/*
 * This file is part of the DXX-Rebirth project <http://www.dxx-rebirth.com/>.
 * It is copyright by its individual contributors, as recorded in the
 * project's Git history.  See COPYING.txt at the top level for license
 * terms and a link to the Git history.
 */
/*
 * 
 * Instancing routines
 * 
 */

#include <stdlib.h>
#include "dxxerror.h"

#include "3d.h"
#include "globvars.h"

#define MAX_INSTANCE_DEPTH	5

namespace {

struct instance_context {
	vms_matrix m;
	vms_vector p;
};

}

static array<instance_context, MAX_INSTANCE_DEPTH> instance_stack;

int instance_depth = 0;

//instance at specified point with specified orientation
//if matrix==NULL, don't modify matrix.  This will be like doing an offset   
void g3_start_instance_matrix(const vms_vector &pos,const vms_matrix *orient)
{
	Assert(instance_depth<MAX_INSTANCE_DEPTH);

	instance_stack[instance_depth].m = View_matrix;
	instance_stack[instance_depth].p = View_position;
	instance_depth++;

	//step 1: subtract object position from view position

	if (orient) {
		const auto tempv = vm_vec_sub(View_position, pos);
		//step 2: rotate view vector through object matrix

		vm_vec_rotate(View_position,tempv,*orient);

		//step 3: rotate object matrix through view_matrix (vm = ob * vm)

		View_matrix = vm_matrix_x_matrix(vm_transposed_matrix(*orient),View_matrix);
	}
}


//instance at specified point with specified orientation
//if angles==NULL, don't modify matrix.  This will be like doing an offset
void g3_start_instance_angles(const vms_vector &pos,const vms_angvec *angles)
{
	if (angles==NULL) {
		g3_start_instance_matrix(pos,NULL);
		return;
	}
	const auto tm = vm_angles_2_matrix(*angles);
	g3_start_instance_matrix(pos,&tm);
}


//pops the old context
void g3_done_instance()
{
	instance_depth--;

	Assert(instance_depth >= 0);

	View_position = instance_stack[instance_depth].p;
	View_matrix = instance_stack[instance_depth].m;
}