Selectable: Avoid pushing span-column background if clipped.

imgui_widgets.cpp

@@ -5909,10 +5909,6 @@ bool ImGui::Selectable(const char* label, bool selected, ImGuiSelectableFlags fl
     ImGuiContext& g = *GImGui;
     const ImGuiStyle& style = g.Style;
 
-    const bool span_all_columns = (flags & ImGuiSelectableFlags_SpanAllColumns) != 0;
-    if (span_all_columns && window->DC.CurrentColumns) // FIXME-OPT: Avoid if vertically clipped.
-        PushColumnsBackground();
-
     // Submit label or explicit size to ItemSize(), whereas ItemAdd() will submit a larger/spanning rectangle.
     ImGuiID id = window->GetID(label);
     ImVec2 label_size = CalcTextSize(label, NULL, true);
@@ -5923,6 +5919,7 @@ bool ImGui::Selectable(const char* label, bool selected, ImGuiSelectableFlags fl
 
     // Fill horizontal space
     // We don't support (size < 0.0f) in Selectable() because the ItemSpacing extension would make explicitely right-aligned sizes not visibly match other widgets.
+    const bool span_all_columns = (flags & ImGuiSelectableFlags_SpanAllColumns) != 0;
     const float min_x = span_all_columns ? window->ParentWorkRect.Min.x : pos.x;
     const float max_x = span_all_columns ? window->ParentWorkRect.Max.x : window->WorkRect.Max.x;
     if (size_arg.x == 0.0f || (flags & ImGuiSelectableFlags_SpanAvailWidth))
@@ -5947,6 +5944,15 @@ bool ImGui::Selectable(const char* label, bool selected, ImGuiSelectableFlags fl
     }
     //if (g.IO.KeyCtrl) { GetForegroundDrawList()->AddRect(bb.Min, bb.Max, IM_COL32(0, 255, 0, 255)); }
 
+    // Modify ClipRect for the ItemAdd(), faster than doing a PushColumnsBackground/PushTableBackground for every Selectable..
+    const float backup_clip_rect_min_x = window->ClipRect.Min.x;
+    const float backup_clip_rect_max_x = window->ClipRect.Max.x;
+    if (span_all_columns)
+    {
+        window->ClipRect.Min.x = window->ParentWorkRect.Min.x;
+        window->ClipRect.Max.x = window->ParentWorkRect.Max.x;
+    }
+
     bool item_add;
     if (flags & ImGuiSelectableFlags_Disabled)
     {
@@ -5959,13 +5965,21 @@ bool ImGui::Selectable(const char* label, bool selected, ImGuiSelectableFlags fl
     {
         item_add = ItemAdd(bb, id);
     }
-    if (!item_add)
+
+    if (span_all_columns)
     {
-        if (span_all_columns && window->DC.CurrentColumns)
-            PopColumnsBackground();
-        return false;
+        window->ClipRect.Min.x = backup_clip_rect_min_x;
+        window->ClipRect.Max.x = backup_clip_rect_max_x;
     }
 
+    if (!item_add)
+        return false;
+
+    // FIXME: We can standardize the behavior of those two, we could also keep the fast path of override ClipRect + full push on render only,
+    // which would be advantageous since most selectable are not selected.
+    if (span_all_columns && window->DC.CurrentColumns)
+        PushColumnsBackground();
+
     // We use NoHoldingActiveID on menus so user can click and _hold_ on a menu then drag to browse child entries
     ImGuiButtonFlags button_flags = 0;
     if (flags & ImGuiSelectableFlags_NoHoldingActiveID) { button_flags |= ImGuiButtonFlags_NoHoldingActiveId; }