DirectWrite for ImGui

README.md

DirectWrite for ImGui

This is a DirectWrite font loader for ImGui v1.92.9b. It uses C++23 and may need some slight adjustments to fit your needs.

Usage

ImGui::GetIO().Fonts->SetFontLoader(ImDWriteCreateFontLoader());
ImDWriteAddFontFamily(ImGui::GetIO().Fonts, "Segoe UI");

// ...

if (dpi_changed)
{
    const auto scale = (float)dpi / (float)USER_DEFAULT_SCREEN_DPI;
    auto& style = ImGui::GetStyle();

    style.FontSizeBase = 16.0f;
    style.FontScaleDpi = scale;

    ImGui_ImplDX11_InvalidateDeviceObjects();
}

License

If you find this code useful, I'd be happy to hear more about it!

This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or
distribute this software, either in source code form or as a compiled
binary, for any purpose, commercial or non-commercial, and by any
means.

In jurisdictions that recognize copyright laws, the author or authors
of this software dedicate any and all copyright interest in the
software to the public domain. We make this dedication for the benefit
of the public at large and to the detriment of our heirs and
successors. We intend this dedication to be an overt act of
relinquishment in perpetuity of all present and future rights to this
software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR
OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

For more information, please refer to <https://unlicense.org/>

imgui_dwrite.cpp

#define NOMINMAX
#define WIN32_LEAN_AND_MEAN
#include <dwrite_3.h>

#include "imgui_dwrite.h"
#include "imgui_internal.h"

namespace {

#define RETURN_FALSE_IF(cond) \
    do {                      \
        if (cond) {           \
            IM_ASSERT(false); \
            return false;     \
        }                     \
    } while (0)

#define RETURN_FALSE_IF_FAILED(hr) \
    RETURN_FALSE_IF(FAILED(hr))

template<typename T>
struct com_ptr {
    ~com_ptr() {
        if (m_ptr) {
            m_ptr->Release();
        }
    }

    T* get() const {
        return m_ptr;
    }

    T* operator->() const {
        return m_ptr;
    }

    T** addressof() {
        return &m_ptr;
    }

private:
    T* m_ptr = nullptr;
};

template<typename T>
struct unique_im {
    unique_im(T* ptr) : m_ptr(ptr) {
    }

    ~unique_im() {
        IM_DELETE(m_ptr);
    }

    T* operator->() {
        return m_ptr;
    }

    T* detach() {
        auto ptr = m_ptr;
        m_ptr = nullptr;
        return ptr;
    }

private:
    T* m_ptr = nullptr;
};

struct TextAnalysisSource final : IDWriteTextAnalysisSource {
    TextAnalysisSource(const wchar_t* locale, const wchar_t* text, const UINT32 textLength) noexcept : m_locale{locale}, m_text{text}, m_text_length{textLength} {
    }

    ULONG STDMETHODCALLTYPE AddRef() noexcept override {
        return 1;
    }

    ULONG STDMETHODCALLTYPE Release() noexcept override {
        return 1;
    }

    HRESULT STDMETHODCALLTYPE QueryInterface(const IID& riid, void** ppvObject) noexcept override {
        if (IsEqualGUID(riid, __uuidof(IDWriteTextAnalysisSource))) {
            *ppvObject = this;
            return S_OK;
        }

        *ppvObject = nullptr;
        return E_NOINTERFACE;
    }

    HRESULT STDMETHODCALLTYPE GetTextAtPosition(UINT32 textPosition, const WCHAR** textString, UINT32* textLength) noexcept override {
        textPosition = ImMin(textPosition, m_text_length);
        *textString = m_text + textPosition;
        *textLength = m_text_length - textPosition;
        return S_OK;
    }

    HRESULT STDMETHODCALLTYPE GetTextBeforePosition(UINT32 textPosition, const WCHAR** textString, UINT32* textLength) noexcept override {
        textPosition = ImMin(textPosition, m_text_length);
        *textString = m_text;
        *textLength = textPosition;
        return S_OK;
    }

    DWRITE_READING_DIRECTION STDMETHODCALLTYPE GetParagraphReadingDirection() noexcept override {
        return DWRITE_READING_DIRECTION_LEFT_TO_RIGHT;
    }

    HRESULT STDMETHODCALLTYPE GetLocaleName(UINT32 textPosition, UINT32* textLength, const WCHAR** localeName) noexcept override {
        *textLength = m_text_length - textPosition;
        *localeName = m_locale;
        return S_OK;
    }

