com.almasb.fxgl.physics.box2d.collision.Distance Maven / Gradle / Ivy
/*
* FXGL - JavaFX Game Library. The MIT License (MIT).
* Copyright (c) AlmasB ([email protected]).
* See LICENSE for details.
*/
package com.almasb.fxgl.physics.box2d.collision;
import com.almasb.fxgl.core.math.Vec2;
import com.almasb.fxgl.physics.box2d.collision.shapes.*;
import com.almasb.fxgl.physics.box2d.common.JBoxSettings;
import com.almasb.fxgl.physics.box2d.common.JBoxUtils;
import com.almasb.fxgl.physics.box2d.common.Rotation;
import com.almasb.fxgl.physics.box2d.common.Transform;
// updated to rev 100
/**
* This is non-static for faster pooling. To get an instance, use the {@link SingletonPool}, don't
* construct a distance object.
*
* @author Daniel Murphy
*/
public class Distance {
public static final int MAX_ITERS = 20;
public static int GJK_CALLS = 0;
public static int GJK_ITERS = 0;
public static int GJK_MAX_ITERS = 20;
/**
* GJK using Voronoi regions (Christer Ericson) and Barycentric coordinates.
*/
private class SimplexVertex {
public final Vec2 wA = new Vec2(); // support point in shapeA
public final Vec2 wB = new Vec2(); // support point in shapeB
public final Vec2 w = new Vec2(); // wB - wA
public float a; // barycentric coordinate for closest point
public int indexA; // wA index
public int indexB; // wB index
public void set(SimplexVertex sv) {
wA.set(sv.wA);
wB.set(sv.wB);
w.set(sv.w);
a = sv.a;
indexA = sv.indexA;
indexB = sv.indexB;
}
}
/**
* Used to warm start Distance. Set count to zero on first call.
*
* @author daniel
*/
public static class SimplexCache {
/** length or area */
public float metric;
public int count;
/** vertices on shape A */
public final int indexA[] = new int[3];
/** vertices on shape B */
public final int indexB[] = new int[3];
public SimplexCache() {
metric = 0;
count = 0;
indexA[0] = Integer.MAX_VALUE;
indexA[1] = Integer.MAX_VALUE;
indexA[2] = Integer.MAX_VALUE;
indexB[0] = Integer.MAX_VALUE;
indexB[1] = Integer.MAX_VALUE;
indexB[2] = Integer.MAX_VALUE;
}
public void set(SimplexCache sc) {
System.arraycopy(sc.indexA, 0, indexA, 0, indexA.length);
System.arraycopy(sc.indexB, 0, indexB, 0, indexB.length);
metric = sc.metric;
count = sc.count;
}
}
private class Simplex {
public final SimplexVertex m_v1 = new SimplexVertex();
public final SimplexVertex m_v2 = new SimplexVertex();
public final SimplexVertex m_v3 = new SimplexVertex();
public final SimplexVertex vertices[] = {m_v1, m_v2, m_v3};
public int m_count;
public void readCache(SimplexCache cache, DistanceProxy proxyA, Transform transformA,
DistanceProxy proxyB, Transform transformB) {
assert cache.count <= 3;
// Copy data from cache.
m_count = cache.count;
for (int i = 0; i < m_count; ++i) {
SimplexVertex v = vertices[i];
v.indexA = cache.indexA[i];
v.indexB = cache.indexB[i];
Vec2 wALocal = proxyA.getVertex(v.indexA);
Vec2 wBLocal = proxyB.getVertex(v.indexB);
Transform.mulToOutUnsafe(transformA, wALocal, v.wA);
Transform.mulToOutUnsafe(transformB, wBLocal, v.wB);
v.w.set(v.wB).subLocal(v.wA);
v.a = 0.0f;
}
// Compute the new simplex metric, if it is substantially different than
// old metric then flush the simplex.
if (m_count > 1) {
float metric1 = cache.metric;
float metric2 = getMetric();
if (metric2 < 0.5f * metric1 || 2.0f * metric1 < metric2 || metric2 < JBoxSettings.EPSILON) {
// Reset the simplex.
m_count = 0;
}
}
// If the cache is empty or invalid ...
