Method Render

tutorials/common/imgui/imgui.cpp:5210–5273

Prepare the data for rendering so you can call GetDrawData() (As with anything within the ImGui:: namspace this doesn't touch your GPU or graphics API at all: it is the role of the ImGui_ImplXXXX_RenderDrawData() function provided by the renderer backend)

// (As with anything within the ImGui:: namspace this doesn't touch your GPU or graphics API at all:
// it is the role of the ImGui_ImplXXXX_RenderDrawData() function provided by the renderer backend)
void ImGui::Render()
{
    ImGuiContext& g = *GImGui;
    IM_ASSERT(g.Initialized);

    if (g.FrameCountEnded != g.FrameCount)
        EndFrame();
    const bool first_render_of_frame = (g.FrameCountRendered != g.FrameCount);
    g.FrameCountRendered = g.FrameCount;
    g.IO.MetricsRenderWindows = 0;

    CallContextHooks(&g, ImGuiContextHookType_RenderPre);

    // Add background ImDrawList (for each active viewport)
    for (int n = 0; n != g.Viewports.Size; n++)
    {
        ImGuiViewportP* viewport = g.Viewports[n];
        viewport->DrawDataBuilder.Clear();
        if (viewport->DrawLists[0] != NULL)
            AddDrawListToDrawData(&viewport->DrawDataBuilder.Layers[0], GetBackgroundDrawList(viewport));
    }

    // Draw modal/window whitening backgrounds
    if (first_render_of_frame)
        RenderDimmedBackgrounds();

    // Add ImDrawList to render
    ImGuiWindow* windows_to_render_top_most[2];
    windows_to_render_top_most[0] = (g.NavWindowingTarget && !(g.NavWindowingTarget->Flags & ImGuiWindowFlags_NoBringToFrontOnFocus)) ? g.NavWindowingTarget->RootWindow : NULL;
    windows_to_render_top_most[1] = (g.NavWindowingTarget ? g.NavWindowingListWindow : NULL);
    for (int n = 0; n != g.Windows.Size; n++)
    {
        ImGuiWindow* window = g.Windows[n];
        IM_MSVC_WARNING_SUPPRESS(6011); // Static Analysis false positive "warning C6011: Dereferencing NULL pointer 'window'"
        if (IsWindowActiveAndVisible(window) && (window->Flags & ImGuiWindowFlags_ChildWindow) == 0 && window != windows_to_render_top_most[0] && window != windows_to_render_top_most[1])
            AddRootWindowToDrawData(window);
    }
    for (int n = 0; n < IM_ARRAYSIZE(windows_to_render_top_most); n++)
        if (windows_to_render_top_most[n] && IsWindowActiveAndVisible(windows_to_render_top_most[n])) // NavWindowingTarget is always temporarily displayed as the top-most window
            AddRootWindowToDrawData(windows_to_render_top_most[n]);

    // Draw software mouse cursor if requested by io.MouseDrawCursor flag
    if (g.IO.MouseDrawCursor && first_render_of_frame && g.MouseCursor != ImGuiMouseCursor_None)
        RenderMouseCursor(g.IO.MousePos, g.Style.MouseCursorScale, g.MouseCursor, IM_COL32_WHITE, IM_COL32_BLACK, IM_COL32(0, 0, 0, 48));

    // Setup ImDrawData structures for end-user
    g.IO.MetricsRenderVertices = g.IO.MetricsRenderIndices = 0;
    for (int n = 0; n < g.Viewports.Size; n++)
    {
        ImGuiViewportP* viewport = g.Viewports[n];
        viewport->DrawDataBuilder.FlattenIntoSingleLayer();

        // Add foreground ImDrawList (for each active viewport)
        if (viewport->DrawLists[1] != NULL)
            AddDrawListToDrawData(&viewport->DrawDataBuilder.Layers[0], GetForegroundDrawList(viewport));

        SetupViewportDrawData(viewport, &viewport->DrawDataBuilder.Layers[0]);
        ImDrawData* draw_data = &viewport->DrawDataP;