Series
Metal Gear
20 games, 1987–2018.
Games
Interactive: timeline (needs JavaScript)
The series by yearMechanics
A marked cell changed from the game before. “Uses” means the game has the mechanic, with no variant recorded yet.
Every claim, by mechanic and game
| Concept | Metal Gear
1987 | Snake's Revenge
1990 | Metal Gear Solid
1998 |
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| Alert phase | | | - In Metal Gear Solid Integral (SLPM-86247), the enemy commander keeps one alert value and a mode: 0 (TOP_COMM_TRAVEL), 1 (TOP_COMM_ALERT), and 2, which sets GM_AlertMode to ALERT_EVASION; the atlas reads 0 as infiltration. Each update,
s00a_command_800CF6A0 sets the value to the highest alert_level among its active guards, or lowers it by 4 when it is more than 4 above that, and raises it to TOPCOMMAND.alert, which the security camera and searchlight code set to 255 (ENE_SetTopCommAL). A patrolling guard (think1 0, think2 0) whose alert_level passes 2, after three frames of full sight from 0 (computed), goes to a reaction state: on its first frame it puts a mark over its head (ENE_PutMark, mark 0), and after 20 updates it switches to its alert routines (think1 1) and sets alert_level to 255. In mode 0, a value of 255 calls GM_AlertModeSet(3) (ALERT_ACTIVE), which plays SE_ALERT_SIREN when the mode was ALERT_OFF, and enters mode 1; it adds 1 to GM_EnemyWatchCount unless COM_GameStatus bit 2 is set. Once the commander leaves mode 0, every guard still in its patrol routines switches to its alert routines. Mode 1 has no timer: it lasts until the value falls to 0, which starts mode 2 with a counter of 300 that drops by 1 each update. A value of 255 during mode 2 returns to mode 1; when the counter runs out, the commander returns to mode 0 and ALERT_OFF. The game waits DG_FrameRate = 2 vertical blanks per frame, 30 frames a second on a 60 Hz display, so the evasion phase lasts 10 seconds (computed). The stage script's l option sets COM_EYE_LENGTH separately for modes 0, 1, and 2, 4,000 in each by default. Code - In Metal Gear Solid Integral (SLPM-86247), the radar (
draw_radar) draws the map only in ALERT_OFF. In ALERT_ACTIVE and ALERT_EVASION, and in ALERT_OFF while GM_GameStatus has STATE_CHAFF or STATE_JAMMING set (shown as ALERT_JAMMING), it draws a status panel (menu_radar_draw_state) in its place, playing SE_RADAR_JAMMED when jamming begins from ALERT_OFF; for alert and evasion the panel draws GM_AlertLevel as a gauge. When the panel ends, the map returns behind a sweep while a counter set to 93 falls by 2 per frame, about 47 frames (computed), with SE_RADAR_CHIME, which the decompilers' comment says plays when evasion or jamming ends. In ALERT_OFF, with no override function set, the radar isn't drawn in a duct (PLAYER_INTRUDE) or with the radar turned off in the options. On the map, each guard's cone comes from its sight: its facing, vision.length, and twice vision.angle as the width (s00a_command_800C9878). Code
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| Noise detection | | | - In Metal Gear Solid Integral (SLPM-86247), a noise is a power, a length, and a position (GM_SetNoise), and a noise replaces the current one only if its power is higher, or equal with a length at least as long. A guard whose
field_BA3 bit 1 is set (its setup sets it) hears the current noise by its power (s00a_command_800C9930): 5 within 1,500 units, 200 within COM_NOISEMODE_DIS (8,000 by default; a stage script's y option sets it), 255 at any distance, and 100 only if it is the guard the commander picked; for every power but 255 the guard must be on Snake's map, and 255 has its own test on GM_ClaymoreMap. Other powers aren't heard, such as the 4 of Snake's kick. For a 100, the commander (s00a_command_800CF9A0), outside mode 1, picks the guard within COM_NOISEMODE_DIS of the noise whose HZD_ZoneDistance to it is under 300 and least; that guard hears it and clears it, so one guard answers. Knocking on a wall makes a 100: sna_knock_80054D68 probes the wall beside Snake and, when the surface's attribute code is under 4, starts NewAfterSe, which 6 frames later plays the knock and calls GM_SetNoise(100, 16) at Snake's position. A footstep makes a 100 when Snake isn't in a duct (PLAYER_INTRUDE) and the stage script's n list gives the floor under him a nonzero noise flag. Explosions (blast.c) and stun grenades (stngrnd.c) make a 255. A patrolling guard (think2 0, s00a_command_800CD210) answers a heard noise (field_BA1 bit 1) after bits 4 and 2 and before footprints (bit 16) and sight; for a 255 it goes to the same reaction state as a sighting (think2 7), which after 21 updates (computed) sets its alert_level to 255. Code
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| Vision cone | | | - In Metal Gear Solid Integral (SLPM-86247, the Japanese re-release the decompilation builds), a guard's sight check
s00a_command_800C9E68 updates its result vision.field_B92 for one guard per commander update, the guard whose field_B78 equals the commander's update count field_0x0C modulo field_0x08, the number of guard slots it loops over; between turns the result stands. Snake can't be seen off the guard's map or with the player status PLAYER_INTRUDE or PLAYER_HIDDEN set. Otherwise he is seen when he is within COM_EYE_LENGTH + 2,000 units (a 3D distance) and within 2,000 units of the guard's height, and either closer than 500 units or less than vision.angle from the guard's facing, with no wall or floor (HZD_OnlineHazardCheck, HZD_CHK_ALL) and no target flagged TARGET_SEEK (GM_OnlineTargetCheckAny) on the line between them. The guard's setup sets vision.angle to 512 of the 4,096 units in a turn, a cone of 45° either side of the facing, 90° across (computed), and vision.length to COM_EYE_LENGTH, 4,000 units unless a stage script's l option sets it; some guard actions set the length to 3,000 or 0. The result is 1 for a sighting beyond vision.length and 2 within it, and 0 whenever Snake has the Stealth item equipped, unless the guard's param_blood is 83. Every frame, s00a_command_800C9D7C moves the guard's alert_level (0 to 255): up 1 at a result of 2, down 1 at 1, and down COM_ALERT_DECREMENT at 0 (4 by default; a stage script's t option of 1 or 2 makes it 3 or 2). On the result-0 branch one exception holds the level where it is instead of lowering it: when the guard's last sighting was a 2 and Snake has PLAYER_INTRUDE or PLAYER_NOHIDDEN set, isn't hidden, and the guard's vision.length isn't 0. Code - In Metal Gear Solid Integral (SLPM-86247), a guard looks for footprints only if its stage script gives it the
c option, which sets field_BA3 bit 0x10, and not in the commander's mode 1, TOP_COMM_ALERT (s00a_command_800C9D28 skips the check there, though not in evasion). The check (s00a_command_800C9C7C) runs when AsiatoCheck passes and the guard isn't already in think2 5, and takes the nearest of the 48 footprint slots (AsiatoPositions) whose pad is 1 that lies within vision.length (a horizontal distance) and less than vision.angle from the guard's facing, with no wall between (SearchNearAsiato): the sight cone, without its 500-unit ring or its outer band. A patrolling guard that finds one goes to think2 5 if none of field_BA1 bits 4, 2, and 1 (the last a heard noise) ranks above it. Code
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