Tables: sharing splitter and sort buffers between tables, reducing memory footprints. (#3740)

+ GC pass on that data.

docs/CHANGELOG.txt

@@ -50,6 +50,7 @@ Other Changes:
 - Nav: Fixed Tabbing initial activation from skipping the first item if it is tabbable through. (#787)
 - Tables: Expose TableSetColumnEnabled() in public api. (#3935)
 - Tables: Better preserve widths when columns count changes. (#4046)
+- Tables: Sharing more memory buffers between tables, reducing general memory footprints. (#3740)
 - TabBar: Fixed mouse reordering with very fast movements (e.g. crossing multiple tabs in a single
   frame and then immediately standling still (would only affect automation/bots). [@rokups]
 - Drags, Sliders, Inputs: Specifying a NULL format to Float functions default them to "%.3f" to be

imgui.cpp

@@ -4060,6 +4060,9 @@ void ImGui::NewFrame()
     for (int i = 0; i < g.TablesLastTimeActive.Size; i++)
         if (g.TablesLastTimeActive[i] >= 0.0f && g.TablesLastTimeActive[i] < memory_compact_start_time)
             TableGcCompactTransientBuffers(g.Tables.GetByIndex(i));
+    for (int i = 0; i < g.TablesTempDataStack.Size; i++)
+        if (g.TablesTempDataStack[i].LastTimeActive >= 0.0f && g.TablesTempDataStack[i].LastTimeActive < memory_compact_start_time)
+            TableGcCompactTransientBuffers(&g.TablesTempDataStack[i]);
     if (g.GcCompactAll)
         GcCompactTransientMiscBuffers();
     g.GcCompactAll = false;

imgui_internal.h

@@ -2154,9 +2154,7 @@ struct ImGuiTable
     ImGuiWindow*                OuterWindow;                // Parent window for the table
     ImGuiWindow*                InnerWindow;                // Window holding the table data (== OuterWindow or a child window)
     ImGuiTextBuffer             ColumnsNames;               // Contiguous buffer holding columns names
-    ImDrawListSplitter          DrawSplitter;               // We carry our own ImDrawList splitter to allow recursion (should move to ImGuiTableTempDataB)
-    ImGuiTableColumnSortSpecs   SortSpecsSingle;
-    ImVector<ImGuiTableColumnSortSpecs> SortSpecsMulti;     // FIXME-OPT: Using a small-vector pattern would be good.
+    ImDrawListSplitter*         DrawSplitter;               // Shortcut to TempData->DrawSplitter while in table. Isolate draw commands per columns to avoid switching clip rect constantly
     ImGuiTableSortSpecs         SortSpecs;                  // Public facing sorts specs, this is what we return in TableGetSortSpecs()
     ImGuiTableColumnIdx         SortSpecsCount;
     ImGuiTableColumnIdx         ColumnsEnabledCount;        // Number of enabled columns (<= ColumnsCount)
@@ -2203,13 +2201,19 @@ struct ImGuiTable
     IMGUI_API ~ImGuiTable()     { IM_FREE(RawData); }
 };
 
-// Transient data that are only needed between BeginTable() and EndTable(), those buffers are shared.
-// Accessing those requires chasing an extra pointer so for very frequently used data we leave them in the main table structure.
-// FIXME-TABLE: more transient data could be stored here: DrawSplitter (!), SortSpecs? incoming RowData?
+// Transient data that are only needed between BeginTable() and EndTable(), those buffers are shared (1 per level of stacked table).
+// - Accessing those requires chasing an extra pointer so for very frequently used data we leave them in the main table structure.
+// - We also leave out of this structure data that tend to be particularly useful for debugging/metrics.
+// FIXME-TABLE: more transient data could be stored here: DrawSplitter, incoming RowData?
 struct ImGuiTableTempData
 {
     int                         TableIndex;                 // Index in g.Tables.Buf[] pool
+    float                       LastTimeActive;             // Last timestamp this structure was used
+
     ImVec2                      UserOuterSize;              // outer_size.x passed to BeginTable()
+    ImDrawListSplitter          DrawSplitter;
+    ImGuiTableColumnSortSpecs   SortSpecsSingle;
+    ImVector<ImGuiTableColumnSortSpecs> SortSpecsMulti;     // FIXME-OPT: Using a small-vector pattern would be good.
 
