papercraft/stl_3d.c

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#include "stl_3d.h"
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
static const int debug = 0;
typedef struct
{
char header[80];
uint32_t num_triangles;
} __attribute__((__packed__))
stl_3d_file_header_t;
typedef struct
{
v3_t normal;
v3_t p[3];
uint16_t attr;
} __attribute__((__packed__))
stl_3d_file_triangle_t;
/** Find or create a vertex */
static stl_vertex_t *
stl_vertex_find(
stl_vertex_t * const vertices,
int * num_vertex_ptr,
const v3_t * const p
)
{
const int num_vertex = *num_vertex_ptr;
for (int x = 0 ; x < num_vertex ; x++)
{
stl_vertex_t * const v = &vertices[x];
if (v3_eq(&v->p, p))
return v;
}
if (debug)
fprintf(stderr, "%d: %f,%f,%f\n",
num_vertex,
p->p[0],
p->p[1],
p->p[2]
);
stl_vertex_t * const v = &vertices[(*num_vertex_ptr)++];
v->p = *p;
return v;
}
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/** Check to see if the two faces share an edge.
* \return 0 if no common edge, 1 if there is a shared link
*/
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static int
stl_has_edge(
const stl_face_t * const f,
const stl_vertex_t * const v1,
const stl_vertex_t * const v2
)
{
if (f->vertex[0] != v1 && f->vertex[1] != v1 && f->vertex[2] != v1)
return 0;
if (f->vertex[0] != v2 && f->vertex[1] != v2 && f->vertex[2] != v2)
return 0;
return 1;
}
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/** Compute the angle between the two planes.
* This is an approximation:
* \return 0 == coplanar, negative == valley, positive == mountain.
*/
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static double
stl_angle(
const stl_face_t * const f1,
const stl_face_t * const f2
)
{
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// find the four distinct points
v3_t x1 = f1->vertex[0]->p;
v3_t x2 = f1->vertex[1]->p;
v3_t x3 = f1->vertex[2]->p;
v3_t x4;
for (int i = 0 ; i < 3 ; i++)
{
x4 = f2->vertex[i]->p;
if (v3_eq(&x1, &x4))
continue;
if (v3_eq(&x2, &x4))
continue;
if (v3_eq(&x3, &x4))
continue;
break;
}
// (x3-x1) . ((x2-x1) X (x4-x3)) == 0
v3_t dx31 = v3_sub(x3, x1);
v3_t dx21 = v3_sub(x2, x1);
v3_t dx43 = v3_sub(x4, x3);
v3_t cross = v3_cross(dx21, dx43);
float dot = v3_dot(dx31, cross);
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if (debug)
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fprintf(stderr, "dot %f:\n %f,%f,%f\n %f,%f,%f\n %f,%f,%f\n %f,%f,%f\n",
dot,
x1.p[0], x1.p[1], x1.p[2],
x2.p[0], x2.p[1], x2.p[2],
x3.p[0], x3.p[1], x3.p[2],
x4.p[0], x4.p[1], x4.p[2]
);
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//int check = -EPS < dot && dot < +EPS;
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int check = -10 < dot && dot < +10;
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// if the dot product is not close enough to zero, they
// are not coplanar.
if (check)
return 0;
if (dot < 0)
return -1;
else
return +1;
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}
static void
stl_find_neighbors(
stl_3d_t * const stl,
stl_face_t * const f1
)
{
for(int i = 0 ; i < 3 ; i++)
{
const stl_vertex_t * const v1 = f1->vertex[(i+0) % 3];
const stl_vertex_t * const v2 = f1->vertex[(i+1) % 3];
for(int j = 0 ; j < stl->num_face ; j++)
{
stl_face_t * const f2 = &stl->face[j];
// skip this triangle against itself
if (f1 == f2)
continue;
// find if these two triangles share an edge
if (!stl_has_edge(f2, v1, v2))
continue;
f1->face[i] = f2;
f1->angle[i] = stl_angle(f1, f2);
}
}
}
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stl_3d_t *
stl_3d_parse(
int fd
)
{
ssize_t rc;
stl_3d_file_header_t hdr;
rc = read(fd, &hdr, sizeof(hdr));
if (rc != sizeof(hdr))
return NULL;
const int num_triangles = hdr.num_triangles;
fprintf(stderr, "%d triangles\n", num_triangles);
stl_3d_file_triangle_t * fts;
const size_t file_len = num_triangles * sizeof(*fts);
fts = calloc(1, file_len);
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rc = read(fd, fts, file_len);
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if (rc < 0 || (size_t) rc != file_len)
return NULL;
stl_3d_t * const stl = calloc(1, sizeof(*stl));
*stl = (stl_3d_t) {
.num_vertex = 0,
.num_face = num_triangles,
.vertex = calloc(num_triangles, sizeof(*stl->vertex)),
.face = calloc(num_triangles, sizeof(*stl->face)),
};
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// build the unique set of vertices and their connection
// to each face.
