From 565baddfbf4e9f05ad0b83a5e619415f64b5f983 Mon Sep 17 00:00:00 2001
From: Samuel Prevost <samuel@infinic.com>
Date: Fri, 1 May 2026 00:12:08 +0200
Subject: [PATCH] feat(crop): rotate + crop step between deskew and measure

---
 src/App.vue                             |   4 +-
 src/components/CorrectedImageViewer.vue |  86 +++-
 src/components/CropViewer.vue           | 507 ++++++++++++++++++++++++
 src/components/DeskewViewer.vue         |   8 +-
 src/components/ImageUpload.vue          |  42 +-
 src/components/MeasureViewer.vue        | 160 +++++++-
 src/components/StepIndicator.vue        |   3 +-
 src/lib/crop-cache.ts                   |  49 +++
 src/lib/crop-transform.ts               |  90 +++++
 src/lib/upload-cache.ts                 |   8 +
 src/stores/app.ts                       |  29 +-
 src/types/index.ts                      |  40 +-
 12 files changed, 994 insertions(+), 32 deletions(-)
 create mode 100644 src/components/CropViewer.vue
 create mode 100644 src/lib/crop-cache.ts
 create mode 100644 src/lib/crop-transform.ts

diff --git a/src/App.vue b/src/App.vue
index 0877451..3517d7c 100644
--- a/src/App.vue
+++ b/src/App.vue
@@ -5,6 +5,7 @@ import ImageUpload from "@/components/ImageUpload.vue"
 import ExifViewer from "@/components/ExifViewer.vue"
 import DatumEditor from "@/components/DatumEditor.vue"
 import DeskewViewer from "@/components/DeskewViewer.vue"
+import CropViewer from "@/components/CropViewer.vue"
 import MeasureViewer from "@/components/MeasureViewer.vue"
 import ThemeToggle from "@/components/ThemeToggle.vue"
 import SkwikLogo from "@/components/SkwikLogo.vue"
@@ -76,7 +77,8 @@ const store = useAppStore()
             <ExifViewer v-else-if="store.currentStep === 2" />
             <DatumEditor v-else-if="store.currentStep === 3" />
             <DeskewViewer v-else-if="store.currentStep === 4" />
-            <MeasureViewer v-else-if="store.currentStep === 5" />
+            <CropViewer v-else-if="store.currentStep === 5" />
+            <MeasureViewer v-else-if="store.currentStep === 6" />
         </main>
 
         <!-- Footer is fixed to the bottom. On mobile we tuck the theme
diff --git a/src/components/CorrectedImageViewer.vue b/src/components/CorrectedImageViewer.vue
index 2f1dd52..cbca346 100644
--- a/src/components/CorrectedImageViewer.vue
+++ b/src/components/CorrectedImageViewer.vue
@@ -2,7 +2,7 @@
 import { ref, computed, onMounted, onUnmounted, watch } from "vue"
 import { useMediaQuery } from "@vueuse/core"
 import { nanoid } from "nanoid"
-import type { Point } from "@/types"
+import type { ImagePreTransform, Point } from "@/types"
 import type {
     LineMeasurement,
     RectMeasurement,
@@ -16,9 +16,37 @@ import { useAppStore } from "@/stores/app"
 import { loadMeasurements, saveMeasurements } from "@/lib/measurement-cache"
 import { loadZoom, saveZoom } from "@/lib/zoom-cache"
 
+// `imageTransform` is an optional pre-transform from
+// "deskewed-image space" (the original untransformed measurement
+// coordinate frame) to the bitmap space of the image actually shown
+// by `imageUrl`. Used by the Crop & Rotate step so measurements stay
+// anchored to the deskewed image while the user views a rotated +
+// cropped sub-bitmap. The mapping is:
+//
+//   measurement_pt → rotate around (srcW/2, srcH/2) by rotationDeg
+//                  → translate by (rotW/2, rotH/2)
+//                  → subtract (cropX, cropY) → bitmap_pt
+//
+// When omitted (or set to identity values), behaviour is unchanged.
+//
+// The viewer does NOT rewrite stored measurement coordinates when the
+// transform changes; it only adjusts the draw-time projection. This is
+// option (b) from the task brief and means changing the crop/rotation
+// never invalidates persisted measurements.
 const props = defineProps<{
     imageUrl: string
     scalePxPerMm: number
+    /** Optional pre-transform; identity when not supplied. */
+    imageTransform?: ImagePreTransform
+}>()
+
+// Emit when the measurement set changes (add / mutate / delete) so the
+// parent can refresh the recent-uploads gallery thumbnail. Fired
+// debounced (via the same `measurements` deep watcher that persists to
+// localStorage) so high-frequency interactions like dragging an
+// endpoint don't thrash the encoder.
+const emit = defineEmits<{
+    (event: "measurements-changed"): void
 }>()
 
 const isMobile = useMediaQuery("(max-width: 767px)")
@@ -356,25 +384,68 @@ function makeLiveCtx(): RenderCtx {
     }
 }
 
-function imgToCtx(pt: Point, t: RenderCtx): Point {
+// Project a measurement point from deskewed-image space into the
+// shown bitmap's coordinate frame. When no `imageTransform` is set we
+// short-circuit to the identity for a tiny perf win and to keep the
+// behaviour pixel-identical for the legacy non-cropped path.
+function imgPreTransform(pt: Point): Point {
+    const tr = props.imageTransform
+    if (!tr) return pt
+    const r = (tr.rotationDeg * Math.PI) / 180
+    const cx = tr.srcW / 2
+    const cy = tr.srcH / 2
+    const dx = pt.x - cx
+    const dy = pt.y - cy
+    const cos = Math.cos(r)
+    const sin = Math.sin(r)
+    const rx = dx * cos - dy * sin + tr.rotW / 2
+    const ry = dx * sin + dy * cos + tr.rotH / 2
+    return { x: rx - tr.cropX, y: ry - tr.cropY }
+}
+
+// Inverse of `imgPreTransform`: bitmap-space → deskewed-image space.
+// Used by `screenToImg` so pointer-driven placements / drags stay in
+// the canonical measurement coordinate frame.
+function imgPreTransformInverse(pt: Point): Point {
+    const tr = props.imageTransform
+    if (!tr) return pt
+    const r = (tr.rotationDeg * Math.PI) / 180
+    const cx = tr.srcW / 2
+    const cy = tr.srcH / 2
+    const rx = pt.x + tr.cropX
+    const ry = pt.y + tr.cropY
+    const dx = rx - tr.rotW / 2
+    const dy = ry - tr.rotH / 2
+    const cos = Math.cos(r)
+    const sin = Math.sin(r)
     return {
-        x: pt.x * t.scale + t.offsetX,
-        y: pt.y * t.scale + t.offsetY,
+        x: dx * cos + dy * sin + cx,
+        y: -dx * sin + dy * cos + cy,
+    }
+}
+
+function imgToCtx(pt: Point, t: RenderCtx): Point {
+    const b = imgPreTransform(pt)
+    return {
+        x: b.x * t.scale + t.offsetX,
+        y: b.y * t.scale + t.offsetY,
     }
 }
 
