Tables: moved + renamed TableSetupDrawChannels(), TableMergeDrawChannels() to their own section.

ago%!(EXTRA string=5 years) · 5180025de5
parent b7c83e4bac
commit 5180025de5
2 changed files with 257 additions and 247 deletions
--- a/imgui_internal.h
+++ b/imgui_internal.h
@ -2283,12 +2283,12 @@ namespace ImGui
    IMGUI_API ImGuiTable*   TableFindByID(ImGuiID id);
    IMGUI_API bool          BeginTableEx(const char* name, ImGuiID id, int columns_count, ImGuiTableFlags flags = 0, const ImVec2& outer_size = ImVec2(0, 0), float inner_width = 0.0f);
    IMGUI_API void          TableBeginApplyRequests(ImGuiTable* table);
-    IMGUI_API void          TableUpdateDrawChannels(ImGuiTable* table);
+    IMGUI_API void          TableSetupDrawChannels(ImGuiTable* table);
    IMGUI_API void          TableUpdateLayout(ImGuiTable* table);
    IMGUI_API void          TableUpdateBorders(ImGuiTable* table);
    IMGUI_API void          TableDrawBorders(ImGuiTable* table);
    IMGUI_API void          TableDrawContextMenu(ImGuiTable* table);
-    IMGUI_API void          TableReorderDrawChannelsForMerge(ImGuiTable* table);
+    IMGUI_API void          TableMergeDrawChannels(ImGuiTable* table);
    IMGUI_API void          TableSortSpecsSanitize(ImGuiTable* table);
    IMGUI_API void          TableSortSpecsBuild(ImGuiTable* table);
    IMGUI_API void          TableFixColumnSortDirection(ImGuiTableColumn* column);
--- a/imgui_tables.cpp
+++ b/imgui_tables.cpp
@ -6,6 +6,7 @@
 Index of this file:
 // [SECTION] Tables: BeginTable, EndTable, etc.
 // [SECTION] Tables: Drawing
 // [SECTION] Tables: Sorting
 // [SECTION] Tables: Headers
 // [SECTION] Tables: Context Menu
@ -81,7 +82,7 @@ Index of this file:
 // - TableSetupColumn()                         user submit columns details (optional)
 // - TableSetupScrollFreeze()                   user submit scroll freeze information (optional)
 // - TableUpdateLayout() [Internal]             automatically called by the FIRST call to TableNextRow() or TableHeadersRow(): lock all widths, columns positions, clipping rectangles
-//    | TableUpdateDrawChannels()               - setup ImDrawList channels
+//    | TableSetupDrawChannels()                - setup ImDrawList channels
 //    | TableUpdateBorders()                    - detect hovering columns for resize, ahead of contents submission
 //    | TableDrawContextMenu()                  - draw right-click context menu
 //-----------------------------------------------------------------------------
@ -99,7 +100,7 @@ Index of this file:
 //-----------------------------------------------------------------------------
 // - EndTable()                                 user ends the table
 //    | TableDrawBorders()                      - draw outer borders, inner vertical borders
-//    | TableReorderDrawChannelsForMerge()      - merge draw channels if clipping isn't required
+//    | TableMergeDrawChannels()                - merge draw channels if clipping isn't required
 //    | EndChild()                              - (if ScrollX/ScrollY is set)
 //-----------------------------------------------------------------------------
@ -938,7 +939,7 @@ void    ImGui::TableUpdateLayout(ImGuiTable* table)
        table->Flags &= ~ImGuiTableFlags_Resizable;
    // Allocate draw channels
-    TableUpdateDrawChannels(table);
+    TableSetupDrawChannels(table);
    // Borders
    if (table->Flags & ImGuiTableFlags_Resizable)
@ -1111,7 +1112,7 @@ void    ImGui::EndTable()
    // Flatten channels and merge draw calls
    if ((table->Flags & ImGuiTableFlags_NoClip) == 0)
-        TableReorderDrawChannelsForMerge(table);
+        TableMergeDrawChannels(table);
    table->DrawSplitter.Merge(inner_window->DrawList);
    if (!(table->Flags & ImGuiTableFlags_ScrollX) && inner_window != outer_window)
@ -1394,247 +1395,6 @@ void ImGui::TableSetColumnWidth(int column_n, float width)
    }
 }
 // Allocate draw channels. Called by TableUpdateLayout()
 // - We allocate them following storage order instead of display order so reordering columns won't needlessly
 //   increase overall dormant memory cost.
 // - We isolate headers draw commands in their own channels instead of just altering clip rects.
 //   This is in order to facilitate merging of draw commands.
 // - After crossing FreezeRowsCount, all columns see their current draw channel changed to a second set of channels.
