예제 #1
0
void GCodeFileWriter::FinishAndCloseFile(void) {
    SPolygon sp;
    ZERO(&sp);
    sel.AssemblePolygon(&sp, NULL);

    int i;
    for(i = 0; i < SS.gCode.passes; i++) {
        double depth = (SS.gCode.depth / SS.gCode.passes)*(i+1);

        SContour *sc;
        for(sc = sp.l.First(); sc; sc = sp.l.NextAfter(sc)) {
            if(sc->l.n < 2) continue;

            SPoint *pt = sc->l.First();
            fprintf(f, "G00 X%s Y%s\r\n",
                    SS.MmToString(pt->p.x), SS.MmToString(pt->p.y));
            fprintf(f, "G01 Z%s F%s\r\n",
                SS.MmToString(depth), SS.MmToString(SS.gCode.plungeFeed));

            pt = sc->l.NextAfter(pt);
            for(; pt; pt = sc->l.NextAfter(pt)) {
                fprintf(f, "G01 X%s Y%s F%s\r\n",
                        SS.MmToString(pt->p.x), SS.MmToString(pt->p.y),
                        SS.MmToString(SS.gCode.feed));
            }
            // Move up to a clearance plane 5mm above the work.
            fprintf(f, "G00 Z%s\r\n", 
                SS.MmToString(SS.gCode.depth < 0 ? +5 : -5));
        }
    }

    sp.Clear();
    sel.Clear();
    fclose(f);
}
예제 #2
0
void Group::FillLoopSetAsPolygon(SBezierLoopSet *sbls) {
    SPolygon sp = {};
    sbls->MakePwlInto(&sp);
    ssglDepthRangeOffset(1);
    ssglFillPolygon(&sp);
    ssglDepthRangeOffset(0);
    sp.Clear();
}
예제 #3
0
void SSurface::TriangulateInto(SShell *shell, SMesh *sm) {
    SEdgeList el = {};

    MakeEdgesInto(shell, &el, AS_UV);

    SPolygon poly = {};
    if(el.AssemblePolygon(&poly, NULL, true)) {
        int i, start = sm->l.n;
        if(degm == 1 && degn == 1) {
            // A surface with curvature along one direction only; so
            // choose the triangulation with chords that lie as much
            // as possible within the surface. And since the trim curves
            // have been pwl'd to within the desired chord tol, that will
            // produce a surface good to within roughly that tol.
            //
            // If this is just a plane (degree (1, 1)) then the triangulation
            // code will notice that, and not bother checking chord tols.
            poly.UvTriangulateInto(sm, this);
        } else {
            // A surface with compound curvature. So we must overlay a
            // two-dimensional grid, and triangulate around that.
            poly.UvGridTriangulateInto(sm, this);
        }

        STriMeta meta = { face, color };
        for(i = start; i < sm->l.n; i++) {
            STriangle *st = &(sm->l.elem[i]);
            st->meta = meta;
            st->an = NormalAt(st->a.x, st->a.y);
            st->bn = NormalAt(st->b.x, st->b.y);
            st->cn = NormalAt(st->c.x, st->c.y);
            st->a = PointAt(st->a.x, st->a.y);
            st->b = PointAt(st->b.x, st->b.y);
            st->c = PointAt(st->c.x, st->c.y);
            // Works out that my chosen contour direction is inconsistent with
            // the triangle direction, sigh.
            st->FlipNormal();
        }
    } else {
        dbp("failed to assemble polygon to trim nurbs surface in uv space");
    }

    el.Clear();
    poly.Clear();
}
예제 #4
0
void Polyhedron::add(const QVector<Vec3f> &verts, const Vec3f &normal)
{
	if(verts.size() < 3) return;

	SPolygon p;

	for(int i=0; i<verts.size(); i++)
	{
		p.addUniqueVert(verts[i]);
	}

	if(p.vertices.size() < 3)
	{
		return;
	}

	//Check normal direction
	Plane polyPlane(p.vertices[0], p.vertices[1], p.vertices[2], SPolygon::CCW);

