Jump, fall and land

1. Choose the mode first. Gameplay: the engine owns the arc, the sprite is a set of poses picked by vertical speed (up, invert, fall) plus a landing one-shot. Timed strip (enemy, cutscene, fighter): you draw every frame. Never play a gameplay air phase by time; it desyncs from the physics.
2. Space the arc by gravity: widest at launch and landing, tightest at the apex. For apex height H and 8 air frames the heights are 0, ½, ⅘, 1, 1, ⅘, ½, 0 × H (derived from a parabola; 12 px → 0, 6, 10, 12, 12, 10, 6, 0). On the way down gaps grow as odd numbers, 1 : 3 : 5. Hold the apex frame 1.5–2× the others. Conflict resolved: one web note says to cluster drawings at take-off; the animation books and physics put the dense spacing at the apex.
3. Anticipation is a crouch, and it costs input lag. Player jump: no crouch, rise on the next frame. Fighters keep a 3–5 frame pre-jump (50–83 ms at 60 Hz) because it is game data; enemies, bosses, cutscenes get 2 frames at 100–120 ms.
4. Put the squash on the landing, not on the launch. Landing = the crouch drawing, held 1–2 frames, 60–120 ms. Equal depth is the default; go 1 row deeper after a fall longer than ~1.5× the jump height. Scale the squash by fall speed, not by material height (a 1.6 × 0.4 cap in one shipped game).
5. Contact before squash; keep one toe down at launch. Bounce: contact frame (normal shape, just touching), then squash for one frame (a second squash frame makes it a frog hop), then stretch away. Jump: the rear toe is still on the ground in the launch drawing; leaving takes no extra contact frame. The foot never teleports.
6. Keep the ground pivot fixed. The foot contact pixel sits on one canvas coordinate on every ground frame (registration cross, cel op move for offsets). The hitbox is fixed across frames and never larger than the sprite.
7. Stretch where it is fast, squash where it stops. Launch and the last fall frame stretch along the motion; the apex is the rest shape; contact squashes. Area stays constant ±2 %: width ×1.25 → height ×0.8. Hard things barely squash (steel ball: tiny bounce, then roll); jelly squashes 2 : ½.
8. Floating is cured by action inside the action. The air phase needs at least two sub-motions: arms 1 frame late, back leg 1 frame behind, hair or cape trailing up on the fall. A rigid pose slid along the arc floats.
9. Give up and down different poses. One rising pose, one falling pose, a 1-frame bridge at the sign change (the apex). The viewer reads vertical speed from the pose alone: rising = limbs trailing, falling = arms up, legs reaching, head level. Add a forward variant when horizontal speed > 0.
10. Light falls slow, heavy falls fast. Cloth, feathers, leaves: 6–10 frames of easing with ±1–2 px sway. Heavy: 2–3 frames of acceleration, then terminal speed (constant spacing) and a hard stop with 1 bounce frame. Past ~½ sprite height of travel per frame (derived) add a stretch frame or trail; fast motion otherwise vanishes.
11. The landing is interruptible. 2–3 frames, cancelled by input or a new state. Dust at take-off and at any landing from a fall ≥ half terminal speed: 4 frames, 60 ms, on its own layer.
12. Flips: tuck to a ball of ~55–60 % standing height, rotate 90–120° per frame, 6–8 frames at 80 ms (derived).

Timed 8-frame strip, 32 px, mixed timing (derived from the plates of a standing broad jump; head dy in px, + is up):

Then 2 rise frames back to stand, 120 ms each. Cartoon strip: crouch 2 @ 100–120, launch 1 @ 60–80, rise 2 @ 80, apex 1–2 @ 100–120, fall 2 @ 80, land 1–2 @ 100–120, recover 2 @ 80–100 (≈ 1.0–1.2 s).

Shipped: Celeste's Madeline has jumpSlow 4, jumpFast 4, fall 8, fallSlow 2, fallFast 2, bigFall 11 and a 19-frame recovery; squash is code (jump 0.6 × 1.4, landing up to 1.6 × 0.4, back to 1.0 in ~0.23 s), dust only on hard landings. An 8×16 run-and-gun hero: up pose, down pose, landing = crouch at 60 ms, no anticipation.

Heights below count fill rows, outline excluded; light upper-left, far limbs darker.

