如何判断字体是否支持代理项对Unicode字符?

😉 Windows 10 Arial字体实际上不支持字符。Windows 10使用 "Segoe UI Emoji" 作为特定代码点的备用字体。

所以首先我们必须弄清楚是否使用了回退字体。然后检查字形索引,看看它是否是豆腐字符(通常显示为方形符号) ▯ )

我们可以使用元文件来确定是否使用了字体替换。选择要显示的字体 HDC

使用 ScriptGetFontProperties 查找不支持的图示符的值。

使用 GetCharacterPlacement 查找字符串的图示符索引。如果glyph索引与不支持的glyph匹配,则代码点将被打印为tofu .

如果您尝试打印汉字等,则必须选择合适的字体(SimSun为中文)

这部分由 IMLangFontLink . 这是一种不同类型的字体替换。 下面的示例将测试单个代码点(它可以扩展为处理字符串)。

Segoe UI 选择字体,然后选择汉字 请 ,它将切换 微软雅黑效果 到 SimSun

对于表情符号,它将切换 到 Segoe UI Emoji

另请参见中的这篇文章 oldnewthing TextOut 处理它(在Windows 10中处理正确,因此结果显示正常)

#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <windows.h>
#include <usp10.h>
#include <AtlBase.h>
#include <AtlCom.h>
#include <mlang.h>

#pragma comment(lib, "Usp10.lib")

int CALLBACK metafileproc(HDC, HANDLETABLE*, const ENHMETARECORD *record,
    int, LPARAM logfont)
{
    if(record->iType == EMR_EXTCREATEFONTINDIRECTW)
    {
        auto ptr = (const EMREXTCREATEFONTINDIRECTW*)record;
        *(LOGFONT*)logfont = ptr->elfw.elfLogFont;
    }
    return 1;
}

HFONT GetFallbackFont(const wchar_t *str, HFONT hfont_test)
{
    //use metafile to find the fallback font
    auto metafile_hdc = CreateEnhMetaFile(NULL, NULL, NULL, NULL);
    auto metafile_oldfont = SelectObject(metafile_hdc, hfont_test);

    SCRIPT_STRING_ANALYSIS ssa;
    ScriptStringAnalyse(metafile_hdc, str, wcslen(str), 0, -1,
        SSA_METAFILE | SSA_FALLBACK | SSA_GLYPHS | SSA_LINK,
        0, NULL, NULL, NULL, NULL, NULL, &ssa);
    ScriptStringOut(ssa, 0, 0, 0, NULL, 0, 0, FALSE);
    ScriptStringFree(&ssa);

    SelectObject(metafile_hdc, metafile_oldfont);
    auto hmetafile = CloseEnhMetaFile(metafile_hdc);

    LOGFONT logfont = { 0 };
    EnumEnhMetaFile(0, hmetafile, metafileproc, &logfont, NULL);
    wprintf(L"Selecting fallback font: %s\n", logfont.lfFaceName);
    HFONT hfont = CreateFontIndirect(&logfont);
    DeleteEnhMetaFile(hmetafile);

    return hfont;
}

//IsTofu is for testing emojis
//It accepts a Unicode string
bool IsTofuError(HDC hdc, HFONT hfont_test, const wchar_t *str)
{
    if(wcsstr(str, L" "))
    {
        wprintf(L"*** cannot test strings containing blank space\n");
    }

    auto hfont = GetFallbackFont(str, hfont_test);
    auto oldfont = SelectObject(hdc, hfont);

    //find the characters not supported in this font
    //note, blank space is blank, unsupported fonts can be blank also
    SCRIPT_CACHE sc = NULL;
    SCRIPT_FONTPROPERTIES fp = { sizeof(fp) };
    ScriptGetFontProperties(hdc, &sc, &fp);
    ScriptFreeCache(&sc);
    wprintf(L"SCRIPT_FONTPROPERTIES:\n");
    wprintf(L" Blank: %d, Default: %d, Invalid: %d\n",
        fp.wgBlank, fp.wgDefault, fp.wgInvalid);

