Xref: utzoo comp.sys.apollo:2741 comp.graphics:5913 comp.sys.misc:2292
Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!mit-eddie!apollo!oj
From: oj@apollo.COM (Ellis Oliver Jones)
Newsgroups: comp.sys.apollo,comp.graphics,comp.sys.misc
Subject: Re: --- ... --- SOS gmr3d library SOS --- ... ---
Summary: you cannot double buffer on 590 in borrow_rgb mode
Keywords: grm3d : how to
Message-ID: <4387d9a3.d5b2@apollo.COM>
Date: 30 May 89 12:51:00 GMT
References: <1239@geocub.greco-prog.fr>
Reply-To: oj@apollo.com (Ollie Jones)
Organization: Apollo Computer, Chelmsford, MA
Lines: 31

In article <1239@geocub.greco-prog.fr> haberstr@goofi.UUCP (Haberstrau Marianne) writes:
>We are trying to use gmr_$init in borrow_rgb mode, with 24 planes, obviously,
>but we always obtain this message : "No more fast buffers...".

The DN590 can be used either 
   * with 8-plane (256 colors) pseudocolor DOUBLE buffered
     To do this, init with gpr_$borrow, then call gpr_$allocate_buffer.

   * with 24-plane (2^24 color shades) true color SINGLE buffered
      To do this, init with gpr_$borrow_rgb.  However, you cannot
      call gpr_$allocate_buffer in this mode, because there's
      no second buffer available in the hardware.  If you do 
      call gpr_$allocate_buffer, you get the 
      "No more fast buffers.." message.

There are a total of 24 planes of video RAM in the 590.  These
can be allocated either as a single buffer of 24-plane RGB pixel
values, or as two 8-plane buffers of 8-bit pseudocolor pixel
values.  We didn't build in enough VRAM for double-buffered
true color because, at the time we built the 590, VRAM was
expensive, bulky and consumed mass quantities of power.
(On the other hand, now VRAM is still expensive, but it's
smaller and consumes somewhat less power).

(In case you were wondering about the missing 8 planes in double
buffered pseudocolor mode:  because of the way the display
hardware is designed, you can't write arbitrary data into them.)

Is your gpr_$borrow_rgb program is calling gpr_$allocate_buffer?
I hope this helps.
/Ollie Jones