M0: workspace, geometry foundation, sketch constraint solver, kernel boundary

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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bherbruckandClaude Opus 5.5 committed 2026-10-07 17:01:29 +00:00
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//! The constraint solver.
//!
//! Unknowns are the coordinates of every non-fixed point and the radius of every circle. Each
//! constraint contributes residuals (zero when satisfied, in millimetres so that all rows have a
//! comparable scale). The system is split into connected components and each is solved with a
//! damped Gauss–Newton (Levenberg–Marquardt) iteration on a dense Jacobian built from local
//! central differences. Small steps from the current positions are preferred, so
//! under-constrained sketches move as little as possible. Afterwards the rank of the Jacobian
//! gives the remaining degrees of freedom and which points are fully determined.
use serde::{Deserialize, Serialize};
use solvecraft_geom::Vec2;
use crate::linalg::{Mat, determined_vars, solve as lin_solve};
use crate::model::{ConstraintKind, CurveKind, Sketch};
const MAX_ITERS: usize = 200;
/// Converged when every residual is below this (mm).
const TOL: f64 = 1e-9;
/// A solution is accepted when every residual is below this (mm).
const ACCEPT: f64 = 1e-6;
#[derive(Clone, Copy, Debug, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum SolveStatus {
/// All constraints satisfied.
Solved,
/// The constraints conflict (or the solver could not satisfy them); geometry was left as it
/// was before solving.
Failed,
}
#[derive(Clone, Debug, Serialize, Deserialize)]
pub struct SolveReport {
pub status: SolveStatus,
/// Remaining degrees of freedom (0 = fully constrained).
pub dof: usize,
pub iterations: usize,
pub max_residual: f64,
/// Constraints still violated after a failed solve.
pub failing: Vec<String>,
/// Per point: fully determined by constraints (fixed points count as determined).
pub point_determined: Vec<bool>,
/// Per curve: all of its defining values determined.
pub curve_determined: Vec<bool>,
}
impl SolveReport {
pub fn ok(&self) -> bool {
self.status == SolveStatus::Solved
}
pub fn fully_constrained(&self) -> bool {
self.dof == 0
}
}
/// Variable layout: point → (x var, y var), circle → radius var.
struct Layout {
pvar: Vec<Option<usize>>,
rvar: Vec<Option<usize>>,
n: usize,
}
fn layout(sk: &Sketch) -> Layout {
let mut fixed: Vec<bool> = sk.points.iter().map(|p| p.fixed).collect();
for c in &sk.constraints {
if let ConstraintKind::Fix { p } = c.kind
&& let Some(f) = fixed.get_mut(p)
{
*f = true;
}
}
let mut n = 0;
let pvar = fixed
.iter()
.map(|f| {
if *f {
None
} else {
n += 2;
Some(n - 2)
}
})
.collect();
let rvar = sk
.curves
.iter()
.map(|c| match c.kind {
CurveKind::Circle { .. } => {
n += 1;
Some(n - 1)
}
_ => None,
})
.collect();
Layout { pvar, rvar, n }
}
/// Read-only view of the sketch with variable values substituted.
struct State<'a> {
sk: &'a Sketch,
lay: &'a Layout,
x: &'a [f64],
}
impl State<'_> {
fn p(&self, i: usize) -> Vec2 {
match self.lay.pvar.get(i).copied().flatten() {
Some(v) => Vec2::new(self.x.get(v).copied().unwrap_or(0.0), self.x.get(v + 1).copied().unwrap_or(0.0)),
None => self.sk.points.get(i).map(|p| p.pos).unwrap_or_default(),
}
}
fn line(&self, l: usize) -> (Vec2, Vec2) {
match self.sk.curves.get(l).map(|c| &c.kind) {
Some(CurveKind::Line { a, b }) => (self.p(*a), self.p(*b)),
_ => (Vec2::ZERO, Vec2::X),
}
}
/// Centre and radius of a circle or arc.
