OpenGL - 旋转问题 - Qt

Question

我正在尝试学习||在 Qt 中编写 openGL 代码。我做了一个显示两个数字的应用程序。一个是三角形“A”，另一个三角形“B”与“A”相同，只是它围绕 z 轴旋转了 -90 度（z 轴垂直于计算机屏幕）。现在，问题是旋转会改变尺寸。我在下面发布“main.cpp”，

#include <QApplication>
#include <QHBoxLayout>
#include <QMessageBox>
#include <QtOpenGL/QGLWidget>
#include <QWidget>

class MyOpenGL:public QGLWidget
{
public:
    MyOpenGL(QWidget * parent);
    ~MyOpenGL();
    void initializeGL();
    void resizeGL(int w, int h);
    void paintGL();
};

MyOpenGL::MyOpenGL(QWidget *parent):QGLWidget(QGLFormat(QGL::SampleBuffers),parent)
{
    setAutoFillBackground(false);
}

MyOpenGL::~MyOpenGL()
{

}

void MyOpenGL::initializeGL()
{
    glShadeModel(GL_SMOOTH);
    glClearColor(0.0f,0.0f,0.0f,0.0f);
    glClearDepth(1.0f);
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);
    glHint(GL_PERSPECTIVE_CORRECTION_HINT,GL_NICEST);
}

void MyOpenGL::resizeGL(int w, int h)
{
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45.0f,width()/height(),10.0f,100.0f);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

void MyOpenGL::paintGL()
{
    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

    //glTranslatef(0.0,0.0,-10.0);

    glBegin(GL_TRIANGLES);
    glColor3f(1.0f,0.0f,0.0f);
    glVertex3f(-1.0f,0.0f,-10.0f);
    glColor3f(0.0f,1.0f,0.0f);
    glVertex3f(1.0f,0.0f,-10.0f);
    glColor3f(0.0f,0.0f,1.0f);
    glVertex3f(0.0f,4.0f,-10.0f);
    glEnd();

    glRotatef(90.0,0.0f,0.0f,-1.0f);

    glBegin(GL_TRIANGLES);
    glColor3f(1.0f,0.0f,0.0f);
    glVertex3f(-1.0f,0.0f,-10.0f);
    glColor3f(0.0f,1.0f,0.0f);
    glVertex3f(1.0f,0.0f,-10.0f);
    glColor3f(0.0f,0.0f,1.0f);
    glVertex3f(0.0f,4.0f,-10.0f);
    glEnd();

    glLoadIdentity();
}

int main(int argc,char * argv[])
{
    QApplication app(argc,argv);

    MyOpenGL * f = new MyOpenGL(NULL);
    f->show();

    return app.exec();
}

这是专业文件

SOURCES += \
    main.cpp

QT += opengl

这是生成的应用程序的屏幕截图

据我所知，旋转不会改变尺寸。但是这里的维度正在发生变化。如果有人在这个问题上消除了我的疑问，我将非常感谢他/她。

Answer 1

我无法确定发生了什么，但我确实看到可能存在一些问题。

gluPerspective(45.0f,width()/height(),10.0f,100.0f);

如果width 和height 都返回整数（并且它们可能确实如此），那么一个除以另一个将得到一个整数。这不会给你一个适当的纵横比。将其中一个投射到浮点数上以获得真实的纵横比。

接下来，尝试在 paintGL 函数的顶部调用 glLoadIdentity()。

Answer 2

如果您需要 2D 渲染，请使用 gluOrtho2D 而不是 gluPerspective（3D 渲染）。

其实这不是问题，这只是一个 3D 物体在 2D 平面上的正常投影。

Answer 3

你需要设置视图：

void MyOpenGL::resizeGL(int w, int h)
{
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glViewport(0,0,w,h);
    gluPerspective(45.0f,(double)w/(double)h,10.0f,100.0f);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    updateGL();
}

另外，渲染图像时不需要重置投影矩阵：

void MyOpenGL::paintGL()
{
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();


    glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);

    //glTranslatef(0.0,0.0,-10.0);

    glBegin(GL_TRIANGLES);
    glColor3f(1.0f,0.0f,0.0f);
    glVertex3f(-1.0f,0.0f,-10.0f);
    glColor3f(0.0f,1.0f,0.0f);
    glVertex3f(1.0f,0.0f,-10.0f);
    glColor3f(0.0f,0.0f,1.0f);
    glVertex3f(0.0f,4.0f,-10.0f);
    glEnd();

    glRotatef(90.0,0.0f,0.0f,-1.0f);

    glBegin(GL_TRIANGLES);
    glColor3f(1.0f,0.0f,0.0f);
    glVertex3f(-1.0f,0.0f,-10.0f);
    glColor3f(0.0f,1.0f,0.0f);
    glVertex3f(1.0f,0.0f,-10.0f);
    glColor3f(0.0f,0.0f,1.0f);
    glVertex3f(0.0f,4.0f,-10.0f);
    glEnd();
}

但正如有人所说，尝试使用 glOrtho 而不是 gluPerspective

Answer 4

为了做一个旋转，你必须先把东西带到原点，然后旋转，然后把它带到你想要的地方。