if (m_count == 0) {
SimplexVertex v = vertices[0];
v.indexA = 0;
v.indexB = 0;
Vec2 wALocal = proxyA.getVertex(0);
Vec2 wBLocal = proxyB.getVertex(0);
Transform.mulToOutUnsafe(transformA, wALocal, v.wA);
Transform.mulToOutUnsafe(transformB, wBLocal, v.wB);
v.w.set(v.wB).subLocal(v.wA);
m_count = 1;
}
}
public void writeCache(SimplexCache cache) {
cache.metric = getMetric();
cache.count = m_count;
for (int i = 0; i < m_count; ++i) {
cache.indexA[i] = vertices[i].indexA;
cache.indexB[i] = vertices[i].indexB;
}
}
private final Vec2 e12 = new Vec2();
public final void getSearchDirection(final Vec2 out) {
switch (m_count) {
case 1:
out.set(m_v1.w).negateLocal();
return;
case 2:
e12.set(m_v2.w).subLocal(m_v1.w);
// use out for a temp variable real quick
out.set(m_v1.w).negateLocal();
float sgn = Vec2.cross(e12, out);
if (sgn > 0f) {
// Origin is left of e12.
Vec2.crossToOutUnsafe(1f, e12, out);
return;
} else {
// Origin is right of e12.
Vec2.crossToOutUnsafe(e12, 1f, out);
return;
}
default:
assert false;
out.setZero();
return;
}
}
// djm pooled
private final Vec2 case2 = new Vec2();
private final Vec2 case22 = new Vec2();
/**
* this returns pooled objects. don't keep or modify them
*
* @return
*/
public void getClosestPoint(final Vec2 out) {
switch (m_count) {
case 0:
assert false;
out.setZero();
return;
case 1:
out.set(m_v1.w);
return;
case 2:
case22.set(m_v2.w).mulLocal(m_v2.a);
case2.set(m_v1.w).mulLocal(m_v1.a).addLocal(case22);
out.set(case2);
return;
case 3:
out.setZero();
return;
default:
assert false;
out.setZero();
return;
}
}
// djm pooled, and from above
private final Vec2 case3 = new Vec2();
private final Vec2 case33 = new Vec2();
public void getWitnessPoints(Vec2 pA, Vec2 pB) {
switch (m_count) {
case 0:
assert false;
break;
case 1:
pA.set(m_v1.wA);
pB.set(m_v1.wB);
break;
case 2:
case2.set(m_v1.wA).mulLocal(m_v1.a);
pA.set(m_v2.wA).mulLocal(m_v2.a).addLocal(case2);
// m_v1.a * m_v1.wA + m_v2.a * m_v2.wA;
// *pB = m_v1.a * m_v1.wB + m_v2.a * m_v2.wB;
case2.set(m_v1.wB).mulLocal(m_v1.a);
pB.set(m_v2.wB).mulLocal(m_v2.a).addLocal(case2);
break;
case 3:
pA.set(m_v1.wA).mulLocal(m_v1.a);
case3.set(m_v2.wA).mulLocal(m_v2.a);
case33.set(m_v3.wA).mulLocal(m_v3.a);
pA.addLocal(case3).addLocal(case33);
pB.set(pA);
// *pA = m_v1.a * m_v1.wA + m_v2.a * m_v2.wA + m_v3.a * m_v3.wA;
// *pB = *pA;
break;
default:
assert false;
break;
}
}
// djm pooled, from above
public float getMetric() {
switch (m_count) {
case 0:
assert false;
return 0.0f;
case 1:
return 0.0f;
case 2:
return JBoxUtils.distance(m_v1.w, m_v2.w);
case 3:
case3.set(m_v2.w).subLocal(m_v1.w);
case33.set(m_v3.w).subLocal(m_v1.w);
// return Vec2.cross(m_v2.w - m_v1.w, m_v3.w - m_v1.w);
return Vec2.cross(case3, case33);
default:
assert false;
return 0.0f;
}
}
// djm pooled from above
/**
* Solve a line segment using barycentric coordinates.
*/
public void solve2() {
// Solve a line segment using barycentric coordinates.
//
// p = a1 * w1 + a2 * w2
// a1 + a2 = 1
//
// The vector from the origin to the closest point on the line is
// perpendicular to the line.
