godot/servers/physics_2d/body_pair_2d_sw.cpp

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/*  body_pair_2d_sw.cpp                                                  */
/*************************************************************************/
/*                       This file is part of:                           */
/*                           GODOT ENGINE                                */
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/* Copyright (c) 2007-2014 Juan Linietsky, Ariel Manzur.                 */
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#include "body_pair_2d_sw.h"
#include "collision_solver_2d_sw.h"
#include "space_2d_sw.h"


#define POSITION_CORRECTION
#define ACCUMULATE_IMPULSES

void BodyPair2DSW::_add_contact(const Vector2& p_point_A,const Vector2& p_point_B,void *p_self) {

	BodyPair2DSW *self = (BodyPair2DSW *)p_self;

	self->_contact_added_callback(p_point_A,p_point_B);

}

void BodyPair2DSW::_contact_added_callback(const Vector2& p_point_A,const Vector2& p_point_B) {

	// check if we already have the contact

	Vector2 local_A = A->get_inv_transform().basis_xform(p_point_A);
	Vector2 local_B = B->get_inv_transform().basis_xform(p_point_B-offset_B);

	int new_index = contact_count;

	ERR_FAIL_COND( new_index >= (MAX_CONTACTS+1) );

	Contact contact;

	contact.acc_normal_impulse=0;
	contact.acc_bias_impulse=0;
	contact.acc_tangent_impulse=0;
	contact.local_A=local_A;
	contact.local_B=local_B;
	contact.reused=true;
	contact.normal=(p_point_A-p_point_B).normalized();

	// attempt to determine if the contact will be reused

	real_t recycle_radius_2 = space->get_contact_recycle_radius() * space->get_contact_recycle_radius();

	for (int i=0;i<contact_count;i++) {

		Contact& c = contacts[i];
		if (
		c.local_A.distance_squared_to( local_A ) < (recycle_radius_2) &&
		c.local_B.distance_squared_to( local_B ) < (recycle_radius_2) ) {

			contact.acc_normal_impulse=c.acc_normal_impulse;
			contact.acc_tangent_impulse=c.acc_tangent_impulse;
			contact.acc_bias_impulse=c.acc_bias_impulse;
			new_index=i;			
			break;
		}
	}

	// figure out if the contact amount must be reduced to fit the new contact

	if (new_index == MAX_CONTACTS) {

		// remove the contact with the minimum depth

		int least_deep=-1;
		real_t min_depth=1e10;


		for (int i=0;i<=contact_count;i++) {

			Contact& c = (i==contact_count)?contact:contacts[i];
			Vector2 global_A = A->get_transform().basis_xform(c.local_A);
			Vector2 global_B = B->get_transform().basis_xform(c.local_B)+offset_B;

			Vector2 axis = global_A - global_B;
			float depth = axis.dot( c.normal );


			if (depth<min_depth) {

				min_depth=depth;
				least_deep=i;
			}
		}

		ERR_FAIL_COND(least_deep==-1);

		if (least_deep < contact_count) { //replace the last deep contact by the new one

			contacts[least_deep]=contact;
		}

		return;
	}

	contacts[new_index]=contact;

	if (new_index==contact_count) {

		contact_count++;
	}

}

void BodyPair2DSW::_validate_contacts() {

	//make sure to erase contacts that are no longer valid

	real_t max_separation = space->get_contact_max_separation();
	real_t max_separation2 = max_separation*max_separation;

	for (int i=0;i<contact_count;i++) {

		Contact& c = contacts[i];

		bool erase=false;
		if (c.reused==false) {
			//was left behind in previous frame
			erase=true;
		} else {
			c.reused=false;

			Vector2 global_A = A->get_transform().basis_xform(c.local_A);
			Vector2 global_B = B->get_transform().basis_xform(c.local_B)+offset_B;
			Vector2 axis = global_A - global_B;
			float depth = axis.dot( c.normal );



			if (depth < -max_separation || (global_B + c.normal * depth - global_A).length_squared() > max_separation2) {
				erase=true;
			}
		}

		if (erase) {
			// contact no longer needed, remove


			if ((i+1) < contact_count) {
				// swap with the last one
				SWAP( contacts[i], contacts[ contact_count-1 ] );

