Tables: sharing transient buffers between tables, reducing memory footprints. (#3740)

imgui.cpp

@@ -4204,7 +4204,9 @@ void ImGui::Shutdown(ImGuiContext* context)
     g.ShrinkWidthBuffer.clear();
 
     g.Tables.Clear();
-    g.CurrentTableStack.clear();
+    for (int i = 0; i < g.TablesTempDataStack.Size; i++)
+        g.TablesTempDataStack[i].~ImGuiTableTempData();
+    g.TablesTempDataStack.clear();
     g.DrawChannelsTempMergeBuffer.clear();
 
     g.ClipboardHandlerData.clear();

imgui_internal.h

@@ -130,10 +130,11 @@ struct ImGuiTabBar;                 // Storage for a tab bar
 struct ImGuiTabItem;                // Storage for a tab item (within a tab bar)
 struct ImGuiTable;                  // Storage for a table
 struct ImGuiTableColumn;            // Storage for one column of a table
+struct ImGuiTableTempData;          // Temporary storage for one table (one per table in the stack), shared between tables.
 struct ImGuiTableSettings;          // Storage for a table .ini settings
 struct ImGuiTableColumnsSettings;   // Storage for a column .ini settings
 struct ImGuiWindow;                 // Storage for one window
-struct ImGuiWindowTempData;         // Temporary storage for one window (that's the data which in theory we could ditch at the end of the frame)
+struct ImGuiWindowTempData;         // Temporary storage for one window (that's the data which in theory we could ditch at the end of the frame, in practice we currently keep it for each window)
 struct ImGuiWindowSettings;         // Storage for a window .ini settings (we keep one of those even if the actual window wasn't instanced during this session)
 
 // Use your programming IDE "Go to definition" facility on the names of the center columns to find the actual flags/enum lists.
@@ -1516,8 +1517,9 @@ struct ImGuiContext
 
     // Table
     ImGuiTable*                     CurrentTable;
+    int                             CurrentTableStackIdx;
     ImPool<ImGuiTable>              Tables;
-    ImVector<ImGuiPtrOrIndex>       CurrentTableStack;
+    ImVector<ImGuiTableTempData>    TablesTempDataStack;
     ImVector<float>                 TablesLastTimeActive;       // Last used timestamp of each tables (SOA, for efficient GC)
     ImVector<ImDrawChannel>         DrawChannelsTempMergeBuffer;
 
@@ -1694,6 +1696,7 @@ struct ImGuiContext
         memset(DragDropPayloadBufLocal, 0, sizeof(DragDropPayloadBufLocal));
 
         CurrentTable = NULL;
+        CurrentTableStackIdx = -1;
         CurrentTabBar = NULL;
 
         LastValidMousePos = ImVec2(0.0f, 0.0f);
@@ -2089,12 +2092,13 @@ struct ImGuiTableCellData
     ImGuiTableColumnIdx         Column;     // Column number
 };
 
