401 lines
7.3 KiB
C
401 lines
7.3 KiB
C
/** \file
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* Unfold an STL file into a set of laser-cutable polygons.
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*
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <stdint.h>
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#include <unistd.h>
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#include <math.h>
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#ifndef M_PI
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#define M_PI 3.1415926535897932384
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#endif
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#define EPS 0.0001
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typedef struct
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{
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char header[80];
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uint32_t num_triangles;
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} __attribute__((__packed__))
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stl_header_t;
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typedef struct
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{
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float p[3];
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} v3_t;
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typedef struct
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{
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v3_t normal;
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v3_t p[3];
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uint16_t attr;
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} __attribute__((__packed__))
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stl_face_t;
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typedef struct face face_t;
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struct face
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{
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float sides[3];
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face_t * next[3];
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int next_edge[3];
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int coplanar[3];
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int used;
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};
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static int
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v3_eq(
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const v3_t * v1,
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const v3_t * v2
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)
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{
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float dx = v1->p[0] - v2->p[0];
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float dy = v1->p[1] - v2->p[1];
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float dz = v1->p[2] - v2->p[2];
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if (-EPS < dx && dx < EPS
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&& -EPS < dy && dy < EPS
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&& -EPS < dz && dz < EPS)
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return 1;
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return 0;
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}
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static int
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edge_eq(
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const stl_face_t * const t0,
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const stl_face_t * const t1,
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int e0,
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int e1
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)
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{
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const v3_t * const v0 = &t0->p[e0];
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const v3_t * const v1 = &t0->p[e1];
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if (v3_eq(v0, &t1->p[0]) && v3_eq(v1, &t1->p[1]))
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return 1;
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if (v3_eq(v0, &t1->p[1]) && v3_eq(v1, &t1->p[0]))
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return 1;
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if (v3_eq(v0, &t1->p[0]) && v3_eq(v1, &t1->p[2]))
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return 1;
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if (v3_eq(v0, &t1->p[2]) && v3_eq(v1, &t1->p[0]))
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return 1;
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if (v3_eq(v0, &t1->p[1]) && v3_eq(v1, &t1->p[2]))
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return 1;
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if (v3_eq(v0, &t1->p[2]) && v3_eq(v1, &t1->p[1]))
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return 1;
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return 0;
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}
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/* Compare two edges in two triangles.
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*
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* note that if the windings are all the same, the edges will
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* compare in the opposite order (for example, the edge from 0 to 1
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* compares to the edge from 2 to 1 in the other triangle).
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*/
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static int
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edge_eq2(
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const stl_face_t * const t0,
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const stl_face_t * const t1,
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int e0,
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int e1
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)
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{
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const v3_t * const v00 = &t0->p[e0];
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const v3_t * const v01 = &t0->p[(e0+1) % 3];
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const v3_t * const v10 = &t1->p[e1];
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const v3_t * const v11 = &t1->p[(e1+1) % 3];
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if (v3_eq(v00, v11) && v3_eq(v01, v10))
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return 1;
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return 0;
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}
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double
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v3_len(
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const v3_t * const v0,
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const v3_t * const v1
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)
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{
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float dx = v0->p[0] - v1->p[0];
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float dy = v0->p[1] - v1->p[1];
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float dz = v0->p[2] - v1->p[2];
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return sqrt(dx*dx + dy*dy + dz*dz);
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}
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void
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svg_line(
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float x1,
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float y1,
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float x2,
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float y2
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)
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{
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printf("<line x1=\"%f\" y1=\"%f\" x2=\"%f\" y2=\"%f\" style=\"stroke:rgb(255,255,0);\"/>\n",
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x1,
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y1,
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x2,
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y2
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);
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}
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/** recursively try to fix up the triangles.
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*
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* returns 0 if this should be unwound, 1 if was successful
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*/
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int
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recurse(
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face_t * const f,
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int start_edge
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)
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{
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static int depth;
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depth++;
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// flag that we are looking into this one
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f->used = 1;
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// print out a svg group for this triangle, starting with
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// the incoming edge
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float a = f->sides[(start_edge + 0) % 3];
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float c = f->sides[(start_edge + 1) % 3];
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float b = f->sides[(start_edge + 2) % 3];
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float x2 = (a*a + b*b - c*c) / (2*a);
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float y2 = sqrt(b*b - x2*x2);
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// before drawing the triangle, check to see if any of the
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// edges are coplanar and if so, don't draw the edge
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if (!f->coplanar[(0+start_edge) % 3])
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svg_line(0, 0, a, 0);
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if (!f->coplanar[(1+start_edge) % 3])
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svg_line(a, 0, x2, y2);
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if (!f->coplanar[(2+start_edge) % 3])
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svg_line(x2, y2, 0, 0);
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//printf("%p %d %f %f %f\n", f, start_edge, f->sides[0], f->sides[1], f->sides[2]);
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for(int pass = 0 ; pass < 2 ; pass++)
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{
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// for each edge, find the triangle that matches
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for (int edge = 0 ; edge < 3 ; edge++)
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{
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face_t * const f2 = f->next[(edge+start_edge) % 3];
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if (f2->used)
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continue;
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if (pass == 0 && !f->coplanar[(edge+start_edge) % 3])
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continue;
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// create a group that translates and rotates
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// such that it lines up with this edge
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float trans_x, trans_y, rotate;
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if (edge == 0)
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{
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trans_x = a;
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trans_y = 0;
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rotate = 180;
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} else
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if (edge == 1)
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{
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trans_x = x2;
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trans_y = y2;
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rotate = -atan2(y2, a-x2) * 180 / M_PI;
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} else
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if (edge == 2)
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{
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trans_x = 0;
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trans_y = 0;
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rotate = atan2(y2, x2) * 180 / M_PI;
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}
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printf("<!-- edge %d --><g transform=\"translate(%f,%f) rotate(%f)\">\n",
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edge,
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trans_x,
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trans_y,
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rotate
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);
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recurse(f2, f->next_edge[(edge+start_edge) % 3]);
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printf("</g>\n");
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}
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}
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// no success
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return 0;
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}
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v3_t v3_sub(v3_t a, v3_t b)
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{
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v3_t c = { .p = {
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a.p[0] - b.p[0],
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a.p[1] - b.p[1],
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a.p[2] - b.p[2],
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} };
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return c;
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}
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float v3_dot(v3_t a, v3_t b)
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{
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return a.p[0]*b.p[0] + a.p[1]*b.p[1] + a.p[2]*b.p[2];
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}
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v3_t v3_cross(v3_t u, v3_t v)
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{
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float u1 = u.p[0];
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float u2 = u.p[1];
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float u3 = u.p[2];
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float v1 = v.p[0];
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float v2 = v.p[1];
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float v3 = v.p[2];
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v3_t c = { .p = {
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u2*v3 - u3*v2,
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u3*v1 - u1*v3,
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u1*v2 - u2*v1,
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}};
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return c;
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}
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int
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coplanar_check(
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const stl_face_t * const f1,
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const stl_face_t * const f2
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)
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{
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// find the four distinct points
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v3_t x1 = f1->p[0];
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v3_t x2 = f1->p[1];
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v3_t x3 = f1->p[2];
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v3_t x4;
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for (int i = 0 ; i < 3 ; i++)
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{
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x4 = f2->p[i];
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if (v3_eq(&x1, &x4))
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continue;
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if (v3_eq(&x2, &x4))
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continue;
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if (v3_eq(&x3, &x4))
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continue;
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break;
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}
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// (x3-x1) . ((x2-x1) X (x4-x3)) == 0
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v3_t dx31 = v3_sub(x3, x1);
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v3_t dx21 = v3_sub(x2, x1);
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v3_t dx43 = v3_sub(x4, x3);
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v3_t cross = v3_cross(dx21, dx43);
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float dot = v3_dot(dx31, cross);
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int check = -EPS < dot && dot < +EPS;
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//fprintf( stderr, "%p %p %s\n", f1, f2, check ? "yes" : "no");
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return check;
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}
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int main(void)
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{
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const size_t max_len = 1 << 20;
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uint8_t * const buf = calloc(max_len, 1);
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ssize_t rc = read(0, buf, max_len);
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if (rc == -1)
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return EXIT_FAILURE;
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const stl_header_t * const hdr = (const void*) buf;
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const stl_face_t * const stl_faces = (const void*)(hdr+1);
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const int num_triangles = hdr->num_triangles;
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fprintf(stderr, "header: '%s'\n", hdr->header);
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fprintf(stderr, "num: %d\n", num_triangles);
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face_t * const faces = calloc(num_triangles, sizeof(*faces));
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// convert the stl triangles into faces
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for (int i = 0 ; i < num_triangles ; i++)
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{
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const stl_face_t * const stl = &stl_faces[i];
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face_t * const f = &faces[i];
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f->sides[0] = v3_len(&stl->p[0], &stl->p[1]);
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f->sides[1] = v3_len(&stl->p[1], &stl->p[2]);
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f->sides[2] = v3_len(&stl->p[2], &stl->p[0]);
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}
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// look to see if there is a matching point
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// in the faces that we've already built
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for (int i = 0 ; i < num_triangles ; i++)
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{
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const stl_face_t * const stl = &stl_faces[i];
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face_t * const f = &faces[i];
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for (int j = 0 ; j < num_triangles ; j++)
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{
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if (i == j)
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continue;
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const stl_face_t * const stl2 = &stl_faces[j];
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face_t * const f2 = &faces[j];
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for (int edge = 0 ; edge < 3 ; edge++)
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{
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if (f->next[edge])
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continue;
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for (int edge2 = 0 ; edge2 < 3 ; edge2++)
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{
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if (f2->next[edge2])
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continue;
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if (!edge_eq2(stl, stl2, edge, edge2))
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continue;
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f->next[edge] = f2;
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f->next_edge[edge] = edge2;
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f2->next[edge2] = f;
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f2->next_edge[edge2] = edge;
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f->coplanar[edge] =
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f2->coplanar[edge2] = coplanar_check(stl, stl2);
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}
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}
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}
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// all three edges should be matched
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if (f->next[0] && f->next[1] && f->next[2])
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continue;
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fprintf(stderr, "%d: missing edges?\n", i);
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}
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// we now have a graph that shows the connection between
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// all of the faces and their sizes. start converting them
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printf("<svg xmlns=\"http://www.w3.org/2000/svg\">\n");
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//for (int i = 0 ; i < num_triangles ; i++)
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recurse(&faces[0], 0);
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printf("</svg>\n");
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return 0;
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}
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