openCV上图片显示中文c++

准备材料：
1、中文汉字库
2、中文显示扩展类

cvxFont.h

#ifndef OPENCVUNICODE_CVXFONT_H
#define OPENCVUNICODE_CVXFONT_H

#include 
#include FT_FREETYPE_H
#include 

#include 
#include 
#include 
#include 

namespace cvx {
    struct FontProperty {
        int fontSize;           // font size (pixel)
        double spaceRatio;       // ratio of distance when meet a space, base on font size
        double fontRatio;        // ratio of distance between each character, base on font size
        double fontRotateAngle;  // rotate angle
        double fontDiaphaneity;  // merge ratio
        bool fontIsUnderline;   // underline
        bool fontIsVertical;    // put text in vertical
    };

    class CvxFont
    {
    public:

        explicit CvxFont(const cv::String& fontType);
        virtual ~CvxFont();

        void setFontSize(int fontSize);
        void setSpaceRatio(const double spaceRatio) { m_font->spaceRatio = spaceRatio; }
        void setFontRatio(const double fontRatio) { m_font->fontRatio = fontRatio; }
        void setRotateAngle(const double angle) { m_font->fontRotateAngle = angle; }
        void setUnderline(const bool isUnderline) { m_font->fontIsUnderline = isUnderline; }
        void setDiaphaneity(const double diaphaneity) { m_font->fontDiaphaneity = diaphaneity; }
        void setVertical(const bool vertical) { m_font->fontIsVertical = vertical; }

        [[nodiscard]] int getFontSize() const { return m_font->fontSize; }
        [[nodiscard]] double getSpaceRatio() const { return m_font->spaceRatio; }
        [[nodiscard]] double getFontRatio() const { return m_font->fontRatio; }
        [[nodiscard]] double getAngle() const { return m_font->fontRotateAngle; }
        [[nodiscard]] bool getUnderline() const { return m_font->fontIsUnderline; }
        [[nodiscard]] double getDiaphaneity() const { return m_font->fontDiaphaneity; }
        [[nodiscard]] bool getVertical() const { return m_font->fontIsVertical; }

    private:
        void initFont();
        void rotateFont(double angle);
        void putTextStr(cv::Mat& img, const cv::String& text, cv::Point pos, const cv::Scalar& color);
        void putWChar(cv::Mat& img, uint32_t wc, cv::Point& pos, const cv::Scalar& color);
        friend void putText(cv::Mat&, const std::string&, cv::Point, cvx::CvxFont&, int, const cv::Scalar&);
        FT_Library   m_library{};   // font library
        FT_Face      m_face{};      // font type
        FT_Matrix    m_matrix{};
        FT_Vector    m_pen{};
        FT_Error     m_error;

        FontProperty* m_font;
        long m_maxDiffHeight{ 0 };

    };

    void putText(cv::Mat& img, const std::string& text, cv::Point pos, cvx::CvxFont& fontFace, int fontSize, const cv::Scalar& color);
    void putSymbols(cv::Mat& img, std::vector<uint32_t>& symbols, cv::Point pos, cvx::CvxFont& fontFace, int fontSize, const cv::Scalar& color);
    void putOneSymbol(cv::Mat& img, uint32_t symbol, cv::Point pos, cvx::CvxFont& fontFace, int fontSize, const cv::Scalar& color);
}

#endif //OPENCVUNICODE_CVXFONT_H

cvxFont.cpp

#include "CvxFont.h"
#include 
#include 
#include 
#include 
#include 

cvx::CvxFont::CvxFont(const cv::String& fontType)
{
    assert(!fontType.empty());
    m_error = FT_Init_FreeType(&m_library);
    if (m_error){
        std::cerr << "library initial error!" << std::endl;
        return;
    }
    m_error = FT_New_Face(m_library, fontType.c_str(), 0, &m_face);
    if (m_error == FT_Err_Unknown_File_Format){
        std::cerr << "unsupported font format!" << std::endl;
        return;
    }
    else if (m_error){
        std::cerr << " can not open font files" << std::endl;
        return;
    }
    // use default parameters
    m_font = new FontProperty;
    initFont();
    setlocale(LC_ALL, "");
}

