Re: [PyOpenGL-Users] Fade to black?

[Mike C. F. <mcf...@ro...>]

Rene Dudfield wrote:

> Hello.
>
> I was wondering if anyone had an idea on how to do fade to black?
>
> I was thinking of overlaying a texture over the scene and slowly 
> changing the alpha this texture has. 

This should work on anything from a TNT2 onward, though you don't 
actually need it to be a texture unless you are interested in having the 
fade be textured (e.g. having the game logo fade in on a 
black/white/whatever background).  A simple polygon with the required 
color and alpha should work.

> But would that work ok on slower hardware?  If it is slow any other 
> ways to do fade to black(or from black, or to/from white etc)? 

I would strongly suggest just implementing it first and seeing if it 
really is slow, I wouldn't expect it to be too slow if your game is 
running reasonably well before the fade starts, yes there will be a lot 
of overdraw, but you can disable depth buffer updates, so only 
one/(three) buffers are getting changed.  Possible optimization strategies:

    * use overlays where available
          o i.e. render your transparency as an overlay rather than part
            of your main scene
          o if not, do a screen-capture to a bitmap and just blit the
            bitmap, then the fading polygon each time you want to
            increase the fading level, you may find that using the
            captured bitmap as a texture works considerably faster
    * use screendoor transparency
          o only likely to be useful on very old hardware, (e.g. TNT or
            previous)
    * use solid-color polygon instead of textured (likely only an issue
      if the texture is very large)
    * do a screen capture, turn it to a texture  and blend it *on top
      of* a solid-color background of the target color (i.e. glClear)
      each frame with altered alpha level, opaque at start, transparent
      to end (saves extra geometry/overdraw).

Have fun,
Mike

_______________________________________
  Mike C. Fletcher
  Designer, VR Plumber, Coder
  http://members.rogers.com/mcfletch/