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papercraft/hiddenwire.c

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/** \file
* Render a hidden wireframe version of an STL file.
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdarg.h>
#include <unistd.h>
#include <math.h>
#include <err.h>
#include <assert.h>
#include <getopt.h>
#include "v3.h"
#include "camera.h"
static const char usage[] =
"Usage: hiddenwire [options] file.stl > file.svg\n"
"\n"
"Options:\n"
" -h | -? | --help Help\n"
" -v | --verbose Enable debugging output\n"
" -c | --camera x,y,z Camera position\n"
" -l | --lookat x,y,z Target\n"
" -u | --up x,y,z Up vector\n"
" -F | --fov deg Field-of-view angle\n"
" -s | --scale s Scale factor\n"
" -p | --prune s Prune lines shorter than s\n"
" --no-backface Disable backface culling\n"
" --no-coplanar Disable coplanar merging\n"
" --no-hiddenwire Disable hidden wire frame removal\n"
"\n";
static const struct option long_options[] = {
{ "help", 0, NULL, 'h' },
{ "verbose", 0, NULL, 'v' },
{ "no-backface", 0, NULL, 'B' },
{ "no-coplanar", 0, NULL, 'C' },
{ "no-hiddenwire", 0, NULL, 'H' },
{ "camera", 1, NULL, 'c' },
{ "lookat", 1, NULL, 'l' },
{ "up", 1, NULL, 'u' },
{ "scale", 1, NULL, 's' },
{ "prune", 1, NULL, 'p' },
{ "fov", 1, NULL, 'F' },
{ NULL, 0, NULL, 0 },
};
#ifndef M_PI
#define M_PI 3.1415926535897932384
#endif
static int debug = 0;
typedef struct
{
char header[80];
uint32_t num_triangles;
} __attribute__((__packed__))
stl_header_t;
typedef struct
{
v3_t normal;
v3_t p[3];
uint16_t attr;
} __attribute__((__packed__))
stl_face_t;
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
float min[3]; // camera space
float max[3]; // camera space
tri_t * next;
tri_t ** prev;
};
typedef struct _seg_t seg_t;
struct _seg_t {
v3_t p[2];
v3_t src[2];
seg_t * next;
};
void
svg_line(
const char * color,
const float * p1,
const float * p2,
float thick
)
{
printf("<line x1=\"%fpx\" y1=\"%fpx\" x2=\"%fpx\" y2=\"%fpx\" stroke=\"%s\" stroke-width=\"%.1fpx\"/>\n",
p1[0],
p1[1],
p2[0],
p2[1],
color,
thick
);
}
static inline int
v2_eq(
const float p0[],
const float p1[],
const float eps
)
{
const float dx = p0[0] - p1[0];
const float dy = p0[1] - p1[1];
// are the points within epsilon of each other?
if (-eps < dx && dx < eps
&& -eps < dy && dy < eps)
return 1;
// nope, not equal
return 0;
}
/** 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
)
{
const float p0_x = p0->p[0];
const float p0_y = p0->p[1];
const float p0_z = p0->p[2];
const float p1_x = p1->p[0];
const float p1_y = p1->p[1];
const float p1_z = p1->p[2];
const float p2_x = p2->p[0];
const float p2_y = p2->p[1];
const float p2_z = p2->p[2];
const float p3_x = p3->p[0];
const float p3_y = p3->p[1];
const float p3_z = p3->p[2];
const float s1_x = p1_x - p0_x;
const float s1_y = p1_y - p0_y;
const float s2_x = p3_x - p2_x;
const float s2_y = p3_y - p2_y;
// compute r x s
const float d = -s2_x * s1_y + s1_x * s2_y;
// if they are close to parallel, then we do not need to check
// for intersection (we define that as "non-intersecting")
if (-EPS < d && d < EPS)
return -1;
// Compute how far along each line they would interesect
