Physical Character Walk On Grid Box Cause Small jump

[IvanXuff]

When I was building a white model of a building, I found that my physical character would jump slightly. After checking, I found that the jump was between two boxes. At first, I thought it was due to the gap caused by Convex.

But when I overlapped the two boxes, it would also cause a small jump when it walked towards the seam.

QQ2025616-14121.mp4

And because I used an inverted cone as a character instead of a capsule, my jump was very obvious

In addition, if I scale a box with a Convex of 0 to a large size. My character walking on it sometimes has a very large jump, but when my Convex is larger than a value, this jump will disappear.

[jrouwe]

This only works if you:

• Enable CharacterBaseSettings::mEnhancedInternalEdgeRemoval
• When the bodies you're walking on are part of one body (i.e. they need to be in a CompoundShape).
• When the edges of the bodies you're walking on are touching (ignoring the convex radius)

In general I would recommend not using Character but CharacterVirtual for player character movement as that suffers less from 'ghost collisions' even if the conditions listed above are not met.

[IvanXuff]

Thank you for your reply.
Even when I use CharacterVirtual, ghost collisions still affect non-character entities — for example, a ball rolling on the ground with some speed may bounce when passing over a seam.
So, is enabling mEnhancedInternalEdgeRemoval and carefully aligning the boxes the only way to avoid this issue?

[jrouwe]

So, is enabling mEnhancedInternalEdgeRemoval and carefully aligning the boxes the only way to avoid this issue?

If combined with using compound shapes it is the only way to completely eliminate ghost collisions.

You can also lower the value of PhysicsSettings::mSpeculativeContactDistance and PhysicsSettings::mPenetrationSlop to reduce (but not eliminate) ghost collisions.

[IvanXuff]

I found that even if all shapes are combined into a compound shape, the ConvexRadius of all shapes must be set to 0 to completely eliminate the small jumps, right?

That's my test code

`

// Create 'player' character
Ref<CharacterSettings> settings = new CharacterSettings();
settings->mMaxSlopeAngle = DegreesToRadians(45.0f);
settings->mLayer = Layers::MOVING;
settings->mShape = mStandingShape;
settings->mFriction = 0.5f;
settings->mSupportingVolume = Plane(Vec3::sAxisY(), -cCharacterRadiusStanding); // Accept contacts that touch the lower sphere of the capsule
settings->mEnhancedInternalEdgeRemoval = true;
mCharacter = new Character(settings, RVec3(0, 25, 0), Quat::sIdentity(), 0, mPhysicsSystem);
mCharacter->AddToPhysicsSystem(EActivation::Activate);

	// Create a 10x10 grid of boxes as a compound shape
RefConst<Shape> box = new BoxShape(Vec3(sBoxSize, sBoxSize, sBoxSize), 0); // Variable box size

float spacing = sBoxSize * 2.0f; // Box width (no gaps between boxes)
float totalWidth = spacing * 10.0f;
float offsetX = -totalWidth * 0.5f + sBoxSize; // Start position to center the 10x10 grid
float offsetZ = -totalWidth * 0.5f + sBoxSize;

// Create compound shape settings
Ref<StaticCompoundShapeSettings> compoundSettings = new StaticCompoundShapeSettings();

// Add all boxes to the compound shape
for (int x = 0; x < 10; ++x)
{
	for (int z = 0; z < 10; ++z)
	{
		Vec3 position(offsetX + x * spacing, 0, offsetZ + z * spacing);
		compoundSettings->AddShape(position, Quat::sIdentity(), box);
	}
}

// Create the compound shape and add it as a single body
RefConst<Shape> compoundShape = compoundSettings->Create().Get();
BodyCreationSettings compoundBodySettings(compoundShape, RVec3(0, 20, 0), Quat::sIdentity(), EMotionType::Static, Layers::NON_MOVING);
compoundBodySettings.mEnhancedInternalEdgeRemoval = true;
mBodyInterface->CreateAndAddBody(compoundBodySettings, EActivation::DontActivate);`

[jrouwe]

the ConvexRadius of all shapes must be set to 0 to completely eliminate the small jumps, right?

In the EnhancedInternalEdgeRemovalTest in the Samples this is not needed to set the convex radius to 0, but if the convex radius is too big then it eventually will create jumps yes.