 // - We only use the dummy draw channel so we can push a null clipping rectangle into it without affecting other
 //   channels, while simplifying per-row/per-cell overhead. It will be empty and discarded when merged.
 // - We allocate 1 or 2 background draw channels. This is because we know PushTableBackground() is only used for
 //   horizontal spanning. If we allowed vertical spanning we'd need one background draw channel per merge group (1-4).
 // Draw channel allocation (before merging):
 // - NoClip                       --> 2+D+1 channels: bg0 + bg1 + foreground (same clip rect == 1 draw call) (FIXME-TABLE: could merge bg1 and foreground?)
 // - Clip                         --> 2+D+N channels
 // - FreezeRows                   --> 2+D+N*2 (unless scrolling value is zero)
 // - FreezeRows || FreezeColunns  --> 3+D+N*2 (unless scrolling value is zero)
 // Where D is 1 if any column is clipped or hidden (dummy channel) otherwise 0.
 void ImGui::TableUpdateDrawChannels(ImGuiTable* table)
 {
    const int freeze_row_multiplier = (table->FreezeRowsCount > 0) ? 2 : 1;
    const int channels_for_row = (table->Flags & ImGuiTableFlags_NoClip) ? 1 : table->ColumnsEnabledCount;
    const int channels_for_bg = 1 + 1 * freeze_row_multiplier;
    const int channels_for_dummy = (table->ColumnsEnabledCount < table->ColumnsCount || table->EnabledUnclippedMaskByIndex != 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->DummyDrawChannel = (ImU8)((channels_for_dummy > 0) ? channels_total - 1 : -1);
    table->Bg1DrawChannelCurrent = TABLE_DRAW_CHANNEL_BG1_FROZEN;
    table->Bg1DrawChannelUnfrozen = (ImU8)((table->FreezeRowsCount > 0) ? 2 + channels_for_row : TABLE_DRAW_CHANNEL_BG1_FROZEN);
    int draw_channel_current = 2;
    for (int column_n = 0; column_n < table->ColumnsCount; column_n++)
    {
        ImGuiTableColumn* column = &table->Columns[column_n];
        if (!column->IsClipped)
        {
            column->DrawChannelFrozen = (ImU8)(draw_channel_current);
            column->DrawChannelUnfrozen = (ImU8)(draw_channel_current + (table->FreezeRowsCount > 0 ? channels_for_row + 1 : 0));
            if (!(table->Flags & ImGuiTableFlags_NoClip))
                draw_channel_current++;
        }
        else
        {
            column->DrawChannelFrozen = column->DrawChannelUnfrozen = table->DummyDrawChannel;
        }
        column->DrawChannelCurrent = column->DrawChannelFrozen;
    }
 }
 // This function reorder draw channels based on matching clip rectangle, to facilitate merging them. Called by EndTable().
 //
 // Columns where the contents didn't stray off their local clip rectangle can be merged. To achieve
 // this we merge their clip rect and make them contiguous in the channel list, so they can be merged
 // by the call to DrawSplitter.Merge() following to the call to this function.
 //
 // We reorder draw commands by arranging them into a maximum of 4 distinct groups:
 //
 //   1 group:               2 groups:              2 groups:              4 groups:
 //   [ 0. ] no freeze       [ 0. ] row freeze      [ 01 ] col freeze      [ 01 ] row+col freeze
 //   [ .. ]  or no scroll   [ 2. ]  and v-scroll   [ .. ]  and h-scroll   [ 23 ]  and v+h-scroll
 //
 // Each column itself can use 1 channel (row freeze disabled) or 2 channels (row freeze enabled).
 // When the contents of a column didn't stray off its limit, we move its channels into the corresponding group
 // based on its position (within frozen rows/columns groups or not).
 // At the end of the operation our 1-4 groups will each have a ImDrawCmd using the same ClipRect.
 //
 // This function assume that each column are pointing to a distinct draw channel,
 // otherwise merge_group->ChannelsCount will not match set bit count of merge_group->ChannelsMask.
 //
 // Column channels will not be merged into one of the 1-4 groups in the following cases:
 // - The contents stray off its clipping rectangle (we only compare the MaxX value, not the MinX value).
 //   Direct ImDrawList calls won't be taken into account by default, if you use them make sure the ImGui:: bounds
 //   matches, by e.g. calling SetCursorScreenPos().
 // - The channel uses more than one draw command itself. We drop all our attempt at merging stuff here..
 //   we could do better but it's going to be rare and probably not worth the hassle.
 // Columns for which the draw channel(s) haven't been merged with other will use their own ImDrawCmd.