const float r0 = ( s2_x * (p0_y - p2_y) - s2_y * (p0_x - p2_x)) / d;
const float r1 = (-s1_y * (p0_x - p2_x) + s1_x * (p0_y - p2_y)) / d;
// if they are not within the ratio (0,1), then the intersecton occurs
// outside of the segments and is not of concern
if (r0 < 0 || r0 > 1)
return -1;
if (r1 < 0 || r1 > 1)
return -1;
// Collision detected with the segments
if(0) fprintf(stderr, "collision: %.0f,%.0f,%.0f->%.0f,%.0f,%.0f %.0f,%.0f,%.0f->%.0f,%.0f,%.0f == %.3f,%.3f\n",
p0_x, p0_y, p0_z,
p1_x, p1_y, p1_z,
p2_x, p2_y, p2_z,
p3_x, p3_y, p2_z,
r0,
r1
);
const float ix = p0_x + (r0 * s1_x);
const float iy = p0_y + (r0 * s1_y);
// compute the z intercept for each on the two different coordinates
if(l0_int)
{
*l0_int = (v3_t){{
ix,
iy,
p0_z + r0 * (p1_z - p0_z)
}};
}
if(l1_int)
{
*l1_int = (v3_t){{
ix,
iy,
p2_z + r1 * (p3_z - p2_z)
}};
}
return r0;
}
tri_t *
tri_new(
const v3_t * p_cam,
const v3_t * p_xyz
)
{
tri_t * const t = calloc(1, sizeof(*t));
if (!t)
return NULL;
for(int i = 0 ; i < 3 ; i++)
t->p[i] = p_cam[i];
// precompute the normals
t->normal = v3_norm(v3_cross(
v3_sub(t->p[1], t->p[0]),
v3_sub(t->p[2], t->p[1])
));
t->normal_xyz = v3_norm(v3_cross(
v3_sub(p_xyz[1], p_xyz[0]),
v3_sub(p_xyz[2], p_xyz[1])
));
// compute the bounding box for the triangle in camera space
for(int j = 0 ; j < 3 ; j++)
{
t->min[j] = min(min(t->p[0].p[j], t->p[1].p[j]), t->p[2].p[j]);
t->max[j] = max(max(t->p[0].p[j], t->p[1].p[j]), t->p[2].p[j]);
}
return t;
}
// insert a triangle into our z-sorted list
void
tri_insert(
tri_t ** zlist,
tri_t * t
)
{
while(1)
{
tri_t * const iter = *zlist;
if (!iter)
break;
// check to see if our new triangle is closer than
// the current triangle
if(iter->min[2] > t->min[2])
break;
zlist = &(iter->next);
}
// either we reached the end of the list,
// or we have found where our new triangle is sorted
t->next = *zlist;
t->prev = zlist;
*zlist = t;
if (t->next)
t->next->prev = &t->next;
}
void
tri_delete(tri_t * t)
{
if (t->next)
t->next->prev = t->prev;
if (t->prev)
*(t->prev) = t->next;
t->next = NULL;
t->prev = NULL;
free(t);
}
seg_t *
seg_new(
const v3_t p0,
const v3_t p1
)
{
seg_t * const s = calloc(1, sizeof(*s));
if (!s)
return NULL;
s->p[0] = p0;
s->p[1] = p1;
s->src[0] = p0;
s->src[1] = p1;
s->next = NULL;
return s;
}
void
seg_print(
const seg_t * const s
)
{
fprintf(stderr, "%.0f,%.0f -> %.0f,%.0f (was %.0f,%.0f -> %.0f,%.0f\n",
s->p[0].p[0],
s->p[0].p[1],
s->p[1].p[0],
s->p[1].p[1],
s->src[0].p[0],
s->src[0].p[1],
s->src[1].p[0],
s->src[1].p[1]
);
}
// Compute the length of a line in screen space, ignoring Z
float
v3_dist_2d(
const v3_t * p0,
const v3_t * p1
)
{
const float dx = p1->p[0] - p0->p[0];
const float dy = p1->p[1] - p0->p[1];
return sqrt(dx*dx + dy*dy);
}
// Compute the 2D area of a triangle in screen space
// using Heron's formula
float
tri_area_2d(
const tri_t * const t
)
{
const float a = v3_dist_2d(&t->p[0], &t->p[1]);
const float b = v3_dist_2d(&t->p[1], &t->p[2]);
const float c = v3_dist_2d(&t->p[2], &t->p[0]);
const float s = (a + b + c) / 2;
return sqrt(s * (s-a) * (s-b) * (s-c));
}
void
tri_print(
const tri_t * const t
)
{
