大家好
我正在使用一个小型MFC应用程序探索OpenGL中的照明，该应用程序绘制了一个以（0，0，0）为中心的立方体和一个光源。
然而，当我设置GL_SPOT_CUTOFF时，光源（如果我可以说-出乎意料地）关闭。
这是cube的代码：

void CGLRenderer::DrawCube(float a)
{
GLfloat mat_ambient[] = { 0.5, 0.5, 0.5, 1.0 };
GLfloat mat_diffuse[] = { 0.8, 0.8, 0.8, 1.0 };
GLfloat mat_specular[] = { 1.0, 1.0, 1.0, 1.0 };
GLfloat mat_emission[] = { 0.0, 0.0, 0.0, 1.0 };
GLfloat mat_shininess = 64.0;
glMaterialfv(GL_FRONT, GL_AMBIENT, mat_ambient);
glMaterialfv(GL_FRONT, GL_DIFFUSE, mat_diffuse);
glMaterialfv(GL_FRONT, GL_SPECULAR, mat_specular);
glMaterialfv(GL_FRONT, GL_EMISSION, mat_emission);
glMaterialf(GL_FRONT, GL_SHININESS, mat_shininess);
//glShadeModel(GL_FLAT);
glEnable(GL_NORMALIZE);
glBegin(GL_QUAD_STRIP);
//front
glColor3f(1.0, 0.0, 0.0);
glNormal3f(0.0, 0.0, 1.0);
glVertex3f(-a / 2, -a / 2, a / 2);
glVertex3f(-a / 2, a / 2, a / 2);
glVertex3f(a / 2, -a / 2, a / 2);
glVertex3f(a / 2, a / 2, a / 2);
//right
glColor3f(0.0, 1.0, 0.0);
glNormal3f(1.0, 0.0, 0.0);
glVertex3f(a / 2, -a / 2, -a / 2);
glVertex3f(a / 2, a / 2, -a / 2);
//back
glColor3f(0.0, 0.0, 1.0);
glNormal3f(0.0, 0.0, -1.0);
glVertex3f(-a / 2, -a / 2, -a / 2);
glVertex3f(-a / 2, a / 2, -a / 2);
//left
glColor3f(0.0, 1.0, 1.0);
glNormal3f(-1.0, 0.0, 0.0);
glVertex3f(-a / 2, -a / 2, a / 2);
glVertex3f(-a / 2, a / 2, a / 2);
glEnd();
glBegin(GL_QUADS);
//top
glColor3f(1.0, 1.0, 0.0);
glNormal3f(0.0, 1.0, 0.0);
glVertex3f(-a / 2, a / 2, a / 2);
glVertex3f(a / 2, a / 2, a / 2);
glVertex3f(a / 2, a / 2, -a / 2);
glVertex3f(-a / 2, a / 2, -a / 2);
//bottom
glColor3f(1.0, 0.0, 1.0);
glNormal3f(0.0, -1.0, 0.0);
glVertex3f(-a / 2, -a / 2, a / 2);
glVertex3f(a / 2, -a / 2, a / 2);
glVertex3f(a / 2, -a / 2, -a / 2);
glVertex3f(-a / 2, -a / 2, -a / 2);
glEnd();
}

字符串
对于光：

void CGLRenderer::SetUpLight()
{
GLfloat mod_ambient[] = { 0.2, 0.2, 0.2, 1.0 };
glLightModelfv(GL_LIGHT_MODEL_AMBIENT, mod_ambient);
glLightModeli(GL_LIGHT_MODEL_TWO_SIDE, GL_FALSE);
glLightModeli(GL_LIGHT_MODEL_LOCAL_VIEWER, GL_TRUE);
GLfloat light0_ambient[] = { 0.2, 0.2, 0.2, 1.0 };
GLfloat light0_specular[] = { 1.0, 1.0, 1.0, 1.0 };
GLfloat light0_diffuse[] = { 1.0, 1.0, 1.0, 1.0 };
GLfloat light0_position[] = { mLight0_x, mLight0_y, mLight0_z, 1.0 };
GLfloat light0_direction[] = { 0.0, 0.0, 0.0}; //at the center of the cube
glLightfv(GL_LIGHT0, GL_AMBIENT, light0_ambient);
glLightfv(GL_LIGHT0, GL_SPECULAR, light0_specular);
glLightfv(GL_LIGHT0, GL_DIFFUSE, light0_diffuse);
glLightfv(GL_LIGHT0, GL_POSITION, light0_position);
glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, light0_direction);
glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, 45.0);
//glLightf(GL_LIGHT0, GL_SPOT_EXPONENT, 2.0);
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
  }

型
无论我为GL_SPOT_CUTOFF设置了什么值（0.0-90.0），light 0都会熄灭。有什么线索吗？我对OpenGL很陌生，所以我相信我的代码缺少了什么或者做错了什么。
这是在不设置GL_SPOT_CUTOFF x1c 0d1x的情况下进行的
此时GL_SPOT_CUTOFF设置为45.0

白色点表示light 0的GL_POSITION。