Function ImGuiListClipper_StepInternal

tutorials/common/imgui/imgui.cpp:2740–2861

}

static bool ImGuiListClipper_StepInternal(ImGuiListClipper* clipper)
{
    ImGuiContext& g = *GImGui;
    ImGuiWindow* window = g.CurrentWindow;
    ImGuiListClipperData* data = (ImGuiListClipperData*)clipper->TempData;
    IM_ASSERT(data != NULL && "Called ImGuiListClipper::Step() too many times, or before ImGuiListClipper::Begin() ?");

    ImGuiTable* table = g.CurrentTable;
    if (table && table->IsInsideRow)
        ImGui::TableEndRow(table);

    // No items
    if (clipper->ItemsCount == 0 || GetSkipItemForListClipping())
        return false;

    // While we are in frozen row state, keep displaying items one by one, unclipped
    // FIXME: Could be stored as a table-agnostic state.
    if (data->StepNo == 0 && table != NULL && !table->IsUnfrozenRows)
    {
        clipper->DisplayStart = data->ItemsFrozen;
        clipper->DisplayEnd = ImMin(data->ItemsFrozen + 1, clipper->ItemsCount);
        if (clipper->DisplayStart < clipper->DisplayEnd)
            data->ItemsFrozen++;
        return true;
    }

    // Step 0: Let you process the first element (regardless of it being visible or not, so we can measure the element height)
    bool calc_clipping = false;
    if (data->StepNo == 0)
    {
        clipper->StartPosY = window->DC.CursorPos.y;
        if (clipper->ItemsHeight <= 0.0f)
        {
            // Submit the first item (or range) so we can measure its height (generally the first range is 0..1)
            data->Ranges.push_front(ImGuiListClipperRange::FromIndices(data->ItemsFrozen, data->ItemsFrozen + 1));
            clipper->DisplayStart = ImMax(data->Ranges[0].Min, data->ItemsFrozen);
            clipper->DisplayEnd = ImMin(data->Ranges[0].Max, clipper->ItemsCount);
            data->StepNo = 1;
            return true;
        }
        calc_clipping = true;   // If on the first step with known item height, calculate clipping.
    }

    // Step 1: Let the clipper infer height from first range
    if (clipper->ItemsHeight <= 0.0f)
    {
        IM_ASSERT(data->StepNo == 1);
        if (table)
            IM_ASSERT(table->RowPosY1 == clipper->StartPosY && table->RowPosY2 == window->DC.CursorPos.y);

        clipper->ItemsHeight = (window->DC.CursorPos.y - clipper->StartPosY) / (float)(clipper->DisplayEnd - clipper->DisplayStart);
        bool affected_by_floating_point_precision = ImIsFloatAboveGuaranteedIntegerPrecision(clipper->StartPosY) || ImIsFloatAboveGuaranteedIntegerPrecision(window->DC.CursorPos.y);
        if (affected_by_floating_point_precision)
            clipper->ItemsHeight = window->DC.PrevLineSize.y + g.Style.ItemSpacing.y; // FIXME: Technically wouldn't allow multi-line entries.

        IM_ASSERT(clipper->ItemsHeight > 0.0f && "Unable to calculate item height! First item hasn't moved the cursor vertically!");
        calc_clipping = true;   // If item height had to be calculated, calculate clipping afterwards.
    }