Suzy B Software 2/Suzy B Software CD-ROM 2 (1994).iso/animatin/anim_q2z/statusdm/programs/gfa_spc/show512.txt

Text File | 1995-04-26 | 5.7 KB | 143 lines

 Object code modules for decompression and display of Spectrum pictures


Note:  these  modules can not be used as part of any  commercial  product
without approval of Trio Engineering, inc.



     The modules can be executed from any program that passes  parameters
on  the stack like in C (examples below are in GFA Basic).  They work  in
both medium and low resolution (color only).

     If you want to show an .SPU (uncompressed) Spectrum picture, you can
do  it right away with the SHOW512.O module.  .SPC  (compressed)  picture
files have to be decompressed first using DECOMP.O module.

     First thing you should do is to reserve memory for the module(s) and
the  picture  files.  The  amount  of  memory  required  by  the  modules
themselves  is  equal  to their size as  disk  files.  Each  uncompressed
Spectrum picture takes 51104 bytes. Compressed files can be anywhere from
2K to 50014 bytes.

     Next load the modules themselves.  The code is position-independent,
so  you  can  load them simply as data files  with  BLOAD.  The  starting
address for each module must be even, of course.

     If you want to decompress an .SPC file first load it to memory (even
address!).  The  decompressor works memory-to-memory,  it does  not  load
files from disk. Call the decompressor with the following command:

A=C:DECOM%(L:SPC%,L:BITM%,L:COLM%)

     DECOM%=Address of the DECOMP.O module
     SPC%=address of the SPC file
     BITM%=address of the decompressed bit map (must be divisible by 256)
     COLM%=address of the decompressed color map (must be even)

     A=0 if OK, -1 if decompression error (bad SPC file)


     The decompressor creates two separate blocks of data: 32000-byte bit
map at BITM% and 19104-byte color map at COLM%. You can put them anywhere
you  want,  they don't have to follow immediately one  another  (although
this is one of the obvious possibilities).

     An  .SPU  file is simply a bit map followed immediately by  a  color
map.  Load it at any address in memory divisible by 256 (SPU%),  and then
you'll have:

     BITM%=SPU%
     COLM%=SPU%+32000

     You also can load the first 32000 bytes of the .SPU file  separately
from the last 19104 bytes, to two different locations in memory.

     When  both the bitmap and the color map are in memory you  can  call
the  SHOW512.O module to display the picture on the  screen.  Here's  the
command to do it:


     VOID C:SHOW%(1,L:BITM%,L:COLM%)


     SHOW%=address of the SHOW512.O module


     To turn the 512-color display off call the SHOW512.O module with the
single parameter 0:

     VOID C:SHOW%(0)



     When you turn the 512-color display off,  SHOW512.O switches to  the
initial screen (restoring the color palette and resolution if necessary).
The  initial  screen itself will not be altered,  unless you used  it  to
store  the bit map portion of the .SPC or .SPU file (which  is  perfectly
all right to do). In this case make your program redraw its main screen.


     The mouse is disabled while the 512-color display is on.  You should
not  try  to  enable it during this period - it will  not  work  properly
anyway.  You  can only use the keyboard to control the program while  the
512 display is on.


     If  you  have several pictures in memory at the same  time  you  can
switch between them instantly without turning the 512-color display  off.
First,  you  have to load each of them to a separate location  in  memory
(and  decompress  if  necessary).  Start to show  the  first  picture  as
described  above,  then continue to call the SHOW512.O module in  exactly
the same way:

     VOID C:SHOW%(1,L:BITM2%,L:COLM2%)

     Use different addresses BITM% and COLM% with each new call.  At  the
end turn the 512 display off as described above.


     Of  course,  you  can make the display time for  each  picture  very
short  to create page-flip animations.  It's easy to control  the  timing
precisely.  When you call the SHOW512.O module it returns control to your
program with a 1/60 sec delay.  Therefore,  if you just make a series  of
calls:

     VOID C:SHOW%(1,L:BITM1%,L:COLM1%)

     VOID C:SHOW%(1,L:BITM2%,L:COLM2%)

     ................................


     you'll have a 60 frames per second animation.  To slow it down  make
one or more VSYNC calls between calls to the SHOW512.O module. Each VSYNC
delays the previous picture display for another 1/60 of a  second.  VSYNC
is the same as VOID XBIOS(37).

     If you want to synchronize picture switching with some other process
(Stereotek glasses,  for instance) keep in mind that the SHOW512.O module
always delays switching for one frame. Here's the timetable:

(1)  You call SHOW512.O with the new picture address.  It always  happens
     when the electron beam is somewhere between the 200-th line and  the
     screen bottom (at any other time the 512-color interrupt routine  is
     executed and your program stands still).

(2)  The current scan continues to the bottom of the screen

(3)  The next scan starts - still showing the _old_ picture

(4)  The  200-th  line  is reached.  SHOW512.O returns  control  to  your
     program. The next scan will show the new picture.



     If  you  use  GFA Basic do not call the SHOW512.O  module  from  the
direct  mode.  After executing any direct command GFA Basic  returns  the
screen resolution to medium,  overriding the low resolution mode selected
by SHOW512.O.  For the same reason you should write your Basic program in
such  a  way  that  it always turns  the  512-color  display  off  before
returning control to the user.