 function imgToScreen(pt: Point): Point {
+    const b = imgPreTransform(pt)
     return {
-        x: pt.x * viewScale.value + viewOffsetX.value,
-        y: pt.y * viewScale.value + viewOffsetY.value,
+        x: b.x * viewScale.value + viewOffsetX.value,
+        y: b.y * viewScale.value + viewOffsetY.value,
     }
 }
 
 function screenToImg(sx: number, sy: number): Point {
-    return {
+    const b: Point = {
         x: (sx - viewOffsetX.value) / viewScale.value,
         y: (sy - viewOffsetY.value) / viewScale.value,
     }
+    return imgPreTransformInverse(b)
 }
 
 // If `snapToAngle` is on, rotate `to` around `from` to the nearest 45°
@@ -2324,6 +2395,7 @@ watch(
         if (store.fileHash) {
             saveMeasurements(store.fileHash, next)
         }
+        emit("measurements-changed")
     },
     { deep: true },
 )
diff --git a/src/components/CropViewer.vue b/src/components/CropViewer.vue
new file mode 100644
index 0000000..ec3ee9f
--- /dev/null
+++ b/src/components/CropViewer.vue
@@ -0,0 +1,507 @@
+<script setup lang="ts">
+import { ref, computed, onMounted, onUnmounted, watch } from "vue"
+import { useAppStore } from "@/stores/app"
+import { Button } from "@/components/ui/button"
+import {
+    Card,
+    CardContent,
+    CardHeader,
+    CardTitle,
+} from "@/components/ui/card"
+import { saveCropRotate, loadCropRotate } from "@/lib/crop-cache"
+import { rotatedBboxSize } from "@/lib/crop-transform"
+import type { Point } from "@/types"
+
+// Crop & Rotate step.
+//   * The user picks an arbitrary rotation in degrees (-180..180).
+//   * Rotation is applied first, around the deskewed image's centre.
+//     The rotated bitmap's axis-aligned bounding box is the canvas the
+//     crop rectangle lives in.
+//   * The crop rectangle is then dragged via 8 handles (4 corners + 4
+//     edge midpoints). It's stored as fractions of the rotated bbox so
+//     the same crop survives a re-deskew at a different output px/mm.
+//
+// Persistence: identical pattern to measurement-cache.ts, keyed by
+// `store.fileHash`. We write to localStorage on every change.
+
+const store = useAppStore()
+
+const containerRef = ref<HTMLDivElement | null>(null)
+const canvasRef = ref<HTMLCanvasElement | null>(null)
+const overlayRef = ref<HTMLCanvasElement | null>(null)
+
+const img = ref<HTMLImageElement | null>(null)
+const imgUrl = ref<string | null>(null)
+
+// Rotation in degrees. Crop fractions of the rotated bbox.
+const rotationDeg = ref(0)
+const cropLeft = ref(0)
+const cropTop = ref(0)
+const cropRight = ref(1)
+const cropBottom = ref(1)
+
+// Live-fit transform from rotated-bbox space → screen canvas pixels.
+// Recomputed on resize / rotation change so the user always sees the
+// whole bbox + a bit of breathing room.
+const fitScale = ref(1)
+const fitOffsetX = ref(0)
+const fitOffsetY = ref(0)
+
+const HANDLE_HIT_PX = 14
+
+const rotBbox = computed(() => {
+    const i = img.value
+    if (!i) return { rotW: 1, rotH: 1 }
+    return rotatedBboxSize(i.naturalWidth, i.naturalHeight, rotationDeg.value)
+})
+
+function persist() {
+    if (!store.fileHash) return
+    const state = {
+        rotationDeg: rotationDeg.value,
+        crop: {
+            left: cropLeft.value,
+            top: cropTop.value,
+            right: cropRight.value,
+            bottom: cropBottom.value,
+        },
+    }
+    store.setCropRotate(state)
+    saveCropRotate(store.fileHash, state)
+}
+
+function loadImage(url: string) {
+    const el = new Image()
+    el.onload = () => {
+        img.value = el
+        fitToContainer()
+        redraw()
+    }
+    el.src = url
+}
+
+function fitToContainer() {
+    const c = containerRef.value
+    const i = img.value
+    if (!c || !i) return
+    const cw = c.clientWidth
+    const ch = c.clientHeight
+    if (canvasRef.value) {
+        canvasRef.value.width = cw
+        canvasRef.value.height = ch
+    }
+    if (overlayRef.value) {
+        overlayRef.value.width = cw
+        overlayRef.value.height = ch
+    }
+    const { rotW, rotH } = rotBbox.value
+    const fit = Math.min(cw / rotW, ch / rotH) * 0.9
+    fitScale.value = fit
+    fitOffsetX.value = (cw - rotW * fit) / 2
+    fitOffsetY.value = (ch - rotH * fit) / 2
+}
+
+function rotatedToScreen(p: Point): Point {
+    return {
+        x: p.x * fitScale.value + fitOffsetX.value,
+        y: p.y * fitScale.value + fitOffsetY.value,
+    }
+}
+
+function screenToRotated(sx: number, sy: number): Point {
+    return {
+        x: (sx - fitOffsetX.value) / fitScale.value,
+        y: (sy - fitOffsetY.value) / fitScale.value,
+    }
+}
+
+function redraw() {
+    drawImage()
+    drawOverlay()
+}
+
+function drawImage() {
+    const canvas = canvasRef.value
+    const i = img.value
+    if (!canvas || !i) return
+    const ctx = canvas.getContext("2d")
+    if (!ctx) return
+    ctx.clearRect(0, 0, canvas.width, canvas.height)
+    const { rotW, rotH } = rotBbox.value
+
+    ctx.save()
+    // Place rotated-bbox origin at fit offset, then scale.
+    ctx.translate(fitOffsetX.value, fitOffsetY.value)
+    ctx.scale(fitScale.value, fitScale.value)
+    // Rotation around the bbox centre — cancels back to deskewed-image
+    // axis-aligned drawing offset by (rotW-srcW)/2 etc.
+    ctx.translate(rotW / 2, rotH / 2)
+    ctx.rotate((rotationDeg.value * Math.PI) / 180)
+    ctx.drawImage(i, -i.naturalWidth / 2, -i.naturalHeight / 2)
+    ctx.restore()
+}
+
+function cropRectScreen(): { x: number; y: number; w: number; h: number } {
+    const { rotW, rotH } = rotBbox.value
+    const tl = rotatedToScreen({ x: cropLeft.value * rotW, y: cropTop.value * rotH })
+    const br = rotatedToScreen({ x: cropRight.value * rotW, y: cropBottom.value * rotH })
+    return { x: tl.x, y: tl.y, w: br.x - tl.x, h: br.y - tl.y }
+}
+
+function drawOverlay() {
+    const canvas = overlayRef.value
+    const i = img.value
+    if (!canvas || !i) return
+    const ctx = canvas.getContext("2d")
+    if (!ctx) return
+    ctx.clearRect(0, 0, canvas.width, canvas.height)
+
+    const r = cropRectScreen()
+
+    // Dim everything outside the crop rect with a 50% black overlay.
+    // Draw a full-canvas dark fill with a punched-out hole — fillRect +
+    // even-odd fill is overkill; clipping with two rects is simpler.
+    ctx.save()
+    ctx.fillStyle = "rgba(0,0,0,0.55)"
+    ctx.fillRect(0, 0, canvas.width, r.y)
+    ctx.fillRect(0, r.y + r.h, canvas.width, canvas.height - (r.y + r.h))
+    ctx.fillRect(0, r.y, r.x, r.h)
+    ctx.fillRect(r.x + r.w, r.y, canvas.width - (r.x + r.w), r.h)
+    ctx.restore()
+
+    // Crop rectangle outline.
+    ctx.save()
+    ctx.strokeStyle = "#fff"
+    ctx.lineWidth = 1.5
+    ctx.setLineDash([6, 4])
+    ctx.strokeRect(r.x, r.y, r.w, r.h)
+    ctx.restore()
+
+    // Rule-of-thirds guides — light grey, no dash.
+    ctx.save()
+    ctx.strokeStyle = "rgba(255,255,255,0.25)"
+    ctx.lineWidth = 1
+    for (let k = 1; k < 3; k++) {
+        const x = r.x + (r.w * k) / 3
+        ctx.beginPath()
+        ctx.moveTo(x, r.y)
+        ctx.lineTo(x, r.y + r.h)
+        ctx.stroke()
+        const y = r.y + (r.h * k) / 3
+        ctx.beginPath()
+        ctx.moveTo(r.x, y)
+        ctx.lineTo(r.x + r.w, y)
+        ctx.stroke()
+    }
+    ctx.restore()
+
+    // Handle dots: 4 corners + 4 edge midpoints.
+    const handles = handlePositionsScreen()
+    ctx.save()
+    ctx.fillStyle = "#fff"
+    ctx.strokeStyle = "rgba(0,0,0,0.5)"
+    ctx.lineWidth = 1
+    for (const h of handles) {
+        ctx.beginPath()
+        ctx.arc(h.pt.x, h.pt.y, 5, 0, Math.PI * 2)
+        ctx.fill()
+        ctx.stroke()
+    }
+    ctx.restore()
+}
+
+type HandleKey =
+    | "tl" | "tr" | "br" | "bl"
+    | "t" | "r" | "b" | "l"
+
+function handlePositionsScreen(): { key: HandleKey; pt: Point }[] {
+    const r = cropRectScreen()
+    const cx = r.x + r.w / 2
+    const cy = r.y + r.h / 2
+    return [
+        { key: "tl", pt: { x: r.x, y: r.y } },
+        { key: "tr", pt: { x: r.x + r.w, y: r.y } },
+        { key: "br", pt: { x: r.x + r.w, y: r.y + r.h } },
+        { key: "bl", pt: { x: r.x, y: r.y + r.h } },
+        { key: "t", pt: { x: cx, y: r.y } },
+        { key: "r", pt: { x: r.x + r.w, y: cy } },
+        { key: "b", pt: { x: cx, y: r.y + r.h } },
+        { key: "l", pt: { x: r.x, y: cy } },
+    ]
+}
+
+interface DragState {
+    handle: HandleKey | "body"
+    /** Crop in fractions at drag start, used as the base for delta updates. */
+    startLeft: number
+    startTop: number
+    startRight: number
+    startBottom: number
+    /** Pointer position in rotated-bbox space at drag start. */
+    startRot: Point
+}
+let drag: DragState | null = null
+
+function pickHandle(sx: number, sy: number): HandleKey | null {
+    for (const h of handlePositionsScreen()) {
+        if (Math.hypot(sx - h.pt.x, sy - h.pt.y) <= HANDLE_HIT_PX) return h.key
+    }
+    return null
+}
+
+function onPointerDown(ev: PointerEvent) {
+    const canvas = overlayRef.value
+    if (!canvas) return
+    const rect = canvas.getBoundingClientRect()
+    const sx = ev.clientX - rect.left
+    const sy = ev.clientY - rect.top
+    const handle = pickHandle(sx, sy)
+    const r = cropRectScreen()
+    const insideBody =
+        handle === null &&
+        sx >= r.x && sx <= r.x + r.w &&
+        sy >= r.y && sy <= r.y + r.h