 //
 // This function is particularly tricky to understand.. take a breath.
 void    ImGui::TableReorderDrawChannelsForMerge(ImGuiTable* table)
 {
    ImGuiContext& g = *GImGui;
    ImDrawListSplitter* splitter = &table->DrawSplitter;
    const bool has_freeze_v = (table->FreezeRowsCount > 0);
    const bool has_freeze_h = (table->FreezeColumnsCount > 0);
    // Track which groups we are going to attempt to merge, and which channels goes into each group.
    struct MergeGroup
    {
        ImRect  ClipRect;
        int     ChannelsCount;
        ImBitArray<IMGUI_TABLE_MAX_DRAW_CHANNELS> ChannelsMask;
    };
    int merge_group_mask = 0x00;
    MergeGroup merge_groups[4];
    memset(merge_groups, 0, sizeof(merge_groups));
    // 1. Scan channels and take note of those which can be merged
    for (int column_n = 0; column_n < table->ColumnsCount; column_n++)
    {
        if (!(table->EnabledUnclippedMaskByIndex & ((ImU64)1 << column_n)))
            continue;
        ImGuiTableColumn* column = &table->Columns[column_n];
        const int merge_group_sub_count = has_freeze_v ? 2 : 1;
        for (int merge_group_sub_n = 0; merge_group_sub_n < merge_group_sub_count; merge_group_sub_n++)
        {
            const int channel_no = (merge_group_sub_n == 0) ? column->DrawChannelFrozen : column->DrawChannelUnfrozen;
            // Don't attempt to merge if there are multiple draw calls within the column
            ImDrawChannel* src_channel = &splitter->_Channels[channel_no];
            if (src_channel->_CmdBuffer.Size > 0 && src_channel->_CmdBuffer.back().ElemCount == 0)
                src_channel->_CmdBuffer.pop_back();
            if (src_channel->_CmdBuffer.Size != 1)
                continue;
            // Find out the width of this merge group and check if it will fit in our column
            // (note that we assume that rendering didn't stray on the left direction. we should need a CursorMinPos to detect it)
            if (!(column->Flags & ImGuiTableColumnFlags_NoClip))
            {
                float content_max_x;
                if (!has_freeze_v)
                    content_max_x = ImMax(column->ContentMaxXUnfrozen, column->ContentMaxXHeadersUsed); // No row freeze
                else if (merge_group_sub_n == 0)
                    content_max_x = ImMax(column->ContentMaxXFrozen, column->ContentMaxXHeadersUsed);   // Row freeze: use width before freeze
                else
                    content_max_x = column->ContentMaxXUnfrozen;                                        // Row freeze: use width after freeze
                if (content_max_x > column->ClipRect.Max.x)
                    continue;
            }
            const int merge_group_n = (has_freeze_h && column_n < table->FreezeColumnsCount ? 0 : 1) + (has_freeze_v && merge_group_sub_n == 0 ? 0 : 2);
            IM_ASSERT(channel_no < IMGUI_TABLE_MAX_DRAW_CHANNELS);
            MergeGroup* merge_group = &merge_groups[merge_group_n];
            if (merge_group->ChannelsCount == 0)
                merge_group->ClipRect = ImRect(+FLT_MAX, +FLT_MAX, -FLT_MAX, -FLT_MAX);
            merge_group->ChannelsMask.SetBit(channel_no);
            merge_group->ChannelsCount++;
            merge_group->ClipRect.Add(src_channel->_CmdBuffer[0].ClipRect);
            merge_group_mask |= (1 << merge_group_n);
        }
        // Invalidate current draw channel
        // (we don't clear DrawChannelFrozen/DrawChannelUnfrozen solely to facilitate debugging/later inspection of data)
        column->DrawChannelCurrent = (ImU8)-1;
    }
    // [DEBUG] Display merge groups
 #if 0
    if (g.IO.KeyShift)
        for (int merge_group_n = 0; merge_group_n < IM_ARRAYSIZE(merge_groups); merge_group_n++)
        {
            MergeGroup* merge_group = &merge_groups[merge_group_n];
            if (merge_group->ChannelsCount == 0)
                continue;
            char buf[32];
            ImFormatString(buf, 32, "MG%d:%d", merge_group_n, merge_group->ChannelsCount);
            ImVec2 text_pos = merge_group->ClipRect.Min + ImVec2(4, 4);
            ImVec2 text_size = CalcTextSize(buf, NULL);
            GetForegroundDrawList()->AddRectFilled(text_pos, text_pos + text_size, IM_COL32(0, 0, 0, 255));
            GetForegroundDrawList()->AddText(text_pos, IM_COL32(255, 255, 0, 255), buf, NULL);
            GetForegroundDrawList()->AddRect(merge_group->ClipRect.Min, merge_group->ClipRect.Max, IM_COL32(255, 255, 0, 255));
        }
 #endif
    // 2. Rewrite channel list in our preferred order
    if (merge_group_mask != 0)
    {
        // We skip channel 0 (Bg0) and 1 (Bg1 frozen) from the shuffling since they won't move - see channels allocation in TableUpdateDrawChannels().