fprintf(stderr, "%.0f,%.0f,%.0f %.0f,%.0f,%.0f %.0f,%.0f,%.0f norm %.3f,%.3f,%.3f\n",
t->p[0].p[0],
t->p[0].p[1],
t->p[0].p[2],
t->p[1].p[0],
t->p[1].p[1],
t->p[1].p[2],
t->p[2].p[0],
t->p[2].p[1],
t->p[2].p[2],
t->normal.p[0],
t->normal.p[1],
t->normal.p[2]
);
}
/* 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
)
{
// the two normals must be parallel-enough
const float angle = v3_mag(v3_sub(t0->normal_xyz, t1->normal_xyz));
if (angle < -coplanar_eps || +coplanar_eps < angle)
return -1;
// find if there are two points shared
unsigned matches = 0;
for(int i = 0 ; i < 3 ; i++)
{
for(int j = 0 ; j < 3 ; j++)
{
if (!v3_eq(&t0->p[i], &t1->p[j]))
continue;
matches |= 1 << i;
break;
}
}
switch(matches)
{
case 0x3: return 0;
case 0x6: return 1;
case 0x5: return 2;
case 0x7:
fprintf(stderr, "uh, three points match?\n");
tri_print(t0);
tri_print(t1);
return -1;
default:
// no shared edge
return -1;
}
}
/*
* 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
)
{
const float t1x = t->p[1].p[0] - t->p[0].p[0];
const float t1y = t->p[1].p[1] - t->p[0].p[1];
const float t1z = t->p[1].p[2] - t->p[0].p[2];
const float t2x = t->p[2].p[0] - t->p[0].p[0];
const float t2y = t->p[2].p[1] - t->p[0].p[1];
const float t2z = t->p[2].p[2] - t->p[0].p[2];
const float px = p->p[0] - t->p[0].p[0];
const float py = p->p[1] - t->p[0].p[1];
const float a = (px * t2y - py * t2x) / (t1x * t2y - t2x * t1y);
const float b = (px * t1y - py * t1x) / (t2x * t1y - t1x * t2y);
const float z = t->p[0].p[2] + a * t1z + b * t2z;
if (zout)
*zout = z;
return 0 <= a && 0 <= b && a + b <= 1;
}
/*
* Recursive algorithm:
* 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.
*/
void
tri_seg_intersect(
const tri_t * zlist,
seg_t * s,
seg_t ** slist_visible
)
{
const float p0z = s->p[0].p[2];
const float p1z = s->p[1].p[2];
const float seg_max_z = max(p0z, p1z);
// avoid processing empty segments
const float seg_len = v3_len(&s->p[0], &s->p[1]);
if (seg_len < EPS)
return;
static int recursive;
recursive++;
//fprintf(stderr, "%d: processing segment ", recursive++); seg_print(s);
for( const tri_t * t = zlist ; t ; t = t->next )
{
// if the segment is closer than the triangle,
// then we no longer have to check any further into
// the zlist (it is sorted by depth).
if (seg_max_z <= t->min[2])
break;
// make sure that we're not comparing to our own triangle
// or one that shares an edge with us (which might be in
// a different order)
if (v2_eq(s->src[0].p, t->p[0].p, 0.0005)
&& v2_eq(s->src[1].p, t->p[1].p, 0.0005))
continue;
if (v2_eq(s->src[0].p, t->p[1].p, 0.0005)
&& v2_eq(s->src[1].p, t->p[2].p, 0.0005))
continue;
if (v2_eq(s->src[0].p, t->p[2].p, 0.0005)
&& v2_eq(s->src[1].p, t->p[0].p, 0.0005))
continue;
if (v2_eq(s->src[0].p, t->p[1].p, 0.0005)
&& v2_eq(s->src[1].p, t->p[0].p, 0.0005))
continue;
if (v2_eq(s->src[0].p, t->p[2].p, 0.0005)
&& v2_eq(s->src[1].p, t->p[1].p, 0.0005))
continue;
if (v2_eq(s->src[0].p, t->p[0].p, 0.0005)
&& v2_eq(s->src[1].p, t->p[2].p, 0.0005))
continue;
float z0, z1;
int inside0 = tri_find_z(t, &s->p[0], &z0);
int inside1 = tri_find_z(t, &s->p[1], &z1);
// if both are inside but the segment is infront of the
// triangle, then we retain the segment.