+    if (!handle && !insideBody) return
+    canvas.setPointerCapture(ev.pointerId)
+    drag = {
+        handle: handle ?? "body",
+        startLeft: cropLeft.value,
+        startTop: cropTop.value,
+        startRight: cropRight.value,
+        startBottom: cropBottom.value,
+        startRot: screenToRotated(sx, sy),
+    }
+}
+
+function onPointerMove(ev: PointerEvent) {
+    if (!drag) return
+    const canvas = overlayRef.value
+    if (!canvas) return
+    const rect = canvas.getBoundingClientRect()
+    const sx = ev.clientX - rect.left
+    const sy = ev.clientY - rect.top
+    const cur = screenToRotated(sx, sy)
+    const { rotW, rotH } = rotBbox.value
+    const dx = (cur.x - drag.startRot.x) / rotW
+    const dy = (cur.y - drag.startRot.y) / rotH
+
+    const minSize = 0.05 // 5% minimum width/height to keep the crop usable.
+    let l = drag.startLeft
+    let t = drag.startTop
+    let r2 = drag.startRight
+    let b = drag.startBottom
+
+    const k = drag.handle
+    if (k === "body") {
+        const w = drag.startRight - drag.startLeft
+        const h = drag.startBottom - drag.startTop
+        let nl = drag.startLeft + dx
+        let nt = drag.startTop + dy
+        nl = Math.min(Math.max(nl, 0), 1 - w)
+        nt = Math.min(Math.max(nt, 0), 1 - h)
+        l = nl
+        t = nt
+        r2 = nl + w
+        b = nt + h
+    } else {
+        if (k === "tl" || k === "l" || k === "bl") {
+            l = Math.min(Math.max(drag.startLeft + dx, 0), drag.startRight - minSize)
+        }
+        if (k === "tr" || k === "r" || k === "br") {
+            r2 = Math.min(Math.max(drag.startRight + dx, drag.startLeft + minSize), 1)
+        }
+        if (k === "tl" || k === "t" || k === "tr") {
+            t = Math.min(Math.max(drag.startTop + dy, 0), drag.startBottom - minSize)
+        }
+        if (k === "bl" || k === "b" || k === "br") {
+            b = Math.min(Math.max(drag.startBottom + dy, drag.startTop + minSize), 1)
+        }
+    }
+
+    cropLeft.value = l
+    cropTop.value = t
+    cropRight.value = r2
+    cropBottom.value = b
+    drawOverlay()
+}
+
+function onPointerUp(ev: PointerEvent) {
+    const canvas = overlayRef.value
+    if (canvas?.hasPointerCapture(ev.pointerId)) {
+        canvas.releasePointerCapture(ev.pointerId)
+    }
+    if (drag) {
+        drag = null
+        persist()
+    }
+}
+
+function resetCrop() {
+    cropLeft.value = 0
+    cropTop.value = 0
+    cropRight.value = 1
+    cropBottom.value = 1
+    rotationDeg.value = 0
+    persist()
+    fitToContainer()
+    redraw()
+}
+
+function onRotationInput(v: number) {
+    if (!Number.isFinite(v)) return
+    // Clamp to [-180, 180] and normalise so the slider/spinbox can't escape.
+    const clamped = Math.min(Math.max(v, -180), 180)
+    rotationDeg.value = clamped
+    fitToContainer()
+    redraw()
+    persist()
+}
+
+function rotateBy(delta: number) {
+    onRotationInput(rotationDeg.value + delta)
+}
+
+let resizeObs: ResizeObserver | null = null
+
+onMounted(() => {
+    if (!store.deskewResult) {
+        store.goToStep(4)
+        return
+    }
+    // Pre-fill from the store / cache so the user's previous crop &
+    // rotation come back when they re-enter the step.
+    const cached = store.fileHash ? loadCropRotate(store.fileHash) : null
+    const seed = cached ?? store.cropRotate
+    rotationDeg.value = seed.rotationDeg
+    cropLeft.value = seed.crop.left
+    cropTop.value = seed.crop.top
+    cropRight.value = seed.crop.right
+    cropBottom.value = seed.crop.bottom
+    if (cached) store.setCropRotate(cached)
+
+    imgUrl.value = URL.createObjectURL(store.deskewResult.correctedImageBlob)
+    loadImage(imgUrl.value)
+
+    if (containerRef.value) {
+        resizeObs = new ResizeObserver(() => {
+            fitToContainer()
+            redraw()
+        })
+        resizeObs.observe(containerRef.value)
+    }
+})
+
+onUnmounted(() => {
+    resizeObs?.disconnect()
+    if (imgUrl.value) URL.revokeObjectURL(imgUrl.value)
+})
+
+watch(rotationDeg, () => {
+    fitToContainer()
+    redraw()
+})
+
+watch([cropLeft, cropTop, cropRight, cropBottom], () => {
+    drawOverlay()
+})
+
+function next() {
+    persist()
+    store.goToStep(6)
+}
+</script>
+
+<template>
+    <div class="space-y-4">
+        <div class="flex flex-wrap items-center justify-between gap-2">
+            <div>
+                <h2 class="text-xl font-semibold">Crop &amp; Rotate</h2>
+                <p class="text-sm text-muted-foreground">
+                    Optionally rotate and crop the deskewed image before
+                    measuring.
+                </p>
+            </div>
+            <div class="flex shrink-0 gap-2">
+                <Button variant="outline" @click="store.goToStep(4)">Back</Button>
+                <Button variant="outline" @click="resetCrop">Reset</Button>
+                <Button @click="next">Next: Measure</Button>
+            </div>
+        </div>
+
+        <Card>
+            <CardHeader class="space-y-2">
+                <CardTitle class="text-base">Rotation</CardTitle>
+                <div class="flex flex-wrap items-center gap-3">
+                    <input
+                        type="range"
+                        min="-180"
+                        max="180"
+                        step="0.1"
+                        :value="rotationDeg"
+                        class="h-2 w-full max-w-md flex-1 accent-primary"
+                        @input="(e) => onRotationInput(Number((e.target as HTMLInputElement).value))"
+                    />
+                    <div class="flex items-center gap-1">
+                        <Button
+                            variant="outline"
+                            size="sm"
+                            class="h-8 px-2"
+                            @click="rotateBy(-90)"
+                            >-90°</Button
+                        >
+                        <Button
+                            variant="outline"
+                            size="sm"
+                            class="h-8 px-2"
+                            @click="rotateBy(-1)"
+                            >-1°</Button
+                        >
+                        <input
+                            type="number"
+                            min="-180"
+                            max="180"
+                            step="0.1"
+                            :value="rotationDeg.toFixed(1)"
+                            class="h-8 w-20 rounded-md border border-input bg-background px-2 text-sm"
+                            @input="(e) => onRotationInput(Number((e.target as HTMLInputElement).value))"
+                        />
+                        <span class="text-sm text-muted-foreground">°</span>
+                        <Button
+                            variant="outline"
+                            size="sm"
+                            class="h-8 px-2"
+                            @click="rotateBy(1)"
+                            >+1°</Button
+                        >
+                        <Button
+                            variant="outline"
+                            size="sm"
+                            class="h-8 px-2"
+                            @click="rotateBy(90)"
+                            >+90°</Button
+                        >
+                    </div>
+                </div>
+            </CardHeader>
+            <CardContent>
+                <div
+                    ref="containerRef"
+                    class="relative h-[calc(100vh-22rem)] min-h-[320px] w-full overflow-hidden rounded-md bg-muted"
+                >
+                    <canvas
+                        ref="canvasRef"
+                        class="absolute inset-0"
+                    />
+                    <canvas
+                        ref="overlayRef"
+                        class="absolute inset-0 touch-none"
+                        @pointerdown="onPointerDown"
+                        @pointermove="onPointerMove"
+                        @pointerup="onPointerUp"
+                        @pointercancel="onPointerUp"
+                    />
+                </div>
+            </CardContent>
+        </Card>
+    </div>
+</template>
diff --git a/src/components/DeskewViewer.vue b/src/components/DeskewViewer.vue
index 04cce22..e6403c3 100644
--- a/src/components/DeskewViewer.vue
+++ b/src/components/DeskewViewer.vue
@@ -301,7 +301,7 @@ async function runDeskew() {
                 <Button
                     :disabled="!store.canProceedToStep5"
                     @click="store.goToStep(5)"
-                    >Next: Measure</Button
+                    >Next: Crop</Button
                 >
             </div>
         </div>
@@ -738,8 +738,8 @@ async function runDeskew() {
                         >Deskewed Preview</CardTitle
                     >
                     <CardDescription>
-                        Continue to <strong>Measure</strong> to add
-                        annotations and download.
+                        Continue to <strong>Crop</strong> to rotate and
+                        crop the result before measuring.
                     </CardDescription>
                 </CardHeader>
                 <CardContent>
@@ -757,7 +757,7 @@ async function runDeskew() {
 
