DirectWrite Performance – Windows Graphics

Introduction

DirectWrite is a high‑performance, native text layout and rendering API designed for Windows applications. This guide covers best‑practice techniques to maximize rendering speed, minimize memory usage, and ensure smooth multithreaded operation.

Key Performance Tips

1. Cache Text Formats

Creating IDWriteTextFormat objects is expensive. Reuse them whenever possible.

static Microsoft::WRL::ComPtr<IDWriteTextFormat> g_pTextFormat;

HRESULT InitTextFormat(IDWriteFactory* pFactory)
{
    return pFactory->CreateTextFormat(
        L"Segoe UI", nullptr, DWRITE_FONT_WEIGHT_NORMAL,
        DWRITE_FONT_STYLE_NORMAL, DWRITE_FONT_STRETCH_NORMAL,
        12.0f, L"", &g_pTextFormat);
}

2. Use Text Layout Caching

Cache IDWriteTextLayout for static strings.

static std::unordered_map<std::wstring, Microsoft::WRL::ComPtr<IDWriteTextLayout>> g_layoutCache;

Microsoft::WRL::ComPtr<IDWriteTextLayout> GetCachedLayout(
    IDWriteFactory* factory, const std::wstring& text)
{
    auto it = g_layoutCache.find(text);
    if (it != g_layoutCache.end())
        return it->second;

    Microsoft::WRL::ComPtr<IDWriteTextFormat> format;
    InitTextFormat(factory); // assume success
    Microsoft::WRL::ComPtr<IDWriteTextLayout> layout;
    factory->CreateTextLayout(text.c_str(), (UINT32)text.size(),
                              g_pTextFormat.Get(), 0.0f, 0.0f, &layout);
    g_layoutCache.emplace(text, layout);
    return layout;
}

Memory Management

Component	Guideline
Font Face Objects	Reuse `IDWriteFontFace` across layouts.
Glyph Buffers	Allocate once per frame; reuse for multiple draws.
Custom Renderer	Prefer IDWritePixelSnapping if hardware acceleration is unavailable.

Multithreading Considerations

All DirectWrite factory methods are thread‑safe; create a single IDWriteFactory and share it.
Do not share IDWriteTextLayout instances across threads without synchronization.
Perform layout creation on worker threads and only render on the UI thread.

Sample Rendering Loop

void Render(ID2D1RenderTarget* rt, IDWriteFactory* dwFactory, const std::wstring& text)
{
    auto layout = GetCachedLayout(dwFactory, text);
    rt->BeginDraw();
    rt->DrawTextLayout(D2D1_POINT_2F{10,10}, layout.Get(),
                       D2D1::ColorF(D2D1::ColorF::White));
    rt->EndDraw();
}