"Sourcerer" <enlorkMAKNI@[EMAIL PROTECTED]
> wrote in message
news:jwnr5c1ltwdo.14dr6h1t1oq0v$.dlg@[EMAIL PROTECTED]
> On Tue, 20 May 2008 14:19:40 -0700 (PDT), fungus wrote:
>
>> On May 20, 9:40 pm, Sourcerer <enlorkMA...@[EMAIL PROTECTED]
> wrote:
>>>
>>> GLfloat lightSourcePosition[] = {10.0, 10.0, 10.0, 0.0};
>>> GLfloat lightSourceDirection[] = {0.0, 0.0, 0.0, 0.0};
>>>
>>> glLightfv(GL_LIGHT0, GL_POSITION, lightSourcePosition);
>>> glLightfv(GL_LIGHT0, GL_SPOT_DIRECTION, lightSourceDirection);
>>>
>>
>> My copy of the manual says: "The position is transformed by the
>> modelview matrix when glLight is called"
>>
>> Maybe that's the problem.
>
> Well, that doesn't really matter (i.e. I could live with that). What
> matters is that the position of the light is transformed every time I
> change the modelview matrix -- after the light is already placed in the
> scene, by doing glLoadIdentity() and gluLookAt() -- and I don't want
that
> to happen.
>
> If that can't work, is there another way to change my perspective in the
> scene which won't move the light with me?
>
> --
> "Let's see what's out there. Engage."
> Jean Luc Picard, Star Trek: TNG, Encounter at Farpoint
> http://pinpoint.wordpress.com/
Check out the FAQ:
"Here are some more specific questions, and their answers:
a.. 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
****ning 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.
a.. How can I make my light stay fixed relative to my scene? How can I
put
a light in the corner and make it stay there while I change my view?
As your view changes, your ModelView matrix also changes. This means
you'll need to respecify the light position, usually at the start of every
frame. A typical application will display a frame with the following
pseudocode:
Set the view transform. Set the light position
//glLightfv(GL_LIGHT_POSITION,.) Send down the scene or model geometry.
Swap
buffers.
If your light source is part of a light fixture, you also may need to
specify a modeling transform, so the light position is in the same
location
as the surrounding fixture geometry.
a.. How can I make a light that moves around in a scene?
Again, you'll need to respecify this light position every time the view
changes. Additionally, this light has a dynamic modeling transform that
also
needs to be in the ModelView matrix before you specify the light position.
In pseudocode, you need to do something like:
Set the view transform Push the matrix stack Set the model transform
to
update the light's position Set the light position
//glLightfv(GL_LIGHT_POSITION,.) Pop the matrix stack Send down the scene
or
model geometry Swap buffers. "
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