    // Get glyph indices for the string
    GCP_RESULTS gcp_results = { sizeof(GCP_RESULTS) };
    gcp_results.nGlyphs = wcslen(str);
    auto wstr_memory = (wchar_t*)calloc(wcslen(str) + 1, sizeof(wchar_t));
    gcp_results.lpGlyphs = wstr_memory;
    GetCharacterPlacement(hdc, str, wcslen(str), 0, &gcp_results, GCP_GLYPHSHAPE);

    //check the characters against wgBlank...
    bool istofu = false;
    wprintf(L"Glyphs:");
    for(UINT i = 0; i < gcp_results.nGlyphs; i++)
    {
        wchar_t n = gcp_results.lpGlyphs[i];
        wprintf(L"%d,", (int)n);
        if(n == fp.wgBlank || n == fp.wgInvalid || n == fp.wgDefault)
            istofu = true;
    }
    wprintf(L"\n");

    free(wstr_memory);
    SelectObject(hdc, oldfont);
    DeleteObject(hfont);

    if (istofu)
        wprintf(L"Tofu error\n\n");

    return istofu;
}

//get_font_link checks if there is font substitution, 
//this usually applies to Asian fonts
//Note, this function doesn't accept a unicode string
//it only takes a single code point. You can imrpove it to accept strings
bool get_font_link(const wchar_t *single_codepoint,
    HDC hdc,
    HFONT &hfont_src,
    HFONT &hfont_dst,
    CComPtr<IMLangFontLink> &ifont,
    CComPtr<IMLangCodePages> &icodepages)
{
    DWORD codepages_dst[100] = { 0 };
    LONG codepages_count = 100;

    DWORD codepages = 0;
    if(FAILED(icodepages->GetStrCodePages(single_codepoint, wcslen(single_codepoint),
        0, codepages_dst, &codepages_count)))
        return false;
    codepages = codepages_dst[0];

    if(FAILED(ifont->MapFont(hdc, codepages_dst[0], hfont_src, &hfont_dst)))
        return false;

    SelectObject(hdc, hfont_dst);
    wchar_t buf[100];
    GetTextFace(hdc, _countof(buf), buf);
    wprintf(L"get_font_link:\nSelecting a different font: %s\n", buf);
    return true;
}

int main()
{
    CoInitialize(NULL);

    {
        CComPtr<IMultiLanguage> imultilang;
        CComPtr<IMLangFontLink> ifont;
        CComPtr<IMLangCodePages> icodepages;
        if(FAILED(imultilang.CoCreateInstance(CLSID_CMultiLanguage))) return 0;
        if(FAILED(imultilang->QueryInterface(&ifont))) return 0;
        if(FAILED(imultilang->QueryInterface(&icodepages))) return 0;

        //const wchar_t *single_codepoint = L"a";
        //const wchar_t *single_codepoint = L"请";
        const wchar_t *single_codepoint = L"😉";

        auto hdc = GetDC(0);
        auto memdc = CreateCompatibleDC(hdc);
        auto hbitmap = CreateCompatibleBitmap(hdc, 1, 1);
        auto oldbmp = SelectObject(memdc, hbitmap);
        auto hfont_src = CreateFont(10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, L"Segoe UI");
        auto oldfont = SelectObject(hdc, hfont_src);

        HFONT hfont_dst = NULL;

        if(IsTofuError(hdc, hfont_src, single_codepoint))
        {
            if(!get_font_link(
                single_codepoint, memdc, hfont_src, hfont_dst, ifont, icodepages))
                wprintf(L"Can't find a substitution!\n");
        }

        SelectObject(memdc, oldbmp);
        SelectObject(memdc, oldfont);
        DeleteObject(hbitmap);
        DeleteDC(memdc);
        ReleaseDC(0, hdc);
        DeleteObject(hfont_src);

        if(ifont && hfont_dst)
            ifont->ReleaseFont(hfont_dst);
    }

    CoUninitialize();

    return 0;
}

输出:

IsTofu 是 false

会的 true

_{使用 GetUniscribeFallbackFont 从…起 this link}

_{注意,Windows文档描述了 GetCharacterPlacement}