     ImRect                      HostBackupWorkRect;         // Backup of InnerWindow->WorkRect at the end of BeginTable()
     ImRect                      HostBackupParentWorkRect;   // Backup of InnerWindow->ParentWorkRect at the end of BeginTable()
@@ -2485,6 +2489,7 @@ namespace ImGui
     IMGUI_API void          TableSetColumnWidthAutoAll(ImGuiTable* table);
     IMGUI_API void          TableRemove(ImGuiTable* table);
     IMGUI_API void          TableGcCompactTransientBuffers(ImGuiTable* table);
+    IMGUI_API void          TableGcCompactTransientBuffers(ImGuiTableTempData* table);
     IMGUI_API void          TableGcCompactSettings();
 
     // Tables: Settings

imgui_tables.cpp

@@ -350,6 +350,8 @@ bool    ImGui::BeginTableEx(const char* name, ImGuiID id, int columns_count, ImG
         g.TablesTempDataStack.resize(g.CurrentTableStackIdx + 1, ImGuiTableTempData());
     ImGuiTableTempData* temp_data = table->TempData = &g.TablesTempDataStack[g.CurrentTableStackIdx];
     temp_data->TableIndex = table_idx;
+    table->DrawSplitter = &table->TempData->DrawSplitter;
+    table->DrawSplitter->Clear();
 
     // Fix flags
     table->IsDefaultSizingPolicy = (flags & ImGuiTableFlags_SizingMask_) == 0;
@@ -475,6 +477,7 @@ bool    ImGui::BeginTableEx(const char* name, ImGuiID id, int columns_count, ImG
     if (table_idx >= g.TablesLastTimeActive.Size)
         g.TablesLastTimeActive.resize(table_idx + 1, -1.0f);
     g.TablesLastTimeActive[table_idx] = (float)g.Time;
+    temp_data->LastTimeActive = (float)g.Time;
     table->MemoryCompacted = false;
 
     // Setup memory buffer (clear data if columns count changed)
@@ -1123,7 +1126,7 @@ void ImGui::TableUpdateLayout(ImGuiTable* table)
     // Initial state
     ImGuiWindow* inner_window = table->InnerWindow;
     if (table->Flags & ImGuiTableFlags_NoClip)
-        table->DrawSplitter.SetCurrentChannel(inner_window->DrawList, TABLE_DRAW_CHANNEL_NOCLIP);
+        table->DrawSplitter->SetCurrentChannel(inner_window->DrawList, TABLE_DRAW_CHANNEL_NOCLIP);
     else
         inner_window->DrawList->PushClipRect(inner_window->ClipRect.Min, inner_window->ClipRect.Max, false);
 }
@@ -1273,7 +1276,7 @@ void    ImGui::EndTable()
 #endif
 
     // Flatten channels and merge draw calls
-    ImDrawListSplitter* splitter = &table->DrawSplitter;
+    ImDrawListSplitter* splitter = table->DrawSplitter;
     splitter->SetCurrentChannel(inner_window->DrawList, 0);
     if ((table->Flags & ImGuiTableFlags_NoClip) == 0)
         TableMergeDrawChannels(table);
@@ -1387,7 +1390,10 @@ void    ImGui::EndTable()
     temp_data = g.CurrentTableStackIdx >= 0 ? &g.TablesTempDataStack[g.CurrentTableStackIdx] : NULL;
     g.CurrentTable = temp_data ? g.Tables.GetByIndex(temp_data->TableIndex) : NULL;
     if (g.CurrentTable)
+    {
         g.CurrentTable->TempData = temp_data;
+        g.CurrentTable->DrawSplitter = &temp_data->DrawSplitter;
+    }
     outer_window->DC.CurrentTableIdx = g.CurrentTable ? g.Tables.GetIndex(g.CurrentTable) : -1;
 }
 
