Metroid, Samus's movement (nmikstas's disassembly of the US NES release)

Every jump takes off with the whole part of Samus's vertical speed at $FC, 4 px/frame up. The High Jump Boots change the gravity, not the speed: SetSamusJump sets SamusGravity to $18, or $12 with the boots. metroid-samus/jump-speed

About: Metroid Jump

Value: -4 px/frame

Cited by: Jump, Metroid

Each frame VertAccelerate adds SamusGravity to the fraction byte of Samus's vertical speed and carries into its whole part, so gravity is SamusGravity/256 px/frame²: $18 (0.09375) in a jump, $12 with the High Jump Boots, $1A after walking off a ledge, and $38 after a hit (computed: 0.0703125, 0.1015625, 0.21875). A fall is capped at 5 px/frame and a rise at 6. metroid-samus/gravity

About: Metroid Gravity

{
 "jump": 0.09375,
 "highJump": 0.0703125,
 "fall": 0.1015625,
 "hit": 0.21875,
 "maxFall": 5,
 "maxRise": 6
}

Cited by: Metroid

Once a jump has carried Samus 32 px up (SamusJmpDsplcmnt at $20), letting go of jump while she still rises calls StopVertMovement, which sets her vertical speed to 0. The running-jump handler does the same past 32 px. metroid-samus/release-cap

About: Metroid Variable jump height

Value: 32 px risen before a release counts

Cited by: Metroid, Variable jump height

On the ground Samus accelerates at $30/256 (0.1875) px/frame² toward SamusHorzSpdMax/16 px/frame, which VertAccelerate sets to $18 (1.5 px/frame) while she is grounded. With no direction held, StopHorzMovement clears her horizontal speed at once. metroid-samus/run

About: Metroid Running

{
 "accel": 0.1875,
 "max": 1.5
}

The accelerations store whole.fraction in two bytes, ObjHorzSpeed and HorzCntrLinear, as the vertical speed does.

Cited by: Metroid

A running jump sets the top speed to $12 (1.125 px/frame). In the air a held direction sets the acceleration toward it; with neither held, a jump still in the plain jump animation loses its horizontal speed, and a somersault keeps its speed and acceleration. metroid-samus/air-run

About: Metroid Air control

Value: 1.125 px/frame

Cited by: Metroid

In a jump from a standstill, LD055 sets the whole part of Samus's horizontal speed outright every frame, 1 px/frame toward a held direction and 0 with neither held. metroid-samus/air-stand

About: Metroid Air control

Value: 1 px/frame

X is $FF, 1 px/frame left, with left held.

Cited by: Metroid

Once Samus is airborne, the run and jump handlers start a jump only while she is in lava. Walking off a ledge makes her airborne at once: VertAccelerate sets the falling gravity on the first frame with nothing below her. metroid-samus/no-air-jump

About: Metroid Coyote time

The atlas hasn't read the pointing-up and morph-ball handlers for jump reads in the air; the ball's jump press unrolls it (metroid-samus/morph-ball).

Cited by: Coyote time, Metroid, Metroid: Zero Mission, Wall jump

Samus is a box around her center: each animation frame's data sets ObjRadY and ObjRadX, the distances from her center to her top or bottom and to her sides. The level checks add these radii to her position, and so does the distance check between her and an enemy. metroid-samus/hitbox

About: Metroid Hitbox

Cited by: Hitbox

Samus rolls into the ball only with the Maru Mari (gr_MARUMARI) and only on the ground. In the ball, Up or a jump press unrolls her unless Down is held, and only if she has room to stand. metroid-samus/morph-ball

About: Metroid Morph ball

Cited by: Morph ball

IsScrewAttackActive counts the Screw Attack as on only in the running state with the item: in a somersault, or in the plain jump animation while Samus still rises. The Samus-enemy crash code at LF282 calls it. metroid-samus/screw-attack

About: Metroid Screw Attack

What LF282 does with the result is uncommented in the disassembly, and the atlas hasn't traced it.

