Vectronix 2/VECTRONIX2.iso/FILES_03/JAG_DOX.ZIP/op.txt

Text File | 1996-01-28 | 23KB | 617 lines

# -------------------------------------------------------------------
# OBJECTPROCESSOR                  (c) Copyright 1995-1996 Nat! & KKP
# -------------------------------------------------------------------
# These are some of the results/guesses that Klaus and Nat! found
# out about the Jaguar. Since we are not under NDA or anything from
# Atari we feel free to give this to you for educational purposes
# only.
#
# Please note, that this is not official documentation from Atari
# or derived work thereof (both of us have never seen the Atari docs)
# and Atari isn't connected with this in any way.
#
# Please use this informationphile as a starting point for your own
# exploration and not as a reference. If you find anything innacurate,
# missing, needing more explanation etc. by all means please write
# to us:
#    [e-mail]
# or
#    [e-mail]
#
# If you could do us a small favor, don't use this information for
# those lame flamewars on r.g.v.a or the mailing list.
#
# HTML soon ?
# -------------------------------------------------------------------
# $Id: op.txt,v 1.10 1996/01/28 20:23:20 nat Exp $
#
# If there are two theories I put the more likely one first.
# -------------------------------------------------------------------
Things to know about the Objectprocessor (OP):

-1 Imagine a phrase being an entity of 64 bits (or 8 bytes for that
   matter).

0. The object list is a linked list.

1. The object list is traversed by the object processor for
   each! scanline.

2. The Objectprocessor probably works like this:

   Whenever a new scanline needs to be displayed, the
   objectprocessor provides a linebuffer to the videosystem. While
   the videosystem is busy displaying this, the OP readies the next
   scanline. (It uses a doublebuffering strategy) It does
   this by traversing the objectlist and interpreting each
   object in sequence. Each object has per scanline the chance
   ONCE to fill the linebuffer. It fills the linebuffer at
   a specified horizontal position for a specified width. The data
   in the linebuffer is always overwritten (except when the
   Read-Modify-Write bit is set). If the active object has the
   transparent bit set, it will not overwrite values in the
   linebuffer when its source pixel has the value zero.
   The 'transparency' check is done before looking up the pixel's
   color in the CLUT (1 - 256 color modes).

2.1   The sooner a object appears in the list the more
   in the background it appears. The linebuffer is initalized with
   the linebufferbackgroundcolor (BG) before the objectprocessor
   starts filling the linebuffer.

   One may also assume that the OP normally traverses the
   linebuffer from left to right, except when the horizontal flip
   bit is set. (Very useful information indeed! (har) )

   Each bitmap object is made up of pixels. These pixels can be either
   contain the color itself (direct) as in CrY and TrueColor modes
   or be an index into a Colorlookuptable (indirect).

2.2   We assume that the OP writes into the linebuffer locally, so that
   the objectdata is read over the bus, but not written into the
   linebuffer over the bus (which would be way evil)

2.3.  The videosystem can deal with 16bit RGB/Crycolor and 24bit RGB
   pixels, the size of the pixels the OP writes into the linebuffer
   and pulls out of the CLUT, depends on the pixeltype chosen for
   the videosystem.

2.4   The object in the objectlist are *modified* by the OP. This means
   that an object list is only good for one frame. You need to
   continually refresh your object list each VBLANK.

3.  ...
4.  ...

5. The last object must be a STOP object.

6. The Objectlist must be doublephrase aligned. This means
   that the lower nybble of the address must be zero.

7. The address of the image of an object must be (as expected)
   phrase aligned (zero in the lower 3 bits)

8. There are five different objects that the Objectprocessor knows
   about. These are:

   1. Bitmapped Object
   2. Scaled bitmapped object
   3. GPU-Object (Calls the GPU to do the displaying ?? )
   4. Branchobject
   5. Stopobject (marks the end of the object list)

   The objects have different sizes. The minimum size of an object
   is a "phrase".