// otherwies we discard the segment
if (inside0 && inside1)
{
if (s->p[0].p[2] <= z0
&& s->p[1].p[2] <= z1)
continue;
recursive--;
return;
}
// split the segment for each intersection with the
// triangle segments and add it to the work queue.
int intersections = 0;
v3_t is[3] = {}; // 3d point of segment intercept
v3_t it[3] = {}; // 3d point of triangle intercept
for(int j = 0 ; j < 3 ; j++)
{
float ratio = hidden_intersect(
&s->p[0], &s->p[1],
&t->p[j], &t->p[(j+1)%3],
&is[intersections],
&it[intersections]
);
if (ratio < 0)
continue;
intersections++;
}
// if none of them intersect, we keep looking
if (intersections == 0)
continue;
if (intersections == 3)
{
// this likely means that the triangle is very, very
// small, so let's just throw away this line segment
recursive--;
return;
}
if (intersections == 2)
{
// figure out how far it is to each of the intersections
const float d00 = v3_len(&s->p[0], &is[0]);
const float d01 = v3_len(&s->p[0], &is[1]);
const float d10 = v3_len(&s->p[1], &is[0]);
const float d11 = v3_len(&s->p[1], &is[1]);
// discard segments that have two interesections that match
// the segment exactly (distance from segment ends to
// intersection point close enough to zero).
if (d00 < EPS && d11 < EPS)
{
recursive--;
return;
}
if (d01 < EPS && d10 < EPS)
{
recursive--;
return;
}
// if the segment intersection is closer than the triangle,
// then we do nothing. degenerate cases are not handled
if (d00 <= d01
&& is[0].p[2] <= it[0].p[2]
&& is[1].p[2] <= it[1].p[2])
continue;
if (d00 > d01
&& is[1].p[2] <= it[0].p[2]
&& is[0].p[2] <= it[1].p[2])
continue;
// segment is behind the triangle,
// we have to create a new segment
// and shorten the existing segment
// find the two intersections that we have
// update the src field
// we need to create a new segment
seg_t * news;
if (d00 < d01)
{
// split from p0 to ix0
news = seg_new(s->p[0], is[0]);
news->src[0] = s->src[0];
news->src[1] = s->src[1];
s->p[0] = is[1];
} else {
// split from p0 to ix1
news = seg_new(s->p[0], is[1]);
news->src[0] = s->src[0];
news->src[1] = s->src[1];
s->p[0] = is[0];
}
// recursively start splitting the new segment
// starting at the next triangle down the z-depth
tri_seg_intersect(zlist->next, news, slist_visible);
// continue splitting our current segment
continue;
}
if (intersections == 1)
{
// if there is an intersection, but the segment intercept
// is closer than the triangle intercept, then no problem.
// we do not bother with degenerate cases of intersecting
// triangles
if (is[0].p[2] <= it[0].p[2]
&& is[1].p[2] <= it[0].p[2])
{
//svg_line("#00FF00", s->p[0].p, s->p[1].p, 10);
continue;
}
if (inside0)
{
// shorten it on the 0 side
s->p[0] = is[0];
// huh? shouldn't we process this one?
return;
continue;
} else
if (inside1)
{
// shorten it on the 1 side
s->p[1] = is[0];
// huh? shouldn't we process this one?
return;
continue;
} else {
// both outside, but an intersection?
// split at that point and hope for the best
seg_t * const news = seg_new(s->p[0], is[0]);
news->src[0] = s->src[0];
news->src[1] = s->src[1];
s->p[0] = is[0];
tri_seg_intersect(zlist->next, news, slist_visible);
// continue splitting our current segment
continue;
}
}
}
// if we've reached here the segment is visible
// and should be added to the visible list
s->next = *slist_visible;
*slist_visible = s;
recursive--;
}
/*
* Fast check to see if t2 is entire occluded by t.