Cited by: Screw Attack

Samus's gear byte, SamusGear, has one bit each for the bombs, High Jump, Long Beam, Screw Attack, Maru Mari, Varia, Wave Beam, and Ice Beam: all eight bits, none for a Space Jump. metroid-samus/gear-bits

About: Metroid Space Jump

Cited by: Space Jump

Each frame, the handler for Samus's state (standing, running, jumping) reads the pad first and then calls SetSamusData, which reaches LavaAndMoveCheck. That routine accelerates and moves her vertically (VertAccelerate, then one pixel at a time), and then horizontally (HorzAccelerate, then one pixel at a time). metroid-samus/frame-order

Cited by: Metroid

Samus's speeds are 8.8 fixed point: a whole byte, ObjVertSpeed or ObjHorzSpeed, and a fraction, VertCntrLinear or HorzCntrLinear. Her position's fraction is one more byte per axis, VertCntrNonLinr or HorzCntrNonLinr. Each frame the speed's fraction is added to it, and she moves the speed's whole part plus the carry, in pixels. The comments call that byte a counter that grows exponentially; in the code it is the fraction of her position. metroid-samus/subpixels

Value: 256 steps per px

Cited by: Metroid

From a standstill, the first frame with Left or Right held doesn't move Samus. SamusStand picks the running state, calls SetSamusData, which moves her at her speed of 0, and only then calls SetSamusRun, which sets her acceleration. Her speed rises from the next frame. metroid-samus/run-start

About: Metroid Running

Cited by: Metroid

Running on the ground, Left or Right against Samus's facing turns her and sets the acceleration toward the new side on that frame, through SetSamusRun, but leaves her speed as it is. She slows by 0.1875 px/frame each frame, passes 0, and speeds up the other way: from 1.5 px/frame, 16 frames to 1.5 px/frame the other way (computed). metroid-samus/turn

About: Metroid Running

Value: 16 frames

Cited by: Metroid

On the ground, the running handler checks Samus's animation before it reads A or the d-pad (LCDBF). Unless it is the running animation (or, with Up held, running and aiming up), it sets that animation and skips the rest of the handler for the frame. A jump press or a released d-pad on that frame is ignored, and she accelerates toward her facing. That happens on her first frame on the ground after a running jump or a fall, and on the frame after a turn: SetSamusRun gives Samus the running animation only if her animation was standing (an_SamusStand), and otherwise the running-and-aiming-up animation (an_SamusRunPntUp). metroid-samus/run-pose

About: Metroid Running

The conformance probe (probes/lab/conformance.mjs) plays turns and landings in the ROM and matches the model, which skips those frames' reads.

Cited by: Metroid

A jump from a standstill starts after the press frame's move: SamusStand calls SetSamusData, which moves her, and then SetSamusJump, so she first rises on the next frame. A running jump's handler calls SetSamusJump (LCD40) before SetSamusData, so she rises on the press frame, and there it sets her top speed for the jump, SamusHorzSpdMax, to $12. metroid-samus/jump-start

About: Metroid Jump

Cited by: Metroid

In a running jump, the air branch of the running handler poses Samus by SamusJmpDsplcmnt, which a jump sets to 0 and each pixel up adds 1 to and each pixel down takes 1 from. Rising at 24 or more (cpy #$18), she somersaults (an_SamusSalto) unless she is firing; falling at less than 24, she takes the plain jump pose (an_SamusJump), as she does from the running pose. The pose decides whether letting go of the d-pad stops her (metroid-samus/air-run). metroid-samus/somersault

About: Metroid Air control

Value: 24 px

Cited by: Metroid

Moving down, and not in the ball, Samus stops when MoveSamusDown finds a solid tile under her: StopVertMovement clears her vertical speed, SamusGravity is set to 0, and the frame goes on to her horizontal move. A jump from a standstill ends on the next frame: SamusJump finds SamusGravity at 0 and calls StopHorzMovement, which stops her and makes her stand, so she doesn't move that frame, and a jump press then does nothing, since the jumping handler starts a jump only in lava. In the ball (sa_Roll), a landing halves her downward speed and turns it upward, a bounce, until the halved whole speed is 0 and she stops. metroid-samus/landing

About: Metroid Jump

In Brinstar's bank, the frames of Samus's running, standing, jumping, and somersault animations all give the radii $0F and $04: 15 px from her center to her top or bottom and 4 px to either side, so her box is 30 px tall and 8 wide (computed). metroid-samus/terrain-box

About: Metroid Hitbox

{
 "x": 4,
 "y": 15
}

The other area banks carry their own copies of these tables; the atlas has read only Brinstar's.

