private void Simulate()
{
// For each node in rope.
for (int i = 0; i < nodes.Length; i++)
{
VerletNode node = nodes[i];
// Acceleration is useful to have around if we want to apply external forces to rope nodes, just add the
// force to `node.acceleration`.
node.acceleration += gravity;
float2 move = node.position - node.oldPosition;
// Limiting maximum move gives the simulation more stability.
if (math.length(move) > maxSimMove)
{
move = math.normalize(move) * maxSimMove;
}
// Calculate new position.
float2 temp = node.position;
node.position += move * (1f - node.friction) + stepTime * stepTime * node.acceleration;
node.oldPosition = temp;
node.acceleration = float2.zero;
node.friction = 0;
nodes[i] = node;
}
}
private void ApplyConstraints()
{
for (int i = 0; i < nodes.Length - 1; i++)
{
VerletNode node1 = nodes[i];
VerletNode node2 = nodes[i + 1];
Constraint constraint1 = constraints[i];
Constraint constraint2 = constraints[i + 1];
// If the node is constrained, we need to set its position early so that the connected node adjusts
// accordingly, but we don't want it to move, so we multiply movement by 0 later if we're constrained.
// For the most part, we don't actually need to check `constraint2` because it's overwritten in the
// Next iteration of the loop. However, the last node never gets to be `node1`, so we have to check both.
float mult1 = 1f, mult2 = 1f;
if (constraint1.enabled)
{
node1.position = constraint1.position;
mult1 = 0f;
}
if (constraint2.enabled)
{
node2.position = constraint2.position;
mult2 = 0f;
}
// Get the current distance between rope nodes.
float2 diff = math.float2(node1.position.x - node2.position.x, node1.position.y - node2.position.y);
float dist = math.length(node1.position - node2.position);
float difference = 0;
// Guard against divide by 0.
if (dist > 0)
{
difference = (dist - nodeDistance) / dist;
}
diff *= .5f * difference;
// Apply correction.
node1.position -= diff * mult1;
node2.position += diff * mult2;
nodes[i] = node1;
nodes[i + 1] = node2;
}
}
private void AdjustCollisions()
{
// Loop through each collider.
for (int i = 0; i < numCollisions; i++)
{
CollisionInfo nc = collisionInfos[i];
// Looping inside the switch statement is marginally faster than the other way around.
switch (nc.colliderType)
{
case ColliderType.Circle: {
float radius = nc.colliderSize.x * math.max(nc.scale.x, nc.scale.y);
// Correct each node which is colliding with this collider.
for (int j = 0; j < nc.numCollisions; j++)
{
VerletNode node = nodes[collidingNodes[i * nodes.Length + j]];
float distance = math.distance(nc.position, node.position);
// Leave if we're not actually colliding.
if (distance - radius > 0)
{
continue;
}
float2 dir = math.normalize(node.position - nc.position);
float2 hitPos = nc.position + dir * radius;
node.position = hitPos;
// Colliding nodes should have some friction on them.
node.friction = friction;
nodes[collidingNodes[nodes.Length * i + j]] = node;
}
}
break;
case ColliderType.Box: {
for (int j = 0; j < nc.numCollisions; j++)
{
VerletNode node = nodes[collidingNodes[i * nodes.Length + j]];
float4 localPoint = math.mul(nc.wtl, math.float4(node.position, 0, 1));
// If distance from center is more than box "radius", then we can't be colliding.
Vector2 half = nc.colliderSize * .5f;
Vector2 scalar = nc.scale;
float dx = localPoint.x;
float px = half.x - Mathf.Abs(dx);
if (px <= 0)
{
continue;
}
float dy = localPoint.y;
float py = half.x - Mathf.Abs(dy);
if (py <= 0)
{
continue;
}
// Need to multiply distance by scale or we'll mess up on scaled box corners.
if (px * scalar.x < py * scalar.y)
{
float sx = Mathf.Sign(dx);
localPoint.x = half.x * sx;
}
else
{
float sy = Mathf.Sign(dy);
localPoint.y = half.y * sy;
}
// Finally get the world space hit position.
float4 hitPos = math.mul(nc.ltw, localPoint);
node.position = hitPos.xy;
node.friction = friction;
nodes[collidingNodes[nodes.Length * i + j]] = node;
}
}
break;
}
}
}
private void Awake()
{
if (totalNodes > MAX_RENDER_POINTS)
{
Debug.LogError("Total nodes is more than MAX_RENDER_POINTS, so won't be able to render the entire rope.");
}
// Buffer for OverlapCircleNonAlloc.
colliderBuffer = new Collider2D[COLLIDER_BUFFER_SIZE];
// Jobs setup.
// You could use `NativeList` for some of these instead, and not worry about all the constants.
nodes = new NativeArray <VerletNode>(totalNodes, Allocator.Persistent);
constraints = new NativeArray <Constraint>(totalNodes, Allocator.Persistent);
collisionInfos = new NativeArray <CollisionInfo>(MAX_ROPE_COLLISIONS, Allocator.Persistent);
collidingNodes = new NativeArray <int>(totalNodes * MAX_ROPE_COLLISIONS, Allocator.Persistent);
renderPositions = new Vector4[totalNodes];
// Spawn nodes starting from the transform position and working down.
Vector2 pos = transform.position;
for (int i = 0; i < nodes.Length; i++)
{
nodes[i] = new VerletNode(pos);
renderPositions[i] = new Vector4(pos.x, pos.y, 1, 1);
pos.y -= nodeDistance;
}
// Mesh setup.
Mesh mesh = new Mesh();
{
Vector3[] vertices = new Vector3[totalNodes * VERTICES_PER_NODE];
int[] triangles = new int[totalNodes * TRIANGLES_PER_NODE * 3];
for (int i = 0; i < totalNodes; i++)
{
// 4 triangles per node, 3 indices per triangle.
int idx = i * TRIANGLES_PER_NODE * 3;
// 8 vertices per node.
int vIdx = i * VERTICES_PER_NODE;
// Unity uses a CLOCKWISE WINDING ORDER -- clockwise tri indices are facing the camera.
triangles[idx + 0] = vIdx; // v1 top
triangles[idx + 1] = vIdx + 1; // v2 bottom
triangles[idx + 2] = vIdx + 2; // v1 bottom
triangles[idx + 3] = vIdx; // v1 top
triangles[idx + 4] = vIdx + 3; // v2 top
triangles[idx + 5] = vIdx + 1; // v2 bottom
triangles[idx + 6] = vIdx + 4; // tl
triangles[idx + 7] = vIdx + 7; // br
triangles[idx + 8] = vIdx + 6; // bl
triangles[idx + 9] = vIdx + 4; // tl
triangles[idx + 10] = vIdx + 5; // tr
triangles[idx + 11] = vIdx + 7; // br
}
// We only really care about the number of vertices, not what they actually are -- the positions aren't used.
mesh.vertices = vertices;
mesh.triangles = triangles;
// Since we pretty much want the rope to always render (it's always going to be on screen if it's active), we
// just set the bounds super large to avoid recalculating the bounds when the rope changes.
mesh.bounds = new Bounds(Vector3.zero, Vector3.one * 100f);
}
GetComponent <MeshFilter>().mesh = mesh;
material = GetComponent <MeshRenderer>().material;
material.SetFloat("_Width", drawWidth);
}
