Metroid - Zero Mission (metroidret's decompilation of the US release)

The mzm decompilation's README names mzm_us.gba, the North American release, as its default build and gives its SHA-1 as 5de8536afe1f0078ee6fe1089f890e8c7aa0a6e8, which is the SHA-1 of the No-Intro file Metroid - Zero Mission (USA).gba. The atlas hasn't built it. mzm/build

Cited by: Metroid: Zero Mission

When a game starts rather than loads a file (gIsLoadingFile clear), SamusInit fills gEquipment with zeros and then sets Samus's maximum and current energy to 99, so she starts with 99 energy, no tanks, and no missiles, super missiles, or power bombs. Metroid starts her with 30 units. mzm/start-energy

About: Metroid: Zero Mission Health upgrade

Value: 99 energy

sStartingHealthAmmo in src/data/block_data.c holds the same starting values (99 energy, 0 of each ammunition) for the tank caps and the pause screen's debug menu. The game counts energy in whole units, where Metroid's health is binary-coded decimal in tenths (metroid/health-format).

Cited by: Health upgrade, Metroid: Zero Mission

On Easy and Normal an energy tank adds 100 to Samus's maximum energy, and on Hard 50, and sets her energy to the new maximum. A tank adds nothing if the maximum plus one more tank would pass 12 tanks plus the starting 99, so the maximum is 1299, or 699 on Hard (computed). In Metroid each tank holds 100 units, up to 6 tanks and 699.9 units, with the same refill. mzm/energy-tank

About: Metroid: Zero Mission Health upgrade

{
 "easy": 100,
 "normal": 100,
 "hard": 50
}

The atlas reads row 7 of sNumberOfTanksPerArea as the game's totals, since the code uses it only as a cap and it sums the area rows. The pause screen's debug menu writes the maximum directly and skips this test.

Cited by: Health upgrade, Metroid: Zero Mission

Missiles, super missiles, and power bombs each have their own maximum and count, and each tank adds to both: 5 missiles, 2 super missiles, or 2 power bombs on Easy and Normal, and 2, 1, or 1 on Hard, from a start of 0 (mzm/start-energy). Missile tanks stop adding past 50 tanks' worth, 250 missiles, or 100 on Hard (computed). Metroid has missiles only, and its tank adds 5 to both the count and the capacity. mzm/ammo-tanks

About: Metroid: Zero Mission Ammunition

{
 "missile": [
  5,
  2
 ],
 "superMissile": [
  2,
  1
 ],
 "powerBomb": [
  2,
  1
 ]
}

The first tank of each ammunition (a maximum of 0 before it) sets isFirstTank, which adds 1 to the banner's message id, from MESSAGE_MISSILE_TANK_ACQUIRED to MESSAGE_FIRST_MISSILE_TANK and likewise for the other two (bg_clip.c line 563; the names are the decompilers').

Cited by: Ammunition, Metroid: Zero Mission

A jump sets Samus's upward yVelocity to 192 (SAMUS_LOW_JUMP_VELOCITY), 232 with the High Jump active, or 212 without the suit, which is checked first. The velocity counts eighths of a subpixel and a pixel is 4 subpixels, so these are 6, 7.25, and 6.625 px/frame (computed). Movement caps the velocity at 192 (24 subpixels, 6 px), so the High Jump's first five frames each rise 6 px (computed). Metroid's jump always takes off at 4 px/frame, and its High Jump Boots lower the gravity instead of raising the speed. mzm/jump-speed

About: Metroid: Zero Mission Jump

[
 6,
 7.25
]

The wall jump also takes the low or High Jump speed (src/samus.c lines 1742-1747, with no suitless case). Samus in the Morph Ball jumps at SAMUS_MORPH_BALL_JUMP_VELOCITY, the same 212. SamusUpdate runs once per frame of play, unless an item pickup's gPreventMovementTimer is running (src/in_game.c).

Cited by: Jump, Metroid: Zero Mission

Out of liquid (or in it with the Gravity Suit) and not held by a Metroid, SamusUpdatePhysics sets the vertical acceleration to 10 each frame, and SamusUpdateVelocityPosition takes it from yVelocity on every frame of the airborne poses while the velocity is at least -231, whether A is held or not: 0.3125 px/frame² (computed). A fall moves at most 128, 4 px/frame. In water, lava, or acid without the Gravity Suit, or out of liquid in a Metroid's grip, the acceleration halves to 5 and both caps drop to 40, 1.25 px/frame. Metroid's jump gravity is 0.09375 px/frame² (0.0703 with the High Jump Boots), and its falls reach 5 px/frame. mzm/gravity

About: Metroid: Zero Mission Gravity

Value: 0.3125 px/frame²

The liquid cases end in a break that only a BUGFIX build drops, so in the US build a Metroid's grip slows Samus only out of liquid, where the default case checks grabbedByMetroid. A shinespark or ballspark moves her by its own yVelocity with no gravity, and SamusGettingHurt can set the acceleration to 0.

Cited by: Gravity, Metroid: Zero Mission

Stepping the code's arithmetic with A held, out of liquid, a jump from the ground peaks about 59 px up (235 subpixels) on its 19th frame, and a High Jump about 83 px (331 subpixels) on its 23rd (computed: each frame moves yVelocity capped at 192 and shifted right 3, then takes 10 from it). mzm/jump-height

About: Metroid: Zero Mission Jump

[
 58.75,
 82.75
]

Not yet measured in the ROM. The shift drops the fraction each frame, so the rise is a little less than v²/2g.

Cited by: Metroid: Zero Mission

On any frame Samus rises (yVelocity above 0) without A held, the mid-air handlers set yVelocity to 0, at any height: SamusMidAir, SamusTurningAroundMidAir, and SamusSpinning, which runs the spin jump, the Space Jump, and the Screw Attack. The check is each handler's last step, so a frame whose earlier branch returns, such as a Space Jump or wall jump press, skips it. Metroid lets a release stop the rise only after 32 px. mzm/release-cap

About: Metroid: Zero Mission Variable jump height

Value: 0 velocity after release

The Morph Ball's mid-air handler, SamusMorphballMidAir, has the same test inside one of its branches (src/samus.c line 5231), not read here in full.

Cited by: Metroid: Zero Mission, Variable jump height

When a spin jump or Screw Attack touches a wall, SamusCheckCollisions sets walljumpTimer to 8 and stores the direction away from the wall. Each time SamusSpinning runs, unless the Space Jump is active and Samus isn't slowed (slowedByLiquid), it takes 1 from a nonzero timer, and if Samus faces away from the wall, a new A press, with a solid block 10 px (40 subpixels) to the wall's side, starts a wall jump. The jump takes off at the normal or High Jump speed (mzm/jump-speed). Metroid takes a jump press in the air only in lava (metroid-samus/no-air-jump), so it has no wall jump. mzm/wall-jump

About: Metroid: Zero Mission Wall jump

Value: 8 frames of the spin handler after the last wall touch

SamusStartingWallJump drops Samus instead if she fires or holds up or down without a side direction; in liquid the wall jump takes off at half the High Jump speed. While the timer runs and she faces away, SamusSpinning cuts her mid-air acceleration to 1.

Cited by: Metroid: Zero Mission, Wall jump