    HRESULT STDMETHODCALLTYPE GetNumberSubstitution(UINT32 textPosition, UINT32* textLength, IDWriteNumberSubstitution** numberSubstitution) noexcept override {
        return E_NOTIMPL;
    }

private:
    const wchar_t* m_locale;
    const wchar_t* m_text;
    UINT32 m_text_length;
};

struct dwrite_font_source {
    com_ptr<IDWriteFactory3> factory;
    com_ptr<IDWriteRenderingParams> rendering_params;
    com_ptr<IDWriteFontFace3> font_face;
    com_ptr<IDWriteFontCollection> font_collection;
    com_ptr<IDWriteFontFallback1> font_fallback;
    wchar_t family_name[IM_COUNTOF(ImFontConfig::Name)];
    float em_per_unit;
    float ascent;  // em
    float descent; // em
};

bool font_src_init(ImFontAtlas*, ImFontConfig* src) {
    unique_im data{IM_NEW(dwrite_font_source)};

    RETURN_FALSE_IF_FAILED(DWriteCreateFactory(DWRITE_FACTORY_TYPE_SHARED, __uuidof(IDWriteFactory3), reinterpret_cast<IUnknown**>(data->factory.addressof())));
    RETURN_FALSE_IF_FAILED(data->factory->CreateRenderingParams(data->rendering_params.addressof()));
    RETURN_FALSE_IF_FAILED(data->factory->GetSystemFontCollection(data->font_collection.addressof(), FALSE));

    com_ptr<IDWriteFontFallback> font_fallback;
    RETURN_FALSE_IF_FAILED(data->factory->GetSystemFontFallback(font_fallback.addressof()));
    RETURN_FALSE_IF_FAILED(font_fallback->QueryInterface(data->font_fallback.addressof()));

    const auto name_utf8_len = static_cast<int>(strnlen(src->Name, IM_COUNTOF(src->Name)));
    const auto name_utf16_len = MultiByteToWideChar(CP_UTF8, 0, src->Name, name_utf8_len, &data->family_name[0], IM_COUNTOF(data->family_name) - 1);
    RETURN_FALSE_IF(name_utf16_len <= 0);
    data->family_name[name_utf16_len] = L'\0';

    UINT32 family_index;
    BOOL family_exists;
    RETURN_FALSE_IF_FAILED(data->font_collection->FindFamilyName(&data->family_name[0], &family_index, &family_exists));
    RETURN_FALSE_IF(!family_exists);

    com_ptr<IDWriteFontFamily> font_family;
    com_ptr<IDWriteFont> font;
    com_ptr<IDWriteFontFace> font_face;
    RETURN_FALSE_IF_FAILED(data->font_collection->GetFontFamily(family_index, font_family.addressof()));
    RETURN_FALSE_IF_FAILED(font_family->GetFirstMatchingFont(DWRITE_FONT_WEIGHT_REGULAR, DWRITE_FONT_STRETCH_NORMAL, DWRITE_FONT_STYLE_NORMAL, font.addressof()));
    RETURN_FALSE_IF_FAILED(font->CreateFontFace(font_face.addressof()));
    RETURN_FALSE_IF_FAILED(font_face->QueryInterface(data->font_face.addressof()));

    DWRITE_FONT_METRICS metrics;
    data->font_face->GetMetrics(&metrics);

    const auto ascent = static_cast<float>(metrics.ascent);
    const auto descent = static_cast<float>(metrics.descent);
    const auto half_line_gap = static_cast<float>(metrics.lineGap) * 0.5f;
    const auto em_per_unit = 1.0f / static_cast<float>(metrics.designUnitsPerEm);
    data->em_per_unit = em_per_unit;
    data->ascent = (ascent + half_line_gap) * em_per_unit;
    data->descent = (descent + half_line_gap) * em_per_unit;

    src->FontLoaderData = data.detach();
    return true;
}

void font_src_destroy(ImFontAtlas*, ImFontConfig* src) {
    IM_DELETE(static_cast<dwrite_font_source*>(src->FontLoaderData));
    src->FontLoaderData = nullptr;
}

bool font_src_contains_glyph(ImFontAtlas*, ImFontConfig* src, ImWchar codepoint) {
    const auto data = static_cast<dwrite_font_source*>(src->FontLoaderData);
    const UINT32 codepoint32 = codepoint;
    UINT16 glyph_index;
    return SUCCEEDED(data->font_face->GetGlyphIndicesW(&codepoint32, 1, &glyph_index)) && glyph_index != 0;
}

bool font_baked_init(ImFontAtlas*, ImFontConfig* src, ImFontBaked* baked, void*) {
    if (!src->MergeMode) {
        const auto data = static_cast<dwrite_font_source*>(src->FontLoaderData);
        baked->Ascent = roundf(baked->Size * data->ascent / (data->ascent + data->descent));
        baked->Descent = baked->Ascent - baked->Size;
    }
    return true;
}