fn round(&self, c: usize) -> (Vec2, f64) {
match self.sk.curves.get(c).map(|c| &c.kind) {
Some(CurveKind::Circle { c: ci, r }) => {
let r = match self.lay.rvar.get(c).copied().flatten() {
Some(v) => self.x.get(v).copied().unwrap_or(*r),
None => *r,
};
(self.p(*ci), r)
}
Some(CurveKind::Arc { c: ci, a, .. }) => {
let cc = self.p(*ci);
(cc, cc.dist(self.p(*a)))
}
_ => (Vec2::ZERO, 0.0),
}
}
fn is_line(&self, c: usize) -> bool {
matches!(self.sk.curves.get(c).map(|c| &c.kind), Some(CurveKind::Line { .. }))
}
}
fn wrap_angle(a: f64) -> f64 {
let t = std::f64::consts::TAU;
let mut a = a % t;
if a > std::f64::consts::PI {
a -= t;
} else if a <= -std::f64::consts::PI {
a += t;
}
a
}
/// Distance from `p` to the infinite line through `a`, `b` (signed by side).
fn line_dist(p: Vec2, a: Vec2, b: Vec2) -> f64 {
let d = b - a;
let l = d.len().max(1e-12);
d.cross(p - a) / l
}
/// Residual rows of one constraint.
fn residuals(s: &State, k: &ConstraintKind, out: &mut Vec<f64>) {
use ConstraintKind::*;
match *k {
Coincident { p, q } => {
let d = s.p(p) - s.p(q);
out.extend([d.x, d.y]);
}
PointOnCurve { p, c } => {
let pp = s.p(p);
if s.is_line(c) {
let (a, b) = s.line(c);
out.push(line_dist(pp, a, b));
} else {
let (cc, r) = s.round(c);
out.push(pp.dist(cc) - r);
}
}
Horizontal { l } => {
let (a, b) = s.line(l);
out.push(b.y - a.y);
}
Vertical { l } => {
let (a, b) = s.line(l);
out.push(b.x - a.x);
}
HorizontalPoints { p, q } => out.push(s.p(q).y - s.p(p).y),
VerticalPoints { p, q } => out.push(s.p(q).x - s.p(p).x),
Parallel { a, b } | Perpendicular { a, b } => {
let (a0, a1) = s.line(a);
let (b0, b1) = s.line(b);
let (da, db) = (a1 - a0, b1 - b0);
let scale = (da.len() + db.len()).max(1e-12);
let v = if matches!(k, Parallel { .. }) { da.cross(db) } else { da.dot(db) };
out.push(v / scale);
}
Collinear { a, b } => {
let (a0, a1) = s.line(a);
let (b0, b1) = s.line(b);
out.push(line_dist(b0, a0, a1));
out.push(line_dist(b1, a0, a1));
}
Tangent { a, b } => {
let (la, lb) = (s.is_line(a), s.is_line(b));
if la || lb {
let (l, c) = if la { (a, b) } else { (b, a) };
let (p0, p1) = s.line(l);
let (cc, r) = s.round(c);
out.push(line_dist(cc, p0, p1).abs() - r);
} else {
let (c1, r1) = s.round(a);
let (c2, r2) = s.round(b);
let d = c1.dist(c2);
let ext = d - (r1 + r2);
let int = d - (r1 - r2).abs();
out.push(if ext.abs() <= int.abs() { ext } else { int });
}
}
Equal { a, b } => {
if s.is_line(a) {
let (a0, a1) = s.line(a);
let (b0, b1) = s.line(b);
out.push(a0.dist(a1) - b0.dist(b1));
} else {
out.push(s.round(a).1 - s.round(b).1);
}
}
Concentric { a, b } => {
let d = s.round(a).0 - s.round(b).0;
out.extend([d.x, d.y]);
}
Midpoint { p, l } => {
let (a, b) = s.line(l);
let d = s.p(p) - (a + b) * 0.5;
out.extend([d.x, d.y]);
}
Symmetric { p, q, l } => {
let (a, b) = s.line(l);
let (pp, qq) = (s.p(p), s.p(q));
let dir = b - a;
let len = dir.len().max(1e-12);
out.push(line_dist((pp + qq) * 0.5, a, b));
out.push((qq - pp).dot(dir) / len);
}
Fix { .. } => {}
Distance { p, q, value } => out.push(s.p(p).dist(s.p(q)) - value),
DistanceX { p, q, value } => out.push((s.p(q).x - s.p(p).x).abs() - value),
DistanceY { p, q, value } => out.push((s.p(q).y - s.p(p).y).abs() - value),
PointLineDistance { p, l, value } => {
let (a, b) = s.line(l);
out.push(line_dist(s.p(p), a, b).abs() - value);
}
Length { l, value } => {
let (a, b) = s.line(l);
out.push(a.dist(b) - value);
}
Radius { c, value } => out.push(s.round(c).1 - value),
Diameter { c, value } => out.push(2.0 * s.round(c).1 - value),
Angle { a, b, value } => {
let (a0, a1) = s.line(a);
let (b0, b1) = s.line(b);
let (da, db) = (a1 - a0, b1 - b0);
let ang = da.cross(db).atan2(da.dot(db));
let scale = 0.5 * (da.len() + db.len());
out.push(wrap_angle(ang - value) * scale.max(1e-6));
}
}
}
/// One residual block: implicit arc radius equality or a user constraint.