   Object type    Number     Size in phrases
   -----------------------------------------
   BIMAP          0           2
   SCALE          1           3 (4?)
   GPU            2           1
   BRANCH         3           1
   STOP           4           1

   It looks like you need to pad your scale objects to four phrases...

9  To keep the Objectprocessor from fetching data (and wasting bandwidth)
   during the VBLANK you usually put two branch objects at the beginning
   of the display list, that branch to the stop object if the first
   displayable scanline has not been reached or the last displayable
   scanline has already been displayed.

10.   Just reading concurrently from the linebuffers while the OP is
   displaying data produces glitches. Advice: Stay out of them!

:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
10             This is what a branch object looks like:
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

Phrase #0:

   63      56        48       40       32        24       16       8    3   0
  +--------^---------^-----+---^--------^--------+--------+--+-----^----+---+
  |        unused          |      Link-address   | unknown|CC|   VCnt   |011|
  +------------------------+---------------------+--------+--+----------+---+
      63 .............43      42..........24      23...16 15.14 13 .... 3


   The branch objects are used to compare the current scanline
   with the value stored in the branch object. Depending on the
   branch instructions comparison mode, the branch is taken
   either on < == != or >. The taken branch taken uses the information
   from the Linkinfo and branches to the phraseindexed
   object. If the comparison fails it simply examines and handles
   the next object in the list.


VCnt:    This is the value you compare the vertical scanline
counter with (VC). For CC code 10 the operation goes:

   if( object->YCnt < VC)
      goto object->link;


Conditioncodes:

        Values     Comparison/Branch
   ------------------------------------------------
      000   Branch on equal            (VCnt==VC)
      001   Branch on less than        (VCnt>VC)
      010   Branch on greater than     (VCnt<VC)
      011   Branch if OP flag is set

Note that 000 is a branch always if VCnt == $7FF (very strange!)


:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
11                This is what a stop object looks like:
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

Phrase #0 (1 of 1):

 63       56        48        40       32        24       16       8    3   0
  +--------^---------^---------^--------^--------^--------^--------^----+---+
  |                                 datafield                           |100|
  +---------------------------------------------------------------------+---+

 There is a datafield in this instruction of unkown size. This may or
 may not be a way to generate horizontal interrupts. Maybe this is just
 a flag that someone can poll from somewhere...


:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
12.               This is what a bitmap object looks like:
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
Phrase #0 (1 of 2):

 63       56        48        40       32        24       16       8    3   0
  +--------^---------^-----+------------^--------+--------^--+-----^----+---+
  |        data-address    |     Link-address    |   Height  |   YPos   |000|
  +------------------------+---------------------+-----------+----------+---+
      63 .............43         42..........24   23 ..... 14 13 ..... 3 2.0
        21 bits           19 bits        10 bits     11 bits  3 bits


  data-address:   Pointer to the bitmap      ***DESTROYED BY THE OP***
  link-address:   Pointer to the next object
  height:         Height in pixels
  y-pos:          Vertical position          ***DESTROYED BY THE OP***
  type:           Object type


data-address:
   An address is a memory address in terms of phrases. To get the
   byte address you have to shift it up by 3. (or in this example
   to get the data-address you would fetch the upper lword with
   the 68K and do):

      move.l   (a0),d0     ; fetch it  (bits 63-32)
      moveq #11,d1         ; or some other less lame way
      lsr.l d1,d0          ; shift it down for phrase address
      lsl.l d1,d0          ; shift it up for byte address

link-address:
   The link address strings the object list together. So it really
   is a linked list, not just an array. OK an array would have
   been better and the link could have been a number of phrases
   to skip. It misses the upper two bits two form a proper full
   24 bit address. This means that objects must reside in the
   lower 4 MB.

height:
   The height of the object is also stored in the first phrase.
   This is the number of pixels an object has in it vertical extent.

ypos:
   The YPos is predictably the vertical position of the object on
   the screen. The vertical position is the halfline vertical
   position.