// release freetype resource
cvx::CvxFont::~CvxFont()
{
    delete m_font;
    FT_Done_Face(m_face);
    FT_Done_FreeType(m_library);
}

void cvx::CvxFont::setFontSize(const int fontSize)
{
    m_font->fontSize = fontSize;
    FT_Set_Pixel_Sizes(m_face, fontSize, 0);
}

// initial font
void cvx::CvxFont::initFont()
{
    setFontSize(16);
    setSpaceRatio(0.5);
    setFontRatio(0);
    setRotateAngle(0);
    setDiaphaneity(1);
    setUnderline(false);
    setVertical(false);
    // set font
    FT_Set_Pixel_Sizes(m_face, getFontSize(), 0);
}

void cvx::CvxFont::rotateFont(double angle) {
    angle = (angle / 360) * 3.14159 * 2;
    /* set up matrix */
    m_matrix.xx = static_cast<FT_Fixed>(cos(angle) * 0x10000L);
    m_matrix.xy = static_cast<FT_Fixed>(-sin(angle) * 0x10000L);
    m_matrix.yx = static_cast<FT_Fixed>(sin(angle) * 0x10000L);
    m_matrix.yy = static_cast<FT_Fixed>(cos(angle) * 0x10000L);

    FT_Set_Transform(m_face, &m_matrix, nullptr);
}

void cvx::CvxFont::putTextStr(cv::Mat& img, const cv::String& text, cv::Point pos, const cv::Scalar& color)
{
    CV_Assert(!img.empty());
    CV_Assert(!text.empty());

    int xStart = pos.x;
    int yStart = pos.y;
    m_maxDiffHeight = 0;

    const char* ptr = text.c_str();
    std::mbtowc(nullptr, nullptr, 0); // reset the conversion state
    const char* end = ptr + std::strlen(ptr);
    int ret;
    for (wchar_t wc; (ret = std::mbtowc(&wc, ptr, end - ptr)) > 0; ptr += ret) {
        putWChar(img, (wc & 0xffffffff), pos, color);
    }

    int xEnd = pos.x;
    int yEnd = pos.y;
    if (getUnderline()) {
        if (getVertical()) {
            cv::line(img, cv::Point(xStart + m_maxDiffHeight, yStart), cv::Point(xStart + m_maxDiffHeight, yEnd), color, 2);
        }
        else {
            cv::line(img, cv::Point(xStart, yStart + m_maxDiffHeight), cv::Point(xEnd, yStart + m_maxDiffHeight), color, 2);
        }
    }

}

void cvx::CvxFont::putWChar(cv::Mat& img, uint32_t wc, cv::Point& pos, const cv::Scalar& color)
{
    rotateFont(getAngle());
    const auto vertical = getVertical();
    const auto size = getFontSize();

    // Converting a Character Code Into a Glyph Index
    FT_UInt glyph_index = FT_Get_Char_Index(m_face, wc);
    FT_Load_Glyph(m_face, glyph_index, FT_LOAD_DEFAULT);
    FT_Render_Glyph(m_face->glyph, FT_RENDER_MODE_MONO);

    FT_GlyphSlot slot = m_face->glyph;
    FT_Bitmap bitmap = slot->bitmap;
    bool isSpace = wc == ' ';

    // get rows and cols of current wide char
    auto rows = bitmap.rows;
    auto cols = bitmap.width;

    cv::Point gPos = pos;
    //gPos.y += m_font->fontSize;
    if (vertical)
    {
        gPos.x += (slot->metrics.vertBearingX >> 6);
        gPos.y += (slot->metrics.vertBearingY >> 6);
        m_maxDiffHeight = std::max(m_maxDiffHeight, rows - (slot->metrics.vertBearingY >> 6));
    }
    else
    {
        gPos.x += (slot->metrics.horiBearingX >> 6);
        gPos.y -= (slot->metrics.horiBearingY >> 6);
        m_maxDiffHeight = std::max(m_maxDiffHeight, rows - (slot->metrics.horiBearingY >> 6));
    }

