# Jump, fall and land A jump is a position curve plus three squashes. Without the curve the character floats; without the squashes there is no weight; without a fall pose the player cannot read which way they are moving. The poses below are 16 px side views facing right; mirror for left. Easing and frame-rate vocabulary: `rules://40-timing-and-spacing`. ## Rules 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). ## By size | Px | Poses | Crouch / land | Stretch | Apex rise (typ., derived) | Frames in air | |----|-------|---------------|---------|------------------|---------------| | 8 | rest, squash, stretch | squash 1 px lower, 2 px wider | 2 px taller, 1–2 px thinner | 6–8 | 2–3, hold the apex | | 16 | 5 (above) | head 3 rows lower (13 vs 16) | +2 rows | 8–12 | 4–6 | | 32 | 6–8 | head −9…−12 px, thighs near horizontal | line toe to hand ≈ 36 px | +10…+14 px for a standing jump | 6–8 | | 64 | 8–12 + smear | knees ~110°, torso 45° forward | +2…+4 px, smear 1 frame | 20–30 | 8–10 | Timed 8-frame strip, 32 px, mixed timing (derived from the plates of a standing broad jump; head dy in px, + is up): | # | Pose | Head dy | ms | |---|------|---------|----| | 1 | stand, arms up | 0 | 120 | | 2 | dip, arms swinging back | −3 | 80 | | 3 | crouch, torso 45° | −9 | 100 | | 4 | push, arms forward | −4 | 60 | | 5 | take-off line, toes on ground | +2 | 60 | | 6 | apex, knees tucking | +10 | 80 | | 7 | descent, legs forward | +6 | 60 | | 8 | landing crouch (= 3) | −9 | 140 | 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. ## Templates 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. ```grid jump-16-crouch 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. ```grid jump-16-launch 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. ```grid jump-16-apex 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. ```grid jump-16-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 --- ...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. ```grid jump-16-land 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. ```grid jump-8-slime-stretch 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. ```grid jump-arc-8f # = height-mark #e8453c = = ground #3a3a4a --- ...##... ........ ..#..#.. ........ ........ ........ .#....#. ........ ........ ........ ........ ........ #......# ======== ``` ## Procedure 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"]`. ## Mistakes - **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. ## Review - 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. ## Sources - 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.