*/
int
tri_behind(
const tri_t * const t,
const tri_t * const t2
)
{
float z0, z1, z2;
int inside0 = tri_find_z(t, &t2->p[0], &z0);
int inside1 = tri_find_z(t, &t2->p[1], &z1);
int inside2 = tri_find_z(t, &t2->p[2], &z2);
// easy check -- if none of the points are inside,
// t2 is not entirely occluded
if (!inside0 || !inside1 || !inside2)
return 0;
// are all of the intersection points ahead of t2?
int behind0 = t2->p[0].p[2] >= z0;
int behind1 = t2->p[1].p[2] >= z1;
int behind2 = t2->p[2].p[2] >= z2;
if (behind0 && behind1 && behind2)
return 1;
// it is a STL violation if they are not all on the
// same side (this would indicate that t and t2 intersect
// go ahead and prune since it will cause problems
if (behind0 || behind1 || behind2)
{
fprintf(stderr, "WARNING: triangles intersect %.0f %.0f %.0f inside %d %d %d behind %d %d %d\n", z0, z1, z2, inside0, inside1, inside2, behind0, behind1, behind2);
tri_print(t);
tri_print(t2);
return 1;
}
// they are all on the same side
return 0;
}
int v3_parse(v3_t * out, const char * str)
{
int rc = sscanf(str, "%f,%f,%f",
&out->p[0],
&out->p[1],
&out->p[2]
);
if (rc != 3)
return -1;
return 0;
}
int onscreen(
const v3_t * const p,
const float width,
const float height
)
{
if (p->p[0] < -width/2 || width/2 < p->p[0])
return 0;
/*
if (p->p[1] < -height/2 || height/2 < p->p[1])
return 0;
*/
/*
if (p->p[0] < 0 || width < p->p[0])
return 0;
if (p->p[1] < 0 || height < p->p[1])
return 0;
*/
return 1;
}
int main(
int argc,
char ** argv
)
{
if (argc <= 1)
{
fprintf(stderr, "%s", usage);
return EXIT_FAILURE;
}
int opt;
int do_backface = 1;
int do_coplanar = 1;
int do_hidden = 1;
v3_t eye = { { 100, 0, 0 } };
v3_t lookat = { { 0, 0, 0 } };
v3_t up = { { 0, 0, 1 } };
float scale = 1;
float fov = 45;
float prune = 0.1;
float width = 4096;
float height = 2048;
while((opt = getopt_long(argc, argv ,"h?vBCHc:l:s:u:p:F:", long_options, NULL)) != -1)
{
switch(opt)
{
case 'h' : case '?':
printf("%s", usage);
return EXIT_SUCCESS;
default:
fprintf(stderr, "%s", usage);
return EXIT_FAILURE;
case 'v': debug++; break;
case 'B': do_backface = 0; break;
case 'C': do_coplanar = 0; break;
case 'H': do_hidden = 0; break;
case 'p': prune = atof(optarg); break;
case 's': scale = atof(optarg); break;
case 'F': fov = atof(optarg); break;
case 'c':
if (v3_parse(&eye, optarg) < 0)
return EXIT_FAILURE;
break;
case 'l':
if (v3_parse(&lookat, optarg) < 0)
return EXIT_FAILURE;
break;
case 'u':
if (v3_parse(&up, optarg) < 0)
return EXIT_FAILURE;
break;
}
}
// todo: sanity check fov, scale, etc
const size_t max_len = 32 << 20;
uint8_t * const buf = calloc(max_len, 1);
size_t offset = 0;
while(1)
{
ssize_t rc = read(0, buf+offset, max_len - offset);
if (rc == -1)
return EXIT_FAILURE;
if (rc == 0)
break;
offset += rc;
}
const stl_header_t * const hdr = (const void*) buf;
const stl_face_t * const stl_faces = (const void*)(hdr+1);
const int num_triangles = hdr->num_triangles;
float coplanar_eps = 0.001;
if(debug)
{
fprintf(stderr, "header: '%s'\n", hdr->header);
fprintf(stderr, "num: %d\n", num_triangles);
}
(void) scale;
const camera_t * const cam = camera_new(eye, lookat, up, fov);
printf("<svg xmlns=\"http://www.w3.org/2000/svg\" width=\"%.0fpx\" height=\"%.0fpx\" viewbox=\"0 0 %.0f %.0f\">\n", width, height, width, height);
float off_x = 0; // width/2;
float off_y = 0; // height/2;
printf("<g transform=\"translate(%f %f)\">\n", off_x, off_y);
int rejected = 0;
tri_t * zlist = NULL;
seg_t * slist = NULL;
seg_t * slist_visible = NULL;
int retained = 0;
int backface = 0;
int small_area = 0;
int behind = 0;
int offscreen = 0;