 Theory 1:
   Like on the Falcon the screen is divided into two horizonzal
   halflines. Except for really wide screens in excess of 1024
   pixels horizontally, you always stay in the first halfline.
   (That's why its eleven bits, and the height is only 10 bits.)
   A problem with this theory is, that the Xpos field is 12 bits
   anyway...

 Theory 2:
   This means that in interlace mode this is the "true"
   vertical position on the screen. In non-interlaced modes
   (non-flicker)  modes, you should multiply your Y-Pos by two and
   stuff that into the object.
   (That's why its eleven bits, and the height is only 10 bits.)

type:
   Lastly the object type indicates with a 0 (000) that this object
   is a normal non-scaled bitmap object.


Phrase #1 (2 of 2):

   63      56        48       40       32        24       16       8       0
  +--------+---------+------+--^--+-----^---+----^----+---+---+----^--------+
  | unused | 1stpix  |flags | idx | iwidth  | dwidth  | p | d |    <XPos>   |
  +--------+---------+------+-----+---------+---------+---+---+-------------+
    63...55 54....49  48..45 44.38  37...28    27..18 17.15 14.12   11.....0
               6bit  4bit  7bit   10bit   10bit  3bit  3bit     12bit

   Curiously there seem to be some unused bits in the top half of
   this second phrase. Anyway starting from the left:

   firstpix:   Pixels to skip
   flags:      How to handle the source data
   index:      Index into the CLUT
   iwidth:     Width of the image
   dwidth:     Offset to the next line of the image
   pitch:      Increment for the Datapointer
   depth:      Pixeldepth of the bitmap
   x-pos:      Horizontal position of the object


1stpix: this is a field of 6 bits that contains the number of
   'bits' to skip before fetching the first pixel. This must be
   used whenever your bitmap data isn't phrase aligned.
   Maybe most often used for CLUT modes.
   You get the value you want to write here by calculating:

   pixelindex * bits_per_pixel (f.e. 8 for 256 color mode)


flags:   You can tell the Objectprocessor the way it should
   handle the display data. These are the values you set here:

   Bit0        Bit1        Bit2        Bit3
    --------------------------------------------------------------
     Horizontal Flip   ReadWriteModify   Transparent   Release

A few guesses as to what each flag does:

Horizonal flip:      Lets the Objectprocessor run
   its path from the other end of the spritedata, which should
   effectively flip you sprite data.

ReadWriteModify:  The object processor reads the the pixel from the
   line buffer does something with the bitmap pixel value
   and the linebuffer pixel value and stores the result back into
   the linebuffer.

   Theory 1. For Crycolor the lower byte of the bitmap pixel value
   is sign extended and added to the lower byte of the linebuffer pixel
   value, thereby increasing or decreasing (depending on the sign)
   the intensity of the linebuffer pixel. This is a 'saturating add'
   meaning that you don't wrap around, but subtractions stick at 0 and
   additions stick at 255.
   The cryhues (upper byte) are mangled even more strangely, the effect
   could (with the right values) be like looking through a colored
   glass (your bitmap object with the RMW-flag set) onto the
   background (the other bitmap objects below it)
   This might be similiar to what happens when gouraudshading. Refer
   to the blitter docs.

   Theory 2. Both values are simply added together


Transparent:      When the source pixel is zero, this
   pixel will not be written. This is the way to achieve
   transparent sprites with the GPU. (Both CLUT and non-CLUT pixels)

Release:    If cleared then the OP 'hogs' the bus for
   the time it takes to fetch the scanline data of the object. If this
   bit is set, then the bustime is shared with other processors. If you
   have lotsa interrupts going, this might be worthwhile.

index (idx):   Index into the ColorLookUpTable (CLUT)
   This information is only used for 1 - 2 or 4 bitplane objects,
   to determine the offset in the CLUT to use.

   1 bitplane           2 bitplane       4 bitplane
   -------------------------------------------------------
        iiiiiiii          iiiiii0         iiiii00

   The value is shifted left once and then used as an index into
   the CLUT. Note that in 2 + 4 bitplane modes not all bits are in
   used, because the lower bits are replaced with the pixel value.

