Disable and enable of lights

I was just wondering if I would gain speed or loose it if I disabled lights with glDisable when there isn't anything to fill their slots and then enable them again when there is, or if I should just give the unused lights some values to make them "dead".

Well you should disable lighting when you are not using it. Otherwise the calculations will be done and will hender performance.

Edit:

Let me elaborate. You can disable/enable individual lights or lighting as a whole.

Code:

---

// Tell opengl we want to use the lighting equation with lights to evalute vertex colors.
glEnable( GL_LIGHTING );
 
// Disable the first light..
glDisable( GL_LIGHT0 );
 
// Enable the second light..
glEnable( GL_LIGHT1 );

---

In that example if you had both lights enabled it would be slower. I think that's fairly obvious. Another light is just more calculations that have to be performed.

Code:

---

// We don't want to use lights to evaluate vertex colors
glDisable( GL_LIGHTING );
 
// Enable the first light..
glEnable( GL_LIGHT0 );
 
// Enable the second light..
glEnable( GL_LIGHT1 );

---

In this example, it doesn't matter that both lights are enabled. They won't be contributing anything to the scene because LIGHTING is disabled. Thus leaving them enabled won't hender performance.

If you are not using a light, absolutely, positively turn it off! Lights tend to use LOTS of processing power; why do you think OpenGL only allows 8 maximum?

OpenGL allows 8 maximum but you can implement your own vertex shaders that does the same OpenGL lighting functionality with as many lights as you wants

Quote:

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Originally Posted by MrWizard

Well you should disable lighting when you are not using it. Otherwise the calculations will be done and will hender performance.

Edit:

Let me elaborate. You can disable/enable individual lights or lighting as a whole.

Code:

---

  // Tell opengl we want to use the lighting equation with lights to evalute vertex colors.
  glEnable( GL_LIGHTING );
 
  // Disable the first light..
  glDisable( GL_LIGHT0 );
 
  // Enable the second light..
  glEnable( GL_LIGHT1 );

---

In that example if you had both lights enabled it would be slower. I think that's fairly obvious. Another light is just more calculations that have to be performed.

Code:

---

  // We don't want to use lights to evaluate vertex colors
  glDisable( GL_LIGHTING );
 
  // Enable the first light..
  glEnable( GL_LIGHT0 );
 
  // Enable the second light..
  glEnable( GL_LIGHT1 );

---

In this example, it doesn't matter that both lights are enabled. They won't be contributing anything to the scene because LIGHTING is disabled. Thus leaving them enabled won't hender performance.

---

Not trying to be rude, but I already know how OpenGL's lighting works :p. I was just wondering if I had a player run through a level and I was doing a lot of glDisable's and glEnable's for the lighting slots if it would be slower than just filling the lights with dead values when they weren't being used. Again, I wasn't trying to be rude. I'm just wondering how slow disabling and enabling lights is.

Lurker: thx

No problem, but it wasn't clear how much you knew about OpenGL from your post. Anyways, what do you mean by "dead values" ? If the lights are enabled it doesn't matter what values you have in them they are going to add to the final pixel color through means of the lighting equation. You would have to disable the specific light so that OpenGL knows that the light source won't contribute to the scene.

I just meant values that would make the light seemingly nonexistent (it would, like you said, contribute to the final pixel colors theoritically though).

turn the lights off, it will be faster.