Metroid Fusion (metroidret's decompilation of the US release)

The mf decompilation's README names mf_us.gba, the North American release, as its default and only supported build and gives its SHA-1 as ca33f4348c2c05dd330d37b97e2c5a69531dfe87, which is the SHA-1 of the No-Intro file Metroid Fusion (USA).gba. The README counts 376 functions not yet decompiled. The atlas hasn't built it. mf/build

The README warns that the decomp "is not shiftable", so it rebuilds the US ROM byte for byte but isn't yet a base for modified builds.

Cited by: Metroid Fusion

When SamusInit runs with no file loading (gIsLoadingFile clear) and an unnamed flag, gUnk_3000be3, clear, it copies sEquipment_Empty into gEquipment: 99 energy of 99, 10 missiles of 10, 10 power bombs of 10, and no weapon flags (MBF_NONE). The atlas reads this as a new game's start. Zero Mission starts with the same 99 energy, but with every ammunition count at 0. mf/start-energy

About: Metroid Fusion Health upgrade

Value: 99 energy

The 10 missiles and 10 power bombs sit in the counters before Samus can use them: the data downloads OR each ability's weapon flag into weaponsStatus (src/event.c line 128), and the pause screen and ending count tanks from these starts, (maxMissiles - STARTING_MISSILES) / MISSILE_INCREASE_AMOUNT (src/menus/pause_screen_map.c lines 540-544).

Cited by: Health upgrade, Metroid Fusion

An energy tank adds 100 to Samus's maximum energy and sets her energy to the new maximum, unless the new maximum would pass MAX_ENERGY_AMOUNT, 20 tanks plus the starting 99, or 2099. The tank code reads no difficulty. Zero Mission's tank also adds 100 and refills, or 50 on Hard, and stops at 12 tanks: 1299 on Easy and Normal and 699 on Hard (computed). mf/energy-tank

About: Metroid Fusion Health upgrade

Value: 100 energy per tank

The test caps tanks by arithmetic alone; how many energy tanks the map holds is in room data the atlas hasn't fetched. The HUD draws the maximum with four digits (src/hud.c).

Cited by: Health upgrade, Metroid Fusion

Samus has one missile count and one power bomb count, each with a maximum. A missile tank adds 5 to both the missile count and its maximum, unless the maximum would pass 255; a power bomb tank adds 2 to both, up to 254. The missile types the downloads add (super, ice, and diffusion missiles, flags in weaponsStatus) draw on that one count. Zero Mission keeps separate counts for missiles, super missiles, and power bombs, and its missile tank also adds 5, or 2 on Hard. mf/ammo-tanks

About: Metroid Fusion Ammunition

{
 "missile": 5,
 "powerBomb": 2
}

From the start of 10 (mf/start-energy), 49 missile tanks reach 255 (computed). The tank adds to the count even before the missile download sets MBF_MISSILES. SpriteUtilRefillSamus adds missiles only when some missile flag is set (src/sprite_util.c lines 2693-2699).

Cited by: Ammunition, Metroid Fusion

A jump sets Samus's upward yVelocity to 170 (SAMUS_LOW_JUMP_VELOCITY), or 220 with the High Jump, with no separate suitless speed. The velocity counts eighths of a subpixel and a pixel is 4 subpixels, so these are 5.3125 and 6.875 px/frame (computed). Movement caps the velocity at 128 (16 subpixels, 4 px), so a jump's first 8 frames each rise 4 px, and a High Jump's first 16 (computed). Zero Mission's jump takes off at 192, or 232 with the High Jump, under a cap of 192: 6 px/frame from the first frame. mf/jump-speed

About: Metroid Fusion Jump

[
 5.3125,
 6.875
]

The wall jump takes the low jump speed even with the High Jump, where Zero Mission's takes either (mzm/wall-jump); in liquid without the Gravity Suit it can take 48 instead (src/samus.c lines 4894-4900). The Space Jump resets the velocity to the same 170 or 220 when A is pressed while falling at a velocity of 78 or more, about 2.4 px/frame (src/samus.c lines 2529-2541).

