如何将“相机”放在 OpenGL 中的立方体内

Posted 2023-02-16

【中文标题】如何将“相机”放在 OpenGL 中的立方体内

【英文标题】：How to put the "camera" inside a cube in OpenGL

【发布时间】：2015-06-19 17:29:20

【问题描述】：

我想出了如何将“相机”放入我创建的立方体中，以便我可以以类似 FPS 的方式移动。我尝试使用 gluLookAt 和 gluPerspective 但我显然错过了一些步骤。在 gluLookAt 之前我应该​​做什么？

这是目前编写的代码：

int rotate_Y; //used to rotate the cube about the Y-axis
int rotate_X; //used to rotate the cube about the X-axis

//the display function draws the scene and redraws it
void display()

    //clear the screen and the z-buffer 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glLoadIdentity(); //resets the transformations

    glRotatef(rotate_X, 1.0, 0.0, 0.0);
    glRotatef(rotate_Y, 0.0, 1.0, 0.0);

    //Front Face of the cube - vertex definition
    glBegin(GL_POLYGON); 
    glColor3f(0.0, 1.0, 0.0);
    glVertex3f(-0.5f, -0.5f, -0.5f);
    glVertex3f(-0.5f, 0.5f, -0.5f);  
    glVertex3f(0.5f, 0.5f, -0.5f);
    glVertex3f(0.5f, -0.5f, -0.5f);
    glEnd();

    //Back Face of the cube - vertex definition
    glBegin(GL_POLYGON);
    glColor3f(1.0, 0.0, 0.0);
    glVertex3f(-0.5f, -0.5f, 0.5f);
    glVertex3f(-0.5f, 0.5f, 0.5f);
    glVertex3f(0.5f, 0.5f, 0.5f);
    glVertex3f(0.5f, -0.5f, 0.5f);
    glEnd();

    //Right Face of the cube - vertex definition
    glBegin(GL_POLYGON);
    glColor3f(1.0, 0.0, 1.0);
    glVertex3f(0.5f, -0.5f, 0.5f);
    glVertex3f(0.5f, 0.5f, 0.5f);
    glVertex3f(0.5f, 0.5f, -0.5f);
    glVertex3f(0.5f, -0.5f, -0.5f);
    glEnd();

    //Left Face of the cube - vertex definition
    glBegin(GL_POLYGON);
    glColor3f(0.7, 0.7, 0.0);
    glVertex3f(-0.5f, -0.5f, -0.5f);
    glVertex3f(-0.5f, 0.5f, -0.5f);
    glVertex3f(-0.5f, 0.5f, 0.5f);
    glVertex3f(-0.5f, -0.5f, 0.5f);
    glEnd();

    //Upper Face of the cube - vertex definition
    glBegin(GL_POLYGON);
    glColor3f(0.7, 0.7, 0.3);
    glVertex3f(-0.5f, 0.5f, 0.5f);
    glVertex3f(-0.5f, 0.5f, -0.5f);
    glVertex3f(0.5f, 0.5f, -0.5f);
    glVertex3f(0.5f, 0.5f, 0.5f);
    glEnd();

    //Bottom Face of the cube - vertex definition
    glBegin(GL_POLYGON);
    glColor3f(0.2, 0.2, 0.8);
    glVertex3f(-0.5f, -0.5f, -0.5f);
    glVertex3f(-0.5f, -0.5f, 0.5f);
    glVertex3f(0.5f, -0.5f, 0.5f);
    glVertex3f(0.5f, -0.5f, -0.5f);
    glEnd();

    glFlush();
    glutSwapBuffers(); //send image to the screen


//the special keys function allows interaction via keys (also special ones)
void specialKeys(int key, int x, int y)
    switch (key)
        case GLUT_KEY_F1:
            exit(0);
            break;
        case GLUT_KEY_LEFT:
            rotate_Y -= 5;
            break;
        case GLUT_KEY_UP:
            rotate_X -= 5;
            break;
        case GLUT_KEY_RIGHT:
            rotate_Y += 5;
            break;
        case GLUT_KEY_DOWN:
            rotate_X += 5;
            break;
    

    glutPostRedisplay(); //request a screen refresh to see changes 



int main(int argc, char*argv[])

    //initialize GLUT 
    glutInit(&argc, argv);

    //request double buffering, RGB colors window and a z-buffer
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);

    //create a window
    glutInitWindowSize(600, 600);
    glutInitWindowPosition(100, 100);
    glutCreateWindow("Space");

    //enable depth
    glEnable(GL_DEPTH_TEST);

    //callback functions
    glutDisplayFunc(display); //display - redraws the scene
    glutSpecialFunc(specialKeys); //special - allows interaction with specialkeys

    //pass control to GLUT for events
    glutMainLoop(); 

    return 0; //this line is never reached

【问题讨论】：

您的代码中没有对gluLookAt 和gluPerspective 的调用。

你可能想阅读OpenGL FAQ

【参考方案1】：

您需要使用glTranslatef(float x,float y,float z) 来移动相机。

请注意，由于 OpenGL 的工作方式，这些变换实际上适用于世界其他地方，而不是相机。所以上面的函数实际上会按照指定的量移动之后绘制的所有东西（而不是相机）。

要让相机移动到某个位置，您需要先否定该位置的所有组件，然后再将它们传递给函数。这将使世界向相反的方向移动，将相机放在您想要的位置。

【讨论】：

没有奇怪，因为没有相机。所有这些矩阵的存在都是为了一个目的：将您想要显示的任何内容粘贴到标准化设备坐标中，从 3D 切换到 2D 变得微不足道。 “相机”只是人类的一个概念，因此他们不会考虑潜在的转换。