flightgear/Scenery/tile.cxx

// tile.cxx -- routines to handle a scenery tile
//
// Written by Curtis Olson, started May 1998.
//
// Copyright (C) 1998  Curtis L. Olson  - curt@infoplane.com
//
// This program is free software; you can redistribute it and/or
// modify it under the terms of the GNU General Public License as
// published by the Free Software Foundation; either version 2 of the
// License, or (at your option) any later version.
//
// This program is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program; if not, write to the Free Software
// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
//
// $Id$
// (Log is kept at end of this file)


#include <Include/fg_constants.h>
#include <Include/fg_types.h>
#include <Math/mat3.h>

#include "tile.hxx"


// return the sign of a value
#define FG_SIGN( x )  ((x) >= 0 ? 1 : -1)

// return min or max of two values
#define FG_MIN(A,B)	((A) < (B) ? (A) :  (B))
#define FG_MAX(A,B)	((A) > (B) ? (A) :  (B))


// Constructor
fgFRAGMENT::fgFRAGMENT ( void ) {
}


// Add a face to the face list
void fgFRAGMENT::add_face(int n1, int n2, int n3) {
    fgFACE face;

    face.n1 = n1;
    face.n2 = n2;
    face.n3 = n3;

    faces.push_back(face);
}


/*
// return the sign of a value
static int fg_sign( double x ) {
    if ( x >= 0 ) {
	return(1);
    } else {
	return(-1);
    }
}


// return the minimum of the three values
static double fg_min( double a, double b, double c ) {
    double result;
    result = a;
    if (result > b) result = b;
    if (result > c) result = c;

    return(result);
}


// return the maximum of the three values
static double fg_max( double a, double b, double c ) {
    double result;
    result = a;
    if (result < b) result = b;
    if (result < c) result = c;

    return(result);
}
*/


// return the minimum of the three values
static double fg_min3 (double a, double b, double c)
{
    return (a > b ? FG_MIN (b, c) : FG_MIN (a, c));
}


// return the maximum of the three values
static double fg_max3 (double a, double b, double c)
{
  return (a < b ? FG_MAX (b, c) : FG_MAX (a, c));
}


// test if line intesects with this fragment.  p0 and p1 are the two
// line end points of the line.  If side_flag is true, check to see
// that end points are on opposite sides of face.  Returns 1 if it
// does, 0 otherwise.  If it intesects, result is the point of
// intersection

int fgFRAGMENT::intersect( fgPoint3d *end0, fgPoint3d *end1, int side_flag,
			   fgPoint3d *result)
{
    fgTILE *t;
    fgFACE face;
    MAT3vec v1, v2, n, center;
    double p1[3], p2[3], p3[3];
    double a, b, c, d;
    double x0, y0, z0, x1, y1, z1, a1, b1, c1;
    double t1, t2, t3;
    double xmin, xmax, ymin, ymax, zmin, zmax;
    double dx, dy, dz, min_dim, x2, y2, x3, y3, rx, ry;
    int side1, side2;
    list < fgFACE > :: iterator current;
    list < fgFACE > :: iterator last;

    // find the associated tile
    t = (fgTILE *)tile_ptr;

    // printf("Intersecting\n");

    // traverse the face list for this fragment
    current = faces.begin();
    last = faces.end();
    while ( current != last ) {
	face = *current;
	current++;

	// printf(".");

	// get face vertex coordinates
	center[0] = t->center.x;
	center[1] = t->center.y;
	center[2] = t->center.z;

	MAT3_ADD_VEC(p1, t->nodes[face.n1], center);
	MAT3_ADD_VEC(p2, t->nodes[face.n2], center);
	MAT3_ADD_VEC(p3, t->nodes[face.n3], center);

	// printf("point 1 = %.2f %.2f %.2f\n", p1[0], p1[1], p1[2]);
	// printf("point 2 = %.2f %.2f %.2f\n", p2[0], p2[1], p2[2]);
	// printf("point 3 = %.2f %.2f %.2f\n", p3[0], p3[1], p3[2]);