	//Might need to reverse the vertex order
	if(polyPlane.normal.dot(normal) < 0.0f) p.reverseOrder();

	polygons.append(p);
}
예제 #5
0
void SolveSpaceUI::MenuAnalyze(int id) {
    SS.GW.GroupSelection();
#define gs (SS.GW.gs)

    switch(id) {
        case GraphicsWindow::MNU_STEP_DIM:
            if(gs.constraints == 1 && gs.n == 0) {
                Constraint *c = SK.GetConstraint(gs.constraint[0]);
                if(c->HasLabel() && !c->reference) {
                    SS.TW.shown.dimFinish = c->valA;
                    SS.TW.shown.dimSteps = 10;
                    SS.TW.shown.dimIsDistance =
                        (c->type != Constraint::ANGLE) &&
                        (c->type != Constraint::LENGTH_RATIO) &&
                        (c->type != Constraint::LENGTH_DIFFERENCE);
                    SS.TW.shown.constraint = c->h;
                    SS.TW.shown.screen = TextWindow::SCREEN_STEP_DIMENSION;

                    // The step params are specified in the text window,
                    // so force that to be shown.
                    SS.GW.ForceTextWindowShown();

                    SS.ScheduleShowTW();
                    SS.GW.ClearSelection();
                } else {
                    Error("Constraint must have a label, and must not be "
                          "a reference dimension.");
                }
            } else {
                Error("Bad selection for step dimension; select a constraint.");
            }
            break;

        case GraphicsWindow::MNU_NAKED_EDGES: {
            SS.nakedEdges.Clear();

            Group *g = SK.GetGroup(SS.GW.activeGroup);
            SMesh *m = &(g->displayMesh);
            SKdNode *root = SKdNode::From(m);
            bool inters, leaks;
            root->MakeCertainEdgesInto(&(SS.nakedEdges),
                SKdNode::NAKED_OR_SELF_INTER_EDGES, true, &inters, &leaks);

            InvalidateGraphics();

            const char *intersMsg = inters ?
                "The mesh is self-intersecting (NOT okay, invalid)." :
                "The mesh is not self-intersecting (okay, valid).";
            const char *leaksMsg = leaks ?
                "The mesh has naked edges (NOT okay, invalid)." :
                "The mesh is watertight (okay, valid).";

            std::string cntMsg = ssprintf("\n\nThe model contains %d triangles, from "
                            "%d surfaces.", g->displayMesh.l.n, g->runningShell.surface.n);

            if(SS.nakedEdges.l.n == 0) {
                Message("%s\n\n%s\n\nZero problematic edges, good.%s",
                    intersMsg, leaksMsg, cntMsg.c_str());
            } else {
                Error("%s\n\n%s\n\n%d problematic edges, bad.%s",
                    intersMsg, leaksMsg, SS.nakedEdges.l.n, cntMsg.c_str());
            }
            break;
        }

        case GraphicsWindow::MNU_INTERFERENCE: {
            SS.nakedEdges.Clear();

            SMesh *m = &(SK.GetGroup(SS.GW.activeGroup)->displayMesh);
            SKdNode *root = SKdNode::From(m);
            bool inters, leaks;
            root->MakeCertainEdgesInto(&(SS.nakedEdges),
                SKdNode::SELF_INTER_EDGES, false, &inters, &leaks);

            InvalidateGraphics();

            if(inters) {
                Error("%d edges interfere with other triangles, bad.",
                    SS.nakedEdges.l.n);
            } else {
                Message("The assembly does not interfere, good.");
            }
            break;
        }

        case GraphicsWindow::MNU_VOLUME: {
            SMesh *m = &(SK.GetGroup(SS.GW.activeGroup)->displayMesh);

            double vol = 0;
            int i;
            for(i = 0; i < m->l.n; i++) {
                STriangle tr = m->l.elem[i];

                // Translate to place vertex A at (x, y, 0)
                Vector trans = Vector::From(tr.a.x, tr.a.y, 0);
                tr.a = (tr.a).Minus(trans);
                tr.b = (tr.b).Minus(trans);
                tr.c = (tr.c).Minus(trans);

                // Rotate to place vertex B on the y-axis. Depending on
                // whether the triangle is CW or CCW, C is either to the
                // right or to the left of the y-axis. This handles the
                // sign of our normal.
                Vector u = Vector::From(-tr.b.y, tr.b.x, 0);
                u = u.WithMagnitude(1);
                Vector v = Vector::From(tr.b.x, tr.b.y, 0);
                v = v.WithMagnitude(1);
                Vector n = Vector::From(0, 0, 1);

                tr.a = (tr.a).DotInToCsys(u, v, n);
                tr.b = (tr.b).DotInToCsys(u, v, n);
                tr.c = (tr.c).DotInToCsys(u, v, n);

                n = tr.Normal().WithMagnitude(1);

                // Triangles on edge don't contribute
                if(fabs(n.z) < LENGTH_EPS) continue;

                // The plane has equation p dot n = a dot n
                double d = (tr.a).Dot(n);
                // nx*x + ny*y + nz*z = d
                // nz*z = d - nx*x - ny*y
                double A = -n.x/n.z, B = -n.y/n.z, C = d/n.z;

                double mac = tr.c.y/tr.c.x, mbc = (tr.c.y - tr.b.y)/tr.c.x;
                double xc = tr.c.x, yb = tr.b.y;

                // I asked Maple for
                //    int(int(A*x + B*y +C, y=mac*x..(mbc*x + yb)), x=0..xc);
                double integral =
                    (1.0/3)*(
                        A*(mbc-mac)+
                        (1.0/2)*B*(mbc*mbc-mac*mac)
                    )*(xc*xc*xc)+
                    (1.0/2)*(A*yb+B*yb*mbc+C*(mbc-mac))*xc*xc+
                    C*yb*xc+
                    (1.0/2)*B*yb*yb*xc;

                vol += integral;
            }

            std::string msg = ssprintf("The volume of the solid model is:\n\n""    %.3f %s^3",
                vol / pow(SS.MmPerUnit(), 3),
                SS.UnitName());

            if(SS.viewUnits == SolveSpaceUI::UNIT_MM) {
                msg += ssprintf("\n    %.2f mL", vol/(10*10*10));
            }
            msg += "\n\nCurved surfaces have been approximated as triangles.\n"
                   "This introduces error, typically of around 1%.";
            Message("%s", msg.c_str());
            break;
        }

        case GraphicsWindow::MNU_AREA: {
            Group *g = SK.GetGroup(SS.GW.activeGroup);
            if(g->polyError.how != Group::POLY_GOOD) {
                Error("This group does not contain a correctly-formed "
                      "2d closed area. It is open, not coplanar, or self-"
                      "intersecting.");
                break;
            }
            SEdgeList sel = {};
            g->polyLoops.MakeEdgesInto(&sel);
            SPolygon sp = {};
            sel.AssemblePolygon(&sp, NULL, true);
            sp.normal = sp.ComputeNormal();
            sp.FixContourDirections();
            double area = sp.SignedArea();
            double scale = SS.MmPerUnit();
            Message("The area of the region sketched in this group is:\n\n"
                    "    %.3f %s^2\n\n"
                    "Curves have been approximated as piecewise linear.\n"
                    "This introduces error, typically of around 1%%.",
                area / (scale*scale),
                SS.UnitName());
            sel.Clear();
            sp.Clear();
            break;
        }

        case GraphicsWindow::MNU_SHOW_DOF:
            // This works like a normal solve, except that it calculates
            // which variables are free/bound at the same time.
            SS.GenerateAll(SolveSpaceUI::GENERATE_ALL, true);
            break;

        case GraphicsWindow::MNU_TRACE_PT:
            if(gs.points == 1 && gs.n == 1) {
                SS.traced.point = gs.point[0];
                SS.GW.ClearSelection();
            } else {
                Error("Bad selection for trace; select a single point.");
            }
            break;

        case GraphicsWindow::MNU_STOP_TRACING: {
            std::string exportFile;
            if(GetSaveFile(&exportFile, "", CsvFileFilter)) {
                FILE *f = ssfopen(exportFile, "wb");
                if(f) {
                    int i;
                    SContour *sc = &(SS.traced.path);
                    for(i = 0; i < sc->l.n; i++) {
                        Vector p = sc->l.elem[i].p;
                        double s = SS.exportScale;
                        fprintf(f, "%.10f, %.10f, %.10f\r\n",
                            p.x/s, p.y/s, p.z/s);
                    }
                    fclose(f);
                } else {
                    Error("Couldn't write to '%s'", exportFile.c_str());
                }
            }
            // Clear the trace, and stop tracing
            SS.traced.point = Entity::NO_ENTITY;
            SS.traced.path.l.Clear();
            InvalidateGraphics();
            break;
        }

        default: oops();
    }
}
예제 #6
0
//-----------------------------------------------------------------------------
// An export helper function. We start with a list of Bezier curves, and
// assemble them into loops. We find the outer loops, and find the outer loops'
// inner loops, and group them accordingly.
//-----------------------------------------------------------------------------
void SBezierLoopSetSet::FindOuterFacesFrom(SBezierList *sbl, SPolygon *spxyz,
                                   SSurface *srfuv,
                                   double chordTol,
                                   bool *allClosed, SEdge *notClosedAt,
                                   bool *allCoplanar, Vector *notCoplanarAt,
                                   SBezierList *openContours)
{
    SSurface srfPlane;
    if(!srfuv) {
        Vector p, u, v;
        *allCoplanar =
            sbl->GetPlaneContainingBeziers(&p, &u, &v, notCoplanarAt);
        if(!*allCoplanar) {
            // Don't even try to assemble them into loops if they're not
            // all coplanar.
            if(openContours) {
                SBezier *sb;
                for(sb = sbl->l.First(); sb; sb = sbl->l.NextAfter(sb)) {
                    openContours->l.Add(sb);
                }
            }
            return;
        }
        // All the curves lie in a plane through p with basis vectors u and v.
        srfPlane = SSurface::FromPlane(p, u, v);
        srfuv = &srfPlane;
    }

    int i, j;
    // Assemble the Bezier trim curves into closed loops; we also get the
    // piecewise linearization of the curves (in the SPolygon spxyz), as a
    // calculation aid for the loop direction.
    SBezierLoopSet sbls = SBezierLoopSet::From(sbl, spxyz, chordTol,
                                               allClosed, notClosedAt,
                                               openContours);
    if(sbls.l.n != spxyz->l.n) return;

    // Convert the xyz piecewise linear to uv piecewise linear.
    SPolygon spuv;
    ZERO(&spuv);
    SContour *sc;
    for(sc = spxyz->l.First(); sc; sc = spxyz->l.NextAfter(sc)) {
        spuv.AddEmptyContour();
        SPoint *pt;
        for(pt = sc->l.First(); pt; pt = sc->l.NextAfter(pt)) {
            double u, v;
            srfuv->ClosestPointTo(pt->p, &u, &v);
            spuv.l.elem[spuv.l.n - 1].AddPoint(Vector::From(u, v, 0));
        }
    }
    spuv.normal = Vector::From(0, 0, 1); // must be, since it's in xy plane now

    static const int OUTER_LOOP = 10;
    static const int INNER_LOOP = 20;
    static const int USED_LOOP  = 30;
    // Fix the contour directions; we do this properly, in uv space, so it
    // works for curved surfaces too (important for STEP export).
    spuv.FixContourDirections();
    for(i = 0; i < spuv.l.n; i++) {
        SContour    *contour = &(spuv.l.elem[i]);
        SBezierLoop *bl = &(sbls.l.elem[i]);
        if(contour->tag) {
            // This contour got reversed in the polygon to make the directions
            // consistent, so the same must be necessary for the Bezier loop.
            bl->Reverse();
        }
        if(contour->IsClockwiseProjdToNormal(spuv.normal)) {
            bl->tag = INNER_LOOP;
        } else {
            bl->tag = OUTER_LOOP;
        }
    }

    bool loopsRemaining = true;
    while(loopsRemaining) {
        loopsRemaining = false;
        for(i = 0; i < sbls.l.n; i++) {
            SBezierLoop *loop = &(sbls.l.elem[i]);
            if(loop->tag != OUTER_LOOP) continue;

            // Check if this contour contains any outer loops; if it does, then
            // we should do those "inner outer loops" first; otherwise we
            // will steal their holes, since their holes also lie inside this
            // contour.
            for(j = 0; j < sbls.l.n; j++) {
                SBezierLoop *outer = &(sbls.l.elem[j]);
                if(i == j) continue;
                if(outer->tag != OUTER_LOOP) continue;

                Vector p = spuv.l.elem[j].AnyEdgeMidpoint();
                if(spuv.l.elem[i].ContainsPointProjdToNormal(spuv.normal, p)) {
                    break;
                }
            }
            if(j < sbls.l.n) {
                // It does, can't do this one yet.
                continue;
            }

            SBezierLoopSet outerAndInners;
            ZERO(&outerAndInners);
            loopsRemaining = true;
            loop->tag = USED_LOOP;
            outerAndInners.l.Add(loop);
            int auxA = 0;
            if(loop->l.n > 0) auxA = loop->l.elem[0].auxA;

            for(j = 0; j < sbls.l.n; j++) {
                SBezierLoop *inner = &(sbls.l.elem[j]);
                if(inner->tag != INNER_LOOP) continue;
                if(inner->l.n < 1) continue;
                if(inner->l.elem[0].auxA != auxA) continue;

                Vector p = spuv.l.elem[j].AnyEdgeMidpoint();
                if(spuv.l.elem[i].ContainsPointProjdToNormal(spuv.normal, p)) {
                    outerAndInners.l.Add(inner);
                    inner->tag = USED_LOOP;
                }
            }
            
            outerAndInners.point  = srfuv->PointAt(0, 0);
            outerAndInners.normal = srfuv->NormalAt(0, 0);
            l.Add(&outerAndInners);
        }
    }

    // If we have poorly-formed loops--for example, overlapping zero-area
    // stuff--then we can end up with leftovers. We use this function to
    // group stuff into closed paths for export when possible, so it's bad
    // to screw up on that stuff. So just add them onto the open curve list.
    // Very ugly, but better than losing curves.
    for(i = 0; i < sbls.l.n; i++) {
        SBezierLoop *loop = &(sbls.l.elem[i]);
        if(loop->tag == USED_LOOP) continue;

        if(openContours) {
            SBezier *sb;
            for(sb = loop->l.First(); sb; sb = loop->l.NextAfter(sb)) {
                openContours->l.Add(sb);
            }
        }
        loop->Clear();
        // but don't free the used loops, since we shallow-copied them to
        // ourself
    }

    sbls.l.Clear(); // not sbls.Clear(), since that would deep-clear
    spuv.Clear();
}
예제 #7
0
void StepFileWriter::ExportSurface(SSurface *ss, SBezierList *sbl) {
    int i, j, srfid = id;

    // First, we create the untrimmed surface. We always specify a rational
    // B-spline surface (in fact, just a Bezier surface).
    fprintf(f, "#%d=(\n", srfid);
    fprintf(f, "BOUNDED_SURFACE()\n");
    fprintf(f, "B_SPLINE_SURFACE(%d,%d,(", ss->degm, ss->degn);
    for(i = 0; i <= ss->degm; i++) {
        fprintf(f, "(");
        for(j = 0; j <= ss->degn; j++) {
            fprintf(f, "#%d", srfid + 1 + j + i*(ss->degn + 1));
            if(j != ss->degn) fprintf(f, ",");
        }
        fprintf(f, ")");
        if(i != ss->degm) fprintf(f, ",");
    }
    fprintf(f, "),.UNSPECIFIED.,.F.,.F.,.F.)\n");
    fprintf(f, "B_SPLINE_SURFACE_WITH_KNOTS((%d,%d),(%d,%d),",
        (ss->degm + 1), (ss->degm + 1),
        (ss->degn + 1), (ss->degn + 1));
    fprintf(f, "(0.000,1.000),(0.000,1.000),.UNSPECIFIED.)\n");
    fprintf(f, "GEOMETRIC_REPRESENTATION_ITEM()\n");
    fprintf(f, "RATIONAL_B_SPLINE_SURFACE((");
    for(i = 0; i <= ss->degm; i++) {
        fprintf(f, "(");
        for(j = 0; j <= ss->degn; j++) {
            fprintf(f, "%.10f", ss->weight[i][j]);
            if(j != ss->degn) fprintf(f, ",");
        }
        fprintf(f, ")");
        if(i != ss->degm) fprintf(f, ",");
    }
    fprintf(f, "))\n");
    fprintf(f, "REPRESENTATION_ITEM('')\n");
    fprintf(f, "SURFACE()\n");
    fprintf(f, ");\n");

    // The control points for the untrimmed surface.
    for(i = 0; i <= ss->degm; i++) {
        for(j = 0; j <= ss->degn; j++) {
            fprintf(f, "#%d=CARTESIAN_POINT('',(%.10f,%.10f,%.10f));\n",
                srfid + 1 + j + i*(ss->degn + 1),
                CO(ss->ctrl[i][j]));
        }
    }
    fprintf(f, "\n");

    id = srfid + 1 + (ss->degm + 1)*(ss->degn + 1);

    // Now we do the trim curves. We must group each outer loop separately
    // along with its inner faces, so do that now.
    SBezierLoopSetSet sblss;
    ZERO(&sblss);
    SPolygon spxyz;
    ZERO(&spxyz);
    bool allClosed;
    SEdge notClosedAt;
    // We specify a surface, so it doesn't check for coplanarity; and we
    // don't want it to give us any open contours. The polygon and chord
    // tolerance are required, because they are used to calculate the
    // contour directions and determine inner vs. outer contours.
    sblss.FindOuterFacesFrom(sbl, &spxyz, ss,
                             SS.ChordTolMm() / SS.exportScale,
                             &allClosed, &notClosedAt,
                             NULL, NULL,
                             NULL);

    // So in our list of SBezierLoopSet, each set contains at least one loop
    // (the outer boundary), plus any inner loops associated with that outer
    // loop.
    SBezierLoopSet *sbls;
    for(sbls = sblss.l.First(); sbls; sbls = sblss.l.NextAfter(sbls)) {
        SBezierLoop *loop = sbls->l.First();

        List<int> listOfLoops;
        ZERO(&listOfLoops);
        // Create the face outer boundary from the outer loop.
        int fob = ExportCurveLoop(loop, false);
        listOfLoops.Add(&fob);

        // And create the face inner boundaries from any inner loops that
        // lie within this contour.
        loop = sbls->l.NextAfter(loop);
        for(; loop; loop = sbls->l.NextAfter(loop)) {
            int fib = ExportCurveLoop(loop, true);
            listOfLoops.Add(&fib);
        }

        // And now create the face that corresponds to this outer loop
        // and all of its holes.
        int advFaceId = id;
        fprintf(f, "#%d=ADVANCED_FACE('',(", advFaceId);
        int *fb;
        for(fb = listOfLoops.First(); fb; fb = listOfLoops.NextAfter(fb)) {
            fprintf(f, "#%d", *fb);
            if(listOfLoops.NextAfter(fb) != NULL) fprintf(f, ",");
        }

        fprintf(f, "),#%d,.T.);\n", srfid);
        fprintf(f, "\n");
        advancedFaces.Add(&advFaceId);

        id++;
        listOfLoops.Clear();
    }
    sblss.Clear();
    spxyz.Clear();
}
예제 #8
0
void SolveSpace::ExportLinesAndMesh(SEdgeList *sel, SBezierList *sbl, SMesh *sm,
                                    Vector u, Vector v, Vector n,
                                        Vector origin, double cameraTan,
                                    VectorFileWriter *out)
{
    double s = 1.0 / SS.exportScale;

    // Project into the export plane; so when we're done, z doesn't matter,
    // and x and y are what goes in the DXF.
    SEdge *e;
    for(e = sel->l.First(); e; e = sel->l.NextAfter(e)) {
        // project into the specified csys, and apply export scale
        (e->a) = e->a.InPerspective(u, v, n, origin, cameraTan).ScaledBy(s);
        (e->b) = e->b.InPerspective(u, v, n, origin, cameraTan).ScaledBy(s);
    }

    SBezier *b;
    if(sbl) {
        for(b = sbl->l.First(); b; b = sbl->l.NextAfter(b)) {
            *b = b->InPerspective(u, v, n, origin, cameraTan);
            int i;
            for(i = 0; i <= b->deg; i++) {
                b->ctrl[i] = (b->ctrl[i]).ScaledBy(s);
            }
        }
    }

    // If cutter radius compensation is requested, then perform it now
    if(fabs(SS.exportOffset) > LENGTH_EPS) {
        // assemble those edges into a polygon, and clear the edge list
        SPolygon sp;
        ZERO(&sp);
        sel->AssemblePolygon(&sp, NULL);
        sel->Clear();

        SPolygon compd;
        ZERO(&compd);
        sp.normal = Vector::From(0, 0, -1);
        sp.FixContourDirections();
        sp.OffsetInto(&compd, SS.exportOffset*s);
        sp.Clear();

        compd.MakeEdgesInto(sel);
        compd.Clear();
    }

    // Now the triangle mesh; project, then build a BSP to perform
    // occlusion testing and generated the shaded surfaces.
    SMesh smp;
    ZERO(&smp);
    if(sm) {
        Vector l0 = (SS.lightDir[0]).WithMagnitude(1),
               l1 = (SS.lightDir[1]).WithMagnitude(1);
        STriangle *tr;
        for(tr = sm->l.First(); tr; tr = sm->l.NextAfter(tr)) {
            STriangle tt = *tr;
            tt.a = (tt.a).InPerspective(u, v, n, origin, cameraTan).ScaledBy(s);
            tt.b = (tt.b).InPerspective(u, v, n, origin, cameraTan).ScaledBy(s);
            tt.c = (tt.c).InPerspective(u, v, n, origin, cameraTan).ScaledBy(s);

            // And calculate lighting for the triangle
            Vector n = tt.Normal().WithMagnitude(1);
            double lighting = SS.ambientIntensity +
                                  max(0, (SS.lightIntensity[0])*(n.Dot(l0))) +
                                  max(0, (SS.lightIntensity[1])*(n.Dot(l1)));
            double r = min(1, REDf  (tt.meta.color)*lighting),
                   g = min(1, GREENf(tt.meta.color)*lighting),
                   b = min(1, BLUEf (tt.meta.color)*lighting);
            tt.meta.color = RGBf(r, g, b);
            smp.AddTriangle(&tt);
        }
    }

    // Use the BSP routines to generate the split triangles in paint order.
    SBsp3 *bsp = SBsp3::FromMesh(&smp);
    SMesh sms;
    ZERO(&sms);
    bsp->GenerateInPaintOrder(&sms);
    // And cull the back-facing triangles
    STriangle *tr;
    sms.l.ClearTags();
    for(tr = sms.l.First(); tr; tr = sms.l.NextAfter(tr)) {
        Vector n = tr->Normal();
        if(n.z < 0) {
            tr->tag = 1;
        }
    }
    sms.l.RemoveTagged();

    // And now we perform hidden line removal if requested
    SEdgeList hlrd;
    ZERO(&hlrd);
    if(sm && !SS.GW.showHdnLines) {
        SKdNode *root = SKdNode::From(&smp);

        // Generate the edges where a curved surface turns from front-facing
        // to back-facing.
        if(SS.GW.showEdges) {
            root->MakeCertainEdgesInto(sel, SKdNode::TURNING_EDGES,
                        false, NULL, NULL);
        }

        root->ClearTags();
        int cnt = 1234;

        SEdge *se;
        for(se = sel->l.First(); se; se = sel->l.NextAfter(se)) {
            if(se->auxA == Style::CONSTRAINT) {
                // Constraints should not get hidden line removed; they're
                // always on top.
                hlrd.AddEdge(se->a, se->b, se->auxA);
                continue;
            }

            SEdgeList out;
            ZERO(&out);
            // Split the original edge against the mesh
            out.AddEdge(se->a, se->b, se->auxA);
            root->OcclusionTestLine(*se, &out, cnt);
            // the occlusion test splits unnecessarily; so fix those
            out.MergeCollinearSegments(se->a, se->b);
            cnt++;
            // And add the results to our output
            SEdge *sen;
            for(sen = out.l.First(); sen; sen = out.l.NextAfter(sen)) {
                hlrd.AddEdge(sen->a, sen->b, sen->auxA);
            }
            out.Clear();
        }

        sel = &hlrd;
    }

    // We kept the line segments and Beziers separate until now; but put them
    // all together, and also project everything into the xy plane, since not
    // all export targets ignore the z component of the points.
    for(e = sel->l.First(); e; e = sel->l.NextAfter(e)) {
        SBezier sb = SBezier::From(e->a, e->b);
        sb.auxA = e->auxA;
        sbl->l.Add(&sb);
    }
    for(b = sbl->l.First(); b; b = sbl->l.NextAfter(b)) {
        for(int i = 0; i <= b->deg; i++) {
            b->ctrl[i].z = 0;
        }
    }

    // If possible, then we will assemble these output curves into loops. They
    // will then get exported as closed paths.
    SBezierLoopSetSet sblss;
    ZERO(&sblss);
    SBezierList leftovers;
    ZERO(&leftovers);
    SSurface srf = SSurface::FromPlane(Vector::From(0, 0, 0),
                                       Vector::From(1, 0, 0),
                                       Vector::From(0, 1, 0));
    SPolygon spxyz;
    ZERO(&spxyz);
    bool allClosed;
    SEdge notClosedAt;
    sbl->l.ClearTags();
    sblss.FindOuterFacesFrom(sbl, &spxyz, &srf,
                             SS.ChordTolMm()*s,
                             &allClosed, &notClosedAt,
                             NULL, NULL,
                             &leftovers);
    for(b = leftovers.l.First(); b; b = leftovers.l.NextAfter(b)) {
        sblss.AddOpenPath(b);
    }

    // Now write the lines and triangles to the output file
    out->Output(&sblss, &sms);

    leftovers.Clear();
    spxyz.Clear();
    sblss.Clear();
    smp.Clear();
    sms.Clear();
    hlrd.Clear();
}