Path: utzoo!attcan!uunet!zephyr!tektronix!psueea!jove.cs.pdx.edu!bartonr
From: bartonr@jove.cs.pdx.edu (Robert Barton)
Newsgroups: comp.sys.amiga.tech
Subject: CAMG
Message-ID: <1405@psueea.UUCP>
Date: 25 Jun 89 04:43:20 GMT
Sender: news@psueea.UUCP
Reply-To: bartonr@jove.cs.pdx.edu (Robert Barton)
Organization: Dept. of Computer Science, Portland State University; Portland OR
Lines: 38


 In article <12340@well.UUCP> shf@well.UUCP (Stuart H. Ferguson) writes:
> 1.) Many programs write inconsistent ILBM's.  Some even create 640 x 200
> bitmaps with no CAMG chunk and ask for a pixel aspect ratio of 10/11.

  Well, 640x200 could be HIRES and LACE, in which case the standard aspect ratio
is 10/11 (although the actual value is closer to 6/7).  Or it could be a lo-res,
non-interlaced superbitmap.

> 2.) Many ILBM's are not created on Amigas.  For them, the CAMG chunk is
> much less meaningful and may be missing.  Here the pixel aspect ratio is
> much more important to observe.
> 3.) Many ILBM's are not displayed on Amigas.  Same caveats as above.  (We're
> talking device-independent here, folks...) 

  I don't think I have seen any so far that weren't created on an Amiga, but the
standard is certainly designed to make that possible.  Other machines should
not write CAMG chunks, and just skip them when reading.  Amiga programs that
read these "foreign" files will have to try and match the aspect ratio in the
BMHD with one of the Amiga's 3 possible ratios, recognizing that one of these
ratios covers both lo-res non-interlace and hi-res interlace.

> 4.) Many bits in the viewmodes word as used in the graphics library are
> very dangerous to just jam into a new viewport.  Bits such as VP_HIDE and
> the GENLOCK bits.  Always be sure to mask these out when writing and
> especially when reading (kids, you don't know where these files have been...)

  Good point.  There is additional information along these lines in the IFF
section of the new Includes & Autodocs, including some defines you can use to
mask off the inappropriate ViewModes bits.

> 5.) The ECS viewmodes, support for multisync monitors, and the way the
> system people plan to address this in the future will make this CAMG issue --
> let's just say -- VERY interesting.  (You think it's hard to understand NOW...)

  If there are going to be some new ViewModes bits with ECS, it would be nice
if their definitions could be released as soon as possible so programs can be
designed to work with the new modes.