Purple Martians
Technical Code Descriptions
Game Moves Array
Overview
Variables
Array elements
Types of game moves
How game_move entries are added in single player mode
How game move entries are added in netgame
How controls are set from game move array
Run demo game mode
Overview
The game moves array is the heart of the entire game control system.
It contains every input from every player, indexed by the frame number.
The array does not store an entry for every frame, only when a player's controls have changed.
Players controls are never set directly, even in single player mode.
When a player's control inputs change, a new entry is made into the array at that frame number.
In another function, the game move array is used to set players controls when the frame numbers match.
This method is not needed for single player mode, but it is essential for netgame and demo game replaying.
So, in the interests of keeping things consistant, it is also the method used for single player.
Variables
extern int game_moves[1000000][4];
The game_moves array can hold 1 million game moves.
1 million might seem excessive but with 8 players at 40fps, you could theoretically get 320 game moves per second.
(In reality a human player can't press the controls fast enough to make 40 moves per second!)
But at the worst case, that's 19200 game_moves per minute or 1,152,000 game_moves per hour.
extern int game_move_entry_pos;
The current entry position of the array.
When a new move is added, it is added at this position, and then this position is incremented.
extern int game_move_current_pos;
The current read position of the array.
Used only for demo game playing to keep track of the current read position of the array.
Array elements
Each game move entry has 4 elements:
game_moves[x][0]; // frame_num
game_moves[x][1]; // game move type
game_moves[x][2]; // player number
game_moves[x][3]; // comp_move
A player's controls are encoded into a bitfield called 'comp_move' with these values:
1 [LEFT]
2 [RIGHT]
4 [UP]
8 [DOWN]
16 [JUMP]
32 [FIRE]
Types of game moves
Type 5 - Regular game move
game_moves[x][0]; // frame_num
game_moves[x][1]; // game_move type = 5 (regular game move)
game_moves[x][2]; // player number
game_moves[x][3]; // comp_move
Type 6 - Level done
game_moves[x][0]; // frame_num
game_moves[x][1]; // game_move type = 6 (level done)
game_moves[x][2]; // not used
game_moves[x][3]; // not used
Type 1 - Player state change
game_moves[x][0]; // frame_num
game_moves[x][1]; // game_move type = 1 (player state)
game_moves[x][2]; // player number
game_moves[x][3]; // val
if ((val > 0) && (val < 16)) // make player active and set color
{
players[p].active = 1;
players[p].color = val;
}
if (val > 63) // make player inactive and log reason
{
players1[p].active = 0;
players1[p].quit_reason = val;
}
How game_move entries are added in single player mode
void set_comp_move_from_player_key_check(int p)
{
int cm = 0;
if (key[players1[p].left_key]) cm += 1;
if (key[players1[p].right_key]) cm += 2;
if (key[players1[p].up_key]) cm += 4;
if (key[players1[p].down_key]) cm += 8;
if (key[players1[p].jump_key]) cm += 16;
if (key[players1[p].fire_key]) cm += 32;
// if menu key ignore everything else and set to 127
if (key[players1[p].menu_key]) cm = 127;
if (key[ALLEGRO_KEY_ESCAPE]) cm = 127;
players1[p].comp_move = cm;
}
if (players1[p].comp_move != players1[p].old_comp_move)
{
players1[p].old_comp_move = players1[p].comp_move;
add_game_move(frame_num, 5, p, players1[p].comp_move);
}
void add_game_move(int pc, int type, int data1, int data2)
{
game_moves[game_move_entry_pos][0] = pc;
game_moves[game_move_entry_pos][1] = type;
game_moves[game_move_entry_pos][2] = data1;
game_moves[game_move_entry_pos][3] = data2;
game_move_entry_pos++;
}
How game move entries are added in netgame
In netgame, things are done differently.
In client mode, when a control changes happens, it's NOT put in the client's local game moves array, instead it's sent to the server:
set_comp_move_from_player_key_check(p);
if (players1[p].old_comp_move != players1[p].comp_move) // players controls have changed
{
players1[p].old_comp_move = players1[p].comp_move;
Packet("cdat");
PacketPut1ByteInt(p);
PacketPut4ByteInt(frame_num + control_lead_frames); // add control_lead_frames to frame_num
PacketPut1ByteInt(players1[p].comp_move);
ClientSend(packetbuffer, packetsize);
}
When the server receives the packet, the client's game move is puts in the server's master game moves array.
if(PacketRead("cdat"))
{
int p = PacketGet1ByteInt();
int fn = PacketGet4ByteInt();
int cm = PacketGet1ByteInt();
add_game_move(fn, 5, p, cm); // add to game_move array
}
The server synchronizes its master game moves array back to all the clients.
When a client gets the data back from the server, it adds it to its local game_moves array.
From there it is applied the same as any other entry in the game move array.
