QOpenGLWidget 中freetype渲染汉字的程序

以下是一个简单的在QOpenGLWidget中使用freetype库渲染汉字的示例程序：

#include <QOpenGLWidget>
#include <QOpenGLFunctions>
#include <ft2build.h>
#include FT_FREETYPE_H

class GLWidget : public QOpenGLWidget, protected QOpenGLFunctions
{
public:
    GLWidget(QWidget *parent = 0) : QOpenGLWidget(parent), m_fontSize(32) {}

protected:
    virtual void initializeGL()
    {
        initializeOpenGLFunctions();

        // 初始化freetype库
        FT_Library ft;
        if (FT_Init_FreeType(&ft)) {
            qFatal("Failed to initialize FreeType library");
        }

        // 加载字体文件
        FT_Face face;
        if (FT_New_Face(ft, "/path/to/font.ttf", 0, &face)) {
            qFatal("Failed to load font");
        }

        // 设置字体大小
        FT_Set_Pixel_Sizes(face, 0, m_fontSize);

        // 构建字形纹理
        glGenTextures(1, &m_textureId);
        glBindTexture(GL_TEXTURE_2D, m_textureId);
        glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        // 预先渲染所有需要的字符
        for (int i = 0; i < 256; ++i) {
            if (FT_Load_Char(face, i, FT_LOAD_RENDER)) {
                qWarning("Failed to load glyph for character %d", i);
                continue;
            }

            glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, face->glyph->bitmap.width, face->glyph->bitmap.rows, 0, GL_RED, GL_UNSIGNED_BYTE, face->glyph->bitmap.buffer);

            Character character = {
                m_textureId,
                QVector2D(face->glyph->bitmap.width, face->glyph->bitmap.rows),
                QVector2D(face->glyph->bitmap_left, m_fontSize - face->glyph->bitmap_top),
                face->glyph->advance.x
            };

            m_characters.insert(i, character);
        }

        // 释放资源
        FT_Done_Face(face);
        FT_Done_FreeType(ft);

        // 设置OpenGL状态
        glEnable(GL_BLEND);
        glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    }

    virtual void paintGL()
    {
        glClear(GL_COLOR_BUFFER_BIT);

        // 绘制文本
        QString text = "你好，世界！";
        QVector2D position(50, 50);
        for (int i = 0; i < text.length(); ++i) {
            QChar c = text.at(i);

            if (!m_characters.contains(c.unicode())) {
                qWarning("Character %d not found in font", c.unicode());
                continue;
            }

            Character character = m_characters.value(c.unicode());

            glBindTexture(GL_TEXTURE_2D, character.textureId);

            QVector2D topLeft = position + character.bearing;
            QVector2D bottomRight = topLeft + character.size;

            GLfloat vertices[] = {
                topLeft.x(), topLeft.y(), 0.0f, 0.0f,
                bottomRight.x(), topLeft.y(), 1.0f, 0.0f,
                bottomRight.x(), bottomRight.y(), 1.0f, 1.0f,
                topLeft.x(), bottomRight.y(), 0.0f, 1.0f
            };

            GLuint indices[] = {
                0, 1, 2,
                2, 3, 0
            };

            glEnableVertexAttribArray(0);
            glEnableVertexAttribArray(1);
            glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat), vertices);
            glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 4 * sizeof(GLfloat), vertices + 2);
            glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, indices);
            glDisableVertexAttribArray(0);
            glDisableVertexAttribArray(1);

            position += QVector2D(character.advance, 0);
        }
    }

private:
    struct Character {
        GLuint textureId;
        QVector2D size;
        QVector2D bearing;
        GLuint advance;
    };

    QHash<int, Character> m_characters;
    GLuint m_textureId;
    int m_fontSize;
};

这个程序使用了freetype库来加载指定的字体文件，预先渲染了需要的所有字符，并将它们存储在一个哈希表中以供使用。在绘制时，程序会遍历需要绘制的字符串，对于每个字符找到对应的字符纹理并绘制出来。