[Plib-users] Applying the same texture twice

[<jo...@lu...>]

Hi all,

first of all a thank you for probiding and maintaining plib!

I got a minor problem with textures and ssg. I am drawing icons in 
a loop, and it can sometimes happen that the same icon (i.e. texture)
has to be drawn twice:

      for(i ...) {
        //(1)
        icon(i) -> apply ();   //icon(i) is an ssgSimpleState
        glBegin ( GL_QUADS ) ;
          glColor4f    ( 1, 1, 1, 1 ) ;
          glTexCoord2f ( 0, 0 ) ; glVertex2i ( x   , y    ) ;
          glTexCoord2f ( 1, 0 ) ; glVertex2i ( x+55, y    ) ;
          glTexCoord2f ( 1, 1 ) ; glVertex2i ( x+55, y+55 ) ;
          glTexCoord2f ( 0, 1 ) ; glVertex2i ( x   , y+55 ) ;
        glEnd () ;
      }

If it happens that icon(i)==icon(i+1), the second icon does
not get displayed. This seems to be caused by the lazy evaluation 
in apply(), since it does not bind the texture the second time. It
figures out that the texture wasn't changed, and does not to the 
glBindTExture call again. I don't know enough about OpenGL to know 
if this is correct, but for now I assume it is. 

Since I assume that I am not the only person having this experienced,
and I am not much of an OpenGL wizard: what is the proper solution 
to handle this?

I can work around the problem by either:
1) call icon->force()  at (1), since this will bind the texture 
   again (even if it's not changed). To optimise this further:
   I can compare icon(i) with the previous icon and only
   do this (probably expensive) force() call if the same icon is
   drawn twice (which is really an exception)
2) I can manually bind the texture at (1)
3) I can probably reset the current texture to 0 before
   calling apply()
4) ???

Any comments and suggestions are welcome!

Thanks a lot!
    Joerg