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for(int i = 0 ; i < num_triangles ; i++)
{
const stl_3d_file_triangle_t * const ft = &fts[i];
stl_face_t * const f = &stl->face[i];
for (int j = 0 ; j < 3 ; j++)
{
const v3_t * const p = &ft->p[j];
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stl_vertex_t * const v = stl_vertex_find(
stl->vertex,
&stl->num_vertex,
p
);
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// add this vertex to this face
f->vertex[j] = v;
// and add this face to the vertex
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v->face[v->num_face] = f;
v->face_num[v->num_face] = j;
v->num_face++;
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}
}
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// build the connections between each face
for(int i = 0 ; i < num_triangles ; i++)
{
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stl_face_t * const f = &stl->face[i];
stl_find_neighbors(stl, f);
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}
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return stl;
}
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/** Starting at a point, trace the coplanar polygon and return a
* list of vertices.
*/
int
stl_trace_face(
const stl_3d_t * const stl,
const stl_face_t * const f_start,
const stl_vertex_t ** vertex_list,
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int * const face_used,
const int start_vertex
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)
{
const stl_face_t * f = f_start;
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int i = start_vertex;
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int vertex_count = 0;
do {
const stl_vertex_t * const v1 = f->vertex[(i+0) % 3];
const stl_vertex_t * const v2 = f->vertex[(i+1) % 3];
const stl_face_t * const f_next = f->face[i];
fprintf(stderr, "%p %d: %f,%f,%f\n", f, i, v1->p.p[0], v1->p.p[1], v1->p.p[2]);
if (face_used)
face_used[f - stl->face] = 1;
if (!f_next || f->angle[i] != 0)
{
// not coplanar or no connection.
// add the NEXT vertex on this face and continue
vertex_list[vertex_count++] = v2;
i = (i+1) % 3;
continue;
}
// coplanar; figure out which vertex on the next
// face we start at
int i_next = -1;
for (int j = 0 ; j < 3 ; j++)
{
if (f_next->vertex[j] != v1)
continue;
i_next = j;
break;
}
if (i_next == -1)
abort();
// move to the new face
f = f_next;
i = i_next;
// keep going until we reach our starting face
// at vertex 0.
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} while (f != f_start || i != start_vertex);
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return vertex_count;
}
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void
refframe_init(
refframe_t * ref,
const v3_t p0,
const v3_t p1,
const v3_t p2
)
{
ref->origin = p0;
const v3_t dx = v3_norm(v3_sub(p1, ref->origin));
const v3_t dy = v3_norm(v3_sub(p2, ref->origin));
ref->x = dx;
ref->z = v3_norm(v3_cross(dx, dy));
ref->y = v3_norm(v3_cross(ref->x, ref->z));
}
void
v3_project(
const refframe_t * const ref,
const v3_t p_in,
double * const x_out,
double * const y_out
)
{
v3_t p = v3_sub(p_in, ref->origin);
double x = ref->x.p[0]*p.p[0] + ref->x.p[1]*p.p[1] + ref->x.p[2]*p.p[2];
double y = ref->y.p[0]*p.p[0] + ref->y.p[1]*p.p[1] + ref->y.p[2]*p.p[2];
double z = ref->z.p[0]*p.p[0] + ref->z.p[1]*p.p[1] + ref->z.p[2]*p.p[2];
fprintf(stderr, "%f,%f,%f\n", x, y, z);
*x_out = x;
*y_out = y;
}
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// Determines the intersection point of the line defined by points A and B with the
// line defined by points C and D.
//
// Returns YES if the intersection point was found, and stores that point in X,Y.