             <div class="flex justify-center pb-8">
                 <Button size="lg" @click="store.goToStep(5)">
-                    Continue to Measure
+                    Continue to Crop
                     <svg
                         xmlns="http://www.w3.org/2000/svg"
                         width="18"
diff --git a/src/components/ImageUpload.vue b/src/components/ImageUpload.vue
index fa4652a..640e84f 100644
--- a/src/components/ImageUpload.vue
+++ b/src/components/ImageUpload.vue
@@ -9,6 +9,10 @@ import {
     clearCache as clearMeasurementCache,
     loadMeasurements,
 } from "@/lib/measurement-cache"
+import {
+    clearCache as clearCropCache,
+    loadCropRotate,
+} from "@/lib/crop-cache"
 import {
     saveUpload,
     loadUpload,
@@ -82,11 +86,26 @@ async function refreshRecentUploads() {
             }
         }
         // Mint preview URLs for every entry; we keep them alive for the
-        // lifetime of this page mount (revoked in onUnmounted).
+        // lifetime of this page mount (revoked in onUnmounted). Prefer
+        // the annotated thumbnail (rotation + crop + measurements baked
+        // in) generated by the Measure step; fall back to the deskew
+        // result, then the raw original. Existing URL is replaced when
+        // the preview blob has changed since the last refresh.
+        const prevById = new Map<string, Blob>()
+        for (const u of recentUploads.value) {
+            const prev = u.previewBlob ?? u.correctedBlob ?? u.originalBlob
+            prevById.set(u.hash, prev)
+        }
         for (const u of all) {
+            const next = u.previewBlob ?? u.correctedBlob ?? u.originalBlob
+            const prev = prevById.get(u.hash)
+            const existing = recentUrls.value.get(u.hash)
+            if (existing && prev !== next) {
+                URL.revokeObjectURL(existing)
+                recentUrls.value.delete(u.hash)
+            }
             if (!recentUrls.value.has(u.hash)) {
-                const preview = u.correctedBlob ?? u.originalBlob
-                recentUrls.value.set(u.hash, URL.createObjectURL(preview))
+                recentUrls.value.set(u.hash, URL.createObjectURL(next))
             }
         }
         recentUploads.value = all
@@ -108,6 +127,7 @@ function handleClearCacheClick() {
         clearCache()
         clearMeasurementCache()
         clearZoomCache()
+        clearCropCache()
         // IndexedDB clear is async but the UI doesn't depend on its
         // completion — fire and forget, then reload the gallery.
         void clearUploads().then(() => refreshRecentUploads())
@@ -165,6 +185,9 @@ async function restoreUpload(hash: string) {
 