-// FIXME-TABLE: transient data could be stored in a per-stacked table structure: DrawSplitter, SortSpecs, incoming RowData
+// FIXME-TABLE: more transient data could be stored in a per-stacked table structure: DrawSplitter, SortSpecs, incoming RowData
 struct ImGuiTable
 {
     ImGuiID                     ID;
     ImGuiTableFlags             Flags;
     void*                       RawData;                    // Single allocation to hold Columns[], DisplayOrderToIndex[] and RowCellData[]
+    ImGuiTableTempData*         TempData;                   // Transient data while table is active. Point within g.CurrentTableStack[]
     ImSpan<ImGuiTableColumn>    Columns;                    // Point within RawData[]
     ImSpan<ImGuiTableColumnIdx> DisplayOrderToIndex;        // Point within RawData[]. Store display order of columns (when not reordered, the values are 0...Count-1)
     ImSpan<ImGuiTableCellData>  RowCellData;                // Point within RawData[]. Store cells background requests for current row.
@@ -2146,22 +2150,13 @@ struct ImGuiTable
     ImRect                      Bg0ClipRectForDrawCmd;      // Actual ImDrawCmd clip rect for BG0/1 channel. This tends to be == OuterWindow->ClipRect at BeginTable() because output in BG0/BG1 is cpu-clipped
     ImRect                      Bg2ClipRectForDrawCmd;      // Actual ImDrawCmd clip rect for BG2 channel. This tends to be a correct, tight-fit, because output to BG2 are done by widgets relying on regular ClipRect.
     ImRect                      HostClipRect;               // This is used to check if we can eventually merge our columns draw calls into the current draw call of the current window.
-    ImRect                      HostBackupWorkRect;         // Backup of InnerWindow->WorkRect at the end of BeginTable()
-    ImRect                      HostBackupParentWorkRect;   // Backup of InnerWindow->ParentWorkRect at the end of BeginTable()
     ImRect                      HostBackupInnerClipRect;    // Backup of InnerWindow->ClipRect during PushTableBackground()/PopTableBackground()
-    ImVec2                      HostBackupPrevLineSize;     // Backup of InnerWindow->DC.PrevLineSize at the end of BeginTable()
-    ImVec2                      HostBackupCurrLineSize;     // Backup of InnerWindow->DC.CurrLineSize at the end of BeginTable()
-    ImVec2                      HostBackupCursorMaxPos;     // Backup of InnerWindow->DC.CursorMaxPos at the end of BeginTable()
-    ImVec2                      UserOuterSize;              // outer_size.x passed to BeginTable()
-    ImVec1                      HostBackupColumnsOffset;    // Backup of OuterWindow->DC.ColumnsOffset at the end of BeginTable()
-    float                       HostBackupItemWidth;        // Backup of OuterWindow->DC.ItemWidth at the end of BeginTable()
-    int                         HostBackupItemWidthStackSize;// Backup of OuterWindow->DC.ItemWidthStack.Size at the end of BeginTable()
     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 (FIXME: could be stored outside, worst case we need 1 splitter per recursing table)
+    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 work be good.
+    ImVector<ImGuiTableColumnSortSpecs> SortSpecsMulti;     // FIXME-OPT: Using a small-vector pattern would be good.
     ImGuiTableSortSpecs         SortSpecs;                  // Public facing sorts specs, this is what we return in TableGetSortSpecs()
     ImGuiTableColumnIdx         SortSpecsCount;
     ImGuiTableColumnIdx         ColumnsEnabledCount;        // Number of enabled columns (<= ColumnsCount)
@@ -2208,6 +2203,26 @@ 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?
+struct ImGuiTableTempData
+{
+    int                         TableIndex;                 // Index in g.Tables.Buf[] pool
+    ImVec2                      UserOuterSize;              // outer_size.x passed to BeginTable()
+
+    ImRect                      HostBackupWorkRect;         // Backup of InnerWindow->WorkRect at the end of BeginTable()
+    ImRect                      HostBackupParentWorkRect;   // Backup of InnerWindow->ParentWorkRect at the end of BeginTable()
+    ImVec2                      HostBackupPrevLineSize;     // Backup of InnerWindow->DC.PrevLineSize at the end of BeginTable()
+    ImVec2                      HostBackupCurrLineSize;     // Backup of InnerWindow->DC.CurrLineSize at the end of BeginTable()
+    ImVec2                      HostBackupCursorMaxPos;     // Backup of InnerWindow->DC.CursorMaxPos at the end of BeginTable()
+    ImVec1                      HostBackupColumnsOffset;    // Backup of OuterWindow->DC.ColumnsOffset at the end of BeginTable()
+    float                       HostBackupItemWidth;        // Backup of OuterWindow->DC.ItemWidth at the end of BeginTable()
+    int                         HostBackupItemWidthStackSize;//Backup of OuterWindow->DC.ItemWidthStack.Size at the end of BeginTable()
+
+    IMGUI_API ImGuiTableTempData() { memset(this, 0, sizeof(*this)); LastTimeActive = -1.0f; }
+};
+
 // sizeof() ~ 12
 struct ImGuiTableColumnSettings
 {

imgui_tables.cpp

@@ -343,6 +343,14 @@ bool    ImGui::BeginTableEx(const char* name, ImGuiID id, int columns_count, ImG
     if (instance_no > 0)
         IM_ASSERT(table->ColumnsCount == columns_count && "BeginTable(): Cannot change columns count mid-frame while preserving same ID");
 
+    // Acquire temporary buffers
+    const int table_idx = g.Tables.GetIndex(table);
+    g.CurrentTableStackIdx++;
+    if (g.CurrentTableStackIdx + 1 > g.TablesTempDataStack.Size)
+        g.TablesTempDataStack.resize(g.CurrentTableStackIdx + 1, ImGuiTableTempData());
+    ImGuiTableTempData* temp_data = table->TempData = &g.TablesTempDataStack[g.CurrentTableStackIdx];
+    temp_data->TableIndex = table_idx;
+
     // Fix flags
     table->IsDefaultSizingPolicy = (flags & ImGuiTableFlags_SizingMask_) == 0;
     flags = TableFixFlags(flags, outer_window);
@@ -356,7 +364,7 @@ bool    ImGui::BeginTableEx(const char* name, ImGuiID id, int columns_count, ImG
     table->ColumnsCount = columns_count;
     table->IsLayoutLocked = false;
     table->InnerWidth = inner_width;
-    table->UserOuterSize = outer_size;
+    temp_data->UserOuterSize = outer_size;
 