// e12 = w2 - w1
// dot(p, e) = 0
// a1 * dot(w1, e) + a2 * dot(w2, e) = 0
//
// 2-by-2 linear system
// [1 1 ][a1] = [1]
// [w1.e12 w2.e12][a2] = [0]
//
// Define
// d12_1 = dot(w2, e12)
// d12_2 = -dot(w1, e12)
// d12 = d12_1 + d12_2
//
// Solution
// a1 = d12_1 / d12
// a2 = d12_2 / d12
final Vec2 w1 = m_v1.w;
final Vec2 w2 = m_v2.w;
e12.set(w2).subLocal(w1);
// w1 region
float d12_2 = -Vec2.dot(w1, e12);
if (d12_2 <= 0.0f) {
// a2 <= 0, so we clamp it to 0
m_v1.a = 1.0f;
m_count = 1;
return;
}
// w2 region
float d12_1 = Vec2.dot(w2, e12);
if (d12_1 <= 0.0f) {
// a1 <= 0, so we clamp it to 0
m_v2.a = 1.0f;
m_count = 1;
m_v1.set(m_v2);
return;
}
// Must be in e12 region.
float inv_d12 = 1.0f / (d12_1 + d12_2);
m_v1.a = d12_1 * inv_d12;
m_v2.a = d12_2 * inv_d12;
m_count = 2;
}
// djm pooled, and from above
private final Vec2 e13 = new Vec2();
private final Vec2 e23 = new Vec2();
private final Vec2 w1 = new Vec2();
private final Vec2 w2 = new Vec2();
private final Vec2 w3 = new Vec2();
/**
* Solve a line segment using barycentric coordinates.
* Possible regions:
* - points[2]
* - edge points[0]-points[2]
* - edge points[1]-points[2]
* - inside the triangle
*/
public void solve3() {
w1.set(m_v1.w);
w2.set(m_v2.w);
w3.set(m_v3.w);
// Edge12
// [1 1 ][a1] = [1]
// [w1.e12 w2.e12][a2] = [0]
// a3 = 0
e12.set(w2).subLocal(w1);
float w1e12 = Vec2.dot(w1, e12);
float w2e12 = Vec2.dot(w2, e12);
float d12_1 = w2e12;
float d12_2 = -w1e12;
// Edge13
// [1 1 ][a1] = [1]
// [w1.e13 w3.e13][a3] = [0]
// a2 = 0
e13.set(w3).subLocal(w1);
float w1e13 = Vec2.dot(w1, e13);
float w3e13 = Vec2.dot(w3, e13);
float d13_1 = w3e13;
float d13_2 = -w1e13;
// Edge23
// [1 1 ][a2] = [1]
// [w2.e23 w3.e23][a3] = [0]
// a1 = 0
e23.set(w3).subLocal(w2);
float w2e23 = Vec2.dot(w2, e23);
float w3e23 = Vec2.dot(w3, e23);
float d23_1 = w3e23;
float d23_2 = -w2e23;
// Triangle123
float n123 = Vec2.cross(e12, e13);
float d123_1 = n123 * Vec2.cross(w2, w3);
float d123_2 = n123 * Vec2.cross(w3, w1);
float d123_3 = n123 * Vec2.cross(w1, w2);
// w1 region
if (d12_2 <= 0.0f && d13_2 <= 0.0f) {
m_v1.a = 1.0f;
m_count = 1;
return;
}
// e12
if (d12_1 > 0.0f && d12_2 > 0.0f && d123_3 <= 0.0f) {
float inv_d12 = 1.0f / (d12_1 + d12_2);
m_v1.a = d12_1 * inv_d12;
m_v2.a = d12_2 * inv_d12;
m_count = 2;
return;
}
// e13
if (d13_1 > 0.0f && d13_2 > 0.0f && d123_2 <= 0.0f) {
float inv_d13 = 1.0f / (d13_1 + d13_2);
m_v1.a = d13_1 * inv_d13;
m_v3.a = d13_2 * inv_d13;
m_count = 2;
m_v2.set(m_v3);
return;
}
// w2 region
if (d12_1 <= 0.0f && d23_2 <= 0.0f) {
m_v2.a = 1.0f;
m_count = 1;
m_v1.set(m_v2);
return;
}
// w3 region
if (d13_1 <= 0.0f && d23_1 <= 0.0f) {
m_v3.a = 1.0f;
m_count = 1;
m_v1.set(m_v3);
return;
}
// e23
if (d23_1 > 0.0f && d23_2 > 0.0f && d123_1 <= 0.0f) {
float inv_d23 = 1.0f / (d23_1 + d23_2);
m_v2.a = d23_1 * inv_d23;
m_v3.a = d23_2 * inv_d23;
m_count = 2;
m_v1.set(m_v3);
return;
}
// Must be in triangle123
float inv_d123 = 1.0f / (d123_1 + d123_2 + d123_3);
m_v1.a = d123_1 * inv_d123;
m_v2.a = d123_2 * inv_d123;
m_v3.a = d123_3 * inv_d123;
m_count = 3;
}
}
/**
* A distance proxy is used by the GJK algorithm. It encapsulates any shape. jbox2dTODO: see if we can
* just do assignments with m_vertices, instead of copying stuff over
*
* @author daniel
*/
public static class DistanceProxy {
public final Vec2[] m_vertices;
public int m_count;
public float m_radius;
public final Vec2[] m_buffer;
public DistanceProxy() {
m_vertices = new Vec2[JBoxSettings.maxPolygonVertices];
for (int i = 0; i < m_vertices.length; i++) {
m_vertices[i] = new Vec2();
}
m_buffer = new Vec2[2];
m_count = 0;
m_radius = 0f;
}
/**
* Initialize the proxy using the given shape. The shape must remain in scope while the proxy is
* in use.
