Method UpdatePlatformWindows

imgui_tiny_app/imgui/imgui.cpp:17413–17506

Called by user at the end of the main loop, after EndFrame() This will handle the creation/update of all OS windows via function defined in the ImGuiPlatformIO api.

// Called by user at the end of the main loop, after EndFrame()
// This will handle the creation/update of all OS windows via function defined in the ImGuiPlatformIO api.
void ImGui::UpdatePlatformWindows()
{
    ImGuiContext& g = *GImGui;
    IM_ASSERT(g.FrameCountEnded == g.FrameCount && "Forgot to call Render() or EndFrame() before UpdatePlatformWindows()?");
    IM_ASSERT(g.FrameCountPlatformEnded < g.FrameCount);
    g.FrameCountPlatformEnded = g.FrameCount;
    if (!(g.ConfigFlagsCurrFrame & ImGuiConfigFlags_ViewportsEnable))
        return;

    // Create/resize/destroy platform windows to match each active viewport.
    // Skip the main viewport (index 0), which is always fully handled by the application!
    for (int i = 1; i < g.Viewports.Size; i++)
    {
        ImGuiViewportP* viewport = g.Viewports[i];

        // Destroy platform window if the viewport hasn't been submitted or if it is hosting a hidden window
        // (the implicit/fallback Debug##Default window will be registering its viewport then be disabled, causing a dummy DestroyPlatformWindow to be made each frame)
        bool destroy_platform_window = false;
        destroy_platform_window |= (viewport->LastFrameActive < g.FrameCount - 1);
        destroy_platform_window |= (viewport->Window && !IsWindowActiveAndVisible(viewport->Window));
        if (destroy_platform_window)
        {
            DestroyPlatformWindow(viewport);
            continue;
        }

        // New windows that appears directly in a new viewport won't always have a size on their first frame
        if (viewport->LastFrameActive < g.FrameCount || viewport->Size.x <= 0 || viewport->Size.y <= 0)
            continue;

        // Create window
        const bool is_new_platform_window = (viewport->PlatformWindowCreated == false);
        if (is_new_platform_window)
        {
            IMGUI_DEBUG_LOG_VIEWPORT("[viewport] Create Platform Window %08X '%s'\n", viewport->ID, viewport->Window ? viewport->Window->Name : "n/a");
            g.PlatformIO.Platform_CreateWindow(viewport);
            if (g.PlatformIO.Renderer_CreateWindow != NULL)
                g.PlatformIO.Renderer_CreateWindow(viewport);
            g.PlatformWindowsCreatedCount++;
            viewport->LastNameHash = 0;
            viewport->LastPlatformPos = viewport->LastPlatformSize = ImVec2(FLT_MAX, FLT_MAX); // By clearing those we'll enforce a call to Platform_SetWindowPos/Size below, before Platform_ShowWindow (FIXME: Is that necessary?)
            viewport->LastRendererSize = viewport->Size;                                       // We don't need to call Renderer_SetWindowSize() as it is expected Renderer_CreateWindow() already did it.
            viewport->PlatformWindowCreated = true;
        }

        // Apply Position and Size (from ImGui to Platform/Renderer backends)
        if ((viewport->LastPlatformPos.x != viewport->Pos.x || viewport->LastPlatformPos.y != viewport->Pos.y) && !viewport->PlatformRequestMove)
            g.PlatformIO.Platform_SetWindowPos(viewport, viewport->Pos);
        if ((viewport->LastPlatformSize.x != viewport->Size.x || viewport->LastPlatformSize.y != viewport->Size.y) && !viewport->PlatformRequestResize)
            g.PlatformIO.Platform_SetWindowSize(viewport, viewport->Size);
        if ((viewport->LastRendererSize.x != viewport->Size.x || viewport->LastRendererSize.y != viewport->Size.y) && g.PlatformIO.Renderer_SetWindowSize)
            g.PlatformIO.Renderer_SetWindowSize(viewport, viewport->Size);
        viewport->LastPlatformPos = viewport->Pos;
        viewport->LastPlatformSize = viewport->LastRendererSize = viewport->Size;

        // Update title bar (if it changed)
        if (ImGuiWindow* window_for_title = GetWindowForTitleDisplay(viewport->Window))
        {