enum Block<'a> {
Arc { c: usize, a: usize, b: usize },
User(usize, &'a ConstraintKind),
}
fn block_residuals(s: &State, b: &Block, out: &mut Vec<f64>) {
match b {
Block::Arc { c, a, b } => {
let cc = s.p(*c);
out.push(cc.dist(s.p(*b)) - cc.dist(s.p(*a)));
}
Block::User(_, k) => residuals(s, k, out),
}
}
/// Variables a block depends on.
fn block_vars(sk: &Sketch, lay: &Layout, b: &Block) -> Vec<usize> {
let mut v = Vec::new();
let pt = |v: &mut Vec<usize>, p: usize| {
if let Some(x) = lay.pvar.get(p).copied().flatten() {
v.extend([x, x + 1]);
}
};
let curve = |v: &mut Vec<usize>, c: usize| match sk.curves.get(c).map(|c| &c.kind) {
Some(CurveKind::Line { a, b }) => {
pt(v, *a);
pt(v, *b);
}
Some(CurveKind::Circle { c: ci, .. }) => {
pt(v, *ci);
if let Some(r) = lay.rvar.get(c).copied().flatten() {
v.push(r);
}
}
Some(CurveKind::Arc { c, a, b }) => {
pt(v, *c);
pt(v, *a);
pt(v, *b);
}
None => {}
};
use ConstraintKind::*;
match b {
Block::Arc { c, a, b } => {
pt(&mut v, *c);
pt(&mut v, *a);
pt(&mut v, *b);
}
Block::User(_, k) => match **k {
Coincident { p, q } | HorizontalPoints { p, q } | VerticalPoints { p, q } => {
pt(&mut v, p);
pt(&mut v, q);
}
Distance { p, q, .. } | DistanceX { p, q, .. } | DistanceY { p, q, .. } => {
pt(&mut v, p);
pt(&mut v, q);
}
PointOnCurve { p, c } | Midpoint { p, l: c } | PointLineDistance { p, l: c, .. } => {
pt(&mut v, p);
curve(&mut v, c);
}
Horizontal { l } | Vertical { l } | Length { l, .. } | Radius { c: l, .. } | Diameter { c: l, .. } => curve(&mut v, l),
Parallel { a, b }
| Perpendicular { a, b }
| Collinear { a, b }
| Tangent { a, b }
| Equal { a, b }
| Concentric { a, b }
| Angle { a, b, .. } => {
curve(&mut v, a);
curve(&mut v, b);
}
Symmetric { p, q, l } => {
pt(&mut v, p);
pt(&mut v, q);
curve(&mut v, l);
}
Fix { .. } => {}
},
}
v.sort_unstable();
v.dedup();
v
}
fn find(parent: &mut [usize], mut i: usize) -> usize {
while let Some(&p) = parent.get(i) {
if p == i {
break;
}
let gp = parent.get(p).copied().unwrap_or(p);
if let Some(slot) = parent.get_mut(i) {
*slot = gp;
}
i = p;
}
i
}
/// Residual vector and Jacobian (rows × all n vars) for the given blocks.
