One-way platforms
Jump up through it, land on top of it.
Platforms you can jump up through from below but stand on from above are everywhere in platformers. The rule is simple: only collide when the character is falling and their feet were above the platform last frame. Add "hold down and jump to drop through" and players can move freely between floors.
Try this: Jump up through the platforms, then hold ↓ and press jump to drop down. Switch one-way off with O to bonk your head.
Jump up through a platform.
Prompt bit
Works for 2D or 3D in any engine (Unity, Unreal, Godot, web). Paste the short one for a quick fix, or the detailed one when you want it done properly.
Make one-way platforms: collide only when the character is moving down and their feet were at or above the platform top on the previous step, and let down plus jump ignore that platform for 0.25 s so they drop through cleanly instead of snapping back.
Implement one-way (jump-through) platforms (2D, or thin 3D ledges; Unity PlatformEffector2D and Godot one_way_collision already do this). Mark platforms on their own layer. When resolving vertical collision, only collide if the character's vertical velocity is downward (or zero) and the bottom of their collider on the previous step was at or above the platform top (minus a small tolerance of 2 to 4 pixels). Ignore side and bottom contacts entirely. Drop-through: when the player holds down and presses jump while standing on a one-way platform, ignore that specific platform for 0.25 s (or until their top is below it), and do not count it for the ground check. Moving platforms need the same rule using relative velocity. Make sure the ground check, coyote time and the jump buffer treat one-way platforms like ground only from above. Enemies and items should follow the same rule. Expose tolerance and drop time.
Where it's used
- Platformers: stacked ledges and tree branches
- Metroidvanias: vertical shafts with drop-down floors
- Platform fighters: Smash-style stages
- Beat 'em ups: crates and balconies
- 3D platformers: thin ledges and clouds
Common mistakes
Colliding whenever velocity is downward even if the feet are already below the top (characters pop up through), drop-through that ignores every platform at once, ground checks that still see the platform while dropping, and side collisions with the platform edge.
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