	// calculate two edge vectors, and the face normal
	MAT3_SUB_VEC(v1, p2, p1);
	MAT3_SUB_VEC(v2, p3, p1);
	MAT3cross_product(n, v1, v2);

	// calculate the plane coefficients for the plane defined by
	// this face.  If n is the normal vector, n = (a, b, c) and p1
	// is a point on the plane, p1 = (x0, y0, z0), then the
	// equation of the line is a(x-x0) + b(y-y0) + c(z-z0) = 0
	a = n[0];
	b = n[1];
	c = n[2];
	d = a * p1[0] + b * p1[1] + c * p1[2];
	// printf("a, b, c, d = %.2f %.2f %.2f %.2f\n", a, b, c, d);

	// printf("p1(d) = %.2f\n", a * p1[0] + b * p1[1] + c * p1[2]);
	// printf("p2(d) = %.2f\n", a * p2[0] + b * p2[1] + c * p2[2]);
	// printf("p3(d) = %.2f\n", a * p3[0] + b * p3[1] + c * p3[2]);

	// calculate the line coefficients for the specified line
	x0 = end0->x;  x1 = end1->x;
	y0 = end0->y;  y1 = end1->y;
	z0 = end0->z;  z1 = end1->z;

	if ( fabs(x1 - x0) > FG_EPSILON ) {
	    a1 = 1.0 / (x1 - x0);
	} else {
	    // we got a big divide by zero problem here
	    a1 = 0.0;
	}
	b1 = y1 - y0;
	c1 = z1 - z0;

	// intersect the specified line with this plane
	t1 = b * b1 * a1;
	t2 = c * c1 * a1;

	// printf("a = %.2f  t1 = %.2f  t2 = %.2f\n", a, t1, t2);

	if ( fabs(a + t1 + t2) > FG_EPSILON ) {
	    result->x = (t1*x0 - b*y0 + t2*x0 - c*z0 + d) / (a + t1 + t2);
	    t3 = a1 * (result->x - x0);
	    result->y = b1 * t3 + y0;
	    result->z = c1 * t3 + z0;	    
	    // printf("result(d) = %.2f\n", 
	    //        a * result->x + b * result->y + c * result->z);
	} else {
	    // no intersection point
	    continue;
	}

	if ( side_flag ) {
	    // check to see if end0 and end1 are on opposite sides of
	    // plane
	    if ( (result->x - x0) > FG_EPSILON ) {
		t1 = result->x; t2 = x0; t3 = x1;
	    } else if ( (result->y - y0) > FG_EPSILON ) {
		t1 = result->y; t2 = y0; t3 = y1;
	    } else if ( (result->z - z0) > FG_EPSILON ) {
		t1 = result->z; t2 = z0; t3 = z1;
	    } else {
		// everything is too close together to tell the difference
		// so the current intersection point should work as good
		// as any
		return(1);
	    }
	    side1 = FG_SIGN (t1 - t2);
	    side2 = FG_SIGN (t1 - t3);
	    if ( side1 == side2 ) {
		// same side, punt
		continue;
	    }
	}

	// check to see if intersection point is in the bounding
	// cube of the face
	xmin = fg_min3 (p1[0], p2[0], p3[0]);
	xmax = fg_max3 (p1[0], p2[0], p3[0]);
	ymin = fg_min3 (p1[1], p2[1], p3[1]);
	ymax = fg_max3 (p1[1], p2[1], p3[1]);
	zmin = fg_min3 (p1[2], p2[2], p3[2]);
	zmax = fg_max3 (p1[2], p2[2], p3[2]);
	// printf("bounding cube = %.2f,%.2f,%.2f  %.2f,%.2f,%.2f\n",
	//        xmin, ymin, zmin, xmax, ymax, zmax);
	// punt if outside bouding cube
	if ( result->x < xmin ) {
	    continue;
	} else if ( result->x > xmax ) {
	    continue;
	} else if ( result->y < ymin ) {
	    continue;
	} else if ( result->y > ymax ) {
	    continue;
	} else if ( result->z < zmin ) {
	    continue;
	} else if ( result->z > zmax ) {
	    continue;
	}