UINT16 map_codepoint_with_fallback(dwrite_font_source* data, ImWchar codepoint, IDWriteFontFace3** font_face) {
    const UINT32 codepoint32 = codepoint;
    UINT16 glyph_index;
    if (FAILED(data->font_face->GetGlyphIndicesW(&codepoint32, 1, &glyph_index))) {
        return 0;
    }
    if (glyph_index != 0) {
        data->font_face->AddRef();
        *font_face = data->font_face.get();
        return glyph_index;
    }

#ifdef IMGUI_USE_WCHAR32
    wchar_t text[2];
    UINT32 text_length;
    if (codepoint > 0xFFFF) {
        text[0] = static_cast<wchar_t>(0xD800 + ((codepoint - 0x10000) >> 10));
        text[1] = static_cast<wchar_t>(0xDC00 + ((codepoint - 0x10000) & 0x3FF));
        text_length = 2;
    } else {
        text[0] = static_cast<wchar_t>(codepoint);
        text_length = 1;
    }
#else
    const auto text = reinterpret_cast<const wchar_t*>(&codepoint);
    constexpr UINT32 text_length = 1;
#endif

    TextAnalysisSource analysis_source{ImDWriteGetUserDefaultLocaleName(), text, text_length};
    UINT32 mapped_length;
    float scale;
    IDWriteFontFace5* font_face5;
    if (FAILED(data->font_fallback->MapCharacters(
            /* analysisSource     */ &analysis_source,
            /* textPosition       */ 0,
            /* textLength         */ text_length,
            /* baseFontCollection */ data->font_collection.get(),
            /* baseFamilyName     */ &data->family_name[0],
            /* fontAxisValues     */ nullptr,
            /* fontAxisValueCount */ 0,
            /* mappedLength       */ &mapped_length,
            /* scale              */ &scale,
            /* mappedFontFace     */ &font_face5
        ))) {
        return 0;
    }

    // NOTE: MapCharacters() can return S_OK and yet mappedFontFace can be null.
    // This indicates that no font contains the requested codepoint.
    if (!font_face5 || FAILED(font_face5->GetGlyphIndicesW(&codepoint32, 1, &glyph_index))) {
        glyph_index = 0;
    }

    *font_face = font_face5;
    return glyph_index;
}

bool font_baked_load_glyph(ImFontAtlas* atlas, ImFontConfig* src, ImFontBaked* baked, void*, ImWchar codepoint, ImFontGlyph* out_glyph, float* out_advance_x) {
    const auto data = static_cast<dwrite_font_source*>(src->FontLoaderData);

    com_ptr<IDWriteFontFace3> font_face;
    const auto glyph_index = map_codepoint_with_fallback(data, codepoint, font_face.addressof());
    if (glyph_index == 0) {
        return false;
    }

    DWRITE_GLYPH_METRICS glyph_metrics;
    RETURN_FALSE_IF_FAILED(font_face->GetDesignGlyphMetrics(&glyph_index, 1, &glyph_metrics, FALSE));

    const auto font_size = baked->Size / (data->ascent + data->descent);
    const auto advance_x = roundf(static_cast<float>(glyph_metrics.advanceWidth) * data->em_per_unit * font_size);

    if (out_advance_x) {
        *out_advance_x = advance_x;
        return true;
    }

    static constexpr DWRITE_GLYPH_OFFSET zero_offset{};
    const DWRITE_GLYPH_RUN glyph_run{
        .fontFace = font_face.get(),
        .fontEmSize = font_size,
        .glyphCount = 1,
        .glyphIndices = &glyph_index,
        .glyphAdvances = &advance_x,
        .glyphOffsets = &zero_offset,
        .isSideways = FALSE,
        .bidiLevel = 0,
    };

