OpenGL states and performances

Hi all,

I have some questions about OpenGL.
I am actually writing a 2D tile based game.
I decided to choose OpenGL as I have never really been "allright" with
DX.
The main engine is almost finished but I'm worrying by some technical
points (of view...)

I really worry about the way I'm using OpenGL and particularly about
Texturing and its respective states.
For example:


1) The back and foreground of the game is based on tile. tiles are
extracted from 1 or N textures.
For each tile, the texture should be bound and the triangles/quads are
drawn.
But before binding the texID I store the current texID in a variable
so that it is bound
only if it's different from the current one.
Is it a good to achieve it ?


2) My sprites are composed of key-frames.
Each frame is grabbed from a Sprite-sheet using texture coordinates.
When a sprite is display I apply the same rule than above so that if
several sprites to be displayed are grabbed  from a same sheet,
the texID is bound just one time.


For displaying the sprites I use to activate the alpha channel
therefore I might use glEnable(GL_ALPHA_CHANNEL) etc.
But some other elements (backgrounds, tiles, sprites) may not use it.
At which moment should I enable/disable the GL_ALPHA_CHANNEL ?
I have a Texure2D c++ class in wich I store the GL_RGBA information.
heres a pseudo code:

Texture2D::bind()
{
  if( Texture2D::current_tex_id != this->mTexID) {
  	glBindTexture(GL_TEXTURE_2D, mTexID);

  	if( mUseAlpha ) {
  	  glEnable(GL_ALPHA_CHANNEL);
  	  glAlphaFunc(...)
  	}
  	else {
  	  glDisable(GL_ALPHA_CHANNEL);
  	  ...
  	}
  }
}

Does it make sense for you ?

You might think I worry about ridiculous details as I don't display
millions of triangles,
but I try no to make too many ugly  things .

Basically, I ignore what's the cost of OpenGL state-change function
calls.
Should we limit the glIsEnable(xxx) and glGetIntegerv(xxx) ?



Thanks for your feedback.

Zyend