3D Free Grounder

GS_PhysicsRayGrounderComponent is the standard grounder for walking characters. Each physics tick it casts a ray downward from the unit’s capsule base, evaluates the slope, applies gravity when airborne, and updates the MoverContext with ground normal and grounding state.

Grounding mode name: "Free"

For usage guides and setup examples, see The Basics: GS_Unit.

Contents

• How It Works
• Ground Check
• Grounding Move
• Grounding State Changes
• Editor-Exposed Settings
• Extension Guide
• See Also

How It Works

Each post-physics tick, the grounder runs two operations in order:

1. GroundCheck() — determines contact, slope, and normal
2. GroundingMove() — applies gravity or snap force based on contact result

Ground Check

GroundCheck() casts a sphere (matching the capsule base radius) downward from the unit’s feet:

1. If the ray hits geometry within groundCheckDistance:
   • Computes slope angle from the hit normal vs. world up.
   • Updates MoverContextRequestBus::SetGroundNormal(hitNormal).
   • If slope angle ≤ maxWalkAngle (from the MoverContext): reports Grounded.
   • If slope angle > maxWalkAngle: reports Sliding.
   • Resets coyote timer.
2. If no hit:
   • Increments coyoteTimer.
   • If coyoteTimer < coyoteTime: still reports Grounded (coyote grace period).
   • If coyoteTimer ≥ coyoteTime: reports Falling.

Grounding Move

GroundingMove() applies vertical forces based on the current state:

Grounded: Applies a downward TimedSpringDamper to keep the unit snapped to the surface without bouncing.

Falling: Applies manual gravity — adds gravityScale * AZ::Physics::DefaultGravity to the rigid body’s linear velocity each frame:

AZ::Vector3 velocity = rigidBody->GetLinearVelocity();
velocity.SetZ(velocity.GetZ() + gravity * delta);
rigidBody->SetLinearVelocity(velocity);

Sliding: Does not override vertical velocity — the Free Mover’s AccelerationSpringDamper handles the slide direction entirely.

Grounding State Changes

GroundingStateChange(newState) is called whenever the ground state changes:

When returning to Grounded from Sliding, the grounder calls ChangeMovementMode("Free") to restore locomotion.

Editor-Exposed Settings

Extension Guide

Extend GS_PhysicsRayGrounderComponent to add custom ground detection or state reactions.

#pragma once
#include <Source/Unit/Grounder/GS_PhysicsRayGrounderComponent.h>

namespace MyProject
{
    class MyGrounder : public GS_Unit::GS_PhysicsRayGrounderComponent
    {
    public:
        AZ_COMPONENT_DECL(MyGrounder);
        static void Reflect(AZ::ReflectContext* context);

    protected:
        void GroundingStateChange(AZ::u32 newState) override;
    };
}

void MyGrounder::GroundingStateChange(AZ::u32 newState)
{
    // Call base to handle mode switching
    GS_PhysicsRayGrounderComponent::GroundingStateChange(newState);

    if (newState == 0)
    {
        // Unit became airborne — trigger jump animation, etc.
    }
}

See Also

• Grounders — Grounder base class and class hierarchy
• Slide Mover — Activated when this grounder reports Sliding state
• Mover Context — Receives ground normal and state from this grounder
• Springs Utility — TimedSpringDamper used for ground snap

Get GS_Unit

GS_Unit — Explore this gem on the product page and add it to your project.