        const int LEADING_DRAW_CHANNELS = 2;
        g.DrawChannelsTempMergeBuffer.resize(splitter->_Count - LEADING_DRAW_CHANNELS); // Use shared temporary storage so the allocation gets amortized
        ImDrawChannel* dst_tmp = g.DrawChannelsTempMergeBuffer.Data;
        ImBitArray<IMGUI_TABLE_MAX_DRAW_CHANNELS> remaining_mask;                       // We need 132-bit of storage
        remaining_mask.ClearBits();
        remaining_mask.SetBitRange(LEADING_DRAW_CHANNELS, splitter->_Count - 1);
        remaining_mask.ClearBit(table->Bg1DrawChannelUnfrozen);
        IM_ASSERT(has_freeze_v == false || table->Bg1DrawChannelUnfrozen != TABLE_DRAW_CHANNEL_BG1_FROZEN);
        int remaining_count = splitter->_Count - (has_freeze_v ? LEADING_DRAW_CHANNELS + 1 : LEADING_DRAW_CHANNELS);
        //ImRect host_rect = (table->InnerWindow == table->OuterWindow) ? table->InnerClipRect : table->HostClipRect;
        ImRect host_rect = table->HostClipRect;
        for (int merge_group_n = 0; merge_group_n < IM_ARRAYSIZE(merge_groups); merge_group_n++)
        {
            if (int merge_channels_count = merge_groups[merge_group_n].ChannelsCount)
            {
                MergeGroup* merge_group = &merge_groups[merge_group_n];
                ImRect merge_clip_rect = merge_group->ClipRect;
                // Extend outer-most clip limits to match those of host, so draw calls can be merged even if
                // outer-most columns have some outer padding offsetting them from their parent ClipRect.
                // The principal cases this is dealing with are:
                // - On a same-window table (not scrolling = single group), all fitting columns ClipRect -> will extend and match host ClipRect -> will merge
                // - Columns can use padding and have left-most ClipRect.Min.x and right-most ClipRect.Max.x != from host ClipRect -> will extend and match host ClipRect -> will merge
                // FIXME-TABLE FIXME-WORKRECT: We are wasting a merge opportunity on tables without scrolling if column doesn't fit
                // within host clip rect, solely because of the half-padding difference between window->WorkRect and window->InnerClipRect.
                if ((merge_group_n & 1) == 0 || !has_freeze_h)
                    merge_clip_rect.Min.x = ImMin(merge_clip_rect.Min.x, host_rect.Min.x);
                if ((merge_group_n & 2) == 0 || !has_freeze_v)
                    merge_clip_rect.Min.y = ImMin(merge_clip_rect.Min.y, host_rect.Min.y);
                if ((merge_group_n & 1) != 0)
                    merge_clip_rect.Max.x = ImMax(merge_clip_rect.Max.x, host_rect.Max.x);
                if ((merge_group_n & 2) != 0 && (table->Flags & ImGuiTableFlags_NoHostExtendY) == 0)
                    merge_clip_rect.Max.y = ImMax(merge_clip_rect.Max.y, host_rect.Max.y);
 #if 0
                GetOverlayDrawList()->AddRect(merge_group->ClipRect.Min, merge_group->ClipRect.Max, IM_COL32(255, 0, 0, 200), 0.0f, ~0, 1.0f);
                GetOverlayDrawList()->AddLine(merge_group->ClipRect.Min, merge_clip_rect.Min, IM_COL32(255, 100, 0, 200));
                GetOverlayDrawList()->AddLine(merge_group->ClipRect.Max, merge_clip_rect.Max, IM_COL32(255, 100, 0, 200));
 #endif
                remaining_count -= merge_group->ChannelsCount;
                for (int n = 0; n < IM_ARRAYSIZE(remaining_mask.Storage); n++)
                    remaining_mask.Storage[n] &= ~merge_group->ChannelsMask.Storage[n];
                for (int n = 0; n < splitter->_Count && merge_channels_count != 0; n++)
                {
                    // Copy + overwrite new clip rect
                    if (!merge_group->ChannelsMask.TestBit(n))
                        continue;
