Research: Let's research the OAM-System

[knizz]

Warning: Confusion ahead.

Structures

00000000 coords              struc @ (sizeof=0x4)
00000000 x:                  .short
00000002 y:                  .short
00000004 coords              ends

00000000 oam                 struc @ (sizeof=0x8)
00000000 y:                  .byte
00000001 flags1:             .byte
00000002 x:                  .byte
00000003 msb_of_x_and_flags2:.byte
00000004 tile_prio_pal:      .short
00000006 irrelevant:         .short
00000008 oam                 ends

00000000 animation           struc @ (sizeof=0x4)
00000000 frame:              .half @ Internally: 0xFFFD=>animcmd1 0xFFFE=>animcmd2
00000000                           @ 0xFFFF=>animcmd3 any other number (=framenr) =>animcmd4
00000002 duration:           .half
00000004 animation           ends
(read http://www.pokecommunity.com/showthread.php?t=236456 for details)

00000000 object_template     struc @ (sizeof=0x18)
00000000 field_0:            .short
00000002 field_2:            .short
00000004 oam:                .long                 @ offset
00000008 animation_table:    .long                 @ offset
0000000C gfx_table:          .long                 @ offset
00000010 animation_table2:   .long                 @ offset
00000014 callback:           .long                 @ offset
00000018 object_template     ends

00000000 oam_thingie         struc @ (sizeof=0x44)
00000000 final_oam:          oam
00000008 animation_table:    .long                 @ offset
0000000C field_C:            .byte
0000000D field_D:            .byte
0000000E field_E:            .byte
0000000F field_F:            .byte
00000010 field_10:           .long                 @ offset
00000014 my_object_template: .long                @ offset
00000018 field_18:           .long
0000001C callback:           .long                 @ offset
00000020 pos_1:              coords
00000024 pos_2:              coords
00000028 pos_3_x:            .byte  @ These coordinates are subtracted from actual position!
00000029 pos_3_y:            .byte  @ It is used to center the sprites. So most of the times pos_3_x=width/2 and pos_3_y=height/2
0000002A anim_nr:            .byte
0000002B anim_frame:         .byte
0000002C time:               .byte
0000002D field_2D:           .byte
0000002E ipos:               coords ?
00000032 ivel:               coords ?            @ It seems like this is the private area
00000032                                         @ for functions managing a single oam.
00000032                                         @ Moving objects use ipos and ivel to save
00000032                                         @ the position and velocity. But they have
00000032                                         @ to be transferred to pos_1 manually. And
00000032                                         @ NPCs use the first byte of ivel to store
00000032                                         @ their current state.
...
00000042 field_42:           .byte
00000043 field_43:           .byte
00000044 oam_thingie         ends

And the rest
03003128(oam_buffer) is an array of "oam"-structures.
0202063C(oam_pre_buffer) is an array of "oam_thingie"-structures. It has an "oam"-structure at its beginning but it isn't used at first. When all changes to the other structure-fields are applied the function 08006BF4 transfers the data from other structure-fields into the oam-structure at the beginning. The "animation_table" points to another pointer that points to a list of animation-entries. (read http://www.pokecommunity.com/showthread.php?t=236456 for details)

Spoiler:

Small animation-table experiment: I changed some bytes in VBA-SDL like to this. This is an animation table. It ends with ffff 0000.
08f00000: 0000 0006 0001 0006 0002 0006 0003 0006 ................
08f00010: ffff 0000 ffff ffff ffff ffff ffff ffff ................
To apply this animation to the bag-item-icon write 08f00000 to 083d4278 (with the "ew"-command).

Also each oam can have a callback function. 08006B5C iterates through oam_pre_buffer and calls these functions.

It seems like 08231CA0 is a oam_thingie too.

There are four functions I know that deal with the template:
08007094 (pointer in R1; called by the functions below; copies many fields from the template to a "oam_thingie")
08006F8C (pointer in R0)
08006FE0 (pointer in R0)
080071EC (pointer in R0)

This is the complete "oam_thingie"-dump of the bag-item-icon: ("my_object_template" underlined)
0202063c: 8008007c 00003518 083d4278 00000000 |....5..xB=.....
0202064c: 08231cfc 03007d78 00000000 0800760d ..#.x}.......v..
0202065c: 00000000 008c0018 0000f0f0 00000000 ................
0202066c: 00000000 00000000 00000000 58010000 ...............X
0202067c: 00000118

The callback of the item-icon is "bx 0". The callback of the associated template is simply 00000000.

