Method Solve

blocks/Box2D/src/Box2D/Dynamics/b2World.cpp:386–574

Find islands, integrate and solve constraints, solve position constraints

// Find islands, integrate and solve constraints, solve position constraints
void b2World::Solve(const b2TimeStep& step)
{
	m_profile.solveInit = 0.0f;
	m_profile.solveVelocity = 0.0f;
	m_profile.solvePosition = 0.0f;

	// Size the island for the worst case.
	b2Island island(m_bodyCount,
					m_contactManager.m_contactCount,
					m_jointCount,
					&m_stackAllocator,
					m_contactManager.m_contactListener);

	// Clear all the island flags.
	for (b2Body* b = m_bodyList; b; b = b->m_next)
	{
		b->m_flags &= ~b2Body::e_islandFlag;
	}
	for (b2Contact* c = m_contactManager.m_contactList; c; c = c->m_next)
	{
		c->m_flags &= ~b2Contact::e_islandFlag;
	}
	for (b2Joint* j = m_jointList; j; j = j->m_next)
	{
		j->m_islandFlag = false;
	}

	// Build and simulate all awake islands.
	int32 stackSize = m_bodyCount;
	b2Body** stack = (b2Body**)m_stackAllocator.Allocate(stackSize * sizeof(b2Body*));
	for (b2Body* seed = m_bodyList; seed; seed = seed->m_next)
	{
		if (seed->m_flags & b2Body::e_islandFlag)
		{
			continue;
		}

		if (seed->IsAwake() == false || seed->IsActive() == false)
		{
			continue;
		}

		// The seed can be dynamic or kinematic.
		if (seed->GetType() == b2_staticBody)
		{
			continue;
		}

		// Reset island and stack.
		island.Clear();
		int32 stackCount = 0;
		stack[stackCount++] = seed;
		seed->m_flags |= b2Body::e_islandFlag;

		// Perform a depth first search (DFS) on the constraint graph.
		while (stackCount > 0)
		{
			// Grab the next body off the stack and add it to the island.