c++ - glOrtho 不改变 2D 窗口中的坐标系？

Question

所以除非我理解错了，否则在默认的 OpenGL 窗口中坐标 (0,0) 位于屏幕的中心。我已经使用 glOrtho/glViewport 设置了以下调整大小功能，将左上角设置为 (0,0)。但出于某种原因，在 (0,0) 处绘制点仍然显示在屏幕中央(并且仍在 -1/1 范围内)。

主要

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.setTitle("OpenGL");
    w.resize(500,500);
    w.show();
    return a.exec();
}

主窗口.cpp

MainWindow::MainWindow(QWidget *parent)
{
    setSurfaceType(QWindow::OpenGLSurface);
    QSurfaceFormat format;
    format.setProfile(QSurfaceFormat::CompatibilityProfile);
    format.setVersion(2,1);

    setFormat(format);
    context =new QOpenGLContext;
    context->setFormat(format);
    context->makeCurrent(this);

    openGLFuncions = context->functions();

}
void MainWindow::resizeGL(int w, int h)
{
    glViewport(0,0,w,h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0,w,h,0.0,-1.0,1.0);
    glMatrixMode(GL_MODELVIEW);
}

void MainWindow::paintGL()
{
    glClearColor(0.0f,0.0f,0.0f,0.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    glPointSize(10.0f);
    glBegin(GL_POINTS);
        glVertex2f(0.5f,0);
    glEnd();

    glFlush();
}

主窗体.h

class MainWindow : public QOpenGLWindow
{
    Q_OBJECT
public:
    MainWindow(QWidget *parent = 0);
    ~MainWindow();
    void updateAnim();
protected:
    virtual void initilizeGL();
    virtual void resizeGL(int w, int h);
    virtual void paintGL();
    void resizeEvent(QResizeEvent *event);
    void paintEvent(QPaintEvent *event);
private:
    QOpenGLContext *context;
    QOpenGLFunctions *openGLFuncions;
};

Answer 1

我建议不要调用任何 OpenGL，MainWindow::initilizeGL 和 MainWindow::paintGL 除外。

向MainWindow类添加状态成员(_vp_valid)，指示视口(viewport)和投影矩阵是否正确设置并初始化为false:

class MainWindow : public QOpenGLWindow
{

    // [...]

private:

   bool _vp_valid = false;

   // [...]
};

如果状态无效，则更新视口(viewport)矩形并在MainWindow::paintGL中设置投影矩阵:

void MainWindow::paintGL()
{
    if ( !_vp_valid )
    {
        _vp_valid = true;
        int w = this->width();
        int h = this->height();

        glViewport(0, 0, w, h);
        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(0.0,w,h,0.0,-1.0,1.0);
        glMatrixMode(GL_MODELVIEW);
    }

    glClearColor(0.0f,0.0f,0.0f,0.0f);
    glClear(GL_COLOR_BUFFER_BIT);

    glPointSize(10.0f);
    glBegin(GL_POINTS);
        glVertex2f(0.5f,0);
    glEnd();

    glFlush();
}

在 MainWindow::resizeGL 中，足以使状态无效:

void MainWindow::resizeGL(int w, int h)
{
    _vp_valid = false;
}