fn system(sk: &Sketch, lay: &Layout, blocks: &[(Block, Vec<usize>)], x: &mut [f64], with_j: bool) -> (Vec<f64>, Option<Mat>, Vec<usize>) {
let mut r = Vec::new();
let mut owner = Vec::new();
for (bi, (b, _)) in blocks.iter().enumerate() {
let before = r.len();
block_residuals(&State { sk, lay, x }, b, &mut r);
owner.extend(std::iter::repeat_n(bi, r.len() - before));
}
if !with_j {
return (r, None, owner);
}
let mut j = Mat::zeros(r.len(), lay.n);
let mut row = 0;
let mut plus = Vec::new();
let mut minus = Vec::new();
for (b, vars) in blocks {
plus.clear();
block_residuals(&State { sk, lay, x }, b, &mut plus);
let rows = plus.len();
for &v in vars {
let Some(x0) = x.get(v).copied() else { continue };
let h = 1e-7 * x0.abs().max(1.0);
if let Some(xv) = x.get_mut(v) {
*xv = x0 + h;
}
plus.clear();
block_residuals(&State { sk, lay, x }, b, &mut plus);
if let Some(xv) = x.get_mut(v) {
*xv = x0 - h;
}
minus.clear();
block_residuals(&State { sk, lay, x }, b, &mut minus);
if let Some(xv) = x.get_mut(v) {
*xv = x0;
}
for k in 0..rows {
let d = (plus.get(k).copied().unwrap_or(0.0) - minus.get(k).copied().unwrap_or(0.0)) / (2.0 * h);
j.set(row + k, v, d);
}
}
row += rows;
}
(r, Some(j), owner)
}
fn max_abs(v: &[f64]) -> f64 {
v.iter().fold(0.0_f64, |m, x| if x.is_finite() { m.max(x.abs()) } else { f64::INFINITY })
}
fn norm2(v: &[f64]) -> f64 {
v.iter().map(|x| x * x).sum()
}
/// Levenberg–Marquardt on one component (variables `vars`, blocks `blocks`). Returns iterations.
fn lm(sk: &Sketch, lay: &Layout, blocks: &[(Block, Vec<usize>)], vars: &[usize], x: &mut Vec<f64>) -> usize {
let n = vars.len();
let mut lambda = 1e-3;
let (mut r, _, _) = system(sk, lay, blocks, x, false);
let mut f = norm2(&r);
for it in 0..MAX_ITERS {
if max_abs(&r) < TOL {
return it;
}
let (_, Some(j), _) = system(sk, lay, blocks, x, true) else { return it };
// Normal equations restricted to this component's variables.
let mut a = Mat::zeros(n, n);
let mut g = vec![0.0; n];
for row in 0..j.rows {
let ri = r.get(row).copied().unwrap_or(0.0);
let nz: Vec<(usize, f64)> = vars.iter().enumerate().map(|(li, &v)| (li, j.get(row, v))).filter(|(_, d)| *d != 0.0).collect();
for &(li, di) in &nz {
if let Some(gi) = g.get_mut(li) {
*gi += di * ri;
}
for &(lk, dk) in &nz {
a.add(li, lk, di * dk);
}
}
}
let mut improved = false;
for _ in 0..30 {
let mut m = a.clone();
for i in 0..n {
let d = a.get(i, i);
m.add(i, i, lambda * (d + 1e-9) + 1e-12);
}
let rhs: Vec<f64> = g.iter().map(|v| -v).collect();
let Some(step) = lin_solve(m, rhs) else {
lambda *= 10.0;
continue;
};
let mut trial = x.clone();
for (li, &v) in vars.iter().enumerate() {
if let (Some(t), Some(s)) = (trial.get_mut(v), step.get(li)) {
*t += s;
}
}
let (rt, _, _) = system(sk, lay, blocks, &mut trial, false);
let ft = norm2(&rt);
if ft.is_finite() && ft < f {
*x = trial;
r = rt;
f = ft;
lambda = (lambda / 3.0).max(1e-12);
improved = true;
break;
}
lambda *= 4.0;
if lambda > 1e12 {
break;
}
}
if !improved {
return it;
}
}
MAX_ITERS
}
/// Solve the sketch in place. On failure the geometry is restored and the report lists the
/// violated constraints.
pub fn solve(sk: &mut Sketch) -> SolveReport {
let lay = layout(sk);
let mut x = vec![0.0; lay.n];
for (i, p) in sk.points.iter().enumerate() {
if let Some(v) = lay.pvar.get(i).copied().flatten() {
if let Some(s) = x.get_mut(v) {
*s = p.pos.x;
}
if let Some(s) = x.get_mut(v + 1) {
*s = p.pos.y;
}
}
}
for (i, c) in sk.curves.iter().enumerate() {
if let (CurveKind::Circle { r, .. }, Some(v)) = (&c.kind, lay.rvar.get(i).copied().flatten())
&& let Some(s) = x.get_mut(v)
{
*s = *r;
}
}
let x0 = x.clone();
let mut blocks: Vec<(Block, Vec<usize>)> = Vec::new();
for c in &sk.curves {
if let CurveKind::Arc { c, a, b } = c.kind {
let bl = Block::Arc { c, a, b };
let vars = block_vars(sk, &lay, &bl);
blocks.push((bl, vars));
}
}
for (i, c) in sk.constraints.iter().enumerate() {
let bl = Block::User(i, &c.kind);
let vars = block_vars(sk, &lay, &bl);
blocks.push((bl, vars));
}
// Connected components over variables.
