = 1 << 19,  // No lines drawn
+    ImGuiTreeNodeFlags_DrawLinesFull        = 1 << 20,  // Horizontal lines to child nodes. Vertical line drawn down to TreePop() position: cover full contents. Faster (for large trees).
+    ImGuiTreeNodeFlags_DrawLinesToNodes     = 1 << 21,  // Horizontal lines to child nodes. Vertical line drawn down to bottom-most child node. Slower (for large trees).
 
 #ifndef IMGUI_DISABLE_OBSOLETE_FUNCTIONS
     ImGuiTreeNodeFlags_NavLeftJumpsBackHere = ImGuiTreeNodeFlags_NavLeftJumpsToParent,  // Renamed in 1.92.0

imgui_demo.cpp

@@ -1057,10 +1057,16 @@ static void DemoWindowWidgetsCollapsingHeaders()
     IMGUI_DEMO_MARKER("Widgets/Collapsing Headers");
     if (ImGui::TreeNode("Collapsing Headers"))
     {
+        static bool no_outer_padding = false;
+        ImGuiTreeNodeFlags flags = ImGuiTreeNodeFlags_None;
+        if (no_outer_padding)
+            flags |= ImGuiTreeNodeFlags_NoFrameOuterPadding;
+
         static bool closable_group = true;
         ImGui::Checkbox("Show 2nd header", &closable_group);
-        if (ImGui::CollapsingHeader("Header", ImGuiTreeNodeFlags_None))
+        if (ImGui::CollapsingHeader("Header", flags))
         {
+            ImGui::Checkbox("Remove header outer padding", &no_outer_padding);
             ImGui::Text("IsItemHovered: %d", ImGui::IsItemHovered());
             for (int i = 0; i < 5; i++)
                 ImGui::Text("Some content %d", i);
@@ -4095,6 +4101,7 @@ static void DemoWindowWidgetsTreeNodes()
             ImGui::CheckboxFlags("ImGuiTreeNodeFlags_AllowOverlap", &base_flags, ImGuiTreeNodeFlags_AllowOverlap);
             ImGui::CheckboxFlags("ImGuiTreeNodeFlags_Framed", &base_flags, ImGuiTreeNodeFlags_Framed); ImGui::SameLine(); HelpMarker("Draw frame with background (e.g. for CollapsingHeader)");
             ImGui::CheckboxFlags("ImGuiTreeNodeFlags_FramePadding", &base_flags, ImGuiTreeNodeFlags_FramePadding);
+            ImGui::CheckboxFlags("ImGuiTreeNodeFlags_NoFrameOuterPadding", &base_flags, ImGuiTreeNodeFlags_NoFrameOuterPadding);
             ImGui::CheckboxFlags("ImGuiTreeNodeFlags_NavLeftJumpsToParent", &base_flags, ImGuiTreeNodeFlags_NavLeftJumpsToParent);
 
             HelpMarker("Default option for DrawLinesXXX is stored in style.TreeLinesFlags");

imgui_widgets.cpp

@@ -6844,7 +6844,7 @@ bool ImGui::TreeNodeBehavior(ImGuiID id, ImGuiTreeNodeFlags flags, const char* l
     frame_bb.Min.y = window->DC.CursorPos.y + (text_offset_y - padding.y);
     frame_bb.Max.x = span_all_columns ? window->ParentWorkRect.Max.x : (flags & ImGuiTreeNodeFlags_SpanLabelWidth) ? window->DC.CursorPos.x + text_width + padding.x : window->WorkRect.Max.x;
     frame_bb.Max.y = window->DC.CursorPos.y + (text_offset_y - padding.y) + frame_height;
-    if (display_frame)
+    if (display_frame && !(flags & ImGuiTreeNodeFlags_NoFrameOuterPadding))
     {
         const float outer_extend = IM_TRUNC(window->WindowPadding.x * 0.5f); // Framed header expand a little outside of current limits
         frame_bb.Min.x -= outer_extend;