*/
public final void set(final Shape shape, int index) {
switch (shape.getType()) {
case CIRCLE:
final CircleShape circle = (CircleShape) shape;
m_vertices[0].set(circle.center);
m_count = 1;
m_radius = circle.getRadius();
break;
case POLYGON:
final PolygonShape poly = (PolygonShape) shape;
m_count = poly.getVertexCount();
m_radius = poly.getRadius();
for (int i = 0; i < m_count; i++) {
m_vertices[i].set(poly.m_vertices[i]);
}
break;
case CHAIN:
final ChainShape chain = (ChainShape) shape;
assert 0 <= index && index < chain.m_count;
m_buffer[0] = chain.m_vertices[index];
if (index + 1 < chain.m_count) {
m_buffer[1] = chain.m_vertices[index + 1];
} else {
m_buffer[1] = chain.m_vertices[0];
}
m_vertices[0].set(m_buffer[0]);
m_vertices[1].set(m_buffer[1]);
m_count = 2;
m_radius = chain.getRadius();
break;
case EDGE:
EdgeShape edge = (EdgeShape) shape;
m_vertices[0].set(edge.m_vertex1);
m_vertices[1].set(edge.m_vertex2);
m_count = 2;
m_radius = edge.getRadius();
break;
default:
assert false;
}
}
/**
* Get the supporting vertex index in the given direction.
*
* @param d
* @return
*/
public final int getSupport(final Vec2 d) {
int bestIndex = 0;
float bestValue = Vec2.dot(m_vertices[0], d);
for (int i = 1; i < m_count; i++) {
float value = Vec2.dot(m_vertices[i], d);
if (value > bestValue) {
bestIndex = i;
bestValue = value;
}
}
return bestIndex;
}
/**
* Get the supporting vertex in the given direction.
*
* @param d
* @return
*/
public final Vec2 getSupportVertex(final Vec2 d) {
int bestIndex = 0;
float bestValue = Vec2.dot(m_vertices[0], d);
for (int i = 1; i < m_count; i++) {
float value = Vec2.dot(m_vertices[i], d);
if (value > bestValue) {
bestIndex = i;
bestValue = value;
}
}
return m_vertices[bestIndex];
}
/**
* Get the vertex count.
*
* @return
*/
public final int getVertexCount() {
return m_count;
}
/**
* Get a vertex by index. Used by Distance.
*
* @param index
* @return
*/
public final Vec2 getVertex(int index) {
assert 0 <= index && index < m_count;
return m_vertices[index];
}
}
private Simplex simplex = new Simplex();
private int[] saveA = new int[3];
private int[] saveB = new int[3];
private Vec2 closestPoint = new Vec2();
private Vec2 d = new Vec2();
private Vec2 temp = new Vec2();
private Vec2 normal = new Vec2();
/**
* Compute the closest points between two shapes. Supports any combination of: CircleShape and
* PolygonShape. The simplex cache is input/output. On the first call set SimplexCache.count to
* zero.
*
* @param output
* @param cache
* @param input
*/
@SuppressWarnings("PMD.EmptyIfStmt")
public final void distance(final DistanceOutput output, final SimplexCache cache,
final DistanceInput input) {
GJK_CALLS++;
final DistanceProxy proxyA = input.proxyA;
final DistanceProxy proxyB = input.proxyB;
Transform transformA = input.transformA;
Transform transformB = input.transformB;
// Initialize the simplex.
simplex.readCache(cache, proxyA, transformA, proxyB, transformB);
// Get simplex vertices as an array.
SimplexVertex[] vertices = simplex.vertices;
// These store the vertices of the last simplex so that we
// can check for duplicates and prevent cycling.