1 · Crouch (anticipation). Side view, facing right, 13 rows tall against 16 standing. Hips back and low, thigh forward, shin short, torso leaning, arm swung back (opposite to travel). Enemies and cutscenes only; a player sprite skips it.

O = outline        #2b1d2e
S = skin-light     #f2b48a
s = skin-shadow    #c47a5a
C = cloth-mid      #4a86c8
c = cloth-shadow   #2f5a96
A = cloth-light    #7db4e6
a = sleeve-shadow  #2f5a96
P = pants          #5a4a7a
p = pants-shadow   #3e3358
B = boots          #5b3a29
b = boots-shadow   #3b2519
H = hair           #6b3a2a
---
.......OOO..
......OHHHO.
.....OHHHHSO
.....OHHSOSO
....OOOHSSSO
...OCCCOsSO.
...OCAAaOO..
.OOAAAAaO...
OSSSAaOOO...
OSSCcPPpO...
OccccPPpO...
.OOPPPpO....
..OPPOOO....
.OBBBBObO...
..OOOOOO....

2 · Launch (stretch). 18 rows: one diagonal line from toe to fingertip, arm up and forward, rear toe still on the ground. One frame, 60–80 ms, or a single smear-stretch frame at speed.

O = outline        #2b1d2e
S = skin-light     #f2b48a
s = skin-shadow    #c47a5a
C = cloth-mid      #4a86c8
c = cloth-shadow   #2f5a96
A = cloth-light    #7db4e6
a = sleeve-shadow  #2f5a96
P = pants          #5a4a7a
p = pants-shadow   #3e3358
B = boots          #5b3a29
b = boots-shadow   #3b2519
H = hair           #6b3a2a
---
........OOO....
.......OHHHO...
......OHHHHSOO.
......OHHSOSSSO
......OOHSAASSO
.....OCCAASSOOO
....OCCAAAaOssO
....OCCAAOOOOO.
...OCCCcOO.....
..OCCCcOppO....
..OccccOppO....
...OPPOpppO....
..OPPpOppO.....
..OPPOOppO.....
.OPPpObbOO.....
.OPPO.OObbO....
OBOO....OO.....
.OBBO..........
..OOBO.........
....O..........

3 · Apex (tuck). Knees up, arms out, the least vertical travel. Back arm and front arm differ (no twins). Doubles as the invert/bridge pose when vertical speed changes sign.

O = outline        #2b1d2e
S = skin-light     #f2b48a
s = skin-shadow    #c47a5a
C = cloth-mid      #4a86c8
c = cloth-shadow   #2f5a96
A = cloth-light    #7db4e6
a = sleeve-shadow  #2f5a96
P = pants          #5a4a7a
p = pants-shadow   #3e3358
B = boots          #5b3a29
b = boots-shadow   #3b2519
H = hair           #6b3a2a
---
......OOO.....
.....OHHHO....
....OHHHHSO...
....OHHSOSO...
....OOHSSSO...
...OCCOsSO....
...OCAAaOOOOO.
.OOAAAAaOaassO
OSSSAaCcassssO
OSSCCCcpOpOOO.
.OOccccPpOO...
...OOOOPPOO...
.....OPPpOO...
.....OPPOpO...
.....OPPObbO..
....OBBBBOO...
.....OOOO.....

4 · Fall. Arms up, legs reaching for the ground, head still level. Cloth and hair would flap upward here. Loopable while the player is airborne.

O = outline        #2b1d2e
S = skin-light     #f2b48a
s = skin-shadow    #c47a5a
C = cloth-mid      #4a86c8
c = cloth-shadow   #2f5a96
A = cloth-light    #7db4e6
a = sleeve-shadow  #2f5a96
P = pants          #5a4a7a
p = pants-shadow   #3e3358
B = boots          #5b3a29
b = boots-shadow   #3b2519
H = hair           #6b3a2a
---
...OOOO....
..OHHSSO...
.OHHHSSOOO.
.OHHSSAOssO
.OOHASaOssO
OCCOAAOsOO.
OCCAAaOO...
OCCAAOO....
OCCCcO.....
OCCCcpO....
OccccPpO...
.OOOOPPO...
..OpOPPpO..
..OppOPPO..
.ObOOOPPO..
..ObOBBOO..
...OOOOBBO.
.....O.OO..