         const cachedDatums = loadDatums(hash) ?? []
         const cachedMeasurements = loadMeasurements(hash) ?? []
+        const cachedCropRotate = loadCropRotate(hash)
+        if (cachedCropRotate) store.setCropRotate(cachedCropRotate)
+        else store.resetCropRotate()
 
         store.setFileHash(hash)
         store.setImage(convertedFile, image)
@@ -200,8 +223,10 @@ async function restoreUpload(hash: string) {
         }
 
         // Bump max step so the indicator surfaces every prior step as
-        // navigable, just like a freshly-completed run would.
-        store.goToStep(5)
+        // navigable, just like a freshly-completed run would. Crop
+        // (step 5) is reachable from the indicator if the user wants to
+        // revisit it.
+        store.goToStep(6)
     } catch (e) {
         error.value =
             e instanceof Error ? e.message : "Failed to reopen image"
@@ -231,6 +256,12 @@ async function handleFile(file: File) {
         const hash = await hashFile(file)
         store.setFileHash(hash)
 
+        // Hydrate any saved rotation/crop for this file so re-uploading
+        // the same image keeps the user's prior framing.
+        const cachedCropRotate = loadCropRotate(hash)
+        if (cachedCropRotate) store.setCropRotate(cachedCropRotate)
+        else store.resetCropRotate()
+
         const cached = loadDatums(hash)
         if (cached && cached.length > 0) {
             store.datums = cached
@@ -257,6 +288,7 @@ async function handleFile(file: File) {
             correctedBlob: existing?.correctedBlob,
             diagnostics: existing?.diagnostics,
             scalePxPerMm: existing?.scalePxPerMm,
+            previewBlob: existing?.previewBlob,
         }).catch(() => {
             // IndexedDB unavailable or quota exceeded — non-fatal,
             // gallery just won't include this upload.
diff --git a/src/components/MeasureViewer.vue b/src/components/MeasureViewer.vue
index bedf58e..9b1245d 100644
--- a/src/components/MeasureViewer.vue
+++ b/src/components/MeasureViewer.vue
@@ -15,6 +15,7 @@ import {
     CardTitle,
 } from "@/components/ui/card"
 import CorrectedImageViewer from "@/components/CorrectedImageViewer.vue"
+import type { ImagePreTransform } from "@/types"
 // `defineExpose` in CorrectedImageViewer makes these methods available on
 // the template ref, but Vue's ComponentPublicInstance type doesn't surface
 // them automatically — we type the ref explicitly so the call is checked.
@@ -25,13 +26,144 @@ type CorrectedImageViewerRef = InstanceType<typeof CorrectedImageViewer> & {
     }) => Promise<Blob>
 }
 import { loadSettings, saveSettings } from "@/lib/settings-cache"
+import {
+    rotatedBboxSize,
+    cropPixels,
+    renderRotatedCropped,
+} from "@/lib/crop-transform"
+import { patchUpload } from "@/lib/upload-cache"
 
 const store = useAppStore()
 const resultUrl = ref<string | null>(null)
+const imageTransform = ref<ImagePreTransform | null>(null)
 const viewerRef = ref<CorrectedImageViewerRef | null>(null)
 const error = ref("")
 const includeScaleBar = ref(false)
 
+// Debounce timer for the recent-uploads thumbnail. Measurement
+// dragging fires the watcher dozens of times a second; we only want
+// one regen per ~500 ms idle period.
+let previewTimer: ReturnType<typeof setTimeout> | null = null
+const PREVIEW_DEBOUNCE_MS = 500
+const PREVIEW_MAX_WIDTH = 400
+
+function downscaleToPreview(srcBlob: Blob): Promise<Blob> {
+    return new Promise((resolve, reject) => {
+        const url = URL.createObjectURL(srcBlob)
+        const el = new Image()
+        el.onload = () => {
+            try {
+                const w = el.naturalWidth
+                const h = el.naturalHeight
+                if (w <= 0 || h <= 0) {
+                    reject(new Error("Empty preview source"))
+                    return
+                }
+                const ratio = Math.min(1, PREVIEW_MAX_WIDTH / w)
+                const tw = Math.max(1, Math.round(w * ratio))
+                const th = Math.max(1, Math.round(h * ratio))
+                const c = document.createElement("canvas")
+                c.width = tw
+                c.height = th
+                const ctx = c.getContext("2d")
+                if (!ctx) {
+                    reject(new Error("No 2D context"))
+                    return
+                }
+                ctx.drawImage(el, 0, 0, tw, th)
+                c.toBlob((b) => {
+                    if (b) resolve(b)
+                    else reject(new Error("preview toBlob failed"))
+                }, "image/png")
+            } finally {
+                URL.revokeObjectURL(url)
+            }
+        }
+        el.onerror = () => {
+            URL.revokeObjectURL(url)
+            reject(new Error("preview load failed"))
+        }
+        el.src = url
+    })
+}
+
+async function regeneratePreview() {
+    const viewer = viewerRef.value
+    const hash = store.fileHash
+    if (!viewer || !hash) return
+    try {
+        const annotated = await viewer.exportWithMeasurements({
+            scope: "full",
+            includeScaleBar: false,
+        })
+        const preview = await downscaleToPreview(annotated)
+        await patchUpload(hash, { previewBlob: preview })
+    } catch {
+        // Preview is a nice-to-have — never block the user on a failure.
+    }
+}
+
+function schedulePreview() {
+    if (previewTimer) clearTimeout(previewTimer)
+    previewTimer = setTimeout(() => {
+        previewTimer = null
+        void regeneratePreview()
+    }, PREVIEW_DEBOUNCE_MS)
+}
+
+// Render the rotation + crop applied to the deskew result and surface
+// it as an object URL + transform for CorrectedImageViewer. We keep
+// the stored measurements in pre-rotate, pre-crop deskewed-image
+// space, and pass a pre-transform so the viewer can draw them on the
+// cropped bitmap correctly. Recomputed on entry to Measure.
+async function buildTransformedSource() {
+    const result = store.deskewResult
+    if (!result) return
+    const url = URL.createObjectURL(result.correctedImageBlob)
+    try {
+        const image = await new Promise<HTMLImageElement>(
+            (resolve, reject) => {
+                const el = new Image()
+                el.onload = () => {
+                    resolve(el)
+                }
+                el.onerror = () => {
+                    reject(new Error("Failed to load deskewed image"))
+                }
+                el.src = url
+            },
+        )
+        const state = store.cropRotate
+        const rot = rotatedBboxSize(
+            image.naturalWidth,
+            image.naturalHeight,
+            state.rotationDeg,
+        )
+        const px = cropPixels(state, rot)
+        const out = renderRotatedCropped(image, state)
+        const blob = await new Promise<Blob>((resolve, reject) => {
+            out.toBlob((b) => {
+                if (b) resolve(b)
+                else reject(new Error("Crop render failed"))
+            }, "image/png")
+        })
+        if (resultUrl.value) URL.revokeObjectURL(resultUrl.value)
+        resultUrl.value = URL.createObjectURL(blob)
+        imageTransform.value = {
+            rotationDeg: state.rotationDeg,
+            srcW: image.naturalWidth,
+            srcH: image.naturalHeight,
+            rotW: rot.rotW,
+            rotH: rot.rotH,
+            cropX: px.cropX,
+            cropY: px.cropY,
+        }
+        schedulePreview()
+    } finally {
+        URL.revokeObjectURL(url)
+    }
+}
+
 onMounted(() => {
     const cached = loadSettings()
     if (cached) {
@@ -39,9 +171,7 @@ onMounted(() => {
     }
 
     if (store.deskewResult) {
-        resultUrl.value = URL.createObjectURL(
-            store.deskewResult.correctedImageBlob,
-        )
+        void buildTransformedSource()
     } else {
         // No result yet — bounce back to Deskew. Should never happen via
         // normal navigation since the Next button is gated, but if a user
@@ -53,6 +183,10 @@ onMounted(() => {
 
 onUnmounted(() => {
     if (resultUrl.value) URL.revokeObjectURL(resultUrl.value)
+    if (previewTimer) {
+        clearTimeout(previewTimer)
+        previewTimer = null
+    }
 })
 
 watch(includeScaleBar, () => {
@@ -138,14 +272,16 @@ function addScaleBar(image: HTMLImageElement): Promise<Blob> {
 }
 
 async function download() {
-    if (!store.deskewResult) return
+    if (!store.deskewResult || !resultUrl.value) return
 
-    let blob: Blob = store.deskewResult.correctedImageBlob
+    // Download the post-crop, post-rotation bitmap so the file matches
+    // what the user has been looking at in the Measure step. When the
+    // user kept the defaults (no rotation, full-image crop) this is
+    // bit-identical to the original deskew blob (modulo PNG re-encode).
+    let blob: Blob = await fetch(resultUrl.value).then((r) => r.blob())
 
     if (includeScaleBar.value) {
-        const imgUrl = URL.createObjectURL(
-            store.deskewResult.correctedImageBlob,
-        )
+        const imgUrl = URL.createObjectURL(blob)
         try {
             const image = await new Promise<HTMLImageElement>(
                 (resolve, reject) => {
@@ -227,9 +363,9 @@ async function downloadMeasured(scope: "full" | "view") {
                 variant="ghost"
                 size="icon"
                 class="shrink-0"
-                aria-label="Back to Deskew"
-                title="Back to Deskew"
-                @click="store.goToStep(4)"
+                aria-label="Back to Crop"
+                title="Back to Crop"
+                @click="store.goToStep(5)"
             >
                 <svg
                     xmlns="http://www.w3.org/2000/svg"
@@ -395,6 +531,8 @@ async function downloadMeasured(scope: "full" | "view") {
                     ref="viewerRef"
                     :image-url="resultUrl"
                     :scale-px-per-mm="store.scalePxPerMm"
+                    :image-transform="imageTransform ?? undefined"
+                    @measurements-changed="schedulePreview"
                 />
             </CardContent>
         </Card>
diff --git a/src/components/StepIndicator.vue b/src/components/StepIndicator.vue
index ae098f6..e73e434 100644
--- a/src/components/StepIndicator.vue
+++ b/src/components/StepIndicator.vue
@@ -10,7 +10,8 @@ const steps: { num: AppStep; label: string }[] = [
     { num: 2, label: "EXIF" },
     { num: 3, label: "Datums" },
     { num: 4, label: "Deskew" },
-    { num: 5, label: "Measure" },
+    { num: 5, label: "Crop" },
+    { num: 6, label: "Measure" },
 ]
 
 function isReachable(num: AppStep): boolean {
diff --git a/src/lib/crop-cache.ts b/src/lib/crop-cache.ts
new file mode 100644
index 0000000..d196fcc
--- /dev/null
+++ b/src/lib/crop-cache.ts
@@ -0,0 +1,49 @@
+import type { CropRotateState } from "@/types"
+
+// Per-file-hash storage of the user's rotation + crop choices for the
+// Crop & Rotate step. Mirrors the shape of `measurement-cache.ts`. We
+// store fractional crop bounds (0..1) of the rotated image so the same
+// crop applies cleanly after a re-deskew at a different output px/mm.
+
+const KEY_PREFIX = "skwik-crop-"
+
+export function saveCropRotate(hash: string, state: CropRotateState): void {
+    try {
+        localStorage.setItem(KEY_PREFIX + hash, JSON.stringify(state))
+    } catch {
+        // localStorage full or unavailable — silently ignore
+    }
+}
+
+export function loadCropRotate(hash: string): CropRotateState | null {
+    try {
+        const raw = localStorage.getItem(KEY_PREFIX + hash)
+        if (!raw) return null
+        const parsed = JSON.parse(raw) as Partial<CropRotateState> | null
+        if (!parsed || typeof parsed !== "object") return null
+        const rot = parsed.rotationDeg
+        const c = parsed.crop
+        if (
+            typeof rot !== "number" ||
+            !c ||
+            typeof c.left !== "number" ||
+            typeof c.top !== "number" ||
+            typeof c.right !== "number" ||
+            typeof c.bottom !== "number"
+        ) {
+            return null
+        }
+        return { rotationDeg: rot, crop: { left: c.left, top: c.top, right: c.right, bottom: c.bottom } }
+    } catch {
+        return null
+    }
+}
+
+export function clearCache(): void {
+    const toRemove: string[] = []
+    for (let i = 0; i < localStorage.length; i++) {
+        const key = localStorage.key(i)
+        if (key?.startsWith(KEY_PREFIX)) toRemove.push(key)
+    }
+    for (const key of toRemove) localStorage.removeItem(key)
+}
diff --git a/src/lib/crop-transform.ts b/src/lib/crop-transform.ts
new file mode 100644
index 0000000..acb3f00
--- /dev/null
+++ b/src/lib/crop-transform.ts
@@ -0,0 +1,90 @@
+import type { CropRotateState } from "@/types"
+
+// Geometry helpers for the Crop & Rotate step. The pipeline:
+//   1. Start in "deskewed image space" (the bitmap produced by the
+//      solver, dimensions deskewW × deskewH).
+//   2. Rotate around the deskewed image's centre by `rotationDeg`.
+//      The rotated bitmap is the axis-aligned bounding box of the
+//      rotated rectangle (rotW × rotH); the original corners get
+//      translated so the bbox starts at (0, 0).
+//   3. Crop a sub-rectangle of that rotated bitmap, defined by
+//      fractions `crop.left/top/right/bottom` of its size.
+// Measurements live in deskewed-image space; the renderer composes this
+// transform on top of the live pan/zoom to project them onto the cropped
+// bitmap, which is what the user is actually looking at.
+
+interface RotatedSize {
+    rotW: number
+    rotH: number
+}
+
+/** Bounding box dimensions of `srcW × srcH` rotated by `rotationDeg`
+ *  around its centre. */
+export function rotatedBboxSize(
+    srcW: number,
+    srcH: number,
+    rotationDeg: number,
+): RotatedSize {
+    const r = (rotationDeg * Math.PI) / 180
+    const c = Math.abs(Math.cos(r))
+    const s = Math.abs(Math.sin(r))
+    return {
+        rotW: srcW * c + srcH * s,
+        rotH: srcW * s + srcH * c,
+    }
+}
+
+interface CropPixels {
+    cropX: number
+    cropY: number
+    cropW: number
+    cropH: number
+}
+
+/** Pixel-space crop rect on the rotated bitmap, derived from the
+ *  fractional crop. Clamped to the rotated bbox so a stale fraction
+ *  never produces a negative-size crop. */
+export function cropPixels(
+    state: CropRotateState,
+    rot: RotatedSize,
+): CropPixels {
+    const left = Math.min(Math.max(state.crop.left, 0), 1)
+    const top = Math.min(Math.max(state.crop.top, 0), 1)
+    const right = Math.min(Math.max(state.crop.right, left), 1)
+    const bottom = Math.min(Math.max(state.crop.bottom, top), 1)
+    return {
+        cropX: left * rot.rotW,
+        cropY: top * rot.rotH,
+        cropW: Math.max(1, (right - left) * rot.rotW),
+        cropH: Math.max(1, (bottom - top) * rot.rotH),
+    }
+}
+
+/** Render the deskewed bitmap onto a fresh canvas with rotation and
+ *  fractional crop applied. Output canvas dims match the cropped sub-
+ *  rectangle in pixels. Used to feed Measure/preview/exports. */
+export function renderRotatedCropped(
+    image: HTMLImageElement | HTMLCanvasElement,
+    state: CropRotateState,
+): HTMLCanvasElement {
+    const srcW = "naturalWidth" in image ? image.naturalWidth : image.width
+    const srcH = "naturalHeight" in image ? image.naturalHeight : image.height
+    const rot = rotatedBboxSize(srcW, srcH, state.rotationDeg)
+    const px = cropPixels(state, rot)
+
+    const out = document.createElement("canvas")
+    out.width = Math.round(px.cropW)
+    out.height = Math.round(px.cropH)
+    const ctx = out.getContext("2d")
+    if (!ctx) return out
+
+    // Draw with the deskewed-bitmap-centre→rotated-bbox-centre transform,
+    // then translate so the crop's top-left corner becomes (0, 0).
+    ctx.save()
+    ctx.translate(-px.cropX, -px.cropY)
+    ctx.translate(rot.rotW / 2, rot.rotH / 2)
+    ctx.rotate((state.rotationDeg * Math.PI) / 180)
+    ctx.drawImage(image, -srcW / 2, -srcH / 2)
+    ctx.restore()
+    return out
+}
diff --git a/src/lib/upload-cache.ts b/src/lib/upload-cache.ts
index 5380475..0ed5c7d 100644
--- a/src/lib/upload-cache.ts
+++ b/src/lib/upload-cache.ts
@@ -24,6 +24,14 @@ export interface UploadRecord {
     correctedBlob?: Blob
     diagnostics?: DeskewDiagnostics
     scalePxPerMm?: number
+    /** Latest annotated thumbnail (cropped, rotated, with measurements
+     *  baked in) generated by the Measure step. Used by the recent-
+     *  uploads gallery so each tile reflects the work the user
+     *  actually did on it, not just the raw deskew result. Optional —
+     *  the gallery falls back to `correctedBlob`/`originalBlob` when
+     *  unset (e.g. a freshly-uploaded image that hasn't reached
+     *  Measure yet). */
+    previewBlob?: Blob
 }
 