   For example in 4-bits-per-pixel mode pixel #7 and an idx value of
   64 gives you an index of (64*2)+7 -> 135

   So you preload the CLUT with the colors you want to use, for
   example green at index #241. When you want to display a small
   green arrow on the screen (as a pointer) for example you set
   your object to transparent, and the index to 120. When the
   object pointer fetches a set pixel, it will write the green
   value into the linebuffer.

iwidth:     Tell the OP how many *phrases* to draw in each
   line. This is the actual number of phrases to draw, not the
   horizontal index to index the next line (dwidth). This is
   probably not just  #pixels_to_draw / bits_per_pixel, but rather
   the number of phrases the object spans. If a 32bit object spans
   two phrases you should enter a two here.

dwidth:     The horizontal phrase offset the OP should use
   to index to the next line. If you data is laid out in
   consecutive strips of horizontal data like this:

screen <destination>:
   00000000000
   11111111111
   22222222222
   33333333333

memory <source>:
   00000000000111111111112222222222233333333333

   then this will be just the same as <iwidth>. But if your data
   is laid out like this:

   00000000000xxxxx11111111111xxxxx22222222222xxxxx33333333333xxxxx

   you should set <dwidth> to the proper offset so that adding
   <dwidth> to the phrase-address will bring you to the next line.
   (This might be useful for 'horizontally scrolling' objects).

pitch (p):  If you so desire you can organize your bitmap
   data in even stranger ways than one would think possible. With
   this value you control the datapointer that the OP uses to
   traverse your bitmap data. This value is added to the
   datapointer after the last fetch. If you use a 0 you will be
   always fetching the same phrase over and over again. Normally
   you set <pitch> to 1, to advance through memory contigously.

depth (d):  The number of bits of each pixel. This
   specifies the rez of the object. You have the choice between
   direct pixel modes (16 or 24/32 bits) and indirect (CLUT)
   pixel modes. Note that using transparency effectively
   reduces the number of available colors by one (color #0).

   Values:

   0  1 bits per pixel  2 colors       CLUT
   1  2 bits per pixel  4 colors       CLUT
   2  4 bits per pixel  16 colors      CLUT
   3  8 bits per pixel  256 colors     CLUT
   4  16 bits per pixel 65536 colors   CRY
   5  24 bits per pixel 16 Mio Colors  TrueColor
   6  unused
   7  unused

xpos:    The horizontal position of the object on the
   screen (or in the linebuffer if you will)



:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
13.            This is what a scaled bitmap object looks like.
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

Phrase #0 (1 of 3):

 63       56        48        40       32       24       16        8    3   0
  +--------^---------^-----+---^--------^--------+--------^--+-----^----+---+
  |       <data-address>   |    <Link-address>   | < Height >|  <YPos>  |001|
  +------------------------+---------------------+-----------+----------+---+
      63 .............43         42..........24   23 ..... 14 13 ..... 3 2.0
        21 bits           19 bits        10 bits     11 bits  3 bits

   Except for the type, which is different, this is just
   the same as the first phrase of the bitmap (non-scaled)
   object.


Phrase #1 (2 of 3):  This is the same as the the 'bitmapped' object


Phrase #2 (3 of 3):

   63      56        48       40       32        24       16       8       0
  +--------^---------^---------^--------^--------+--------+--------+--------+
  |                  unused                      | remain | VScale | HScale |
  +----------------------------------------------+--------+--------+--------+
                                                   23...16  15...8   7...0

  remainder:   Keeps the VScale remainder ***DESTROYED BY THE OP***
  v-scale:     Vertical scaling factor
  h-scale:     Horizontal scaling factor


  The scale is a fractional representation, using 3 bits for the integer
  part and 5 bits for the fractional part. Or in ASCII-Graphics:

   76543210 00100000 or 0x20 is 1.0
   iiifffff 00010000 or 0x10 is 0.5

  The remainder is used by the objectprocessor for the vertical scaling,
  as a memory place. You should initialize it to 0.5 for best results,
  although in a lot of democode its initialized to 1.0.


:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
14.                     The elusive GPU-object
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

Phrase #0 (1 of 1):

 63       56        48        40       32       24       16        8    3   0
  +--------^---------^---------^--------^--------^--------^--------^----+---+
  |                           datafield                                 |010|
  +---------------------------------------------------------------------+---+

   The GPU object gets an interrupt, it is believed that the OP is not
   halted because of this action. You might want to stuff some information
   into the datafield, which the GPU could then read from the OLP registers.
   But what for ?


:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::
15 You can also look at the object in terms of C-structs, that's how
   they'd look like.
:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::

/* DON'T USE THESE BITFIELDS WITH ANYTHING ELSE THAN A
   ***GOOD*** C-COMPILER AND A MOTOROLA PROCESSOR
*/


   #define byte   unsigned char
   #define word   unsigned short
   #define lword  unsigned long
   #define phrase unsigned long long


   typedef struct
   {
       lword   data:21;
       lword   link:19;
       word height:10;
       word ypos:11;
       word type:3;
   } bitmap_obj_phrase_0;


   typedef struct
   {
      word  unused:9;
      word  firstpix:6;
      word  flags:4;
      word  index:7;
      word  iwidth:10;
      word  dwith:10;
      word  pitch:3;
      word  depth:3;
      word  x_pos:12;
   } bitmap_obj_phrase_1;


   typedef struct
   {
      lword   unused:24;
      word    remainder:8;
      word    v_scale:8;
      word    h_scale:8;
   } scale_obj_phrase_2;


   typedef struct
   {
       lword   unused:21;
       lword   link:19;
       word    conditioncode:2;
       word    unused:8;   ;; maybe index to register ?
       word    ypos:11;
       word    type:3;
   } branch_obj_phrase_0;


   typedef struct
   {
       phrase  unused:61;
       word type:3;
   } stop_obj_phrase_0;

   typedef struct
   {
       phrase  unknown:61;
       word type:3;
   } gpu_obj_phrase_0;


   typedef struct
   {
      stop_obj_phrase_0 p0;
   } stop_obj;


   typedef struct
   {
      branch_obj_phrase_0  p0;
   } branch_obj;


   typedef struct
   {
      gpu_obj_phrase_0  p0;
   } gpu_obj;


   typedef struct
   {
      bitmap_obj_phrase_0  p0;
      bitmap_obj_phrase_1  p1;
   } bitmap_obj;


   typedef struct
   {
      bitmap_obj_phrase_0  p0;
      bitmap_obj_phrase_1  p1;
      scale_obj_phrase_2   p2;
      /* need one padding phrase ? */
   } scale_obj;




SMALL DISCUSSION:
   Since the object processor walks the object list for each
   scanline, you should consider the following:

   If you have 64 bitmaps objects in your object list and a
   vertical rez of 240 lines going and a refreshrate of 60Hz
   the Objectprozessor is pulling

   60 hz * 240 lines * 64 objects * 2 phrases =  1.8 Mio phrases/s
   ~ 14.7 Mio bytes/s  for the object processor list alone!
      (ca. 14% of the systems bandwidth)


   If you figure you're using 128x128x16bit sprites fully visible,
   you're doing:

   128x128*16bits/64bits = 4096 phrases a sprite
   64 sprites in 60hz    = 3840 sprites
   yields 15728640 phrases/s or 120 Mbytes/s

   So it is fairly easy to unknowingly saturate the bus with
   a nice object list...
   It should be obvious that non-"truecolor" sprites still make
   lotsa sense, when you're using the OP heavily.

   It would have been better in our opinion, if Atari had used a
   small 2-Kbit hitbuffer (or single bit Z-Buffer) and reversed
   the object order, so that the nearest object comes first and
   the background last in the object list.

   With such a slightly more complicated scheme,the OP could
   run at a rather constant:

      hrez * vrez * refresh * average_bits_per_pixel
      ---------------------------------------------- phrases/s
               64


NEEDED STUFF:
   Need to document the logic setting up objects, that cross
   boundaries (especially the scaled bitmaps)