    // https://stackoverflow.com/questions/52254639/how-to-access-pixels-state-in-monochrome-bitmap-using-freetype2
    for (auto i = 0; i < rows; ++i)
    {
        for (auto j = 0; j < cols; ++j)
        {
            int off = i * slot->bitmap.pitch + j / 8;

            if (slot->bitmap.buffer[off] & (0x80 >> (j % 8)))
            {
                const auto r = gPos.y + i; //vertical ? pos.y + i : pos.y + i + (size - rows); // to make align to bottom
                const auto c = gPos.x + j;

                if (r >= 0 && r < img.rows && c >= 0 && c < img.cols)
                {
                    cv::Vec3b scalar = img.at<cv::Vec3b>(cv::Point(c, r));

                    // merge set color with origin color
                    double p = getDiaphaneity();
                    for (int k = 0; k < 3; ++k)
                    {
                        scalar.val[k] = static_cast<uchar>(scalar.val[k] * (1 - p) + color.val[k] * p);
                    }

                    img.at<cv::Vec3b>(cv::Point(c, r)) = cv::Vec3b(scalar[0], scalar[1], scalar[2]);
                }
            }
        }
    }
    // modify position to next character
    const auto space = static_cast<int>(size * getSpaceRatio());
    const auto sep = static_cast<int>(size * getFontRatio());
    // vertical string or not, default not vertical
    if (vertical){
        const auto moveX = (static_cast<int>(getAngle()) == 0) ?  (slot->metrics.vertAdvance >> 6) : rows + 1;
        pos.y += isSpace ? space : moveX + sep;
    }else{
        const auto moveY = (static_cast<int>(getAngle()) == 0) ? (slot->metrics.horiAdvance >> 6) : cols + 1;
        pos.x += isSpace ? space : moveY + sep;
    }
}

void cvx::putText(cv::Mat& img, const std::string& text, cv::Point pos, cvx::CvxFont& fontFace, int fontSize, const cv::Scalar& color) {
    fontFace.setFontSize(fontSize);
    fontFace.putTextStr(img, text, std::move(pos), color);
    fontFace.initFont();
}

编译脚本：
CmakeLists.txt

cmake_minimum_required(VERSION 3.10)
project(OpenCVUnicode)

set(CMAKE_CXX_STANDARD 14)

find_package(OpenCV REQUIRED)
message(STATUS "OpenCV library status:")
message(STATUS "    version: ${OpenCV_VERSION}")
message(STATUS "    libraries: ${OpenCV_LIBS}")
message(STATUS "    include path: ${OpenCV_INCLUDE_DIRS}")
include_directories(${OpenCV_INCLUDE_DIRS})

find_package(Freetype REQUIRED)
message(STATUS "Freetype library status")
message(STATUS "    ${FREETYPE_INCLUDE_DIRS}")
message(STATUS "    ${FREETYPE_INCLUDE_DIR_ft2build}")
message(STATUS "    ${FREETYPE_INCLUDE_DIR_freetype2}")
include_directories(${FREETYPE_INCLUDE_DIRS})

set(SRC
    main.cpp
    CvxFont.cpp)

add_executable(OpenCVUnicode ${SRC})
target_link_libraries(OpenCVUnicode ${OpenCV_LIBS})
target_link_libraries(OpenCVUnicode ${FREETYPE_LIBRARIES})

测试代码：
main.cpp

#include "CvxFont.h"
using namespace cvx;
int main(int argc, char *argv[])
{
    cvx::CvxFont font("../msgothic.ttc");
    cv::Mat img(400, 800, CV_8UC3, cv::Scalar(0, 0, 0)); // create a black background
    cv::String msg6 = "字符可以被截断 sdfhhklyrt.bdfd";
     // be careful to use the font that support Chinese
    putText(img, msg6, cv::Point(10, 40), font, 18,  cv::Scalar(255, 0, 0));

    cv::imshow("test", img);
    cv::waitKey(0);
    return 0;
}