Method TableUpdateBorders

src/imgui/imgui_tables.cpp:1285–1344

Process hit-testing on resizing borders. Actual size change will be applied in EndTable() - Set table->HoveredColumnBorder with a short delay/timer to reduce visual feedback noise.

// Process hit-testing on resizing borders. Actual size change will be applied in EndTable()
// - Set table->HoveredColumnBorder with a short delay/timer to reduce visual feedback noise.
void ImGui::TableUpdateBorders(ImGuiTable* table)
{
    ImGuiContext& g = *GImGui;
    IM_ASSERT(table->Flags & ImGuiTableFlags_Resizable);

    // At this point OuterRect height may be zero or under actual final height, so we rely on temporal coherency and
    // use the final height from last frame. Because this is only affecting _interaction_ with columns, it is not
    // really problematic (whereas the actual visual will be displayed in EndTable() and using the current frame height).
    // Actual columns highlight/render will be performed in EndTable() and not be affected.
    ImGuiTableInstanceData* table_instance = TableGetInstanceData(table, table->InstanceCurrent);
    const float hit_half_width = ImTrunc(TABLE_RESIZE_SEPARATOR_HALF_THICKNESS * g.CurrentDpiScale);
    const float hit_y1 = (table->FreezeRowsCount >= 1 ? table->OuterRect.Min.y : table->WorkRect.Min.y) + table->AngledHeadersHeight;
    const float hit_y2_body = ImMax(table->OuterRect.Max.y, hit_y1 + table_instance->LastOuterHeight - table->AngledHeadersHeight);
    const float hit_y2_head = hit_y1 + table_instance->LastTopHeadersRowHeight;

    for (int order_n = 0; order_n < table->ColumnsCount; order_n++)
    {
        if (!IM_BITARRAY_TESTBIT(table->EnabledMaskByDisplayOrder, order_n))
            continue;

        const int column_n = table->DisplayOrderToIndex[order_n];
        ImGuiTableColumn* column = &table->Columns[column_n];
        if (column->Flags & (ImGuiTableColumnFlags_NoResize | ImGuiTableColumnFlags_NoDirectResize_))
            continue;

        // ImGuiTableFlags_NoBordersInBodyUntilResize will be honored in TableDrawBorders()
        const float border_y2_hit = (table->Flags & ImGuiTableFlags_NoBordersInBody) ? hit_y2_head : hit_y2_body;
        if ((table->Flags & ImGuiTableFlags_NoBordersInBody) && table->IsUsingHeaders == false)
            continue;

        if (!column->IsVisibleX && table->LastResizedColumn != column_n)
            continue;

        ImGuiID column_id = TableGetColumnResizeID(table, column_n, table->InstanceCurrent);
        ImRect hit_rect(column->MaxX - hit_half_width, hit_y1, column->MaxX + hit_half_width, border_y2_hit);
        ItemAdd(hit_rect, column_id, NULL, ImGuiItemFlags_NoNav);
        //GetForegroundDrawList()->AddRect(hit_rect.Min, hit_rect.Max, IM_COL32(255, 0, 0, 100));

        bool hovered = false, held = false;
        bool pressed = ButtonBehavior(hit_rect, column_id, &hovered, &held, ImGuiButtonFlags_FlattenChildren | ImGuiButtonFlags_PressedOnClick | ImGuiButtonFlags_PressedOnDoubleClick | ImGuiButtonFlags_NoNavFocus);
        if (pressed && IsMouseDoubleClicked(0))
        {
            TableSetColumnWidthAutoSingle(table, column_n);
            ClearActiveID();
            held = false;
        }
        if (held)
        {
            if (table->LastResizedColumn == -1)
                table->ResizeLockMinContentsX2 = table->RightMostEnabledColumn != -1 ? table->Columns[table->RightMostEnabledColumn].MaxX : -FLT_MAX;
            table->ResizedColumn = (ImGuiTableColumnIdx)column_n;
            table->InstanceInteracted = table->InstanceCurrent;
        }
        if ((hovered && g.HoveredIdTimer > TABLE_RESIZE_SEPARATOR_FEEDBACK_TIMER) || held)
        {
            table->HoveredColumnBorder = (ImGuiTableColumnIdx)column_n;
            SetMouseCursor(ImGuiMouseCursor_ResizeEW);
        }