如何让我的灯光相对于我的场景（在立方体中）保持固定？

Question

我一直在画康奈尔盒子。我想在我的 lamp 中放置光（lamp 是放置在右墙上的白色立方体）。会让人产生lamp在发光的错觉。但是我不能将我的光放入立方体中。我尝试设置视图变换然后设置灯光位置，但它不起作用。这是我的简单代码：( lamp 多维数据集已移动 glTranslatef(0.63, 0.3, 0.0))

 void display(void)
{

    glEnable(GL_DEPTH_TEST);
    glViewport(0, 0, 600, 600);
    glClearColor(0.32, 0.32, 0.32, 1);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    // draw cube
    glPushMatrix();
    glTranslatef(0.2, -0.3, 0.4);
    glColor3d(1.0, 0.38, 0.0);
    glutSolidCube(0.2);
    glPopMatrix();
    // draw sphere
    glPushMatrix();
    glTranslatef(0.2, -0.1, 0.4);
    glColor3d(0.71, 0.0, 0.59);
    glutSolidSphere(0.1,100,100);
    glPopMatrix();
    // draw parallelepiped
    glPushMatrix();
    glTranslatef(-0.2, -0.2, 0.25);
    glRotatef(20, 0.0, 1.0, 0.0);
    glColor3d(1.0, 0.38, 0.0);
    glScalef(1, 1.8, 1);
    glutSolidCube(0.2);
    glPopMatrix();
    // draw lamp
    glPushMatrix();
    glTranslatef(0.63, 0.3, 0.0);
    glScalef(1.5, 0.3, 1);
    glColor3d(1.0, 1.0, 1.0);
    glutSolidCube(0.2);
    glPopMatrix();

    glBegin(GL_QUADS);
    glNormal3f(0, 1.0, 0);
    glColor3d(0.69, 0.69, 0.69); // bottom
    glVertex3d(-0.5, -0.5, 0.5);
    glVertex3d(-0.5, -0.5, -0.5);
    glVertex3d(0.5, -0.5, -0.5);
    glVertex3d(0.5, -0.5, 0.5);
    glEnd();
    glBegin(GL_QUADS);
    glNormal3f(0, -1.0, 0);
    glColor3d(0.69, 0.69, 0.69); // top
    glVertex3d(-0.5, 0.5, 0.5);
    glVertex3d(-0.5, 0.5, -0.5);
    glVertex3d(0.5, 0.5, -0.5);
    glVertex3d(0.5, 0.5, 0.5);
    glEnd();
    glBegin(GL_QUADS);
    glNormal3f(-1.0, 0.0, 0.0);
    glColor3d(0.0, 0.79, 0.05); // right
    glVertex3d(0.5, -0.5, 0.5);
    glVertex3d(0.5, 0.5, 0.5);
    glVertex3d(0.5, 0.5, -0.5);
    glVertex3d(0.5, -0.5, -0.5);
    glEnd();
    glBegin(GL_QUADS);
    glNormal3f(1.0, 0.0, 0.0);
    glColor3d(1.0, 0.16, 0.0); // left
    glVertex3d(-0.5, -0.5, 0.5);
    glVertex3d(-0.5, 0.5, 0.5);
    glVertex3d(-0.5, 0.5, -0.5);
    glVertex3d(-0.5, -0.5, -0.5);
    glEnd();
    glBegin(GL_QUADS);
    glNormal3f(0.0, 0.0, 1.0);
    glColor3d(0.69, 0.69, 0.69); // back
    glVertex3d(-0.5, -0.5, -0.5);
    glVertex3d(-0.5, 0.5, -0.5);
    glVertex3d(0.5, 0.5, -0.5);
    glVertex3d(0.5, -0.5, -0.5);
    glEnd();
    glFlush();
    glPopMatrix();
    glutSwapBuffers();