Cited by: Jump, Metroid Fusion

Out of liquid, SamusUpdatePhysics sets the vertical acceleration to 6 and the vertical speed cap to 128, and SamusUpdateVelocityPosition takes 6 from yVelocity on every frame of the airborne poses while the velocity is above -220, whether A is held or not: 0.1875 px/frame², with rises and falls both capped at 4 px/frame (computed). In water, lava, or acid without the Gravity Suit or the flag the decompilers name SMF_SA_X_SUIT, the acceleration drops to 4 and the cap to 48, 0.125 px/frame² and 1.5 px/frame. Zero Mission's gravity is 10, 0.3125 px/frame², with the same 4 px/frame fall cap (computed). mf/gravity

About: Metroid Fusion Gravity

Value: 0.1875 px/frame²

SamusUpdatePhysics sets SMF_SA_X_SUIT whenever the Ice Beam bit is set in beamStatus and clears it otherwise (src/samus.c lines 192-196). Out of liquid, a slowed value of 0x80 also slows Samus; the decompilers' comment calls it "nightmare related".

Cited by: Gravity, Metroid Fusion

Stepping the code's arithmetic with A held, out of liquid, a jump from the ground peaks about 71 px up (283 subpixels) on its 28th frame, and a High Jump 104 px (416 subpixels) on its 36th (computed: each frame moves yVelocity capped at 128 and shifted right 3, then takes 6 from it). The same stepping gives Zero Mission about 59 px on the 19th frame and 83 px on the 23rd (mzm/jump-height), so Fusion's jump is higher and slower. mf/jump-height

About: Metroid Fusion Jump

[
 70.75,
 104
]

Not yet measured in the ROM.

Cited by: Metroid Fusion

On any frame Samus rises (yVelocity above 0) without A held, the mid-air handlers set yVelocity to 0, at any height: SamusMidAir, SamusTurningAroundMidAir, SamusSpinning (which runs the spin jump, the Space Jump, and the Screw Attack), and SamusWallJumping, which also drops a wall jump into a spin. The test is each handler's last step but the wall jump's, so a frame whose earlier branch returns skips it. Zero Mission's first three handlers end with the same test. mf/release-cap

About: Metroid Fusion Variable jump height

Value: 0 velocity after release

SamusMorphBallMidAir has the same test, only while forcedMovement is 0 (src/samus.c lines 2870-2875). SamusMidAir and SamusTurningAroundMidAir turn a new A press into a spin when up and down aren't held, and return before the test.

Cited by: Metroid Fusion, Variable jump height

Touching an absorbable X parasite runs SamusAbsorbX, which refills by its color: a red X (SSC_RED_X_PARASITE) 500 energy, 100 missiles, and 10 power bombs; a green X 2 missiles; any other (yellow) X 10 energy. SpriteUtilRefillSamus adds missiles only once a missile flag is set and power bombs only once the power bomb flag is, and stops each at its maximum. mf/x-absorb

About: Metroid Fusion Item drop table

{
 "yellow": {
  "energy": 10
 },
 "green": {
  "missiles": 2
 },
 "red": {
  "energy": 500,
  "missiles": 100,
  "powerBombs": 10
 }
}

An X marked SSP_X_UNABSORBABLE_BY_SAMUS gives nothing. A core X refills 400 energy, 50 missiles, and 10 power bombs through the same function (src/sprites_AI/core_x.c line 615).

Cited by: Ammunition, Item drop table, Metroid Fusion

When a dying sprite's countdown ends, SpriteDying sets its pose to 0x5B (the decompilers' SPRITE_POSE_TURNING_INTO_X) unless it is a secondary sprite, and an enemy's AI (Choot's, for one) runs XParasiteInit in that pose. The X it becomes takes its color from a number from 1 to 1024, made from the low 2 bits of gSpriteRandomNumber and the 8-bit frame counter, against three weights in that sprite's row of sPrimarySpriteStats: the top red-weight values give red and the next green-weight values green, each only when its weight is above 0, and everything left below the green bound gives yellow, whatever the yellow weight is, unless it is 0, which deletes the X instead. A would-be green X turns yellow when missiles are full and energy isn't, or Samus has no missiles yet; a would-be yellow X turns green when energy is full and missiles aren't. An X from a core X is green when gSpriteRandomNumber is below 5 or that energy test holds, and otherwise yellow; an X placed in a room is yellow. All of this applies only to an X whose sprite property is SSP_X_ABSORBABLE_BY_SAMUS: one marked SSP_X_UNABSORBABLE_BY_SAMUS, or the unnamed SSP_UNKNOWN_40, is always yellow, and any other property deletes the X. mf/x-color

About: Metroid Fusion Item drop table

When the three ranges don't cover the number, the code deletes the X (gCurrentSprite.status = 0); the decompilers' comment says "This point shouldn't be reached if drop chances sum to 1024". The weights themselves are in sPrimarySpriteStats, in src/data, which the atlas hasn't fetched.

Cited by: Item drop table, Metroid Fusion