Question

Guys, how can this be. But in my previous projects, it wasn’t. And I don’t know how I attempt this effect. Tell me the truth, please.

Answer 1

Section 18.050, How can I make my light move or not move and control the light position?:

First, you must understand how the
light position is transformed by
OpenGL.

The light position is transformed by
the contents of the current top of the
ModelView matrix stack when you
specify the light position with a call
to glLightfv( GL_LIGHTn, GL_POSITION, ... ).
If you later change the ModelView
matrix, such as when the view changes
for the next frame, the light position
isn’t automatically retransformed by
the new contents of the ModelView
matrix. If you want to update the
light’s position, you must again
specify the light position with a call
to glLightfv( GL_LIGHTn, GL_POSITION, ... ).

…

• How can I make my light position stay fixed relative to my eye
  position? How do I make a headlight?

You need to specify your light in eye
coordinate space. To do so, set the
ModelView matrix to the identity, then
specify your light position. To make a
headlight (a light that appears to be
positioned at or near the eye and
shining along the line of sight), set
the ModelView to the identity, set the
light position at (or near) the
origin, and set the direction to the
negative Z axis.

When a light’s position is fixed
relative to the eye, you don’t need to
respecify the light position for every
frame. Typically, you specify it once
when your program initializes.