			}

			i--;
			contact_count--;
		}
	}
}


bool BodyPair2DSW::_test_ccd(float p_step,Body2DSW *p_A, int p_shape_A,const Matrix32& p_xform_A,Body2DSW *p_B, int p_shape_B,const Matrix32& p_xform_B,bool p_swap_result) {



	Vector2 motion = p_A->get_linear_velocity()*p_step;
	real_t mlen = motion.length();
	if (mlen<CMP_EPSILON)
		return false;

	Vector2 mnormal = motion / mlen;

	real_t min,max;
	p_A->get_shape(p_shape_A)->project_rangev(mnormal,p_xform_A,min,max);
	bool fast_object = mlen > (max-min)*0.3; //going too fast in that direction

	if (fast_object) { //did it move enough in this direction to even attempt raycast? let's say it should move more than 1/3 the size of the object in that axis
		return false;
	}

	//cast a segment from support in motion normal, in the same direction of motion by motion length
	//support is the worst case collision point, so real collision happened before
	int a;
	Vector2 s[2];
	p_A->get_shape(p_shape_A)->get_supports(p_xform_A.basis_xform(mnormal).normalized(),s,a);
	Vector2 from = p_xform_A.xform(s[0]);
	Vector2 to = from + motion;

	Matrix32 from_inv = p_xform_B.affine_inverse();

	Vector2 local_from = from_inv.xform(from-mnormal*mlen*0.1); //start from a little inside the bounding box
	Vector2 local_to = from_inv.xform(to);

	Vector2 rpos,rnorm;
	if (!p_B->get_shape(p_shape_B)->intersect_segment(local_from,local_to,rpos,rnorm))
		return false;

	//ray hit something


	Vector2 hitpos = p_xform_B.xform(rpos);

	Vector2 contact_A = to;
	Vector2 contact_B = hitpos;

	//create a contact

	if (p_swap_result)
		_contact_added_callback(contact_B,contact_A);
	else
		_contact_added_callback(contact_A,contact_B);


	return true;
}

bool BodyPair2DSW::setup(float p_step) {


	//cannot collide
	if (A->is_shape_set_as_trigger(shape_A) || B->is_shape_set_as_trigger(shape_B) || A->has_exception(B->get_self()) || B->has_exception(A->get_self()) || (A->get_mode()<=Physics2DServer::BODY_MODE_KINEMATIC && B->get_mode()<=Physics2DServer::BODY_MODE_KINEMATIC)) {
		collided=false;
		return false;
	}

	//use local A coordinates to avoid numerical issues on collision detection
	offset_B = B->get_transform().get_origin() - A->get_transform().get_origin();

	_validate_contacts();

	Vector2 offset_A = A->get_transform().get_origin();
	Matrix32 xform_Au = A->get_transform().untranslated();
	Matrix32 xform_A = xform_Au * A->get_shape_transform(shape_A);

	Matrix32 xform_Bu = B->get_transform();
	xform_Bu.elements[2]-=A->get_transform().get_origin();
	Matrix32 xform_B = xform_Bu * B->get_shape_transform(shape_B);

	Shape2DSW *shape_A_ptr=A->get_shape(shape_A);
	Shape2DSW *shape_B_ptr=B->get_shape(shape_B);

	Vector2 motion_A,motion_B;

	if (A->get_continuous_collision_detection_mode()==Physics2DServer::CCD_MODE_CAST_SHAPE) {
		motion_A=A->get_motion();
	} 
	if (B->get_continuous_collision_detection_mode()==Physics2DServer::CCD_MODE_CAST_SHAPE) {
		motion_B=B->get_motion();
	} 
	//faster to set than to check..