The instruction at 08007108 (=STR R1, [R7,#oam_thingie.my_object_template]) should copy the address of the template at R1 (which was copied from R8 which was copied from R1; this is part of the first of the four functions mentioned above) to the "my_object_template"-field of the "oam_thingie" pointed to by R7. So I'm sure I don't misinterpret the meaning of offset 0x14 in "oam_thingie".

The bag-item-icon-"oam_thingie" from above has 03007d78 at the "my_object_template"-field. template-dump: ("animation_table" underlined)
03007d78: 00000000 03007300 081dcc4d 00000000 .....s..M.......
03007d88: 00000000 00000000

This makes sense so far. Now there should be an animation table at 081dcc4d. However there isn't. This is what I find instead:
081dcc4c: 6b646220 d1c62c00 21f07828 70284008 bdk.,..(x.!.@(p
081dcc5c: 3a01464a 2050dd02 dcad182d 63784806 JF.:..P -....Hxc

Did I make a mistake? I can't find one.

Every information about the oam_thingies at 0202063C is appreciated.

[knizz]

00000000 npc_state       struc @ (sizeof=0x24)
00000000 bitfield_DX:    .byte ?
00000001 field_1:        .byte ?
00000002 field_2:        .byte ?
00000003 field_3:        .byte ?
00000004 oamid:          .byte ?
00000005 typeid:         .byte ?          @ Used as index for gender-color-lookup
00000006 running_behaviour:.byte ?
00000007 is_trainer:     .byte ?
00000008 field_8:        .byte ?
00000009 field_9:        .byte ?
0000000A field_A:        .byte ?
0000000B height:         .byte ?          @ Only bits 0x0F define height. I don't know about 0xF0.
0000000C stay_around:    coords ?
00000010 from:           coords ?
00000014 to:             coords ?
00000018 unknown2:       .byte ?
00000019 movement_area:  .byte ?
0000001A field_1A:       .short ?
0000001C the_state:      .byte ?
0000001D sight_distance: .byte ?
0000001E tile_from:      .byte ?
0000001F tile_to:        .byte ?
00000020 unknown1:       .byte ?
00000021 unknown3:       .byte ?
00000022 field_22:       .byte ?
00000023 field_23:       .byte ?
00000024 npc_state       ends

[shiny quagsire]

Lol, I tried this out, and it's pretty cool. I messed with the flags, and made my person a reflection.

The only flags I really found were: normal, no flip, vanish, and reflection

[knizz]

I found the oam-structures for the game-freak-star in the intro.

0840BC2C oam_star:       oam <0, 0, 0, 0x40, 0x800, 0>
0840BC34 oam_sparks:     oam <0, 0, 0, 0, 0x800, 0>
0840BC3C anim_spark_1:   animation <0, 0,  4, 0> @ 0
0840BC3C                 animation < 1, 0,  4, 0>@ 1
0840BC3C                 animation < 2, 0,  4, 0>@ 2
0840BC3C                 animation < 3, 0,  4, 0>@ 3
0840BC3C                 animation <0xFE, 0xFF, 0, 0>@ 4
0840BC50 anim_spark_2:   animation <0, 0,  4, 0> @ 0
0840BC50                 animation < 1, 0,  4, 0>@ 1
0840BC50                 animation < 2, 0,  4, 0>@ 2
0840BC50                 animation < 3, 0,  4, 0>@ 3
0840BC50                 animation <0xFF, 0xFF, 0, 0>@ 4
0840BC64 animtable_sparks:.long anim_spark_1,anim_spark_2@ 0
0840BC6C tpl_star:       object_template <0, 0, oam_star, animtable_empty, 0, off_08231CFC, oac_star+1>
0840BC84 tpl_sparks:     object_template <1, 1, oam_sparks, animtable_sparks, 0, off_08231CFC, oac_sparks+1>

Write 0840bc6c/0840bcbc/0840bcdc to 080EDDD8 and LOL.