QOpenGLShaderProgram绘制文本文字, 给出列子

首先，我们需要加载字体文件，并创建一个QFont对象：

QFont font;
font.setPixelSize(16);

QFontDatabase fontDB;
QString fontPath = "path/to/font.ttf";
int fontId = fontDB.addApplicationFont(fontPath);
QString fontName = fontDB.applicationFontFamilies(fontId).at(0);
font.setFamily(fontName);

然后，我们创建一个QPainter对象，设置字体和颜色，绘制文本文字：

QPainter painter(this);
painter.setFont(font);
painter.setPen(QColor(Qt::white));

QPointF textPos(10, 20);
QString text = "Hello, World!";
painter.drawText(textPos, text);

最后，我们创建一个简单的QOpenGLWidget子类，使用QOpenGLShaderProgram渲染文本文字：

#include <QOpenGLWidget>
#include <QOpenGLShaderProgram>
#include <QOpenGLBuffer>

class TextWidget : public QOpenGLWidget
{
    Q_OBJECT

public:
    explicit TextWidget(QWidget *parent = nullptr);

protected:
    void initializeGL() override;
    void paintGL() override;

private:
    QOpenGLShaderProgram m_program;
    QOpenGLBuffer m_vertexBuffer;
    QOpenGLBuffer m_indexBuffer;
};

TextWidget::TextWidget(QWidget *parent)
    : QOpenGLWidget(parent)
{

}

void TextWidget::initializeGL()
{
    // 顶点数据
    const QVector<float> vertexData = {
        // 位置       // 纹理坐标
        -1.0f,  1.0f, 0.0f, 1.0f,
         1.0f,  1.0f, 1.0f, 1.0f,
         1.0f, -1.0f, 1.0f, 0.0f,
        -1.0f, -1.0f, 0.0f, 0.0f
    };

    // 索引数据
    const QVector<GLuint> indexData = {
        0, 1, 2,
        2, 3, 0
    };

    // 编译顶点着色器
    QOpenGLShader vertexShader(QOpenGLShader::Vertex);
    vertexShader.compileSourceCode(
        "attribute vec2 vertexPosition;\n"
        "attribute vec2 vertexTexCoord;\n"
        "uniform mat4 modelViewProjectionMatrix;\n"
        "varying vec2 texCoord;\n"
        "void main() {\n"
        "  gl_Position = modelViewProjectionMatrix * vec4(vertexPosition, 0.0, 1.0);\n"
        "  texCoord = vertexTexCoord;\n"
        "}\n"
    );

    // 编译片元着色器
    QOpenGLShader fragmentShader(QOpenGLShader::Fragment);
    fragmentShader.compileSourceCode(
        "uniform sampler2D texture;\n"
        "varying vec2 texCoord;\n"
        "void main() {\n"
        "  gl_FragColor = texture2D(texture, texCoord);\n"
        "}\n"
    );

    // 绑定着色器程序
    m_program.addShader(&vertexShader);
    m_program.addShader(&fragmentShader);
    m_program.bindAttributeLocation("vertexPosition", 0);
    m_program.bindAttributeLocation("vertexTexCoord", 1);
    m_program.link();

    // 创建顶点缓冲
    m_vertexBuffer.create();
    m_vertexBuffer.bind();
    m_vertexBuffer.allocate(vertexData.constData(), vertexData.count() * sizeof(GLfloat));
    m_vertexBuffer.release();

    // 创建索引缓冲
    m_indexBuffer.create();
    m_indexBuffer.bind();
    m_indexBuffer.allocate(indexData.constData(), indexData.count() * sizeof(GLuint));
    m_indexBuffer.release();
}

void TextWidget::paintGL()
{
    // 清空背景
    glClearColor(0.2f, 0.2f, 0.2f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    // 绑定着色器程序和缓冲
    m_program.bind();
    m_vertexBuffer.bind();
    m_indexBuffer.bind();

    // 设置模型矩阵和投影矩阵
    QMatrix4x4 modelMatrix;
    modelMatrix.setToIdentity();
    modelMatrix.translate(0.5f, 0.5f, 0.0f);

    QMatrix4x4 projectionMatrix;
    projectionMatrix.setToIdentity();
    projectionMatrix.ortho(-1.0f, 1.0f, -1.0f, 1.0f, -1.0f, 1.0f);

    QMatrix4x4 modelViewProjectionMatrix = projectionMatrix * modelMatrix;
    m_program.setUniformValue("modelViewProjectionMatrix", modelViewProjectionMatrix);

    // 加载字体纹理并绑定到0号纹理单元
    QImage img("path/to/font.jpg");
    GLuint textureId = 0;
    glGenTextures(1, &textureId);
    glBindTexture(GL_TEXTURE_2D, textureId);
    glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, img.width(), img.height(), 0, GL_RGBA, GL_UNSIGNED_BYTE, img.constBits());
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
    glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
    glBindTexture(GL_TEXTURE_2D, 0);

    // 激活纹理单元
    glActiveTexture(GL_TEXTURE0);
    glBindTexture(GL_TEXTURE_2D, textureId);
    m_program.setUniformValue("texture", 0);

    // 绘制
    m_program.enableAttributeArray(0);
    m_program.enableAttributeArray(1);
    m_program.setAttributeBuffer(0, GL_FLOAT, 0, 2, sizeof(GLfloat) * 4);
    m_program.setAttributeBuffer(1, GL_FLOAT, sizeof(GLfloat) * 2, 2, sizeof(GLfloat) * 4);
    glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr);

    // 解绑缓冲
    m_indexBuffer.release();
    m_vertexBuffer.release();
    m_program.disableAttributeArray(0);
    m_program.disableAttributeArray(1);
    m_program.release();
}

这样，我们就可以渲染出一段文本文字。需要注意的是，上述代码中的字体纹理文件是一张包含所有字符的图片，每个字符对应纹理中的一个矩形区域，需要根据需要进行纹理坐标的计算。