                    merge_group->ChannelsMask.ClearBit(n);
                    merge_channels_count--;
                    ImDrawChannel* channel = &splitter->_Channels[n];
                    IM_ASSERT(channel->_CmdBuffer.Size == 1 && merge_clip_rect.Contains(ImRect(channel->_CmdBuffer[0].ClipRect)));
                    channel->_CmdBuffer[0].ClipRect = merge_clip_rect.ToVec4();
                    memcpy(dst_tmp++, channel, sizeof(ImDrawChannel));
                }
            }
            // Make sure Bg1DrawChannelUnfrozen appears in the middle of our groups (whereas Bg0 and Bg1 frozen are fixed to 0 and 1)
            if (merge_group_n == 1 && has_freeze_v)
                memcpy(dst_tmp++, &splitter->_Channels[table->Bg1DrawChannelUnfrozen], sizeof(ImDrawChannel));
        }
        // Append unmergeable channels that we didn't reorder at the end of the list
        for (int n = 0; n < splitter->_Count && remaining_count != 0; n++)
        {
            if (!remaining_mask.TestBit(n))
                continue;
            ImDrawChannel* channel = &splitter->_Channels[n];
            memcpy(dst_tmp++, channel, sizeof(ImDrawChannel));
            remaining_count--;
        }
        IM_ASSERT(dst_tmp == g.DrawChannelsTempMergeBuffer.Data + g.DrawChannelsTempMergeBuffer.Size);
        memcpy(splitter->_Channels.Data + LEADING_DRAW_CHANNELS, g.DrawChannelsTempMergeBuffer.Data, (splitter->_Count - LEADING_DRAW_CHANNELS) * sizeof(ImDrawChannel));
    }
 }
 // We use a default parameter of 'init_width_or_weight == -1',
 // - with ImGuiTableColumnFlags_WidthFixed,    width  <= 0 --> init width == auto
 // - with ImGuiTableColumnFlags_WidthFixed,    width  >  0 --> init width == manual
@ -2212,6 +1972,256 @@ void ImGui::TableSetBgColor(ImGuiTableBgTarget bg_target, ImU32 color, int colum
    }
 }
 //-------------------------------------------------------------------------
 // [SECTION] Tables: Drawing
 //-------------------------------------------------------------------------
 // - TablePushBackgroundChannel() [Internal]
 // - TablePopBackgroundChannel() [Internal]
 // - TableSetupDrawChannels() [Internal]
 // - TableReorderDrawChannelsForMerge() [Internal]
 //-------------------------------------------------------------------------
 // Allocate draw channels. Called by TableUpdateLayout()
 // - We allocate them following storage order instead of display order so reordering columns won't needlessly
 //   increase overall dormant memory cost.
 // - We isolate headers draw commands in their own channels instead of just altering clip rects.
 //   This is in order to facilitate merging of draw commands.
 // - After crossing FreezeRowsCount, all columns see their current draw channel changed to a second set of channels.
 // - We only use the dummy draw channel so we can push a null clipping rectangle into it without affecting other
 //   channels, while simplifying per-row/per-cell overhead. It will be empty and discarded when merged.
 // - We allocate 1 or 2 background draw channels. This is because we know PushTableBackground() is only used for
 //   horizontal spanning. If we allowed vertical spanning we'd need one background draw channel per merge group (1-4).
 // Draw channel allocation (before merging):
 // - NoClip                       --> 2+D+1 channels: bg0 + bg1 + foreground (same clip rect == 1 draw call) (FIXME-TABLE: could merge bg1 and foreground?)
 // - Clip                         --> 2+D+N channels
 // - FreezeRows                   --> 2+D+N*2 (unless scrolling value is zero)
 // - FreezeRows || FreezeColunns  --> 3+D+N*2 (unless scrolling value is zero)
 // Where D is 1 if any column is clipped or hidden (dummy channel) otherwise 0.
