Boosts, boost pads and items

Boost pads, speed items and drift boosts all use one Blueprint node: Set Boost. Version 1.1 adds more ready-made effects for items and hazards, the Kart Intents.

Adding a boost (items, boost pads etc.)

In the Example Project, you can add a long lasting test boost when pressing the upper face button of the gamepad, or by pressing E on the keyboard. It demonstrates the prepared Boost functionality that is implemented for easy usage.

The C++ class exposes a ready-to-use Set Boost function for Blueprints, such that a boost with a specific length (Boost Decay Speed, how fast the boost disappears), New Max Speed and a Boost Acceleration can be applied.

• When ticking Set Speed, the Kart will instantly receive the new Max Speed, otherwise it is only loosely enforced.

• Ticking Reset Boost Progress will reset the boost timer to 0.0 again when this function is called again.

  For example, imagine you activated a boost 5 seconds ago, and it is still lasting and has 1 second of boost left. Now the Kart activates another boost: Should the Kart now only boost for 1 second, because the timer is already ticking, or should the timer reset?

  Resetting is probably what you want most of the time.

• Ticking Async will use functions that should only be run in the async tick thread. You can leave this unticked except if you know what you are doing.

Set Boost parameters

Parameter	Default	What it does
Boost Decay Speed	0	How fast the boost runs out. The boost lasts 1 divided by this value in seconds: 0.25 lasts 4 seconds, 0.5 lasts 2 seconds. At 0 it never runs out.
New Max Speed	0	Top speed while boosting, always set it. The example multiplies the Kart’s Max Speed by 1.1.
Set Speed	On	If the Kart is slower, it jumps straight to the new top speed.
Boost Acceleration	2000	Acceleration while boosting.
Reset Boost Progress	On	Restarts the boost timer if a boost is already running.
Async	Off	Only for calls made from the async physics tick.

BP_KartPawn uses the same function for its drift boosts. Their values come from the drift boost stages, see Drifting.

Kart Intents

Kart Intents are Blueprint functions for one-shot physics changes: drag, pushes, spins, stuns and teleports. Like Set Boost, they work in single player and are safe in multiplayer without any extra Blueprint networking. Coming in 1.1

Find them in the Blueprint action menu under Kart Base Settings > Kart Intents. In the graph they show with spaces, for example Set Kart Linear Damping.

Function	Parameters	Use it for
SetKartLinearDamping	Damping, Duration (default 0)	Oil patch, mud, a slow-down item. Overrides the Kart’s drag. With a Duration above 0 it ends by itself after that many seconds; with 0 it stays until cleared. Takes priority over the Surface Properties table.
ClearKartLinearDamping	none	Leaving the oil patch. Ends the damping override early.
AddKartImpulse	Impulse (world space), Velocity Change (default off)	Bumpers, launch pads, shell hits. Off: an impulse, so heavier Karts move less. On: a direct velocity change in cm/s, whatever the mass.
AddKartAngularImpulse	Angular Impulse In Radians (world axis times strength), Velocity Change (default off)	Spin-outs. Same rules as AddKartImpulse.
StunKart	Duration (seconds)	Banana hit, shock item. The Kart ignores steering, throttle and jump/drift presses, and an active drift ends. A Duration of 0 clears the stun.
ClearKartStun	none	Ending a stun early.
TeleportKart	New Transform, Reset Velocity (default on)	Respawns, “reset to track” buttons, checkpoints. Also resets drift, jump, boost, stun and damping override.

A stun only takes away control. For a full spin-out, combine StunKart with AddKartAngularImpulse (the spin), Set Boost (a speed cap) or SetKartLinearDamping (drag).

Where to call Kart Intents in multiplayer

Call each effect once: on the server for things that happen to a Kart (items, pads, bumpers, behind Switch Has Authority), on the owning client for things the player does (behind Is Locally Controlled). TeleportKart is server only. The full rules, including the limits the server applies to client calls, are in Blueprints in multiplayer. Coming in 1.1

Reading the state

Variable	What it tells you
Is Stunned	True while the Kart is stunned. Works on other players’ Karts too, for effects.
Stun Time Remaining	Seconds of stun left. Not available on other players’ Karts (reads 0).
Linear Damping Override Active	True while a SetKartLinearDamping override is active. Works on other players’ Karts too.

Building a boost pad

A boost pad is a small Actor Blueprint that calls Set Boost when a Kart drives over it.

1. Create a new Blueprint Class with the parent Actor, for example BP_BoostPad.
2. Add a Static Mesh component for the look and a Box Collision component for the trigger. Its default collision preset, OverlapAllDynamic, already overlaps the Kart.
3. Size the box so it covers the pad and is tall enough to reach the Kart’s collision box, which rides above the road on its springs.
4. Select the Box Collision and, in the details panel under Events, click the plus next to On Component Begin Overlap.
5. Drag from Other Actor and add Cast To KartPawnBase. This works for BP_KartPawn and every child Blueprint of it.
6. After the cast, add Switch Has Authority.
7. From Authority, call Set Boost and wire As Kart Pawn Base into Target. Set your values, for example Boost Decay Speed 0.5 for a 2 second boost, and a New Max Speed above the Kart’s Max Speed.
8. Leave Remote empty. For a sound or particles that everyone should see and hear, play them right after the cast, before Switch Has Authority.
9. Place the pad in your level and drive over it.

In single player there is no separate server, so the Authority pin always fires. Coming in 1.1 The same graph also works online.

Next steps

• Tune the drift boost stages in Drifting.
• Slow Karts down on offroad or mud with Surfaces and walls. Coming in 1.1
• React to Karts bumping into each other in Kart collisions. Coming in 1.1