Tables: fixed GetContentRegionAvail().y report not taking account of lower cell padding or of using ImGuiTableFlags_NoHostExtendY. (#6619)

Made GetContentRegionMax() fully defer to WorkRect when inside a table container.

docs/CHANGELOG.txt

@@ -64,6 +64,10 @@ Other changes:
 - InputText: Fixed a case where deactivation frame would write to underlying
   buffer or call CallbackResize although unnecessary, in a frame where the
   return value was false.
+- Tables: fixed GetContentRegionAvail().y report not taking account of lower cell
+  padding or of using ImGuiTableFlags_NoHostExtendY. Not taking it into account
+  would make the idiom of creating vertically bottom-aligned content (e.g. a child
+  window) inside a table make the parent window erroneously have a scrollbar. (#6619)
 - Tables: fixed calculation of multi-instance shared decoration/scrollbar width of
   scrolling tables, to avoid flickering width variation when resizing down a table
   hosting a child window. (#5920, #6619)

imgui.cpp

@@ -9774,9 +9774,7 @@ ImVec2 ImGui::GetContentRegionMax()
 {
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = g.CurrentWindow;
-    ImVec2 mx = window->ContentRegionRect.Max;
+    ImVec2 mx = (window->DC.CurrentColumns || g.CurrentTable) ? window->WorkRect.Max : window->ContentRegionRect.Max;
-    if (window->DC.CurrentColumns || g.CurrentTable)
-        mx.x = window->WorkRect.Max.x;
     return mx - window->Pos;
 }
 
@@ -9785,9 +9783,7 @@ ImVec2 ImGui::GetContentRegionMaxAbs()
 {
     ImGuiContext& g = *GImGui;
     ImGuiWindow* window = g.CurrentWindow;
-    ImVec2 mx = window->ContentRegionRect.Max;
+    ImVec2 mx = (window->DC.CurrentColumns || g.CurrentTable) ? window->WorkRect.Max : window->ContentRegionRect.Max;
-    if (window->DC.CurrentColumns || g.CurrentTable)
-        mx.x = window->WorkRect.Max.x;
     return mx;
 }
 

imgui_tables.cpp

@@ -1126,6 +1126,14 @@ void ImGui::TableUpdateLayout(ImGuiTable* table)
     table->BorderX1 = table->InnerClipRect.Min.x;// +((table->Flags & ImGuiTableFlags_BordersOuter) ? 0.0f : -1.0f);
     table->BorderX2 = table->InnerClipRect.Max.x;// +((table->Flags & ImGuiTableFlags_BordersOuter) ? 0.0f : +1.0f);
 
+    // Setup window's WorkRect.Max.y for GetContentRegionAvail(). Other values will be updated in each TableBeginCell() call.
+    float window_content_max_y;
+    if (table->Flags & ImGuiTableFlags_NoHostExtendY)
+        window_content_max_y = table->OuterRect.Max.y;
+    else
+        window_content_max_y = ImMax(table->InnerWindow->ContentRegionRect.Max.y, (table->Flags & ImGuiTableFlags_ScrollY) ? 0.0f : table->OuterRect.Max.y);
+    table->InnerWindow->WorkRect.Max.y = ImClamp(window_content_max_y - g.Style.CellPadding.y, table->InnerWindow->WorkRect.Min.y, table->InnerWindow->WorkRect.Max.y);
+
     // [Part 9] Allocate draw channels and setup background cliprect
     TableSetupDrawChannels(table);
 
@@ -2011,6 +2019,7 @@ void ImGui::TableBeginCell(ImGuiTable* table, int column_n)
     window->DC.CurrLineTextBaseOffset = table->RowTextBaseline;
     window->DC.NavLayerCurrent = (ImGuiNavLayer)column->NavLayerCurrent;
 
+    // Note how WorkRect.Max.y is only set once during layout
     window->WorkRect.Min.y = window->DC.CursorPos.y;
     window->WorkRect.Min.x = column->WorkMinX;
     window->WorkRect.Max.x = column->WorkMaxX;
@@ -3974,6 +3983,7 @@ void ImGui::BeginColumns(const char* str_id, int columns_count, ImGuiOldColumnFl
     window->DC.ColumnsOffset.x = ImMax(column_padding - window->WindowPadding.x, 0.0f);
     window->DC.CursorPos.x = IM_FLOOR(window->Pos.x + window->DC.Indent.x + window->DC.ColumnsOffset.x);
     window->WorkRect.Max.x = window->Pos.x + offset_1 - column_padding;
+    window->WorkRect.Max.y = window->ContentRegionRect.Max.y;
 }
 
 void ImGui::NextColumn()