// transform the stl by the camera projection and generate
// a z-sorted list of triangles
for (int i = 0 ; i < num_triangles ; i++)
{
const stl_face_t * const stl = &stl_faces[i];
v3_t s[3];
for(int j = 0 ; j < 3 ; j++)
{
// if any points are behind us, reject
// this one
if (!camera_project(cam, &stl->p[j], &s[j]))
{
behind++;
goto reject_early;
}
}
if(debug >= 2)
for(int j = 0 ; j < 3 ; j++)
{
fprintf(stderr, "%.3f %.3f %.3f -> %.3f %.3f %.3f\n",
stl->p[j].p[0],
stl->p[j].p[1],
stl->p[j].p[2],
s[j].p[0],
s[j].p[1],
s[j].p[2]
);
}
tri_t * const tri = tri_new(s, stl->p);
// reject this face if any of the vertices are behind us
if (tri->min[2] < 0)
{
behind++;
goto reject;
}
// do a back-face cull to determine if this triangle
// is not facing us. we have to determine the orientation
// from the winding of the new projection
if (do_backface && tri->normal.p[2] <= 0)
{
backface++;
goto reject;
}
// if it has any off-screen coords, reject it
if (!onscreen(&tri->p[0], width, height)
|| !onscreen(&tri->p[1], width, height)
|| !onscreen(&tri->p[2], width, height))
{
tri_print(tri);
offscreen++;
goto reject;
}
// prune the small triangles in the screen space
if (tri_area_2d(tri) < prune)
{
small_area++;
goto reject;
}
const float a = v3_dist_2d(&tri->p[0], &tri->p[1]);
const float b = v3_dist_2d(&tri->p[1], &tri->p[2]);
const float c = v3_dist_2d(&tri->p[2], &tri->p[0]);
if( a < prune || b < prune || c < prune)
{
small_area++;
goto reject;
}
// it passes the first tests, so insert the triangle
// into the list and the three line segments
tri_insert(&zlist, tri);
retained++;
continue;
reject:
tri_delete(tri);
reject_early:
continue;
}
if (debug)
fprintf(stderr, "Retained %d triangles, rejected %d behind, %d offscreen, %d backface, %d small\n", retained, behind, offscreen, backface, small_area);
// drop any triangles that are totally occluded by another
// triangle. this reduces the amount of work for later
rejected = 0;
for(tri_t * t = zlist ; t ; t = t->next)
{
tri_t * t2_next;
for(tri_t * t2 = zlist ; t2 ; t2 = t2_next)
{
t2_next = t2->next;
if (t == t2)
continue;
if (!tri_behind(t, t2))
continue;
// t2 is occluded by t, remove it from the list
rejected++;
tri_delete(t2);
}
}
if (debug)
fprintf(stderr, "Rejected %d fully occluded triangles\n", rejected);
// generate a list of segments, dropping any coplanar ones
rejected = 0;
for(tri_t * t = zlist ; t ; t = t->next)
{
unsigned matches = 0;
if(do_coplanar)
for(tri_t * t2 = zlist ; t2 ; t2 = t2->next)
{
if (t == t2)
continue;
const int edge = tri_coplanar(t, t2, coplanar_eps);
if (edge < 0)
continue;
matches |= 1 << edge;
}
for(int j = 0 ; j < 3 ; j++)
{
// drop any that are coplanar
if (matches & (1 << j))
{
rejected++;
continue;
}
seg_t * s = seg_new(t->p[j], t->p[(j+1) % 3]);
s->next = slist;
slist = s;
}
}
if (debug)
fprintf(stderr, "Rejected %d coplanar segments\n", rejected);
// we now have a z-sorted list of triangles
rejected = 0;
if(do_hidden)
{
// work on each segment, intersecting it with all of the triangles
int processed = 0;
while(slist)
{
if (++processed % 100 == 0)
fprintf(stderr, "Hidden %d\n", processed);
seg_t * s = slist;
slist = s->next;
tri_seg_intersect(zlist, s, &slist_visible);
}
} else {
// don't do any intersection tests
slist_visible = slist;
slist = NULL;
}
// display all of the visible segments
for(seg_t * s = slist_visible ; s ; s = s->next)
{
svg_line("#FF0000", s->p[0].p, s->p[1].p, 1);
}
if (debug)
fprintf(stderr, "Occluded %d triangles\n", rejected);
printf("</g>\n");
printf("</svg>\n");
return 0;
}
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