papercraft/tri.h

166 lines
3.1 KiB
C
Raw Normal View History

/*
* Triangle manipulations
*/
#ifndef _tri_h_
#define _tri_h_
#include "v3.h"
#include "seg.h"
#include "svg.h"
extern int tri_debug;
typedef struct _tri_t tri_t;
struct _tri_t
{
v3_t p[3]; // camera space
v3_t normal; // camera space
v3_t normal_xyz; // original xyz space
v3_t min; // camera space
v3_t max; // camera space
tri_t * next;
tri_t ** prev;
};
tri_t *
tri_new(
const v3_t * p_cam,
const v3_t * p_xyz
);
// insert a triangle into our z-sorted list
void
tri_insert(
tri_t ** zlist,
tri_t * t
);
void
tri_delete(tri_t * t);
// Compute the 2D area of a triangle in screen space
// using Heron's formula
float
tri_area_2d(
const tri_t * const t
);
void
tri_print(
const tri_t * const t
);
/* Check if two triangles are coplanar and share an edge.
*
* Returns -1 if not coplanar, 0-2 for the edge in t0 that they share.
*/
int
tri_coplanar(
const tri_t * const t0,
const tri_t * const t1,
const float coplanar_eps
);
/*
* Find the Z point of an XY coordinate in a triangle.
*
* p can be written as a combination of t01 and t02,
* p - t0 = a * (t1 - t0) + b * (t2 - t0)
* setting t0 to 0, this becomes:
* p = a * t1 + b * t2
* which is two equations with two unknowns
*
* Returns true if the point is inside the triangle
*/
int
tri_find_z(
const tri_t * const t,
const v3_t * const p,
float * const zout
);
/** Compute the points of intersection for two segments in 2d, and z points.
*
* This is a specialized ray intersection algorithm for the
* hidden wire-frame removal code that computes the intersection
* points for two rays (in 2D, "orthographic") and then computes
* the Z depth for the intersections along each of the segments.
*
* Returns -1 for non-intersecting, otherwise a ratio of how far
* along the intersection is on the l0.
*/
float
hidden_intersect(
const v3_t * const p0,
const v3_t * const p1,
const v3_t * const p2,
const v3_t * const p3,
v3_t * const l0_int,
v3_t * const l1_int
);
/*
* Given a line segment and a list of triangles,
* find if the line segment crosses any triangle.
* If it crosses a triangle the segment will be shortened
* and an additional one might be created.
* Recusively try intersecting the new segment (starting at the same triangle)
* and then continue trying the shortened segment.
*
* Line segments will be added to the visible list.
* Returns the number of new elements created
*/
int
tri_seg_hidden(
const tri_t * zlist,
seg_t * s,
seg_t ** slist_visible
);
/*
* Fast check to see if t2 is entire occluded by t.
*/
int
tri_behind(
const tri_t * const t,
const tri_t * const t2
);
/*
* There are four possible line/triangle intersections.
*/
typedef enum {
tri_no_intersection, // nothing changed
tri_infront, // segment is in front of the triangle
tri_hidden, // segment is completely occluded
tri_clipped, // segment is partially occluded on one end
tri_split, // segment is partially occluded in the middle
} tri_intersect_t;
tri_intersect_t
tri_seg_intersect(
const tri_t * tri,
seg_t * s,
seg_t ** new_seg // only if tri_split
);
v3_t
tri_bary_coord(
const tri_t * const t,
const v3_t * const p
);
#endif