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papercraft/unfold.c
Trammell Hudson 78e2a3ce3f prefer coplanar sections
2014-12-14 13:36:42 -05:00

401 lines
7.3 KiB
C
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/** \file
* Unfold an STL file into a set of laser-cutable polygons.
*
*/
#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <math.h>
#ifndef M_PI
#define M_PI 3.1415926535897932384
#endif
#define EPS 0.0001
typedef struct
{
char header[80];
uint32_t num_triangles;
} __attribute__((__packed__))
stl_header_t;
typedef struct
{
float p[3];
} v3_t;
typedef struct
{
v3_t normal;
v3_t p[3];
uint16_t attr;
} __attribute__((__packed__))
stl_face_t;
typedef struct face face_t;
struct face
{
float sides[3];
face_t * next[3];
int next_edge[3];
int coplanar[3];
int used;
};
static int
v3_eq(
const v3_t * v1,
const v3_t * v2
)
{
float dx = v1->p[0] - v2->p[0];
float dy = v1->p[1] - v2->p[1];
float dz = v1->p[2] - v2->p[2];
if (-EPS < dx && dx < EPS
&& -EPS < dy && dy < EPS
&& -EPS < dz && dz < EPS)
return 1;
return 0;
}
static int
edge_eq(
const stl_face_t * const t0,
const stl_face_t * const t1,
int e0,
int e1
)
{
const v3_t * const v0 = &t0->p[e0];
const v3_t * const v1 = &t0->p[e1];
if (v3_eq(v0, &t1->p[0]) && v3_eq(v1, &t1->p[1]))
return 1;
if (v3_eq(v0, &t1->p[1]) && v3_eq(v1, &t1->p[0]))
return 1;
if (v3_eq(v0, &t1->p[0]) && v3_eq(v1, &t1->p[2]))
return 1;
if (v3_eq(v0, &t1->p[2]) && v3_eq(v1, &t1->p[0]))
return 1;
if (v3_eq(v0, &t1->p[1]) && v3_eq(v1, &t1->p[2]))
return 1;
if (v3_eq(v0, &t1->p[2]) && v3_eq(v1, &t1->p[1]))
return 1;
return 0;
}
/* Compare two edges in two triangles.
*
* note that if the windings are all the same, the edges will
* compare in the opposite order (for example, the edge from 0 to 1
* compares to the edge from 2 to 1 in the other triangle).
*/
static int
edge_eq2(
const stl_face_t * const t0,
const stl_face_t * const t1,
int e0,
int e1
)
{
const v3_t * const v00 = &t0->p[e0];
const v3_t * const v01 = &t0->p[(e0+1) % 3];
const v3_t * const v10 = &t1->p[e1];
const v3_t * const v11 = &t1->p[(e1+1) % 3];
if (v3_eq(v00, v11) && v3_eq(v01, v10))
return 1;
return 0;
}
double
v3_len(
const v3_t * const v0,
const v3_t * const v1
)
{
float dx = v0->p[0] - v1->p[0];
float dy = v0->p[1] - v1->p[1];
float dz = v0->p[2] - v1->p[2];
return sqrt(dx*dx + dy*dy + dz*dz);
}
void
svg_line(
float x1,
float y1,
float x2,
float y2
)
{
printf("<line x1=\"%f\" y1=\"%f\" x2=\"%f\" y2=\"%f\" style=\"stroke:rgb(255,255,0);\"/>\n",
x1,
y1,
x2,
y2
);
}
/** recursively try to fix up the triangles.
*
* returns 0 if this should be unwound, 1 if was successful
*/
int
recurse(
face_t * const f,
int start_edge
)
{
static int depth;
depth++;
// flag that we are looking into this one
f->used = 1;
// print out a svg group for this triangle, starting with
// the incoming edge
float a = f->sides[(start_edge + 0) % 3];
float c = f->sides[(start_edge + 1) % 3];
float b = f->sides[(start_edge + 2) % 3];
float x2 = (a*a + b*b - c*c) / (2*a);
float y2 = sqrt(b*b - x2*x2);
// before drawing the triangle, check to see if any of the
// edges are coplanar and if so, don't draw the edge
if (!f->coplanar[(0+start_edge) % 3])
svg_line(0, 0, a, 0);
if (!f->coplanar[(1+start_edge) % 3])
svg_line(a, 0, x2, y2);
if (!f->coplanar[(2+start_edge) % 3])
svg_line(x2, y2, 0, 0);
//printf("%p %d %f %f %f\n", f, start_edge, f->sides[0], f->sides[1], f->sides[2]);
for(int pass = 0 ; pass < 2 ; pass++)
{
// for each edge, find the triangle that matches
for (int edge = 0 ; edge < 3 ; edge++)
{
face_t * const f2 = f->next[(edge+start_edge) % 3];
if (f2->used)
continue;
if (pass == 0 && !f->coplanar[(edge+start_edge) % 3])
continue;
// create a group that translates and rotates
// such that it lines up with this edge
float trans_x, trans_y, rotate;
if (edge == 0)
{
trans_x = a;
trans_y = 0;
rotate = 180;
} else
if (edge == 1)
{
trans_x = x2;
trans_y = y2;
rotate = -atan2(y2, a-x2) * 180 / M_PI;
} else
if (edge == 2)
{
trans_x = 0;
trans_y = 0;
rotate = atan2(y2, x2) * 180 / M_PI;
}
printf("<!-- edge %d --><g transform=\"translate(%f,%f) rotate(%f)\">\n",
edge,
trans_x,
trans_y,
rotate
);
recurse(f2, f->next_edge[(edge+start_edge) % 3]);
printf("</g>\n");
}
}
// no success
return 0;
}
v3_t v3_sub(v3_t a, v3_t b)
{
v3_t c = { .p = {
a.p[0] - b.p[0],
a.p[1] - b.p[1],
a.p[2] - b.p[2],
} };
return c;
}
float v3_dot(v3_t a, v3_t b)
{
return a.p[0]*b.p[0] + a.p[1]*b.p[1] + a.p[2]*b.p[2];
}
v3_t v3_cross(v3_t u, v3_t v)
{
float u1 = u.p[0];
float u2 = u.p[1];
float u3 = u.p[2];
float v1 = v.p[0];
float v2 = v.p[1];
float v3 = v.p[2];
v3_t c = { .p = {
u2*v3 - u3*v2,
u3*v1 - u1*v3,
u1*v2 - u2*v1,
}};
return c;
}
int
coplanar_check(
const stl_face_t * const f1,
const stl_face_t * const f2
)
{
// find the four distinct points
v3_t x1 = f1->p[0];
v3_t x2 = f1->p[1];
v3_t x3 = f1->p[2];
v3_t x4;
for (int i = 0 ; i < 3 ; i++)
{
x4 = f2->p[i];
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);
int check = -EPS < dot && dot < +EPS;
//fprintf( stderr, "%p %p %s\n", f1, f2, check ? "yes" : "no");
return check;
}
int main(void)
{
const size_t max_len = 1 << 20;
uint8_t * const buf = calloc(max_len, 1);
ssize_t rc = read(0, buf, max_len);
if (rc == -1)
return EXIT_FAILURE;
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;
fprintf(stderr, "header: '%s'\n", hdr->header);
fprintf(stderr, "num: %d\n", num_triangles);
face_t * const faces = calloc(num_triangles, sizeof(*faces));
// convert the stl triangles into faces
for (int i = 0 ; i < num_triangles ; i++)
{
const stl_face_t * const stl = &stl_faces[i];
face_t * const f = &faces[i];
f->sides[0] = v3_len(&stl->p[0], &stl->p[1]);
f->sides[1] = v3_len(&stl->p[1], &stl->p[2]);
f->sides[2] = v3_len(&stl->p[2], &stl->p[0]);
}
// look to see if there is a matching point
// in the faces that we've already built
for (int i = 0 ; i < num_triangles ; i++)
{
const stl_face_t * const stl = &stl_faces[i];
face_t * const f = &faces[i];
for (int j = 0 ; j < num_triangles ; j++)
{
if (i == j)
continue;
const stl_face_t * const stl2 = &stl_faces[j];
face_t * const f2 = &faces[j];
for (int edge = 0 ; edge < 3 ; edge++)
{
if (f->next[edge])
continue;
for (int edge2 = 0 ; edge2 < 3 ; edge2++)
{
if (f2->next[edge2])
continue;
if (!edge_eq2(stl, stl2, edge, edge2))
continue;
f->next[edge] = f2;
f->next_edge[edge] = edge2;
f2->next[edge2] = f;
f2->next_edge[edge2] = edge;
f->coplanar[edge] =
f2->coplanar[edge2] = coplanar_check(stl, stl2);
}
}
}
// all three edges should be matched
if (f->next[0] && f->next[1] && f->next[2])
continue;
fprintf(stderr, "%d: missing edges?\n", i);
}
// we now have a graph that shows the connection between
// all of the faces and their sizes. start converting them
printf("<svg xmlns=\"http://www.w3.org/2000/svg\">\n");
//for (int i = 0 ; i < num_triangles ; i++)
recurse(&faces[0], 0);
printf("</svg>\n");
return 0;
}
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