}

void Initialize() {
    glEnable(GL_LIGHTING);
    glEnable(GL_LIGHT0);
    GLfloat global_ambient[] = { 0.1, 0.1, 0.1, 1.0 };
    glLightModelfv(GL_LIGHT_MODEL_AMBIENT, global_ambient);
    GLfloat ambient[] = { 0.0,0.0,0.0,1.0 };
    GLfloat diffuse[] = { 1.0,1.0,1.0,1.0 };
    GLfloat spec[] = { 1,1,1,1 };
    GLfloat specref[] = { 1,1,1,1 };
    GLfloat lpos[] = { 0.0, 0.0, 0.0, 1.0 };
    glLightfv(GL_LIGHT0, GL_POSITION, lpos);
    glLightfv(GL_LIGHT0, GL_AMBIENT, ambient);
    glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuse);
    glLightfv(GL_LIGHT0, GL_SPECULAR, spec);

    glMaterialfv(GL_FRONT_AND_BACK, GL_SPECULAR, specref);
    glMateriali(GL_FRONT_AND_BACK, GL_SHININESS, 64);
    glEnable(GL_COLOR_MATERIAL);
    glColorMaterial(GL_FRONT_AND_BACK, GL_AMBIENT_AND_DIFFUSE);
}

void exitFunc(unsigned char key, int x, int y) {
    switch (key) {
    case 27:
        exit(0);
        break;
    }
}

void reshape(int w, int h)
{
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glFrustum(-0.35, 0.35, -0.35, 0.35, 1.2, 400.0);
    glMatrixMode(GL_MODELVIEW);
    glTranslatef(0, 0, -2);
}

int main(int argc, char** argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
    glutInitWindowSize(600, 600);
    glutInitWindowPosition(0, 0);
    glutCreateWindow("Cornell Box");
    Initialize();
    glutDisplayFunc(display);
    glutKeyboardFunc(exitFunc);
    glutReshapeFunc(reshape);
    glutIdleFunc(display);

    glutMainLoop();
    return 0;   
}

Answer 1

请注意，几十年来，由 glBegin/glEnd 序列绘制的固定功能管线矩阵堆栈和每个顶点光模型的固定功能管线已被弃用。阅读 Fixed Function Pipeline and see Vertex Specification and Shader 了解最先进的渲染方式。

总之，当灯位由glLightfv(GL_LIGHT0, GL_POSITION, pos)设置后，则 pos乘以当前模型视图矩阵
这意味着如果在设置模型视图矩阵之前设置位置，则灯光位置将放置在世界的绝对坐标中。
如果在设置模型视图矩阵后设置，则可以在模型的坐标系中设置灯光位置。

设置绘制lamp时的灯光位置到"lamp"的中心：

// draw lamp
glPushMatrix();
glTranslatef(0.63, 0.3, 0.0);
glScalef(1.5, 0.3, 1);

GLfloat lpos[] = { 0.0, 0.0, 0.0, 1.0 };
glLightfv(GL_LIGHT0, GL_POSITION, lpos);

glColor3d(1.0, 1.0, 1.0);
glutSolidCube(0.2);
glPopMatrix();

OpenGL 固定函数管道计算每个顶点的光：Gouraud shading。
这可能会导致，如果光矢量相对于表面平面以锐角击中顶点坐标，则无法 "see" 光。

在你的例子中，绿墙几乎没有被点亮，因为光源几乎直接在墙上。 lam本身是不亮的，因为光源在lamp里面，而且是从背面发光。

见

稍微改变灯光的位置，将它放在墙的前面，并将右边的墙镶嵌成 4 个四边形，"see" 我的意思是：

 GLfloat lpos[] = { -0.1, 0.0, 0.0, 1.0 };

// right
glBegin(GL_QUADS);
glNormal3f(-1.0, 0.0, 0.0);
glColor3d(0.0, 0.79, 0.05); 
glVertex3d(0.5,  0.3,  0.5);
glVertex3d(0.5,  0.5,  0.5);
glVertex3d(0.5,  0.5,  0.0);
glVertex3d(0.5,  0.3,  0.0);

glVertex3d(0.5,  0.3,  0.0);
glVertex3d(0.5,  0.5,  0.0);
glVertex3d(0.5,  0.5, -0.5);
glVertex3d(0.5,  0.3, -0.5);

glVertex3d(0.5, -0.5,  0.5);
glVertex3d(0.5,  0.3,  0.5);
glVertex3d(0.5,  0.3,  0.0);
glVertex3d(0.5, -0.5,  0.0);

glVertex3d(0.5, -0.5,  0.0);
glVertex3d(0.5,  0.3,  0.0);
glVertex3d(0.5,  0.3, -0.5);
glVertex3d(0.5, -0.5, -0.5);

glEnd();

如何让我的灯光相对于我的场景（在立方体中）保持固定？

How can I make my light stay fixed relative to my scene (in the cube)?

c

opengl

glut

lighting

opengl-compat