For more details, see: Netgame: Game Move Sync
How controls are set from game move array
This is common to all modes (single player, run demo game, netgame).
Player's controls are set by reading game moves from the array.
void set_controls_from_game_move(int p)
{
// this will search back from entry position until it finds the first 'move' type
// entry that matches the player and is not in the future
int found = 0;
for (int g=game_move_entry_pos; g>0; g--) // look back from entry pos
if ((game_moves[g][1] == 5) && (game_moves[g][2] == p)) // find first that matches type and p
if (game_moves[g][0] <= frame_num) // check to make sure its not in the future
{
set_controls_from_comp_move(g);
game_move_current_pos = g; // for savegame running only
g = 0; // break out of loop
found = 1;
}
if (!found) clear_controls(p); // if no match found (no move entry for player in entire game move array)
}
void set_controls_from_comp_move(int g)
{
int p = game_moves[g][2];
int t = game_moves[g][3];
clear_controls(p);
if (t == 127) { t -= 127; players[p].menu = 1; }
if (t > 31) { t -= 32; players[p].fire = 1; }
if (t > 15) { t -= 16; players[p].jump = 1; }
if (t > 7) { t -= 8; players[p].down = 1; }
if (t > 3) { t -= 4; players[p].up = 1; }
if (t > 1) { t -= 2; players[p].right = 1; }
if (t > 0) { t -= 1; players[p].left = 1; }
}
Run demo game mode
In this mode, the game moves array is loaded from a file. After that, it's played back from the array in the exact same way as every other mode.
When a game is saved to file, the game moves array is simply dumped with a small header of 4 integers:
1 - num of game move entries
2 - deathmatch_pbullets
3 - deathmatch_pbullets_damage
4 - suicide_pbullets
The save game file extension is .gm. If you look at it with a text editor, all you will see a list of numbers like this:
'savegame.gm'
30
0
5
0
0
0
4
0
0
1
0
8
0
5
0
3
It is also saved as human readable text file like this:
'savegame.txt'
number of entries 30
deathmatch_pbullets 0
deathmatch_pbullets_damage 5
suicide_pbullets 0
[ gm][ pc][p][cm]
[ 0][ 0]-------------START (level:4)-------------
[ 1][ 0]-------------PLAYER 0 ACTIVE (color:8)--
[ 2][ 0][0][ 3] [ ][ ][ ][ ][RIGHT][LEFT]
[ 3][ 3][0][ 7] [ ][ ][ ][UP][RIGHT][LEFT]
[ 4][ 4][0][ 6] [ ][ ][ ][UP][RIGHT][ ]
[ 5][ 5][0][38] [FIRE][ ][ ][UP][RIGHT][ ]
[ 6][ 8][0][33] [FIRE][ ][ ][ ][ ][LEFT]
[ 7][ 9][0][ 1] [ ][ ][ ][ ][ ][LEFT]
[ 8][ 12][0][19] [ ][JUMP][ ][ ][RIGHT][LEFT]
[ 9][ 14][0][22] [ ][JUMP][ ][UP][RIGHT][ ]
[ 10][ 15][0][38] [FIRE][ ][ ][UP][RIGHT][ ]
[ 11][ 17][0][33] [FIRE][ ][ ][ ][ ][LEFT]
[ 12][ 18][0][ 1] [ ][ ][ ][ ][ ][LEFT]
[ 13][ 19][0][17] [ ][JUMP][ ][ ][ ][LEFT]
[ 14][ 21][0][19] [ ][JUMP][ ][ ][RIGHT][LEFT]
[ 15][ 23][0][ 6] [ ][ ][ ][UP][RIGHT][ ]
[ 16][ 24][0][34] [FIRE][ ][ ][ ][RIGHT][ ]
[ 17][ 25][0][33] [FIRE][ ][ ][ ][ ][LEFT]
[ 18][ 26][0][ 1] [ ][ ][ ][ ][ ][LEFT]
[ 19][ 27][0][17] [ ][JUMP][ ][ ][ ][LEFT]
[ 20][ 29][0][18] [ ][JUMP][ ][ ][RIGHT][ ]
[ 21][ 31][0][38] [FIRE][ ][ ][UP][RIGHT][ ]
[ 22][ 33][0][32] [FIRE][ ][ ][ ][ ][ ]
[ 23][ 34][0][49] [FIRE][JUMP][ ][ ][ ][LEFT]
[ 24][ 36][0][17] [ ][JUMP][ ][ ][ ][LEFT]
[ 25][ 37][0][19] [ ][JUMP][ ][ ][RIGHT][LEFT]
[ 26][ 38][0][ 6] [ ][ ][ ][UP][RIGHT][ ]
[ 27][ 42][0][ 1] [ ][ ][ ][ ][ ][LEFT]
[ 28][ 43][0][ 0] [ ][ ][ ][ ][ ][ ]
[ 29][ 45]-------------PLAYER 0 INACTIVE-----------