     // When not using a child window, WorkRect.Max will grow as we append contents.
     if (use_child_window)
@@ -405,14 +413,14 @@ bool    ImGui::BeginTableEx(const char* name, ImGuiID id, int columns_count, ImG
     table->HostIndentX = inner_window->DC.Indent.x;
     table->HostClipRect = inner_window->ClipRect;
     table->HostSkipItems = inner_window->SkipItems;
-    table->HostBackupWorkRect = inner_window->WorkRect;
-    table->HostBackupParentWorkRect = inner_window->ParentWorkRect;
-    table->HostBackupColumnsOffset = outer_window->DC.ColumnsOffset;
-    table->HostBackupPrevLineSize = inner_window->DC.PrevLineSize;
-    table->HostBackupCurrLineSize = inner_window->DC.CurrLineSize;
-    table->HostBackupCursorMaxPos = inner_window->DC.CursorMaxPos;
-    table->HostBackupItemWidth = outer_window->DC.ItemWidth;
-    table->HostBackupItemWidthStackSize = outer_window->DC.ItemWidthStack.Size;
+    temp_data->HostBackupWorkRect = inner_window->WorkRect;
+    temp_data->HostBackupParentWorkRect = inner_window->ParentWorkRect;
+    temp_data->HostBackupColumnsOffset = outer_window->DC.ColumnsOffset;
+    temp_data->HostBackupPrevLineSize = inner_window->DC.PrevLineSize;
+    temp_data->HostBackupCurrLineSize = inner_window->DC.CurrLineSize;
+    temp_data->HostBackupCursorMaxPos = inner_window->DC.CursorMaxPos;
+    temp_data->HostBackupItemWidth = outer_window->DC.ItemWidth;
+    temp_data->HostBackupItemWidthStackSize = outer_window->DC.ItemWidthStack.Size;
     inner_window->DC.PrevLineSize = inner_window->DC.CurrLineSize = ImVec2(0.0f, 0.0f);
 
     // Padding and Spacing
@@ -455,8 +463,6 @@ bool    ImGui::BeginTableEx(const char* name, ImGuiID id, int columns_count, ImG
     table->BorderColorLight = GetColorU32(ImGuiCol_TableBorderLight);
 
     // Make table current
-    const int table_idx = g.Tables.GetIndex(table);
-    g.CurrentTableStack.push_back(ImGuiPtrOrIndex(table_idx));
     g.CurrentTable = table;
     outer_window->DC.CurrentTableIdx = table_idx;
     if (inner_window != outer_window) // So EndChild() within the inner window can restore the table properly.
@@ -1205,6 +1211,7 @@ void    ImGui::EndTable()
     const ImGuiTableFlags flags = table->Flags;
     ImGuiWindow* inner_window = table->InnerWindow;
     ImGuiWindow* outer_window = table->OuterWindow;
+    ImGuiTableTempData* temp_data = table->TempData;
     IM_ASSERT(inner_window == g.CurrentWindow);
     IM_ASSERT(outer_window == inner_window || outer_window == inner_window->ParentWindow);
 
@@ -1217,9 +1224,9 @@ void    ImGui::EndTable()
             TableOpenContextMenu((int)table->HoveredColumnBody);
 
     // Finalize table height
-    inner_window->DC.PrevLineSize = table->HostBackupPrevLineSize;
-    inner_window->DC.CurrLineSize = table->HostBackupCurrLineSize;
-    inner_window->DC.CursorMaxPos = table->HostBackupCursorMaxPos;
+    inner_window->DC.PrevLineSize = temp_data->HostBackupPrevLineSize;
+    inner_window->DC.CurrLineSize = temp_data->HostBackupCurrLineSize;
+    inner_window->DC.CursorMaxPos = temp_data->HostBackupCursorMaxPos;
     const float inner_content_max_y = table->RowPosY2;
     IM_ASSERT(table->RowPosY2 == inner_window->DC.CursorPos.y);
     if (inner_window != outer_window)
@@ -1266,10 +1273,11 @@ void    ImGui::EndTable()
 #endif
 
     // Flatten channels and merge draw calls
-    table->DrawSplitter.SetCurrentChannel(inner_window->DrawList, 0);
+    ImDrawListSplitter* splitter = &table->DrawSplitter;
+    splitter->SetCurrentChannel(inner_window->DrawList, 0);
     if ((table->Flags & ImGuiTableFlags_NoClip) == 0)
         TableMergeDrawChannels(table);
-    table->DrawSplitter.Merge(inner_window->DrawList);
+    splitter->Merge(inner_window->DrawList);
 
     // Update ColumnsAutoFitWidth to get us ahead for host using our size to auto-resize without waiting for next BeginTable()
     const float width_spacings = (table->OuterPaddingX * 2.0f) + (table->CellSpacingX1 + table->CellSpacingX2) * (table->ColumnsEnabledCount - 1);
@@ -1311,18 +1319,18 @@ void    ImGui::EndTable()
 
