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Player/Missile graphics

 References

- Player/Missile graphics RAM positioning scheme taken from the book Compute!'s First Book Of Atari Graphics (Introduction To Player/Missile Graphics, Figure 7)
- Memory map taken from the book Mapping The Atari - Revised Edition (article Memory Map)

 Player/Missile graphics scheme

 Player/Missile graphics memory address map

SHADOW REGISTER HARDWARE REGISTER LABEL DESCRIPTION
559 ($22F) 54272 ($D400) SDMCTL Direct Memory Access (DMA) enable flag. Among other things this location manipulates with players and missiles. It defines the playfield size, whether or not the missiles and players are enabled, and the player size resolution. To enable your options by using POKE 559, simply add up the values below to obtain the correct number to POKE into SDMCTL. Note that you must choose only one of the four playfield options appearing at the beginning of the list:
  Option                          Decimal   Bit
  Enable missle DMA                     4   2
  Enable player DMA                     8   3
  Enable player and missile DMA        12   2,3
  One line player resolution           16   4

Note that two-line player resolution is the default and that it is not necessary to add a value to 559 to obtain it. The default is 34 ($22).

623 ($26F) 53275 ($D01B) GPRIOR Priority selection register. Among other things, it also enables you to use all four missiles as a fifth player and allows certain overlapping players to have different colors in the areas of overlap.
  Priority options in order                Decimal Bit
  Player 0-3, plfld 0-3, bckg                 1    0
  Player 0-1, plfld 0-3, player 2-3, bckg     2    1
  Plfld 0-3, player 0-3, bckg                 4    2
  Plfld 0-1, player 0-3, plfld 2-3, bckg      8    3
  Four missiles = fifth player               16    4
  Overlaps of players have 3rd color         32    5
            
It is quite easy to set conflicting priorities for players and playfields. In such a case, areas where both overlap when a conflict occurs will turn black. The same happens if the overlap option is not chosen.
With the color/overlap enable, you can get a multicolor player by combining players. The Atari performs a logical OR to colors of players 0/1 and 2/3 when they overlap. Only the 0/1, 2/3 combinations are allowed; you will not get a third color when players 1 and 3 overlap, for example (you will get black instead). If player one is pink and player 0 is blue, the overlap is green. If you don't enable the overlap option, the area of overlap for all players will be black.
704 ($2C0) 53266 ($D012) PCOLR0 Color of player 0 and missile 0
705 ($2C1) 53267 ($D013) PCOLR1 Color of player 1 and missile 1
706 ($2C2) 53268 ($D014) PCOLR2 Color of player 2 and missile 2
707 ($2C3) 53269 ($D015) PCOLR3 Color of player 3 and missile 3. When the four missiles are combined to make a fifth player, it takes on the color in location 711 (COLOR3).
/ 53248 ($D000) HPOSP0 Horizontal position of player 0. Values from zero to 227 ($E3) are possible but, depending on the size of the playfield, the range can be from 48 ($30) as the leftmost position to 208 ($D0) as the rightmost position. Other positions will be "off screen".

Missile 0 to playfield collision status.
/ 53249 ($D001) HPOSP1 - Horizontal position of player 1.
- Missile 1 to playfield collision status.
/ 53250 ($D002) HPOSP2 - Horizontal position of player 2.
- Missile 2 to playfield collision status.
/ 53251 ($D003) HPOSP3 - Horizontal position of player 3.
- Missile 3 to playfield collision status.
/ 53252 ($D004) HPOSM0 Horizontal position of missile 0. Missiles move horizontally like players. See the note in 53248 ($D000) concerning the use of horizontal registers. Also player 0 to playfield collision status.
/ 53253 ($D005) HPOSM1 - Horizontal position of missile 1
- Player 1 to playfield collision status
/ 53254 ($D006) HPOSM2 - Horizontal position of missile 2
- Player 2 to playfield collision status
/ 53255 ($D007) HPOSM3 - Horizontal position of missile 3
- Player 3 to playfield collision status
/ 53256 ($D008) SIZEP0 M0PL - Size of player 0 (0 = normal, 1 = double, 3 = quadruple)
- Missile 0 to player collision status
/ 53257 ($D009) SIZEP1 M1PL - Size of player 1 (0 = normal, 1 = double, 3 = quadruple)
- Missile 1 to player collision status
/ 53258 ($D00A) SIZEP2 M2PL - Size of player 2 (0 = normal, 1 = double, 3 = quadruple)
- Missile 2 to player collision status
/ 53259 ($D00B) SIZEP3 M3PL - Size of player 3 (0 = normal, 1 = double, 3 = quadruple)
- Missile 3 to player collision status
/ 53260 ($D00C) SIZEM P0PL - Size for all missiles set by bits
- Player 0 to player collision status
/ 53261 ($D00D) GRAFP0 P1PL - Graphics shape for player 0 written directly to the player graphics register. In using these registers, you bypass ANTIC. You only use the GRAFP# registers when you are not using Direct Memory Access (DMA: see GRACTL at 53277). If DMA is enabled, then the graphics registers will be loaded automatically from the area specified by PMBASE (54279; $D407).

The GRAF registers can only write a single byte to the playfield, but it runs the entire height of the screen.

- Player 1 to player collision status
/ 53262 ($D00E) GRAFP1 P2PL - Graphics shape for player 1

- Player 2 to player collision status
/ 53263 ($D00F) GRAFP2 P3PL - Graphics shape for player 2

- Player 3 to player collision status
/ 53264 ($D010) GRAFP3 Graphics shape for player 3
/ 53265 ($D011) GRAFM Graphics for all missiles, not used with DMA. GRAFM works the same as GRAFP0 above. Each pair of bits represents one missile, with the same allocation as in 53260 ($D00C) above.
         Bit  7 6  5 4  3 2  1 0
     Missile  -3-  -2-  -1-  -0-
  
Each bit set will create a vertical line running the entire height of the TV screen. Missile graphics shapes may be set separately from each other by using the appropriate bit pairs. To mask out unwanted players, write zeros to the bits as above.
/ 53276 ($D01C) VDELAY Vertical delay register. Used to give one-line resolution movement capability in the vertical positioning of an object when the two line resolution display is enabled. Setting a bit in VDELAY to one moves the corresponding object down by one TV line. If DMA is enabled, then moving an object by more than one line is accomplished by moving bits in the memory map instead.
     Bit   Decimal   Object
     7       128     Player 3
     6        64     Player 2
     5        32     Player 1
     4        16     Player 0
     3         8     Missile 3
     2         4     Missile 2
     1         2     Missile 1
     0         1     Missile 0
/ 53277 ($D01D) GRACTL Location for turning on players and missiles. To get the values to be POKEd here, add the following options together for the desired function:
                             Decimal   Bit
     To turn on missiles        1       0
     To turn on players         2       1
     To latch trigger inputs    4       2
  
To revoke P/M authorization and turn off both players and missiles, POKE 53277,0.
/ 53278 ($D01E) HITCLR POKE with any number to clear all player/missile collision registers. It is important to clear this register often in a program -- such as a game -- which frequently tests for collisions. Otherwise, old collision values may remain and confuse the program.
/ 54279 ($D407) PMBASE MSB of the player/missile base address used to locate the graphics for your players and missiles (the address equals PMBASE * 256. P/M graphics are tricky to use since there are no direct Atari 8K BASIC commands to either create or move them (there are, however, commands for P/M graphics in BASIC A+, in valFORTH and other utilities).