Method DockNodePreviewDockRender

imgui_tiny_app/imgui/imgui.cpp:19972–20088

}

static void ImGui::DockNodePreviewDockRender(ImGuiWindow* host_window, ImGuiDockNode* host_node, ImGuiWindow* root_payload, const ImGuiDockPreviewData* data)
{
    ImGuiContext& g = *GImGui;
    IM_ASSERT(g.CurrentWindow == host_window);   // Because we rely on font size to calculate tab sizes

    // With this option, we only display the preview on the target viewport, and the payload viewport is made transparent.
    // To compensate for the single layer obstructed by the payload, we'll increase the alpha of the preview nodes.
    const bool is_transparent_payload = g.IO.ConfigDockingTransparentPayload;

    // In case the two windows involved are on different viewports, we will draw the overlay on each of them.
    int overlay_draw_lists_count = 0;
    ImDrawList* overlay_draw_lists[2];
    overlay_draw_lists[overlay_draw_lists_count++] = GetForegroundDrawList(host_window->Viewport);
    if (host_window->Viewport != root_payload->Viewport && !is_transparent_payload)
        overlay_draw_lists[overlay_draw_lists_count++] = GetForegroundDrawList(root_payload->Viewport);

    // Draw main preview rectangle
    const ImU32 overlay_col_main = GetColorU32(ImGuiCol_DockingPreview, is_transparent_payload ? 0.60f : 0.40f);
    const ImU32 overlay_col_drop = GetColorU32(ImGuiCol_DockingPreview, is_transparent_payload ? 0.90f : 0.70f);
    const ImU32 overlay_col_drop_hovered = GetColorU32(ImGuiCol_DockingPreview, is_transparent_payload ? 1.20f : 1.00f);
    const ImU32 overlay_col_lines = GetColorU32(ImGuiCol_NavWindowingHighlight, is_transparent_payload ? 0.80f : 0.60f);

    // Display area preview
    const bool can_preview_tabs = (root_payload->DockNodeAsHost == NULL || root_payload->DockNodeAsHost->Windows.Size > 0);
    if (data->IsDropAllowed)
    {
        ImRect overlay_rect = data->FutureNode.Rect();
        if (data->SplitDir == ImGuiDir_None && can_preview_tabs)
            overlay_rect.Min.y += GetFrameHeight();
        if (data->SplitDir != ImGuiDir_None || data->IsCenterAvailable)
            for (int overlay_n = 0; overlay_n < overlay_draw_lists_count; overlay_n++)
                overlay_draw_lists[overlay_n]->AddRectFilled(overlay_rect.Min, overlay_rect.Max, overlay_col_main, host_window->WindowRounding, CalcRoundingFlagsForRectInRect(overlay_rect, host_window->Rect(), g.Style.DockingSeparatorSize));
    }

    // Display tab shape/label preview unless we are splitting node (it generally makes the situation harder to read)
    if (data->IsDropAllowed && can_preview_tabs && data->SplitDir == ImGuiDir_None && data->IsCenterAvailable)
    {
        // Compute target tab bar geometry so we can locate our preview tabs
        ImRect tab_bar_rect;
        DockNodeCalcTabBarLayout(&data->FutureNode, NULL, &tab_bar_rect, NULL, NULL);
        ImVec2 tab_pos = tab_bar_rect.Min;
        if (host_node && host_node->TabBar)
        {
            if (!host_node->IsHiddenTabBar() && !host_node->IsNoTabBar())
                tab_pos.x += host_node->TabBar->WidthAllTabs + g.Style.ItemInnerSpacing.x; // We don't use OffsetNewTab because when using non-persistent-order tab bar it is incremented with each Tab submission.
            else
                tab_pos.x += g.Style.ItemInnerSpacing.x + TabItemCalcSize(host_node->Windows[0]).x;
        }
        else if (!(host_window->Flags & ImGuiWindowFlags_DockNodeHost))
        {
            tab_pos.x += g.Style.ItemInnerSpacing.x + TabItemCalcSize(host_window).x; // Account for slight offset which will be added when changing from title bar to tab bar
        }

        // Draw tab shape/label preview (payload may be a loose window or a host window carrying multiple tabbed windows)
        if (root_payload->DockNodeAsHost)
            IM_ASSERT(root_payload->DockNodeAsHost->Windows.Size <= root_payload->DockNodeAsHost->TabBar->Tabs.Size);
        ImGuiTabBar* tab_bar_with_payload = root_payload->DockNodeAsHost ? root_payload->DockNodeAsHost->TabBar : NULL;
        const int payload_count = tab_bar_with_payload ? tab_bar_with_payload->Tabs.Size : 1;