     // Pop from id stack
     IM_ASSERT_USER_ERROR(inner_window->IDStack.back() == table->ID + table->InstanceCurrent, "Mismatching PushID/PopID!");
-    IM_ASSERT_USER_ERROR(outer_window->DC.ItemWidthStack.Size >= table->HostBackupItemWidthStackSize, "Too many PopItemWidth!");
+    IM_ASSERT_USER_ERROR(outer_window->DC.ItemWidthStack.Size >= temp_data->HostBackupItemWidthStackSize, "Too many PopItemWidth!");
     PopID();
 
     // Restore window data that we modified
     const ImVec2 backup_outer_max_pos = outer_window->DC.CursorMaxPos;
-    inner_window->WorkRect = table->HostBackupWorkRect;
-    inner_window->ParentWorkRect = table->HostBackupParentWorkRect;
+    inner_window->WorkRect = temp_data->HostBackupWorkRect;
+    inner_window->ParentWorkRect = temp_data->HostBackupParentWorkRect;
     inner_window->SkipItems = table->HostSkipItems;
     outer_window->DC.CursorPos = table->OuterRect.Min;
-    outer_window->DC.ItemWidth = table->HostBackupItemWidth;
-    outer_window->DC.ItemWidthStack.Size = table->HostBackupItemWidthStackSize;
-    outer_window->DC.ColumnsOffset = table->HostBackupColumnsOffset;
+    outer_window->DC.ItemWidth = temp_data->HostBackupItemWidth;
+    outer_window->DC.ItemWidthStack.Size = temp_data->HostBackupItemWidthStackSize;
+    outer_window->DC.ColumnsOffset = temp_data->HostBackupColumnsOffset;
 
     // Layout in outer window
     // (FIXME: To allow auto-fit and allow desirable effect of SameLine() we dissociate 'used' vs 'ideal' size by overriding
@@ -1345,20 +1353,20 @@ void    ImGui::EndTable()
         IM_ASSERT((table->Flags & ImGuiTableFlags_ScrollX) == 0);
         outer_window->DC.CursorMaxPos.x = ImMax(backup_outer_max_pos.x, table->OuterRect.Min.x + table->ColumnsAutoFitWidth);
     }
-    else if (table->UserOuterSize.x <= 0.0f)
+    else if (temp_data->UserOuterSize.x <= 0.0f)
     {
         const float decoration_size = (table->Flags & ImGuiTableFlags_ScrollX) ? inner_window->ScrollbarSizes.x : 0.0f;
-        outer_window->DC.IdealMaxPos.x = ImMax(outer_window->DC.IdealMaxPos.x, table->OuterRect.Min.x + table->ColumnsAutoFitWidth + decoration_size - table->UserOuterSize.x);
+        outer_window->DC.IdealMaxPos.x = ImMax(outer_window->DC.IdealMaxPos.x, table->OuterRect.Min.x + table->ColumnsAutoFitWidth + decoration_size - temp_data->UserOuterSize.x);
         outer_window->DC.CursorMaxPos.x = ImMax(backup_outer_max_pos.x, ImMin(table->OuterRect.Max.x, table->OuterRect.Min.x + table->ColumnsAutoFitWidth));
     }
     else
     {
         outer_window->DC.CursorMaxPos.x = ImMax(backup_outer_max_pos.x, table->OuterRect.Max.x);
     }
-    if (table->UserOuterSize.y <= 0.0f)
+    if (temp_data->UserOuterSize.y <= 0.0f)
     {
         const float decoration_size = (table->Flags & ImGuiTableFlags_ScrollY) ? inner_window->ScrollbarSizes.y : 0.0f;
-        outer_window->DC.IdealMaxPos.y = ImMax(outer_window->DC.IdealMaxPos.y, inner_content_max_y + decoration_size - table->UserOuterSize.y);
+        outer_window->DC.IdealMaxPos.y = ImMax(outer_window->DC.IdealMaxPos.y, inner_content_max_y + decoration_size - temp_data->UserOuterSize.y);
         outer_window->DC.CursorMaxPos.y = ImMax(backup_outer_max_pos.y, ImMin(table->OuterRect.Max.y, inner_content_max_y));
     }
     else
@@ -1374,8 +1382,12 @@ void    ImGui::EndTable()
 
     // Clear or restore current table, if any
     IM_ASSERT(g.CurrentWindow == outer_window && g.CurrentTable == table);
-    g.CurrentTableStack.pop_back();
-    g.CurrentTable = g.CurrentTableStack.Size ? g.Tables.GetByIndex(g.CurrentTableStack.back().Index) : NULL;
+    IM_ASSERT(g.CurrentTableStackIdx >= 0);
+    g.CurrentTableStackIdx--;
+    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;
     outer_window->DC.CurrentTableIdx = g.CurrentTable ? g.Tables.GetIndex(g.CurrentTable) : -1;
 }