Atlas — a fictional example

Atlas

Threads

How PhysWalking resolves floor & step-up

YouHow does PhysWalking step up onto ledges and update the floor?

AnswerHow PhysWalking resolves floor & step-upUCharacterMovementComponent::PhysWalking advances character movement in bounded sub-steps, keeping the capsule grounded across ramps and ledges. MoveAlongFloor projects horizontal velocity onto CurrentFloor and sweeps the capsule. When blocked by a vertical face, StepUp sweeps up by MaxStepHeight, forward, and back down.… 3 source references

1 edit awaiting review

✎Edit to CharacterMovementComponent.cpp awaiting review+3−1

Select a row in the thread to show what it produced.

Build

Configuration

PlatformWin64

Program arguments

More build actions

Build uses Unreal Build Tool · Run starts the selected target's built executable

Ready · Run and Debug build the selected target before launching.

Build / program output

No output received yet.

No build diagnostics retained.

No debugger session. Debug builds the selected target before launching it. Set breakpoints in the Code panel's gutter or with the toggle breakpoint shortcut.

Unreal Build Tool

UnrealEditor.exe · 30.0 s

Stopped · 146,606 samples · 33 threads

User-mode · Requested 1,000 Hz · Measured 1,000 Hz

Whole recording · all threads · Samples · thread start hidden · 146,606 samples · 4.8 of 33 threads running on average · Rendering 22%, Game 7.8%, Physics 3.6%

FunctionSamplesModule

TaskWorker::Run63%0.0%92,178game.exe

Task::Execute63%0.0%92,178game.exe

Anim::EvaluatePose16%0.0%23,521anim.dll

Pose::Sample16%6.4%23,521anim.dll

FunctionSamplesModule

RtlUserThreadStart100%0.0%146,606ntdll.dll

BaseThreadInitThunk100%0.0%146,606kernel32.dll

TaskWorker::Run63%0.0%92,178game.exe

Task::Execute63%0.0%92,178game.exe

Select a function in the call tree, the function list or the timeline to see who calls it.

Select a function in the call tree, the function list or the timeline to see its source.

Select a function in the call tree, the function list or the timeline to see its runs.

Stopped · 30.0 s at 1000 Hz · 146,606 samples from 33 threads · 31 stacks cut short · 0.2% of frames without symbols · 12 late ticks. A thread waiting when sampled counts as busy, so wait functions can show high.

P4Experimental

[object Object].

Engine/Source/Runtime/Engine/Private/Components/CharacterMovementComponent.cpp
    // Integrate pending root motion and velocity for the active movement mode.
    StartNewPhysics(DeltaSeconds, 0);
    UpdateComponentVelocity();
}

void UCharacterMovementComponent::PhysWalking(float deltaTime, int32 Iterations)
{
    SCOPE_CYCLE_COUNTER(STAT_CharPhysWalking);

    while ((deltaTime >= MIN_TICK_TIME) && (Iterations < MaxSimulationIterations))
    {
        Iterations++;
        const float timeTick = GetSimulationTimeStep(deltaTime, Iterations);
        deltaTime -= timeTick;

        const FVector OldLocation = UpdatedComponent->GetComponentLocation();
        FStepDownResult StepDownResult;

        // Project horizontal velocity onto the current floor plane and sweep.
        MoveAlongFloor(Velocity, timeTick, &StepDownResult);

        // Reuse the step-down floor hit when available to avoid a redundant sweep.
        if (StepDownResult.bComputedFloor)
        {
            CurrentFloor = StepDownResult.FloorResult;
        }
        else
        {
            FindFloor(UpdatedComponent->GetComponentLocation(), CurrentFloor, false);
        }

        if (!CurrentFloor.IsWalkableFloor())
        {
            SetMovementMode(MOVE_Falling);
            StartNewPhysics(deltaTime, Iterations);
            return;
        }
    }
}

void UCharacterMovementComponent::MoveAlongFloor(
    const FVector& InVelocity,
    float DeltaSeconds,
    FStepDownResult* OutStepDownResult)
{
    if (!CurrentFloor.IsWalkableFloor())
    {
        return;
    }

    const FVector Delta = FVector(InVelocity.X, InVelocity.Y, 0.f) * DeltaSeconds;