	collided = CollisionSolver2DSW::solve(shape_A_ptr,xform_A,motion_A,shape_B_ptr,xform_B,motion_B,_add_contact,this,&sep_axis);
	if (!collided) {

		//test ccd (currently just a raycast)

		if (A->get_continuous_collision_detection_mode()==Physics2DServer::CCD_MODE_CAST_RAY && A->get_mode()>Physics2DServer::BODY_MODE_KINEMATIC) {
			if (_test_ccd(p_step,A,shape_A,xform_A,B,shape_B,xform_B))
				collided=true;
		}

		if (B->get_continuous_collision_detection_mode()==Physics2DServer::CCD_MODE_CAST_RAY && B->get_mode()>Physics2DServer::BODY_MODE_KINEMATIC) {
			if (_test_ccd(p_step,B,shape_B,xform_B,A,shape_A,xform_A,true))
				collided=true;
		}

		if (!collided)
			return false;

	}

	real_t max_penetration = space->get_contact_max_allowed_penetration();

	float bias = 0.3f;
	if (shape_A_ptr->get_custom_bias() || shape_B_ptr->get_custom_bias()) {

		if (shape_A_ptr->get_custom_bias()==0)
			bias=shape_B_ptr->get_custom_bias();
		else if (shape_B_ptr->get_custom_bias()==0)
			bias=shape_A_ptr->get_custom_bias();
		else
			bias=(shape_B_ptr->get_custom_bias()+shape_A_ptr->get_custom_bias())*0.5;
	}


	cc=0;


	real_t inv_dt = 1.0/p_step;
	for (int i = 0; i < contact_count; i++) {

		Contact& c = contacts[i];

		Vector2 global_A = xform_Au.xform(c.local_A);
		Vector2 global_B = xform_Bu.xform(c.local_B);

		real_t depth = c.normal.dot(global_A - global_B);

		if (depth<=0 || !c.reused) {
			c.active=false;
			continue;
		}

		c.active=true;

		int gather_A = A->can_report_contacts();
		int gather_B = B->can_report_contacts();

		c.rA = global_A;
		c.rB = global_B-offset_B;

		if (gather_A | gather_B) {

			//Vector2 crB( -B->get_angular_velocity() * c.rB.y, B->get_angular_velocity() * c.rB.x );

			global_A+=offset_A;
			global_B+=offset_A;

			if (gather_A) {
				Vector2 crB( -B->get_angular_velocity() * c.rB.y, B->get_angular_velocity() * c.rB.x );
				A->add_contact(global_A,-c.normal,depth,shape_A,global_B,shape_B,B->get_instance_id(),B->get_self(),crB+B->get_linear_velocity());
			}
			if (gather_B) {

				Vector2 crA( -A->get_angular_velocity() * c.rA.y, A->get_angular_velocity() * c.rA.x );
				B->add_contact(global_B,c.normal,depth,shape_B,global_A,shape_A,A->get_instance_id(),A->get_self(),crA+A->get_linear_velocity());
			}
		}

		// Precompute normal mass, tangent mass, and bias.
		real_t rnA = c.rA.dot(c.normal);
		real_t rnB = c.rB.dot(c.normal);
		real_t kNormal = A->get_inv_mass() + B->get_inv_mass();
		kNormal += A->get_inv_inertia() * (c.rA.dot(c.rA) - rnA * rnA) + B->get_inv_inertia() * (c.rB.dot(c.rB) - rnB * rnB);
		c.mass_normal = 1.0f / kNormal;

		Vector2 tangent = c.normal.tangent();
		real_t rtA = c.rA.dot(tangent);
		real_t rtB = c.rB.dot(tangent);
		real_t kTangent = A->get_inv_mass() + B->get_inv_mass();
		kTangent += A->get_inv_inertia() * (c.rA.dot(c.rA) - rtA * rtA) + B->get_inv_inertia() * (c.rB.dot(c.rB) - rtB * rtB);
		c.mass_tangent = 1.0f /  kTangent;



		c.bias = -bias * inv_dt * MIN(0.0f, -depth + max_penetration);
		c.depth=depth;
		//c.acc_bias_impulse=0;


