Belgian Amiga Club - ADF Collection/BS1 part 65.zip/BS1 part 65/Caligari II v2.22.adf/FrameBuffers

Text File | 2018-01-29 | 6KB | 122 lines

                                                      15-Jan-92

Caligari II Framebuffer devices and the Virtual FrameBuffer

    In the Brender section of Caligari there is a button marked
"FrameBuffer". This allows the selection of a framebuffer device
to be used for the display of images. All rendered images in
Caligari are shaded with 32 bits of color and transparency. This
32 bit color information is then reduced for display on whichever
frame buffer has been selected via the "FrameBuffer" button.
All Caligari framebuffers always work in maximum overscan.
Additionally, Caligari maintains what is called a "Virtual
FrameBuffer".

    The virtual framebuffer is a section of memory, whose size
varies depending upon the resolution of the framebuffer, which is
continuously updated as Caligari displays new pixel data. What
this virtual framebuffer allows Caligari to do is display several
images simultaneously, always display an image with an optimal
palette for that particular image (if so desired) and
simultaneously view both 2d images and 3d renderings (very useful
when comparing a texture map image with how it actually renders).
The virtual framebuffer always has at least 24 bits of color
allowing for very faithful conversion of any number of buffered
images with a wide variety of colors to the real framebuffer
for display. All framebuffer devices maintain a virtual
framebuffer.

NOTE: when switching from one display resolution or one
      framebuffer to another the previous framebuffer is cleared!


CHARACTERISTICS OF EACH FRAMEBUFFER

    Caligari2 has four different frame buffer devices which are
as follows:


"caligariHAM-fb.device"

    This is the standard Caligari2 framebuffer display which will
function with any Amiga. The HAM display is pseudo-12 bit so the
number of colors that can actually be displayed is relatively low
compared to the other framebuffers (but it's also free...). Two
resolutions can be selected with either the NTSC or PAL buttons
(368x241, 368x482 and 362x283, 362x566 respectively) from the
"Display" menu.

    When an image is rendered to the HAM display, by
default a grey palette is used. When the image finishes rendering,
the palette is optimized and the image re-displayed. The "Dithr"
button controls whether or not this optimization process takes
place after rendering. Typically, you will not want to optimize
each individual image when animating because this will cause a
very noticable flickering during animation playback. Caligari
will automatically turn of the "Dithr" button after rendering
and optimizing the first frame. This will cause the same palette
to be used for all subsequent frames of the animation. Optionally
you can render a particular frame of the animation, which you
believe has a good representation of the colors used in the
animation, save the palette in the "Images" menu and use it for
rendering all of the frames of the animation. If you are optimizing
palettes in this fashion, be sure to turn off the "Dithr" button
before rendering or Caligari will attempt re-optimize the palette
of the next rendered image!

    We would like to thank Black Belt Systems, Inc. for their help
in the initial stages of the implementation of our HAM color palette
optimization algorithm.


"caligariHAME-fb.device"

    This framebuffer device requires that you have the HAME device
from Black Belt Systems, Inc. and that you have installed the
hame and renderhame libraries supplied on the Caligari distribution
disks. HAME is very similar in theory to HAM, but it works with
a pseudo-18 bit display and a much larger hardware palette. HAME
can produce much more realistic images and is highly recommended if
you desire RGB output. The image resolutions are the same as those
for HAM and the palette optimizing is also very similar. See the
above section on HAM for information on how you should manage your
color palettes as the same rules apply.


"caligariDCTV3-fb.device"
           AND
"caligariDCTV4-fb.device"

    These two devices are very similar and will be dicussed as one
with their differences described later. To use this framebuffer
device you need DCTV from Digital Creations, Inc. and the
dctv.library supplied on the Caligari distribution disks. DCTV can
display a very wide range of colors (approx two million), but at
the expense of resolution. DCTV, in contrast to HAM and HAME, only
outputs in composite video. It is because of this special encoding
that it is possible to display such a wide range of colors. DCTV
does not have a palette as do HAM and HAME; thus there is no need
for a second optimization pass over the image. Two resolutions can
be selected with either the NTSC or PAL buttons (736x241, 736x482
and 724x283, 724x566 respectively) from the "Display" menu.

    The "Dithr" button actually does control whether or not the
dctv.library dithers the 24 bit data when converting it to DCTV
format. In general the "Dithr" button should NOT be on when using
DCTV, especially with texture maps. Sometimes the "Dithr" button
is useful when rendering images which have large areas with very
smooth color transitions. A side-effect of "Dithr" being on is that
you may notice blue colors sometimes become somewhat red-tinted.

    DCTV3 and DCTV4 differ only in the number of Amiga display
bitplanes used to create the DCTV display. DCTV3 uses fewer
bitplanes which allows for faster animation playback at the expense
of the quality of the color. It is usually best to try both on a
short sequence of an animation before deciding which to use. DCTV3
images also take up less space in memory and on disk. Frequently
there is little difference between them, but this of course
depends on the content of the image.

    For more information on DCTV see the DCTV Users Guide.