@@ -1760,7 +1766,7 @@ void ImGui::TableEndRow(ImGuiTable* table)
             // always followed by a change of clipping rectangle we perform the smallest overwrite possible here.
             if ((table->Flags & ImGuiTableFlags_NoClip) == 0)
                 window->DrawList->_CmdHeader.ClipRect = table->Bg0ClipRectForDrawCmd.ToVec4();
-            table->DrawSplitter.SetCurrentChannel(window->DrawList, TABLE_DRAW_CHANNEL_BG0);
+            table->DrawSplitter->SetCurrentChannel(window->DrawList, TABLE_DRAW_CHANNEL_BG0);
         }
 
         // Draw row background
@@ -1832,7 +1838,7 @@ void ImGui::TableEndRow(ImGuiTable* table)
 
         // Update cliprect ahead of TableBeginCell() so clipper can access to new ClipRect->Min.y
         SetWindowClipRectBeforeSetChannel(window, table->Columns[0].ClipRect);
-        table->DrawSplitter.SetCurrentChannel(window->DrawList, table->Columns[0].DrawChannelCurrent);
+        table->DrawSplitter->SetCurrentChannel(window->DrawList, table->Columns[0].DrawChannelCurrent);
     }
 
     if (!(table->RowFlags & ImGuiTableRowFlags_Headers))
@@ -1947,14 +1953,14 @@ void ImGui::TableBeginCell(ImGuiTable* table, int column_n)
     if (table->Flags & ImGuiTableFlags_NoClip)
     {
         // FIXME: if we end up drawing all borders/bg in EndTable, could remove this and just assert that channel hasn't changed.
-        table->DrawSplitter.SetCurrentChannel(window->DrawList, TABLE_DRAW_CHANNEL_NOCLIP);
+        table->DrawSplitter->SetCurrentChannel(window->DrawList, TABLE_DRAW_CHANNEL_NOCLIP);
         //IM_ASSERT(table->DrawSplitter._Current == TABLE_DRAW_CHANNEL_NOCLIP);
     }
     else
     {
         // FIXME-TABLE: Could avoid this if draw channel is dummy channel?
         SetWindowClipRectBeforeSetChannel(window, column->ClipRect);
-        table->DrawSplitter.SetCurrentChannel(window->DrawList, column->DrawChannelCurrent);
+        table->DrawSplitter->SetCurrentChannel(window->DrawList, column->DrawChannelCurrent);
     }
 
     // Logging
@@ -2202,7 +2208,7 @@ void ImGui::TablePushBackgroundChannel()
     // Optimization: avoid SetCurrentChannel() + PushClipRect()
     table->HostBackupInnerClipRect = window->ClipRect;
     SetWindowClipRectBeforeSetChannel(window, table->Bg2ClipRectForDrawCmd);
-    table->DrawSplitter.SetCurrentChannel(window->DrawList, table->Bg2DrawChannelCurrent);
+    table->DrawSplitter->SetCurrentChannel(window->DrawList, table->Bg2DrawChannelCurrent);
 }
 
 void ImGui::TablePopBackgroundChannel()
@@ -2214,7 +2220,7 @@ void ImGui::TablePopBackgroundChannel()
 
     // Optimization: avoid PopClipRect() + SetCurrentChannel()
     SetWindowClipRectBeforeSetChannel(window, table->HostBackupInnerClipRect);
-    table->DrawSplitter.SetCurrentChannel(window->DrawList, column->DrawChannelCurrent);
+    table->DrawSplitter->SetCurrentChannel(window->DrawList, column->DrawChannelCurrent);
 }
 
