Question

我一直在画康奈尔盒子。我想在灯中放光（灯是放在右墙上的白色立方体）。幻灯闪烁。但是我不能把光放到立方体里。我尝试设置视图变换，然后设置灯光位置，但是它不起作用。这是我的简单代码：（灯箱已移动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，自几十年来，不赞成使用glBegin / glEnd序列绘制每个顶点光模型的固定功能管线矩阵堆栈和固定功能管线。阅读有关Fixed Function Pipeline的信息，并参阅Vertex Specification和Shader了解最新的渲染方式。

无论如何，当灯光位置由glLightfv(GL_LIGHT0, GL_POSITION, pos)设置时， 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，则将灯光位置放置在相对于世界的绝对坐标中。
如果在设置模型视图矩阵之后进行设置，则可以在模型的坐标系中设置灯光位置。

将抽灯时的灯光位置设置到“灯”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固定功能管线计算每个顶点的光：Gouraud shading。
如果光矢量以相对于表面平面的锐角撞击顶点坐标，则可能导致您无法“看到”光。

在您的情况下，绿色墙壁几乎没有照明，因为光源几乎直接在墙壁上。 lam本身不发光，因为光源在灯内部，并且是从背面发出的光。

请参见OpenGL Lighting on texture plane is not working

稍微改变灯光位置，将其放在墙的前面，并将右墙细分为4个四边形，以“看到”我的意思：

 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();

如何使光源相对于场景保持固定（在立方体中）？

1 个答案: