From 4a554e2057a29aea2e60ba59343548a509fe81f3 Mon Sep 17 00:00:00 2001
From: sjat <sjat@fisi.nyumbani.baobab.band>
Date: Mon, 8 Jun 2026 22:18:42 +0200
Subject: [PATCH] feat: alignment + projection pipeline

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
---
 src/geometry/transform.test.ts | 36 ++++++++++++++++++++++++++++++++++
 src/geometry/transform.ts      | 27 +++++++++++++++++++++++++
 2 files changed, 63 insertions(+)
 create mode 100644 src/geometry/transform.test.ts
 create mode 100644 src/geometry/transform.ts

diff --git a/src/geometry/transform.test.ts b/src/geometry/transform.test.ts
new file mode 100644
index 0000000..13ebe32
--- /dev/null
+++ b/src/geometry/transform.test.ts
@@ -0,0 +1,36 @@
+import { describe, it, expect } from 'vitest';
+import { applyAlignment, projectSegments, imageToMachine, alignmentFromOrigin } from './transform';
+import type { Vec2, Mat3, Segment, Alignment } from '../types';
+
+const close = (a: Vec2, b: Vec2, eps = 1e-9) =>
+  Math.abs(a[0] - b[0]) < eps && Math.abs(a[1] - b[1]) < eps;
+
+const IDENT: Mat3 = [1, 0, 0, 0, 1, 0, 0, 0, 1];
+
+describe('transform', () => {
+  it('applyAlignment rotates then translates', () => {
+    const a: Alignment = { tx: 5, ty: 1, rot: Math.PI / 2 };
+    // (1,0) rotated 90° → (0,1), then +(5,1) → (5,2)
+    expect(close(applyAlignment(a, [1, 0]), [5, 2])).toBe(true);
+  });
+
+  it('projectSegments applies alignment then homography to every point', () => {
+    const segs: Segment[] = [{ kind: 'cut', points: [[0, 0], [10, 0]] }];
+    const a: Alignment = { tx: 2, ty: 3, rot: 0 };
+    const out = projectSegments(segs, a, IDENT);
+    expect(out[0]!.kind).toBe('cut');
+    expect(close(out[0]!.points[0]!, [2, 3])).toBe(true);
+    expect(close(out[0]!.points[1]!, [12, 3])).toBe(true);
+  });
+
+  it('imageToMachine is the inverse of the homography', () => {
+    const H: Mat3 = [2, 0, 10, 0, 2, 20, 0, 0, 1];
+    // machine (5,5) → image (20,30); invert should return (5,5)
+    expect(close(imageToMachine(H, [20, 30]), [5, 5])).toBe(true);
+  });
+
+  it('alignmentFromOrigin places work-origin at the given machine point', () => {
+    const a = alignmentFromOrigin([7, 9], 0);
+    expect(close(applyAlignment(a, [0, 0]), [7, 9])).toBe(true);
+  });
+});
diff --git a/src/geometry/transform.ts b/src/geometry/transform.ts
new file mode 100644
index 0000000..b3711ff
--- /dev/null
+++ b/src/geometry/transform.ts
@@ -0,0 +1,27 @@
+import type { Vec2, Mat3, Segment, Alignment } from '../types';
+import { applyHomography, invertMat3 } from './homography';
+
+/** Apply per-job alignment to a point: rotate by rot, then translate by (tx,ty). */
+export function applyAlignment(a: Alignment, p: Vec2): Vec2 {
+  const c = Math.cos(a.rot);
+  const s = Math.sin(a.rot);
+  return [a.tx + c * p[0] - s * p[1], a.ty + s * p[0] + c * p[1]];
+}
+
+/** Project work-coordinate segments to image pixels: work → (alignment) → machine → (H) → image. */
+export function projectSegments(segments: Segment[], a: Alignment, H: Mat3): Segment[] {
+  return segments.map((seg) => ({
+    kind: seg.kind,
+    points: seg.points.map((p) => applyHomography(H, applyAlignment(a, p))),
+  }));
+}
+
+/** Convert an image-pixel point to machine mm using the inverse homography. */
+export function imageToMachine(H: Mat3, imagePoint: Vec2): Vec2 {
+  return applyHomography(invertMat3(H), imagePoint);
+}
+
+/** Build an alignment that places the work origin (0,0) at the given machine point. */
+export function alignmentFromOrigin(machinePoint: Vec2, rot: number): Alignment {
+  return { tx: machinePoint[0], ty: machinePoint[1], rot };
+}