Week 7: Same Path, Different Body
Two characters can follow the exact same trajectory and still look like they're jumping for different reasons — because posture was never physics.
5 April 2027
Question#
If two characters follow an identical recorded path through the air — same height, same displacement, same airtime, frame for frame — can they still look like they’re jumping differently? If your answer is yes, what’s left to change once the trajectory is fixed?
Prediction (skip if you’d rather just look)#
Before opening the Lab: name one thing about a jump’s look you’d expect to change even if the path through space doesn’t move at all.
Experiment#
Open the Jump Lab’s posture comparison and load the same fixed trajectory into both bodies. Push one body’s arm swing and landing compression high and the other’s low, leaving the trajectory untouched. Watch both side by side. The paths are identical — you could overlay them and they’d match exactly — but one body reads as loose and reactive, the other as stiff and controlled. See this week’s slides for a worked comparison across all three presets.
Explanation#
Pose parameters — arm swing, leg tuck, landing compression — never feed back into the physics engine. They’re computed from the trajectory after it’s already been decided, not the other way around, which is why the Jump Lab’s posture comparison can hold the path fixed and only vary the body. This matters for more than demonstration purposes: it means a character’s “personality” (how heavy or springy it looks) and a level’s actual difficulty (how far it can jump, how forgiving the timing is) are two completely separate design levers, and changing one is guaranteed not to break the other.
Why this had to be true before this week, not just demonstrated this week
If pose changes had leaked into collision or displacement, every experiment from weeks 4–6 would have been contaminated by whatever posture happened to be selected at the time — a gravity comparison would really have been a gravity-and-posture comparison, silently. The separation isn’t a stage direction for this week’s lesson; it’s a constraint the whole course has been depending on since week 4.
Task#
Using the posture comparison, pick two pose settings you think best express “floaty” and “heavy” as characters, independent of which physics preset either name is attached to. Describe your two choices in one sentence each, and confirm in writing that the trajectory shown for both was identical.
Teaching team
- Marisol Quaye — convenor