 // Allocate draw channels. Called by TableUpdateLayout()
@@ -2240,7 +2246,7 @@ void ImGui::TableSetupDrawChannels(ImGuiTable* table)
     const int channels_for_bg = 1 + 1 * freeze_row_multiplier;
     const int channels_for_dummy = (table->ColumnsEnabledCount < table->ColumnsCount || table->VisibleMaskByIndex != table->EnabledMaskByIndex) ? +1 : 0;
     const int channels_total = channels_for_bg + (channels_for_row * freeze_row_multiplier) + channels_for_dummy;
-    table->DrawSplitter.Split(table->InnerWindow->DrawList, channels_total);
+    table->DrawSplitter->Split(table->InnerWindow->DrawList, channels_total);
     table->DummyDrawChannel = (ImGuiTableDrawChannelIdx)((channels_for_dummy > 0) ? channels_total - 1 : -1);
     table->Bg2DrawChannelCurrent = TABLE_DRAW_CHANNEL_BG2_FROZEN;
     table->Bg2DrawChannelUnfrozen = (ImGuiTableDrawChannelIdx)((table->FreezeRowsCount > 0) ? 2 + channels_for_row : TABLE_DRAW_CHANNEL_BG2_FROZEN);
@@ -2304,7 +2310,7 @@ void ImGui::TableSetupDrawChannels(ImGuiTable* table)
 void ImGui::TableMergeDrawChannels(ImGuiTable* table)
 {
     ImGuiContext& g = *GImGui;
-    ImDrawListSplitter* splitter = &table->DrawSplitter;
+    ImDrawListSplitter* splitter = table->DrawSplitter;
     const bool has_freeze_v = (table->FreezeRowsCount > 0);
     const bool has_freeze_h = (table->FreezeColumnsCount > 0);
     IM_ASSERT(splitter->_Current == 0);
@@ -2475,7 +2481,7 @@ void ImGui::TableDrawBorders(ImGuiTable* table)
         return;
 
     ImDrawList* inner_drawlist = inner_window->DrawList;
-    table->DrawSplitter.SetCurrentChannel(inner_drawlist, TABLE_DRAW_CHANNEL_BG0);
+    table->DrawSplitter->SetCurrentChannel(inner_drawlist, TABLE_DRAW_CHANNEL_BG0);
     inner_drawlist->PushClipRect(table->Bg0ClipRectForDrawCmd.Min, table->Bg0ClipRectForDrawCmd.Max, false);
 
     // Draw inner border and resizing feedback
@@ -2735,8 +2741,9 @@ void ImGui::TableSortSpecsBuild(ImGuiTable* table)
     TableSortSpecsSanitize(table);
 
     // Write output
-    table->SortSpecsMulti.resize(table->SortSpecsCount <= 1 ? 0 : table->SortSpecsCount);
-    ImGuiTableColumnSortSpecs* sort_specs = (table->SortSpecsCount == 0) ? NULL : (table->SortSpecsCount == 1) ? &table->SortSpecsSingle : table->SortSpecsMulti.Data;
+    ImGuiTableTempData* temp_data = table->TempData;
+    temp_data->SortSpecsMulti.resize(table->SortSpecsCount <= 1 ? 0 : table->SortSpecsCount);
+    ImGuiTableColumnSortSpecs* sort_specs = (table->SortSpecsCount == 0) ? NULL : (table->SortSpecsCount == 1) ? &temp_data->SortSpecsSingle : temp_data->SortSpecsMulti.Data;
     if (sort_specs != NULL)
         for (int column_n = 0; column_n < table->ColumnsCount; column_n++)
         {
@@ -3434,8 +3441,6 @@ void ImGui::TableGcCompactTransientBuffers(ImGuiTable* table)
     //IMGUI_DEBUG_LOG("TableGcCompactTransientBuffers() id=0x%08X\n", table->ID);
     ImGuiContext& g = *GImGui;
     IM_ASSERT(table->MemoryCompacted == false);
-    table->DrawSplitter.ClearFreeMemory();
-    table->SortSpecsMulti.clear();
     table->SortSpecs.Specs = NULL;
     table->IsSortSpecsDirty = true;
     table->ColumnsNames.clear();
@@ -3445,6 +3450,13 @@ void ImGui::TableGcCompactTransientBuffers(ImGuiTable* table)
     g.TablesLastTimeActive[g.Tables.GetIndex(table)] = -1.0f;
 }
 
+void ImGui::TableGcCompactTransientBuffers(ImGuiTableTempData* temp_data)
+{
+    temp_data->DrawSplitter.ClearFreeMemory();
+    temp_data->SortSpecsMulti.clear();
+    temp_data->LastTimeActive = -1.0f;
+}
+
 // Compact and remove unused settings data (currently only used by TestEngine)
 void ImGui::TableGcCompactSettings()
 {