CollapsingHeader: When a close button is enabled, better clip the label to avoid overlap. (#600)

docs/CHANGELOG.txt

@@ -51,6 +51,7 @@ Other Changes:
 - Fixed crash when appending with BeginMainMenuBar() more than once and no other window are showing. (#2567)
 - ColorEdit: Fixed the color picker popup only displaying inputs as HSV instead of showing multiple
   options. (#2587, broken in 1.69 by #2384).
+- CollapsingHeader: Better clipping when a close button is enabled and it overlaps the label. (#600)
 - Scrollbar: Very minor bounding box adjustment to cope with various border size.
 - Style: Added style.WindowMenuButtonPosition (left/right, defaults to ImGuiDir_Left) to move the
   collapsing/docking button to the other side of the title bar.

imgui_internal.h

@@ -361,6 +361,12 @@ enum ImGuiSelectableFlagsPrivate_
     ImGuiSelectableFlags_AllowItemOverlap   = 1 << 24
 };
 
+// Extend ImGuiTreeNodeFlags_
+enum ImGuiTreeNodeFlagsPrivate_
+{
+    ImGuiTreeNodeFlags_ClipLabelForTrailingButton = 1 << 20
+};
+
 enum ImGuiSeparatorFlags_
 {
     ImGuiSeparatorFlags_None                = 0,

imgui_widgets.cpp

@@ -5131,8 +5131,8 @@ bool ImGui::TreeNodeBehavior(ImGuiID id, ImGuiTreeNodeFlags flags, const char* l
     if (display_frame)
     {
         // Framed header expand a little outside the default padding
-        frame_bb.Min.x -= (float)(int)(window->WindowPadding.x*0.5f) - 1;
+        frame_bb.Min.x -= (float)(int)(window->WindowPadding.x * 0.5f) - 1;
-        frame_bb.Max.x += (float)(int)(window->WindowPadding.x*0.5f) - 1;
+        frame_bb.Max.x += (float)(int)(window->WindowPadding.x * 0.5f) - 1;
     }
 
     const float text_offset_x = (g.FontSize + (display_frame ? padding.x*3 : padding.x*2));   // Collapser arrow width + Spacing
@@ -5229,6 +5229,8 @@ bool ImGui::TreeNodeBehavior(ImGuiID id, ImGuiTreeNodeFlags flags, const char* l
         RenderFrame(frame_bb.Min, frame_bb.Max, col, true, style.FrameRounding);
         RenderNavHighlight(frame_bb, id, nav_highlight_flags);
         RenderArrow(frame_bb.Min + ImVec2(padding.x, text_base_offset_y), is_open ? ImGuiDir_Down : ImGuiDir_Right, 1.0f);
+        if (flags & ImGuiTreeNodeFlags_ClipLabelForTrailingButton)
+            frame_bb.Max.x -= g.FontSize + style.FramePadding.x;
         if (g.LogEnabled)
         {
             // NB: '##' is normally used to hide text (as a library-wide feature), so we need to specify the text range to make sure the ## aren't stripped out here.
@@ -5355,7 +5357,8 @@ bool ImGui::CollapsingHeader(const char* label, bool* p_open, ImGuiTreeNodeFlags
         return false;
 
     ImGuiID id = window->GetID(label);
-    bool is_open = TreeNodeBehavior(id, flags | ImGuiTreeNodeFlags_CollapsingHeader | (p_open ? ImGuiTreeNodeFlags_AllowItemOverlap : 0), label);
+    flags |= ImGuiTreeNodeFlags_CollapsingHeader | (p_open ? ImGuiTreeNodeFlags_AllowItemOverlap | ImGuiTreeNodeFlags_ClipLabelForTrailingButton : 0);
+    bool is_open = TreeNodeBehavior(id, flags, label);
     if (p_open)
     {
         // Create a small overlapping close button
@@ -5364,8 +5367,9 @@ bool ImGui::CollapsingHeader(const char* label, bool* p_open, ImGuiTreeNodeFlags
         ImGuiContext& g = *GImGui;
         ImGuiItemHoveredDataBackup last_item_backup;
         float button_size = g.FontSize;
-        ImVec2 button_pos = ImVec2(ImMin(window->DC.LastItemRect.Max.x, window->ClipRect.Max.x) - g.Style.FramePadding.x * 2.0f - button_size, window->DC.LastItemRect.Min.y);
+        float button_x = ImMax(window->DC.LastItemRect.Min.x, window->DC.LastItemRect.Max.x - g.Style.FramePadding.x * 2.0f - button_size);
-        if (CloseButton(window->GetID((void*)((intptr_t)id + 1)), button_pos))
+        float button_y = window->DC.LastItemRect.Min.y;
+        if (CloseButton(window->GetID((void*)((intptr_t)id + 1)), ImVec2(button_x, button_y)))
             *p_open = false;
         last_item_backup.Restore();
     }