Re: [Plib-users] Wanted--bitmap

[Steve B. <sjb...@ai...>]

Marlin Mixon wrote:
> 
> Working with viewer.cxx--great program BTW.  Trying to figure out how it
> works.  I was trying to figure out where it generated the bitmap, when it
> dawned on me: duh, it's handled by the video card.  So, ssgLoadAndCull() +
> GLUT basically sends the handle of the 3-d object to the card and the card
> renders the image right?

Well, there's a *bit* more to it than that - there are 30,000 lines of code
between "ssgCullAndDraw" and the graphics card(!) - but essentially, yes.

> Question:  is there a way to get a handle to a bitmap of, say, frame 7?

No.

You can read the contents of the frame buffer do to a 'screen dump' if
that's what you need - but if you were thinking of doing some direct
writing to the screen by simply addressing it as an array - forget it.
3D chipsets are very posessive when it comes to the frame buffer and
*ALL* rendering must go via OpenGL (which is what PLIB uses of course).

"bitmap" is the wrong term BTW since it implies a one bit-per-pixel image.

So, if you want to add a screen dump feature, you could use something like
this:

void do_screen_grab ( int width, int height )
{
  unsigned char pixels [ width * height * 3 ] ;
 
  glReadPixels ( 0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, pixels ) ;
 
  FILE *fd = fopen ( "tmp.ppm", "wa" ) ;
  assert ( fd != NULL ) ;
  fprintf ( fd, "P3\n# Screen Dump\n%d %d\n255\n", width, height ) ;
  for ( int i = height-1 ; i >= 0 ; i-- )
    for ( int j = 0 ; j < width*3 ; j++ )
    {
      fprintf ( fd, "%d ", pixels[i*width*3+j] ) ;
      if ( (j+1)%4 == 0 )
        fprintf ( fd, "\n" ) ;
    }
 
  fclose ( fd ) ;
}

...this writes a file in "ppm" format - which is probably the easiest format to
write out.

glReadPixels does the job of transferring the screen image into main memory.

> One reason why I'm enthusiastic about viewer.cxx is I've got some great
> aircraft models that I downloaded from www.flightsim.com .  One in
> particular is outstanding: a Kawasaki Ki-61 Hien.  File: st-hien2.zip.  The
> airplane is generally similar to a Messershmidt Bf-109, however the paint
> scheme is particularly colorful with some mean looking spotty camo.  The
> original author, Shigeru Tanaka of Kobe Japan does really nice work.  I
> emailed him a few years ago and he said that he was modeling plastic models,
> but most of his collection was destroyed during the Kobe earthquake.  More
> recently he's been shifting his energies to virtual modelling that can be
> shared over the internet.  Anyone who's interested in a copy, just send me
> an email and I'll be happy to pass it on.

I believe Wolfram Kuss is collecting aircraft models for the FlightGear list - if
he doesn't already have this one, I'm *sure* he'd be interested. (He's a regular
on this list BTW).

-- 
Steve Baker   HomeEmail: <sjb...@ai...>
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