let mut parent: Vec<usize> = (0..lay.n).collect();
for (_, vars) in &blocks {
if let Some(&first) = vars.first() {
for &v in vars.iter().skip(1) {
let (ra, rb) = (find(&mut parent, first), find(&mut parent, v));
if let Some(p) = parent.get_mut(ra) {
*p = rb;
}
}
}
}
let mut comps: Vec<(usize, Vec<usize>, Vec<usize>)> = Vec::new(); // (root, vars, block idx)
for v in 0..lay.n {
let r = find(&mut parent, v);
match comps.iter_mut().find(|c| c.0 == r) {
Some(c) => c.1.push(v),
None => comps.push((r, vec![v], Vec::new())),
}
}
let mut constant_blocks = Vec::new();
for (bi, (_, vars)) in blocks.iter().enumerate() {
match vars.first() {
Some(&v) => {
let r = find(&mut parent, v);
if let Some(c) = comps.iter_mut().find(|c| c.0 == r) {
c.2.push(bi);
}
}
None => constant_blocks.push(bi),
}
}
let mut iterations = 0;
// Solve each component; `blocks` is consumed by index so rebuild per component.
let all_blocks = blocks;
for (_, vars, bis) in &comps {
if bis.is_empty() {
continue;
}
let sub: Vec<(Block, Vec<usize>)> = bis
.iter()
.filter_map(|&bi| {
all_blocks.get(bi).map(|(b, v)| {
let b2 = match b {
Block::Arc { c, a, b } => Block::Arc { c: *c, a: *a, b: *b },
Block::User(i, k) => Block::User(*i, k),
};
(b2, v.clone())
})
})
.collect();
iterations += lm(sk, &lay, &sub, vars, &mut x);
}
// Final residuals, Jacobian and analysis over everything.
let (r, j, owner) = system(sk, &lay, &all_blocks, &mut x, true);
let max_residual = max_abs(&r);
let mut failing: Vec<String> = Vec::new();
for (row, v) in r.iter().enumerate() {
if !(v.abs() < ACCEPT)
&& let Some((Block::User(ci, _), _)) = owner.get(row).and_then(|bi| all_blocks.get(*bi))
&& let Some(c) = sk.constraints.get(*ci)
&& !failing.contains(&c.id)
{
failing.push(c.id.clone());
}
}
let _ = constant_blocks;
let status = if max_residual < ACCEPT { SolveStatus::Solved } else { SolveStatus::Failed };
let use_x = if status == SolveStatus::Solved { &x } else { &x0 };
let (det, rank) = match &j {
Some(j) if j.rows > 0 => determined_vars(j, 1e-7),
_ => (vec![false; lay.n], 0),
};
// Write back.
for (i, p) in sk.points.iter_mut().enumerate() {
if let Some(v) = lay.pvar.get(i).copied().flatten() {
p.pos = Vec2::new(use_x.get(v).copied().unwrap_or(p.pos.x), use_x.get(v + 1).copied().unwrap_or(p.pos.y));
}
}
for (i, c) in sk.curves.iter_mut().enumerate() {
if let (CurveKind::Circle { r, .. }, Some(v)) = (&mut c.kind, lay.rvar.get(i).copied().flatten()) {
*r = use_x.get(v).copied().unwrap_or(*r).abs().max(1e-9);
}
}
let vdet = |v: Option<usize>| v.is_none_or(|v| det.get(v).copied().unwrap_or(false));
let pdet = |p: usize| match lay.pvar.get(p).copied().flatten() {
Some(v) => vdet(Some(v)) && vdet(Some(v + 1)),
None => true,
};
let point_determined: Vec<bool> = (0..sk.points.len()).map(pdet).collect();
let curve_determined = sk
.curves
.iter()
.enumerate()
.map(|(i, c)| match c.kind {
CurveKind::Line { a, b } => pdet(a) && pdet(b),
CurveKind::Circle { c, .. } => pdet(c) && vdet(lay.rvar.get(i).copied().flatten()),
CurveKind::Arc { c, a, b } => pdet(c) && pdet(a) && pdet(b),
})
.collect();
SolveReport {
status,
dof: lay.n.saturating_sub(rank),
iterations,
max_residual: if max_residual.is_finite() { max_residual } else { f64::MAX },
failing,
point_determined,
curve_determined,
}
}