 void ImGui::TableSetupDrawChannels(ImGuiTable* table)
 {
    const int freeze_row_multiplier = (table->FreezeRowsCount > 0) ? 2 : 1;
    const int channels_for_row = (table->Flags & ImGuiTableFlags_NoClip) ? 1 : table->ColumnsEnabledCount;
    const int channels_for_bg = 1 + 1 * freeze_row_multiplier;
    const int channels_for_dummy = (table->ColumnsEnabledCount < table->ColumnsCount || table->EnabledUnclippedMaskByIndex != 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->DummyDrawChannel = (ImU8)((channels_for_dummy > 0) ? channels_total - 1 : -1);
    table->Bg1DrawChannelCurrent = TABLE_DRAW_CHANNEL_BG1_FROZEN;
    table->Bg1DrawChannelUnfrozen = (ImU8)((table->FreezeRowsCount > 0) ? 2 + channels_for_row : TABLE_DRAW_CHANNEL_BG1_FROZEN);
    int draw_channel_current = 2;
    for (int column_n = 0; column_n < table->ColumnsCount; column_n++)
    {
        ImGuiTableColumn* column = &table->Columns[column_n];
        if (!column->IsClipped)
        {
            column->DrawChannelFrozen = (ImU8)(draw_channel_current);
            column->DrawChannelUnfrozen = (ImU8)(draw_channel_current + (table->FreezeRowsCount > 0 ? channels_for_row + 1 : 0));
            if (!(table->Flags & ImGuiTableFlags_NoClip))
                draw_channel_current++;
        }
        else
        {
            column->DrawChannelFrozen = column->DrawChannelUnfrozen = table->DummyDrawChannel;
        }
        column->DrawChannelCurrent = column->DrawChannelFrozen;
    }
 }
 // This function reorder draw channels based on matching clip rectangle, to facilitate merging them. Called by EndTable().
 // For simplicity we call it TableMergeDrawChannels() but in fact it only reorder channels + overwrite ClipRect,
 // actual merging is done by table->DrawSplitter.Merge() which is called right after TableMergeDrawChannels().
 //
 // Columns where the contents didn't stray off their local clip rectangle can be merged. To achieve
 // this we merge their clip rect and make them contiguous in the channel list, so they can be merged
 // by the call to DrawSplitter.Merge() following to the call to this function.
 // We reorder draw commands by arranging them into a maximum of 4 distinct groups:
 //
 //   1 group:               2 groups:              2 groups:              4 groups:
 //   [ 0. ] no freeze       [ 0. ] row freeze      [ 01 ] col freeze      [ 01 ] row+col freeze
 //   [ .. ]  or no scroll   [ 2. ]  and v-scroll   [ .. ]  and h-scroll   [ 23 ]  and v+h-scroll
 //
 // Each column itself can use 1 channel (row freeze disabled) or 2 channels (row freeze enabled).
 // When the contents of a column didn't stray off its limit, we move its channels into the corresponding group
 // based on its position (within frozen rows/columns groups or not).
 // At the end of the operation our 1-4 groups will each have a ImDrawCmd using the same ClipRect.
 // This function assume that each column are pointing to a distinct draw channel,
 // otherwise merge_group->ChannelsCount will not match set bit count of merge_group->ChannelsMask.
 //
 // Column channels will not be merged into one of the 1-4 groups in the following cases:
 // - The contents stray off its clipping rectangle (we only compare the MaxX value, not the MinX value).
 //   Direct ImDrawList calls won't be taken into account by default, if you use them make sure the ImGui:: bounds
 //   matches, by e.g. calling SetCursorScreenPos().
 // - The channel uses more than one draw command itself. We drop all our attempt at merging stuff here..
 //   we could do better but it's going to be rare and probably not worth the hassle.
 // Columns for which the draw channel(s) haven't been merged with other will use their own ImDrawCmd.
 //
 // This function is particularly tricky to understand.. take a breath.
 void    ImGui::TableMergeDrawChannels(ImGuiTable* table)
 {
    ImGuiContext& g = *GImGui;
    ImDrawListSplitter* splitter = &table->DrawSplitter;
    const bool has_freeze_v = (table->FreezeRowsCount > 0);
    const bool has_freeze_h = (table->FreezeColumnsCount > 0);
    // Track which groups we are going to attempt to merge, and which channels goes into each group.