#ifdef ACCUMULATE_IMPULSES
		{
			// Apply normal + friction impulse
			Vector2 P = c.acc_normal_impulse * c.normal + c.acc_tangent_impulse * tangent;


			A->apply_impulse(c.rA,-P);
			B->apply_impulse(c.rB, P);
		}

#endif


		c.bounce=MAX(A->get_bounce(),B->get_bounce());
		if (c.bounce) {

			Vector2 crA( -A->get_angular_velocity() * c.rA.y, A->get_angular_velocity() * c.rA.x );
			Vector2 crB( -B->get_angular_velocity() * c.rB.y, B->get_angular_velocity() * c.rB.x );
			Vector2 dv = B->get_linear_velocity() + crB - A->get_linear_velocity() - crA;
			c.bounce = c.bounce * dv.dot(c.normal);
		}


	}

	return true;
}

void BodyPair2DSW::solve(float p_step) {

	if (!collided)
		return;

	for (int i = 0; i < contact_count; ++i) {

		Contact& c = contacts[i];
		cc++;

		if (!c.active)
			continue;


		// Relative velocity at contact

		Vector2 crA( -A->get_angular_velocity() * c.rA.y, A->get_angular_velocity() * c.rA.x );
		Vector2 crB( -B->get_angular_velocity() * c.rB.y, B->get_angular_velocity() * c.rB.x );
		Vector2 dv = B->get_linear_velocity() + crB - A->get_linear_velocity() - crA;

		Vector2 crbA( -A->get_biased_angular_velocity() * c.rA.y, A->get_biased_angular_velocity() * c.rA.x );
		Vector2 crbB( -B->get_biased_angular_velocity() * c.rB.y, B->get_biased_angular_velocity() * c.rB.x );
		Vector2 dbv = B->get_biased_linear_velocity() + crbB - A->get_biased_linear_velocity() - crbA;


		real_t vn = dv.dot(c.normal);
		real_t vbn = dbv.dot(c.normal);
		Vector2 tangent = c.normal.tangent();
		real_t vt = dv.dot(tangent);


		real_t jbn = (c.bias - vbn)*c.mass_normal;
		real_t jbnOld = c.acc_bias_impulse;
		c.acc_bias_impulse = MAX(jbnOld + jbn, 0.0f);

		Vector2 jb = c.normal * (c.acc_bias_impulse - jbnOld);

		A->apply_bias_impulse(c.rA,-jb);
		B->apply_bias_impulse(c.rB, jb);

		real_t jn = -(c.bounce + vn)*c.mass_normal;
		real_t jnOld = c.acc_normal_impulse;
		c.acc_normal_impulse = MAX(jnOld + jn, 0.0f);


		real_t friction = A->get_friction() * B->get_friction();

		real_t jtMax = friction*c.acc_normal_impulse;
		real_t jt = -vt*c.mass_tangent;
		real_t jtOld = c.acc_tangent_impulse;
		c.acc_tangent_impulse = CLAMP(jtOld + jt, -jtMax, jtMax);

		Vector2 j =c.normal * (c.acc_normal_impulse - jnOld) + tangent * ( c.acc_tangent_impulse - jtOld );

		A->apply_impulse(c.rA,-j);
		B->apply_impulse(c.rB, j);


	}
}


BodyPair2DSW::BodyPair2DSW(Body2DSW *p_A, int p_shape_A,Body2DSW *p_B, int p_shape_B) : Constraint2DSW(_arr,2) {

	A=p_A;
	B=p_B;
	shape_A=p_shape_A;
	shape_B=p_shape_B;
	space=A->get_space();
	A->add_constraint(this,0);
	B->add_constraint(this,1);
	contact_count=0;
	collided=false;

}


BodyPair2DSW::~BodyPair2DSW() {

	A->remove_constraint(this);
	B->remove_constraint(this);

}