Cited by: Metroid

Samus moves one pixel at a time, and a step tests the room's 8 px tiles only when the edge she moves toward lies on a tile boundary: MoveSamusUp, MoveSamusDown, MoveSamusLeft, and MoveSamusRight call the crash check only when her center less or plus her radius is a multiple of 8. The check tests the row of tiles above her top or below her bottom, or the column beside her side, across every tile her box spans. On the ground, VertAccelerate makes the same test under her each frame. metroid-samus/tile-checks

Value: 8 px per tile

Up tests the row 8 px above her top edge (the offset ObjRadY+8), down the row at her center plus ObjRadY, left the column 8 px past ObjRadX, right the column at her center plus ObjRadX; with an 8 px tile, each is the tile next to her edge when that edge is on a boundary.

Cited by: Metroid

On the ground, VertAccelerate sets SamusHorzSpdMax to $18 and tests the tiles under Samus before she moves. With none solid, and no elevator or frozen enemy under her, it sets the falling gravity, $1A, and adds it at once, so she is airborne from that frame. The running handler's air branch then turns her running pose into the plain jump pose, so letting go of the d-pad stops her (metroid-samus/air-run), and her top speed stays 1.5 px/frame. metroid-samus/walk-off

About: Metroid Coyote time

Cited by: Metroid

A solid tile beside Samus stops her sideways move for the rest of the frame (CheckStopHorzMvmt). On the ground (SamusGravity 0), and not in the ball, it also calls StopHorzMovement, which clears her speed and acceleration and makes her stand. In the air her speed is kept. metroid-samus/wall-stop

Cited by: Metroid

Blocked moving up, Samus's vertical speed, whole byte and fraction, is shifted right one bit with the sign bit set (sec, ror ObjVertSpeed, ror VertCntrLinear). An upward speed is halved and stays upward, though the comment says the shift reverses her direction. The rest of that frame's rise is dropped. Each later frame that would still move her up is blocked and halved again, until gravity turns her speed downward. metroid-samus/ceiling-hit

About: Metroid Jump

Not measured in the ROM; the conformance probe's start area has no ceiling within a jump.

Cited by: Metroid

Measured in the game, Samus's jump from a standstill peaks at 32 px on frame 10 when A is tapped or held up to 10 frames, and at 84 px on frame 41 when A is held to the top, landing on frames 36 and 86. A running jump, which rises on its press frame, peaks and lands a frame sooner at the same heights. metroid-samus/apex-by-hold

About: Metroid Variable jump height

{
 "tap": {
  "apex": 32,
  "apexAt": 10,
  "airtime": 36
 },
 "full": {
  "apex": 84,
  "apexAt": 41,
  "airtime": 86
 },
 "byHold": {
  "1": {
   "apex": 32,
   "apexAt": 10,
   "airtime": 36
  },
  "2": {
   "apex": 32,
   "apexAt": 10,
   "airtime": 36
  },
  "4": {
   "apex": 32,
   "apexAt": 10,
   "airtime": 36
  },
  "6": {
   "apex": 32,
   "apexAt": 10,
   "airtime": 36
  },
  "8": {
   "apex": 32,
   "apexAt": 10,
   "airtime": 36
  },
  "10": {
   "apex": 32,
   "apexAt": 10,
   "airtime": 36
  },
  "12": {
   "apex": 38,
   "apexAt": 12,
   "airtime": 41
  },
  "16": {
   "apex": 49,
   "apexAt": 16,
   "airtime": 49
  },
  "20": {
   "apex": 59,
   "apexAt": 20,
   "airtime": 56
  },
  "30": {
   "apex": 76,
   "apexAt": 30,
   "airtime": 70
  },
  "50": {
   "apex": 84,
   "apexAt": 41,
   "airtime": 86
  }
 },
 "running": {
  "tap": {
   "apex": 32,
   "apexAt": 9,
   "airtime": 35
  },
  "full": {
   "apex": 84,
   "apexAt": 40,
   "airtime": 85
  }
 }
}

The start state is set by RAM writes in probes/lab/metroid-movement.lua, so the enemies never touch her and her position fractions start at 0; neither changes the jump's arc. A tap and a hold of up to 10 frames give the same jump, because the release counts only once she has risen 32 px (metroid-samus/release-cap), which takes 10 frames.

Cited by: Metroid