    DWRITE_RENDERING_MODE1 renderingMode;
    DWRITE_GRID_FIT_MODE gridFitMode;
    RETURN_FALSE_IF_FAILED(font_face->GetRecommendedRenderingMode(
        /* fontEmSize       */ glyph_run.fontEmSize,
        /* dpiX             */ 96.0f,
        /* dpiY             */ 96.0f,
        /* transform        */ nullptr,
        /* isSideways       */ FALSE,
        /* outlineThreshold */ DWRITE_OUTLINE_THRESHOLD_ANTIALIASED,
        /* measuringMode    */ DWRITE_MEASURING_MODE_NATURAL,
        /* renderingParams  */ data->rendering_params.get(),
        /* renderingMode    */ &renderingMode,
        /* gridFitMode      */ &gridFitMode
    ));

    com_ptr<IDWriteGlyphRunAnalysis> analysis;
    RETURN_FALSE_IF_FAILED(data->factory->CreateGlyphRunAnalysis(
        &glyph_run,
        nullptr,
        renderingMode,
        DWRITE_MEASURING_MODE_NATURAL,
        gridFitMode,
        DWRITE_TEXT_ANTIALIAS_MODE_GRAYSCALE,
        0,
        baked->Ascent,
        analysis.addressof()
    ));

    RECT bounds;
    RETURN_FALSE_IF_FAILED(analysis->GetAlphaTextureBounds(DWRITE_TEXTURE_ALIASED_1x1, &bounds));

    out_glyph->Codepoint = codepoint;
    out_glyph->AdvanceX = advance_x;

    if (IsRectEmpty(&bounds)) {
        return true;
    }

    const auto width = bounds.right - bounds.left;
    const auto height = bounds.bottom - bounds.top;

    ImVector<ImU8> pixels;
    pixels.resize(width * height);
    RETURN_FALSE_IF_FAILED(analysis->CreateAlphaTexture(DWRITE_TEXTURE_ALIASED_1x1, &bounds, pixels.Data, pixels.Size));

    const auto pack_id = ImFontAtlasPackAddRect(atlas, width, height);
    RETURN_FALSE_IF(pack_id == ImFontAtlasRectId_Invalid);

    const auto offset_x = src->GlyphOffset.x;
    const auto offset_y = src->GlyphOffset.y;
    out_glyph->X0 = static_cast<float>(bounds.left) + offset_x;
    out_glyph->Y0 = static_cast<float>(bounds.top) + offset_y;
    out_glyph->X1 = static_cast<float>(bounds.right) + offset_x;
    out_glyph->Y1 = static_cast<float>(bounds.bottom) + offset_y;
    out_glyph->Visible = true;
    out_glyph->PackId = pack_id;

    const auto rect = ImFontAtlasPackGetRect(atlas, pack_id);
    ImFontAtlasBakedSetFontGlyphBitmap(atlas, baked, src, out_glyph, rect, pixels.Data, ImTextureFormat_Alpha8, width);
    return true;
}

} // namespace

const wchar_t* ImDWriteGetUserDefaultLocaleName() {
    static wchar_t localeName[LOCALE_NAME_MAX_LENGTH];

    if (localeName[0] == L'\0') {
        if (!GetUserDefaultLocaleName(localeName, LOCALE_NAME_MAX_LENGTH)) {
            static constexpr wchar_t fallbackLocale[]{L"en-US"};
            memcpy(&localeName[0], &fallbackLocale[0], sizeof(fallbackLocale));
        }
    }

    return &localeName[0];
}

ImFontLoader* ImDWriteCreateFontLoader() {
    static auto loader = [] {
        ImFontLoader loader;
        loader.Name = "DirectWrite";
        loader.FontSrcInit = font_src_init;
        loader.FontSrcDestroy = font_src_destroy;
        loader.FontSrcContainsGlyph = font_src_contains_glyph;
        loader.FontBakedInit = font_baked_init;
        loader.FontBakedDestroy = nullptr;
        loader.FontBakedLoadGlyph = font_baked_load_glyph;
        return loader;
    }();
    return &loader;
}

void ImDWriteAddFontFamily(ImFontAtlas* atlas, const char* family) {
    ImFontConfig config;
    strcpy_s(config.Name, family);
    config.FontLoader = ImDWriteCreateFontLoader();
    atlas->AddFont(&config);
}

imgui_dwrite.h

#pragma once

struct ImFontAtlas;
struct ImFontConfig;
struct ImFontLoader;

const wchar_t* ImDWriteGetUserDefaultLocaleName();
ImFontLoader* ImDWriteCreateFontLoader();
void ImDWriteAddFontFamily(ImFontAtlas* atlas, const char* family);