 let dbPromise: Promise<IDBDatabase> | null = null
diff --git a/src/stores/app.ts b/src/stores/app.ts
index a2e7191..00bc7ef 100644
--- a/src/stores/app.ts
+++ b/src/stores/app.ts
@@ -1,7 +1,14 @@
 import { defineStore } from "pinia"
 import { ref, computed } from "vue"
-import type { AppStep, Datum, DeskewResult, ExifData, Point } from "@/types"
-import { DEFAULT_SCALE_PX_PER_MM } from "@/types"
+import type {
+    AppStep,
+    CropRotateState,
+    Datum,
+    DeskewResult,
+    ExifData,
+    Point,
+} from "@/types"
+import { DEFAULT_SCALE_PX_PER_MM, IDENTITY_CROP_ROTATE } from "@/types"
 import { loadSettings } from "@/lib/settings-cache"
 import { fitEllipse } from "@/lib/ellipse-fit"
 
@@ -27,6 +34,10 @@ export const useAppStore = defineStore("app", () => {
      *  produces a new result; consumers compare against the live
      *  `scalePxPerMm` to detect when measurements need to be rescaled. */
     const lastDeskewScale = ref<number | null>(null)
+    /** Rotation (deg) + fractional crop applied on top of the deskew
+     *  result. Identity = no rotation, full image. Persisted per-hash via
+     *  `src/lib/crop-cache.ts` so it survives reloads and re-deskews. */
+    const cropRotate = ref<CropRotateState>({ ...IDENTITY_CROP_ROTATE })
 
     const canProceedToStep2 = computed(() => loadedImage.value !== null)
     const canProceedToStep3 = computed(() => canProceedToStep2.value)
@@ -48,6 +59,7 @@ export const useAppStore = defineStore("app", () => {
     const canProceedToStep5 = computed(
         () => canProceedToStep4.value && deskewResult.value !== null,
     )
+    const canProceedToStep6 = computed(() => canProceedToStep5.value)
 
     function setImage(file: File, image: HTMLImageElement) {
         originalFile.value = file
@@ -178,6 +190,14 @@ export const useAppStore = defineStore("app", () => {
         fileHash.value = hash
     }
 
+    function setCropRotate(state: CropRotateState) {
+        cropRotate.value = state
+    }
+
+    function resetCropRotate() {
+        cropRotate.value = { ...IDENTITY_CROP_ROTATE }
+    }
+
     function reset() {
         currentStep.value = 1
         maxStepReached.value = 1
@@ -193,6 +213,7 @@ export const useAppStore = defineStore("app", () => {
         fileHash.value = null
         cacheRestoreMessage.value = ""
         lastDeskewScale.value = null
+        cropRotate.value = { ...IDENTITY_CROP_ROTATE }
     }
 
     return {
@@ -214,6 +235,10 @@ export const useAppStore = defineStore("app", () => {
         canProceedToStep3,
         canProceedToStep4,
         canProceedToStep5,
+        canProceedToStep6,
+        cropRotate,
+        setCropRotate,
+        resetCropRotate,
         setImage,
         setExif,
         goToStep,
diff --git a/src/types/index.ts b/src/types/index.ts
index 883b86d..52889e9 100644
--- a/src/types/index.ts
+++ b/src/types/index.ts
@@ -118,7 +118,45 @@ export interface DeskewResult {
     diagnostics: DeskewDiagnostics
 }
 
-export type AppStep = 1 | 2 | 3 | 4 | 5
+export type AppStep = 1 | 2 | 3 | 4 | 5 | 6
+
+/** Crop rectangle stored as fractions (0..1) of the rotated deskewed
+ *  image. Persisting fractions (rather than absolute pixels) means the
+ *  same crop survives a re-deskew at a different output px/mm. */
+export interface CropRectFractions {
+    left: number
+    top: number
+    right: number
+    bottom: number
+}
+
+/** Per-hash post-deskew transform: rotate around the deskewed image's
+ *  centre by `rotationDeg`, then crop the bounding box defined by
+ *  fractional `crop` values of the rotated image. Default is identity:
+ *  rotation 0, crop covering the full image. */
+export interface CropRotateState {
+    rotationDeg: number
+    crop: CropRectFractions
+}
+
+export const IDENTITY_CROP_ROTATE: CropRotateState = {
+    rotationDeg: 0,
+    crop: { left: 0, top: 0, right: 1, bottom: 1 },
+}
+
+/** Pre-transform consumed by `CorrectedImageViewer`: maps measurement
+ *  points from the original deskewed-image space onto the bitmap that
+ *  is actually painted (which may be a rotated + cropped derivative).
+ *  See `CorrectedImageViewer.vue` for the formula. */
+export interface ImagePreTransform {
+    rotationDeg: number
+    srcW: number
+    srcH: number
+    rotW: number
+    rotH: number
+    cropX: number
+    cropY: number
+}
 
 /** Pixels per mm in the output image. Default 10 (= 100 px/cm). */
 export const DEFAULT_SCALE_PX_PER_MM = 10