	// (finally) check to see if the intersection point is
	// actually inside this face

	//first, drop the smallest dimension so we only have to work
	//in 2d.
	dx = xmax - xmin;
	dy = ymax - ymin;
	dz = zmax - zmin;
	min_dim = fg_min3 (dx, dy, dz);
	if ( fabs(min_dim - dx) <= FG_EPSILON ) {
	    // x is the smallest dimension
	    x1 = p1[1]; y1 = p1[2];
	    x2 = p2[1]; y2 = p2[2];
	    x3 = p3[1]; y3 = p3[2];
	    rx = result->y; ry = result->z;
	} else if ( fabs(min_dim - dy) <= FG_EPSILON ) {
	    // y is the smallest dimension
	    x1 = p1[0]; y1 = p1[2];
	    x2 = p2[0]; y2 = p2[2];
	    x3 = p3[0]; y3 = p3[2];
	    rx = result->x; ry = result->z;
	} else if ( fabs(min_dim - dz) <= FG_EPSILON ) {
	    // z is the smallest dimension
	    x1 = p1[0]; y1 = p1[1];
	    x2 = p2[0]; y2 = p2[1];
	    x3 = p3[0]; y3 = p3[1];
	    rx = result->x; ry = result->y;
	} else {
	    // all dimensions are really small so lets call it close
	    // enough and return a successful match
	    return(1);
	}

	// check if intersection point is on the same side of p1 <-> p2 as p3
	side1 = FG_SIGN ((y1 - y2) * ((x3) - x2) / (x1 - x2) + y2 - (y3));
	side2 = FG_SIGN ((y1 - y2) * ((rx) - x2) / (x1 - x2) + y2 - (ry));
	if ( side1 != side2 ) {
	    // printf("failed side 1 check\n");
	    continue;
	}

	// check if intersection point is on correct side of p2 <-> p3 as p1
	side1 = FG_SIGN ((y2 - y3) * ((x1) - x3) / (x2 - x3) + y3 - (y1));
	side2 = FG_SIGN ((y2 - y3) * ((rx) - x3) / (x2 - x3) + y3 - (ry));
	if ( side1 != side2 ) {
	    // printf("failed side 2 check\n");
	    continue;
	}

	// check if intersection point is on correct side of p1 <-> p3 as p2
	side1 = FG_SIGN ((y1 - y3) * ((x2) - x3) / (x1 - x3) + y3 - (y2));
	side2 = FG_SIGN ((y1 - y3) * ((rx) - x3) / (x1 - x3) + y3 - (ry));
	if ( side1 != side2 ) {
	    // printf("failed side 3  check\n");
	    continue;
	}

	// printf( "intersection point = %.2f %.2f %.2f\n", 
	//         result->x, result->y, result->z);
	return(1);
    }

    // printf("\n");

    return(0);
}


// Destructor
fgFRAGMENT::~fgFRAGMENT ( void ) {
    // Step through the face list deleting the items until the list is
    // empty

    // printf("destructing a fragment with %d faces\n", faces.size());

    while ( faces.size() ) {
	//  printf("emptying face list\n");
	faces.pop_front();
    }
}


// Constructor
fgTILE::fgTILE ( void ) {
    nodes = new double[MAX_NODES][3];
}


// Destructor
fgTILE::~fgTILE ( void ) {
    free(nodes);
}


// $Log$
// Revision 1.3  1998/07/16 17:34:24  curt
// Ground collision detection optimizations contributed by Norman Vine.
//
// Revision 1.2  1998/07/12 03:18:28  curt
// Added ground collision detection.  This involved:
// - saving the entire vertex list for each tile with the tile records.
// - saving the face list for each fragment with the fragment records.
// - code to intersect the current vertical line with the proper face in
//   an efficient manner as possible.
// Fixed a bug where the tiles weren't being shifted to "near" (0,0,0)
//
// Revision 1.1  1998/05/23 14:09:21  curt
// Added tile.cxx and tile.hxx.
// Working on rewriting the tile management system so a tile is just a list
// fragments, and the fragment record contains the display list for that fragment.
//