5 · Land (squash). 12 rows: the crouch with the arms thrown forward, held 1–2 frames. Reuse the crouch drawing, 1 row deeper only after a long fall.

O = outline        #2b1d2e
S = skin-light     #f2b48a
s = skin-shadow    #c47a5a
C = cloth-mid      #4a86c8
c = cloth-shadow   #2f5a96
A = cloth-light    #7db4e6
a = sleeve-shadow  #2f5a96
P = pants          #5a4a7a
p = pants-shadow   #3e3358
B = boots          #5b3a29
b = boots-shadow   #3b2519
H = hair           #6b3a2a
---
......OOO....
.....OHHHO...
....OHHHHSO..
....OHHSOSO..
....OOHSSSO..
...OCCOsSO...
..OCCAAaOOOO.
..OCCAAAAaSSO
.OCCCcOASSSSO
OCCCcPPpOOOOO
OccccPPpOOOO.
.OOPPpOO.....
.OBBBBObO....
..OOOOOO.....

8 px stretch. 7×9 (≈ 51 px against 48 for the resting slime, same mass). Rest is idle-8-slime-a, squash is idle-8-slime-b in rules://41-idle-and-breathing: rest → squash → stretch → rest → squash on landing.

O = outline     #2b1d2e
G = body-light  #b9f0a0
F = body-mid    #6fcf6f
N = body-shadow #2f8f5a
---
..OOO..
.OGGFO.
OGFFFFO
OFOFOFO
OFFFFFO
OFFFFFO
ONNNNNO
.ONNNO.
..OOO..

Spacing chart. One column per frame, rows = height above ground (12 px jump): gaps 6, 4, 2, 0, −2, −4, −6. Tightest at the apex, widest at launch and landing. Scale by the fractions in rule 2.

# = height-mark #e8453c
= = ground      #3a3a4a
---
...##...
........
..#..#..
........
........
........
.#....#.
........
........
........
........
........
#......#
========

1. sprite_info; decide gameplay or timed strip. Keep the foot pixel on one x,y. Draw rest, crouch, launch, apex, fall, land with draw op grid, one frame each. look op preview: all silhouettes must differ filled solid (rules://03-silhouette-and-form).
2. Timed strip: lay out heights with the rule 2 fractions; cel op move dy per frame. Keep tween for secondary parts only: whole-pixel rounding stutters a small arc.
3. Squash/stretch: edit the drawing; look op diff against rest for pixel counts. look op onion on the body layer: ghost gaps must show 6 – 4 – 2 – 0 – 2 – 4 – 6, not even steps.
4. frame op set_duration for the strip; tag op create one tag per state: jump-up, fall, land (the land tag plays once). look op filmstrip, then validate with checks: ["animation"].

• Floaty → even spacing, no apex hold, rigid pose. Use the 6-4-2-0 gaps and add two sub-motions.
• Lands without weight / frog hop → no squash, squash on the way up, or two squash frames. One drawing, on contact.
• Late control → anticipation on a player jump. Cut the crouch or shorten it to one frame (≤ 50 ms).
• Teleporting foot → launch frame has both toes off the ground. Keep the rear toe down.
• Growing body → stretch and squash do not conserve area. Count pixels.
• Reads as standing → up and down use the same pose. Different poses, plus a bridge.

• Foot pivot identical on every ground frame; pixel count within ±2 % of rest on every frame.
• Heights follow ½, ⅘, 1, 1, ⅘, ½ (or a deliberate variant); the apex frame is held longest.
• Rising, apex and falling poses differ as flat silhouettes; landing squash is 1–2 frames; a player jump has no crouch before take-off (or ≤ 1 frame), an enemy jump has one.

• Williams, The Animator's Survival Kit (skips, hops, jumps; weight in a jump; bounce contact fix); Blair, Advanced Animation ch. 1; Thomas & Johnston, The Illusion of Life; Muybridge, The Human Figure in Motion (broad jump, high jumps, somersault); Hultgren, Animal Drawing (horse leap); Silber, Pixel Art for Game Developers ch. 8.
• Saint11 Jump, WallSlide, Squash; Slynyrd, Pixelblogs 60 and 64; Celeste Player.cs and frame folders; SF3 frame data.