// Returns NO if there is no determinable intersection point, in which case X,Y will
// be unmodified.
static int
line_intersect(
double Ax, double Ay,
double Bx, double By,
double Cx, double Cy,
double Dx, double Dy,
double *X, double *Y
)
{
// Fail if either line is undefined.
if ((Ax==Bx && Ay==By) || (Cx==Dx && Cy==Dy))
return 0;
// (1) Translate the system so that point A is on the origin.
Bx-=Ax; By-=Ay;
Cx-=Ax; Cy-=Ay;
Dx-=Ax; Dy-=Ay;
// Discover the length of segment A-B.
const double distAB=sqrt(Bx*Bx+By*By);
// (2) Rotate the system so that point B is on the positive X axis.
const double theCos=Bx/distAB;
const double theSin=By/distAB;
double newX=Cx*theCos+Cy*theSin;
Cy =Cy*theCos-Cx*theSin; Cx=newX;
newX=Dx*theCos+Dy*theSin;
Dy =Dy*theCos-Dx*theSin; Dx=newX;
// Fail if the lines are parallel.
if (Cy==Dy) return 0;
// (3) Discover the position of the intersection point along line A-B.
const double ABpos=Dx+(Cx-Dx)*Dy/(Dy-Cy);
// (4) Apply the discovered position to line A-B in the original coordinate system.
*X=Ax+ABpos*theCos;
*Y=Ay+ABpos*theSin;
return 1;
}
/** Compute the inset coordinate.
* http://alienryderflex.com/polygon_inset/
// Given the sequentially connected points (a,b), (c,d), and (e,f), this
// function returns, in (C,D), a bevel-inset replacement for point (c,d).
//
// Note: If vectors (a,b)->(c,d) and (c,d)->(e,f) are exactly 180° opposed,
// or if either segment is zero-length, this function will do
// nothing; i.e. point (C,D) will not be set.
*/
void
refframe_inset(
const refframe_t * const ref,
const double inset_dist,
double * const x_out,
double * const y_out,
const v3_t p0, // previous point
const v3_t p1, // current point to inset
const v3_t p2 // next point
)
{
double a, b, c, d, e, f;
v3_project(ref, p0, &a, &b);
v3_project(ref, p1, &c, &d);
v3_project(ref, p2, &e, &f);
double c1 = c;
double d1 = d;
double c2 = c;
double d2 = d;
// Calculate length of line segments.
const double dx1 = c-a;
const double dy1 = d-b;
const double dist1 = sqrt(dx1*dx1+dy1*dy1);
const double dx2 = e-c;
const double dy2 = f-d;
const double dist2 = sqrt(dx2*dx2+dy2*dy2);
// Exit if either segment is zero-length.
if (dist1==0. || dist2==0.)
{
*x_out = *y_out = 0;
fprintf(stderr, "inset fail\n");
return;
}
// Inset each of the two line segments.
double insetX, insetY;
insetX = dy1/dist1 * inset_dist;
a+=insetX;
c1+=insetX;
insetY = -dx1/dist1 * inset_dist;
b+=insetY;
d1+=insetY;
insetX = dy2/dist2 * inset_dist;
e+=insetX;
c2+=insetX;
insetY = -dx2/dist2 * inset_dist;
f+=insetY;
d2+=insetY;
// If inset segments connect perfectly, return the connection point.
if (c1==c2 && d1==d2)
{
*x_out = c1;
*y_out = d1;
return;
}
// Return the intersection point of the two inset segments (if any).
if (line_intersect(a,b,c1,d1,c2,d2,e,f, x_out, y_out))
return;
*x_out = *y_out = 0;
fprintf(stderr, "inset failed 2\n");
}
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v3_t
refframe_project(
const refframe_t * const ref,
const v3_t p
)
{
v3_t o;
o.p[0] = ref->origin.p[0]
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+ ref->x.p[0] * p.p[0]
+ ref->y.p[0] * p.p[1]
+ ref->z.p[0] * p.p[2];
o.p[1] = ref->origin.p[1]
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+ ref->x.p[1] * p.p[0]
+ ref->y.p[1] * p.p[1]
+ ref->z.p[1] * p.p[2];
o.p[2] = ref->origin.p[2]
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+ ref->x.p[2] * p.p[0]
+ ref->y.p[2] * p.p[1]
+ ref->z.p[2] * p.p[2];
return o;
}