    struct MergeGroup
    {
        ImRect  ClipRect;
        int     ChannelsCount;
        ImBitArray<IMGUI_TABLE_MAX_DRAW_CHANNELS> ChannelsMask;
    };
    int merge_group_mask = 0x00;
    MergeGroup merge_groups[4];
    memset(merge_groups, 0, sizeof(merge_groups));
    // 1. Scan channels and take note of those which can be merged
    for (int column_n = 0; column_n < table->ColumnsCount; column_n++)
    {
        if (!(table->EnabledUnclippedMaskByIndex & ((ImU64)1 << column_n)))
            continue;
        ImGuiTableColumn* column = &table->Columns[column_n];
        const int merge_group_sub_count = has_freeze_v ? 2 : 1;
        for (int merge_group_sub_n = 0; merge_group_sub_n < merge_group_sub_count; merge_group_sub_n++)
        {
            const int channel_no = (merge_group_sub_n == 0) ? column->DrawChannelFrozen : column->DrawChannelUnfrozen;
            // Don't attempt to merge if there are multiple draw calls within the column
            ImDrawChannel* src_channel = &splitter->_Channels[channel_no];
            if (src_channel->_CmdBuffer.Size > 0 && src_channel->_CmdBuffer.back().ElemCount == 0)
                src_channel->_CmdBuffer.pop_back();
            if (src_channel->_CmdBuffer.Size != 1)
                continue;
            // Find out the width of this merge group and check if it will fit in our column
            // (note that we assume that rendering didn't stray on the left direction. we should need a CursorMinPos to detect it)
            if (!(column->Flags & ImGuiTableColumnFlags_NoClip))
            {
                float content_max_x;
                if (!has_freeze_v)
                    content_max_x = ImMax(column->ContentMaxXUnfrozen, column->ContentMaxXHeadersUsed); // No row freeze
                else if (merge_group_sub_n == 0)
                    content_max_x = ImMax(column->ContentMaxXFrozen, column->ContentMaxXHeadersUsed);   // Row freeze: use width before freeze
                else
                    content_max_x = column->ContentMaxXUnfrozen;                                        // Row freeze: use width after freeze
                if (content_max_x > column->ClipRect.Max.x)
                    continue;
            }
            const int merge_group_n = (has_freeze_h && column_n < table->FreezeColumnsCount ? 0 : 1) + (has_freeze_v && merge_group_sub_n == 0 ? 0 : 2);
            IM_ASSERT(channel_no < IMGUI_TABLE_MAX_DRAW_CHANNELS);
            MergeGroup* merge_group = &merge_groups[merge_group_n];
            if (merge_group->ChannelsCount == 0)
                merge_group->ClipRect = ImRect(+FLT_MAX, +FLT_MAX, -FLT_MAX, -FLT_MAX);
            merge_group->ChannelsMask.SetBit(channel_no);
            merge_group->ChannelsCount++;
            merge_group->ClipRect.Add(src_channel->_CmdBuffer[0].ClipRect);
            merge_group_mask |= (1 << merge_group_n);
        }
        // Invalidate current draw channel
        // (we don't clear DrawChannelFrozen/DrawChannelUnfrozen solely to facilitate debugging/later inspection of data)
        column->DrawChannelCurrent = (ImU8)-1;
    }
    // [DEBUG] Display merge groups
 #if 0
    if (g.IO.KeyShift)
        for (int merge_group_n = 0; merge_group_n < IM_ARRAYSIZE(merge_groups); merge_group_n++)
        {
            MergeGroup* merge_group = &merge_groups[merge_group_n];
            if (merge_group->ChannelsCount == 0)
                continue;
            char buf[32];
            ImFormatString(buf, 32, "MG%d:%d", merge_group_n, merge_group->ChannelsCount);
            ImVec2 text_pos = merge_group->ClipRect.Min + ImVec2(4, 4);
            ImVec2 text_size = CalcTextSize(buf, NULL);
            GetForegroundDrawList()->AddRectFilled(text_pos, text_pos + text_size, IM_COL32(0, 0, 0, 255));
            GetForegroundDrawList()->AddText(text_pos, IM_COL32(255, 255, 0, 255), buf, NULL);
            GetForegroundDrawList()->AddRect(merge_group->ClipRect.Min, merge_group->ClipRect.Max, IM_COL32(255, 255, 0, 255));
        }
 #endif
    // 2. Rewrite channel list in our preferred order
    if (merge_group_mask != 0)
    {
        // We skip channel 0 (Bg0) and 1 (Bg1 frozen) from the shuffling since they won't move - see channels allocation in TableUpdateDrawChannels().
        const int LEADING_DRAW_CHANNELS = 2;
        g.DrawChannelsTempMergeBuffer.resize(splitter->_Count - LEADING_DRAW_CHANNELS); // Use shared temporary storage so the allocation gets amortized
        ImDrawChannel* dst_tmp = g.DrawChannelsTempMergeBuffer.Data;
        ImBitArray<IMGUI_TABLE_MAX_DRAW_CHANNELS> remaining_mask;                       // We need 132-bit of storage
        remaining_mask.ClearBits();
        remaining_mask.SetBitRange(LEADING_DRAW_CHANNELS, splitter->_Count - 1);
        remaining_mask.ClearBit(table->Bg1DrawChannelUnfrozen);
        IM_ASSERT(has_freeze_v == false || table->Bg1DrawChannelUnfrozen != TABLE_DRAW_CHANNEL_BG1_FROZEN);
        int remaining_count = splitter->_Count - (has_freeze_v ? LEADING_DRAW_CHANNELS + 1 : LEADING_DRAW_CHANNELS);
        //ImRect host_rect = (table->InnerWindow == table->OuterWindow) ? table->InnerClipRect : table->HostClipRect;
        ImRect host_rect = table->HostClipRect;
        for (int merge_group_n = 0; merge_group_n < IM_ARRAYSIZE(merge_groups); merge_group_n++)
        {
            if (int merge_channels_count = merge_groups[merge_group_n].ChannelsCount)
            {
                MergeGroup* merge_group = &merge_groups[merge_group_n];
                ImRect merge_clip_rect = merge_group->ClipRect;
                // Extend outer-most clip limits to match those of host, so draw calls can be merged even if
                // outer-most columns have some outer padding offsetting them from their parent ClipRect.
