void Viewport::OnPaint3D()
{
/////////////////
// initial stuff
/////////////////
glEnable(GL_DEPTH_TEST); // Enable Depth Testing
glEnable(GL_SCISSOR_TEST); // Enables Scissor Testing
glClearDepth(1.0f); // Depth Buffer Setup
glEnable(GL_COLOR_MATERIAL);

// set the viewport dimension
glViewport(m_rctVp.x, m_rctVp.y, m_rctVp.w, m_rctVp.h);
glScissor(m_rctVp.x, m_rctVp.y, m_rctVp.w, m_rctVp.h);

// clear the background
glClearColor(m_rgbBg.r, m_rgbBg.g, m_rgbBg.b, 1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

glEnable(GL_LIGHTING);


/////////////////
// set the camera
/////////////////
const Vector3D &v3dEye = m_pCamera->GetEyePoint();
const Vector3D &v3dView = m_pCamera->GetViewPoint();

glMatrixMode (GL_PROJECTION);
glLoadIdentity();

// Prevent a divide by zero, when window is too short
// (you cant make a window of zero width).
s32 s32H = Max<s32>(1, m_rctVp.h);
float fRatio = ((flt) m_rctVp.w) / ((flt) s32H);

// Set the correct perspective.
gluPerspective(45, fRatio, 0.1, 1000);

// gluLookAt on modelview stack
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(v3dEye.x, v3dEye.y, v3dEye.z, // eye position
v3dView.x, v3dView.y, v3dView.z, // look at position
0.0f, 1.0f, 0.0f); // up-vector


/////////////////
// set the light
/////////////////
GLfloat arPos[] = {0, 0, 1, 1};
GLfloat arCol[] = {1, 1, 0, 1};
GLfloat arAmbient[] = {0.2, 0.2, 0.2, 1};

glEnable(GL_LIGHT0);

glPushMatrix();
glLightfv(GL_LIGHT0, GL_POSITION, arPos);
glLightfv(GL_LIGHT0, GL_AMBIENT, arAmbient);
glLightfv(GL_LIGHT0, GL_DIFFUSE, arCol);
//glLightf(GL_LIGHT0, GL_SPOT_CUTOFF, 15.); // Frage 2 !!!
glPopMatrix();


////////////////
// set the plane
////////////////
GLfloat arColor[] = {1, 1, 1, 1};
GLfloat ar000[] = {0.0f, 0.0f, 0.0f, 1.0f};
GLfloat arNormal[] = {0, 0, 1};

glPushMatrix();
glMaterialfv(GL_FRONT, GL_AMBIENT, arColor);
glMaterialfv(GL_FRONT, GL_DIFFUSE, arColor);
glMaterialfv(GL_FRONT, GL_SPECULAR, ar000);
glMaterialfv(GL_FRONT, GL_EMISSION, ar000);

glBegin(GL_QUADS);
glNormal3fv(arNormal);
glVertex3d(-1, -1, -0);
glVertex3d(+1, -1, -0);
glVertex3d(+1, +1, -0);
glVertex3d(-1, +1, -0);
glEnd();
glPopMatrix();
} // Viewport::OnPaint3D

ps.: Warum die glPushMatrix()/glPopMatrix()-Aufrufe um glLight und glMaterial herum?

Lampe und Fläche sind mit der GL_MODELVIEW-Matrix eingegeben, müßten sich nach meinem Verständnis also drehen, wenn ich die Szene drehe - das heißt also, Lampe und Fläche sind fix in der Szene.