// (pooled above)
int saveCount = 0;
simplex.getClosestPoint(closestPoint);
float distanceSqr1 = closestPoint.lengthSquared();
float distanceSqr2 = distanceSqr1;
// Main iteration loop
int iter = 0;
while (iter < MAX_ITERS) {
// Copy simplex so we can identify duplicates.
saveCount = simplex.m_count;
for (int i = 0; i < saveCount; i++) {
saveA[i] = vertices[i].indexA;
saveB[i] = vertices[i].indexB;
}
switch (simplex.m_count) {
case 1:
break;
case 2:
simplex.solve2();
break;
case 3:
simplex.solve3();
break;
default:
assert false;
}
// If we have 3 points, then the origin is in the corresponding triangle.
if (simplex.m_count == 3) {
break;
}
// Compute closest point.
simplex.getClosestPoint(closestPoint);
distanceSqr2 = closestPoint.lengthSquared();
// ensure progress
if (distanceSqr2 >= distanceSqr1) {
// break;
}
distanceSqr1 = distanceSqr2;
// get search direction;
simplex.getSearchDirection(d);
// Ensure the search direction is numerically fit.
if (d.lengthSquared() < JBoxSettings.EPSILON * JBoxSettings.EPSILON) {
// The origin is probably contained by a line segment
// or triangle. Thus the shapes are overlapped.
// We can't return zero here even though there may be overlap.
// In case the simplex is a point, segment, or triangle it is difficult
// to determine if the origin is contained in the CSO or very close to it.
break;
}
/*
* SimplexVertex* vertex = vertices + simplex.m_count; vertex.indexA =
* proxyA.GetSupport(MulT(transformA.R, -d)); vertex.wA = Mul(transformA,
* proxyA.GetVertex(vertex.indexA)); Vec2 wBLocal; vertex.indexB =
* proxyB.GetSupport(MulT(transformB.R, d)); vertex.wB = Mul(transformB,
* proxyB.GetVertex(vertex.indexB)); vertex.w = vertex.wB - vertex.wA;
*/
// Compute a tentative new simplex vertex using support points.
SimplexVertex vertex = vertices[simplex.m_count];
Rotation.mulTransUnsafe(transformA.q, d.negateLocal(), temp);
vertex.indexA = proxyA.getSupport(temp);
Transform.mulToOutUnsafe(transformA, proxyA.getVertex(vertex.indexA), vertex.wA);
// Vec2 wBLocal;
Rotation.mulTransUnsafe(transformB.q, d.negateLocal(), temp);
vertex.indexB = proxyB.getSupport(temp);
Transform.mulToOutUnsafe(transformB, proxyB.getVertex(vertex.indexB), vertex.wB);
vertex.w.set(vertex.wB).subLocal(vertex.wA);
// Iteration count is equated to the number of support point calls.
++iter;
++GJK_ITERS;
// Check for duplicate support points. This is the main termination criteria.
boolean duplicate = false;
for (int i = 0; i < saveCount; ++i) {
if (vertex.indexA == saveA[i] && vertex.indexB == saveB[i]) {
duplicate = true;
break;
}
}
// If we found a duplicate support point we must exit to avoid cycling.
if (duplicate) {
break;
}
// New vertex is ok and needed.
++simplex.m_count;
}
GJK_MAX_ITERS = Math.max(GJK_MAX_ITERS, iter);
// Prepare output.
simplex.getWitnessPoints(output.pointA, output.pointB);
output.distance = JBoxUtils.distance(output.pointA, output.pointB);
output.iterations = iter;
// Cache the simplex.
simplex.writeCache(cache);
// Apply radii if requested.
if (input.useRadii) {
float rA = proxyA.m_radius;
float rB = proxyB.m_radius;
if (output.distance > rA + rB && output.distance > JBoxSettings.EPSILON) {
// Shapes are still no overlapped.
// Move the witness points to the outer surface.
output.distance -= rA + rB;
normal.set(output.pointB).subLocal(output.pointA);
normal.getLengthAndNormalize();
temp.set(normal).mulLocal(rA);
output.pointA.addLocal(temp);
temp.set(normal).mulLocal(rB);
output.pointB.subLocal(temp);
} else {
// Shapes are overlapped when radii are considered.
// Move the witness points to the middle.
// Vec2 p = 0.5f * (output.pointA + output.pointB);
output.pointA.addLocal(output.pointB).mulLocal(.5f);
output.pointB.set(output.pointA);
output.distance = 0.0f;
}
}
}
}
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