                // The principal cases this is dealing with are:
                // - On a same-window table (not scrolling = single group), all fitting columns ClipRect -> will extend and match host ClipRect -> will merge
                // - Columns can use padding and have left-most ClipRect.Min.x and right-most ClipRect.Max.x != from host ClipRect -> will extend and match host ClipRect -> will merge
                // FIXME-TABLE FIXME-WORKRECT: We are wasting a merge opportunity on tables without scrolling if column doesn't fit
                // within host clip rect, solely because of the half-padding difference between window->WorkRect and window->InnerClipRect.
                if ((merge_group_n & 1) == 0 || !has_freeze_h)
                    merge_clip_rect.Min.x = ImMin(merge_clip_rect.Min.x, host_rect.Min.x);
                if ((merge_group_n & 2) == 0 || !has_freeze_v)
                    merge_clip_rect.Min.y = ImMin(merge_clip_rect.Min.y, host_rect.Min.y);
                if ((merge_group_n & 1) != 0)
                    merge_clip_rect.Max.x = ImMax(merge_clip_rect.Max.x, host_rect.Max.x);
                if ((merge_group_n & 2) != 0 && (table->Flags & ImGuiTableFlags_NoHostExtendY) == 0)
                    merge_clip_rect.Max.y = ImMax(merge_clip_rect.Max.y, host_rect.Max.y);
 #if 0
                GetOverlayDrawList()->AddRect(merge_group->ClipRect.Min, merge_group->ClipRect.Max, IM_COL32(255, 0, 0, 200), 0.0f, ~0, 1.0f);
                GetOverlayDrawList()->AddLine(merge_group->ClipRect.Min, merge_clip_rect.Min, IM_COL32(255, 100, 0, 200));
                GetOverlayDrawList()->AddLine(merge_group->ClipRect.Max, merge_clip_rect.Max, IM_COL32(255, 100, 0, 200));
 #endif
                remaining_count -= merge_group->ChannelsCount;
                for (int n = 0; n < IM_ARRAYSIZE(remaining_mask.Storage); n++)
                    remaining_mask.Storage[n] &= ~merge_group->ChannelsMask.Storage[n];
                for (int n = 0; n < splitter->_Count && merge_channels_count != 0; n++)
                {
                    // Copy + overwrite new clip rect
                    if (!merge_group->ChannelsMask.TestBit(n))
                        continue;
                    merge_group->ChannelsMask.ClearBit(n);
                    merge_channels_count--;
                    ImDrawChannel* channel = &splitter->_Channels[n];
                    IM_ASSERT(channel->_CmdBuffer.Size == 1 && merge_clip_rect.Contains(ImRect(channel->_CmdBuffer[0].ClipRect)));
                    channel->_CmdBuffer[0].ClipRect = merge_clip_rect.ToVec4();
                    memcpy(dst_tmp++, channel, sizeof(ImDrawChannel));
                }
            }
            // Make sure Bg1DrawChannelUnfrozen appears in the middle of our groups (whereas Bg0 and Bg1 frozen are fixed to 0 and 1)
            if (merge_group_n == 1 && has_freeze_v)
                memcpy(dst_tmp++, &splitter->_Channels[table->Bg1DrawChannelUnfrozen], sizeof(ImDrawChannel));
        }
        // Append unmergeable channels that we didn't reorder at the end of the list
        for (int n = 0; n < splitter->_Count && remaining_count != 0; n++)
        {
            if (!remaining_mask.TestBit(n))
                continue;
            ImDrawChannel* channel = &splitter->_Channels[n];
            memcpy(dst_tmp++, channel, sizeof(ImDrawChannel));
            remaining_count--;
        }
        IM_ASSERT(dst_tmp == g.DrawChannelsTempMergeBuffer.Data + g.DrawChannelsTempMergeBuffer.Size);
        memcpy(splitter->_Channels.Data + LEADING_DRAW_CHANNELS, g.DrawChannelsTempMergeBuffer.Data, (splitter->_Count - LEADING_DRAW_CHANNELS) * sizeof(ImDrawChannel));
    }
 }
 //-------------------------------------------------------------------------
 // [SECTION] Tables: Sorting
 //-------------------------------------------------------------------------