Character Flight and Dash System Development Record

This article records the complete development process of a feature study project for validating the character transformation, flight, and boost dash. The project is based on the UE 5.8.1 engine, with C++ implementing the core logic and Blueprints used only to configure asset references.

— Development record preface

1. Project goals

Implement a complete character form transformation and flight-and-dash system, including the following features:

1. Press T to enter/exit the transformed form
2. After transforming, the character flies forward automatically, and W/A/S/D steers up/down/left/right
3. After transforming, the field of view (FOV) widens from 80 to 120
4. After transforming, press the right mouse button to enter boost mode: speed rises sharply, and a one-shot boost VFX plays
5. Press the right mouse button again to exit boost mode
6. A flash transition VFX plays at the moment of transformation, and the form switches after 0.4 s
7. When exiting the transformation, the character stops moving immediately and does not keep surging forward
8. The form switch is accompanied by a dissolve transition effect (MPC material parameter set reserved)

2. Project structure and tech stack

• Engine version: Unreal Engine 5.8.1
• Development method: C++ core logic + Blueprint configuration references
• Core C++ class: TransformBase (inherits ACharacter)

Key assets

3. Production method and core implementation

3.1 Input binding

The project uses the legacy UInputComponent rather than Enhanced Input, so keys are bound directly with BindKey:

• EKeys::T: triggers entering/exiting the transformed form
• EKeys::RightMouseButton: toggles boost mode

Binding location: TransformBase::SetupPlayerInputComponent

3.2 Form-switching flow

After pressing T, the flow first enters the 0.4 s flash transition stage.

Entering the transformation

1. Call StartDissolveOut() to begin the dissolve fade-out
2. Spawn the NS_SpriteSpawn flash VFX at the character position
3. Execute ExecuteEnterTransform() after 0.4 s
4. Hide the character mesh, spawn the transformation effect Actor, switch to MOVE_Flying mode
5. Set FOV to 120

Exiting the transformation

1. Immediately set bIsInTransformedForm = false and stop the flight logic
2. Immediately zero the velocity, stop movement, and switch back to MOVE_Walking
3. Destroy the transformation effect Actor and restore the character mesh
4. Call StartDissolveIn() to begin the dissolve fade-in
5. Execute ExecuteExitTransform() after 0.4 s
6. Restore FOV to 80

3.3 Flight control

Flight is implemented in Tick() after transformation:

• Automatic forward flight: ViewForward * AutoFlySpeed
• W: fly up (world Z+)
• S: fly down (world Z-, with ground detection to avoid clipping through the ground)
• A: fly left (left of the view direction)
• D: fly right (right of the view direction)

The early implementation used AddMovementInput, but because it is limited by CharacterMovementComponent::MaxAcceleration, the sense of acceleration was not obvious. The final version computes DesiredVelocity directly and smooths MoveComp->Velocity via FMath::VInterpTo, significantly improving acceleration response.

3.4 Boost system

The right mouse button toggles the bIsBoosting state:

• Entering boost: spawn the NS_JiaSu boost VFX at the character position and switch the speed to boost parameters
• Exiting boost: only restore the speed; do not replay the VFX

3.5 Niagara VFX and velocity handoff

The effect Actor spawned after transformation contains multiple Niagara components. In Tick(), the character's world velocity GetVelocity() is read and handed to Niagara via SetVariableVec3("User.FlyVelocity", FlyVel), driving trail, inertia swing, and other particle effects.

4. Issues and fixes during development

5. Modified code files

5.1 Source/Test/Public/TransformCharacter.h

• Added BoostEffect: boost Niagara VFX
• Added bIsBoosting: boost state flag
• Added NormalFlySpeed, NormalSteerSpeed, BoostFlySpeed, BoostSteerSpeed: flight speed parameters
• Added OnBoostInput(): right-mouse-boost input handler
• Added TransformFlashEffect, TransformFlashDelay: flash transition VFX and delay
• Added DissolveMPC, DissolveParamName: dissolve-effect MPC asset and parameter name
• Added TransformVFXBlueprint, SpawnedTransformVFX: transformation effect Blueprint Actor class and instance
• Added dissolve-related private members and functions

5.2 Source/Test/Private/TransformCharacter.cpp

• Load default assets in the constructor: BP_Projectile_Ice, NS_SpriteSpawn, NS_JiaSu
• Set flight-speed defaults in BeginPlay() to prevent Blueprint CDO override
• Bind T and the right mouse button in SetupPlayerInputComponent()
• Implement dissolve animation, flight control, and Niagara velocity handoff in Tick()
• OnTransformInput() implements the full enter/exit transformation flow
• OnBoostInput() implements boost-mode toggling and one-shot VFX playback
• ExecuteEnterTransform() / ExecuteExitTransform() implement the formal enter/exit transformation
• StartDissolveOut() / StartDissolveIn() control the dissolve direction

6. Key parameter summary

7. Takeaways

1. Blueprint CDO overwrites C++ default values: for critical configuration properties (Niagara references, speed values), either force-set them in BeginPlay() or hard-code the path in the constructor via ConstructorHelpers::FObjectFinder.
2. Set flight velocity directly first: AddMovementInput fits the character movement framework better, but is limited by MaxAcceleration; direct Velocity setting feels sharper for fast acceleration.
3. FOV must go through PlayerCameraManager: setting the PlayerController FOV directly is overridden by the camera component.
4. Stopping movement must happen immediately on exiting the transformation: otherwise the character keeps surging forward from inertia, and the feel is damaged.
5. Niagara trails need world space + Inherit Velocity: in local space, particles have no own velocity and no trail forms.
6. A complete recompile is required after editing .h: new UPROPERTY/UFUNCTION members are reflection-structure changes that Live Coding cannot hot-swap.