feat: implement computeCropOrigins

Closes: #427

src/stack/align/utils/__tests__/computeCropOrigins.test.ts

@@ -0,0 +1,59 @@
+import { Image } from '../../../../Image';
+import { Stack } from '../../../../Stack';
+import { computeCropOrigins } from '../computeCropOrigins';
+import { findCommonArea } from '../findCommonArea';
+
+const image1 = new Image(4, 4);
+const image2 = new Image(3, 4);
+const image3 = new Image(6, 5);
+const image4 = new Image(4, 2);
+const absoluteTranslations = [
+  { column: 0, row: 0 },
+  { column: 2, row: -2 },
+  { column: 1, row: 1 },
+  { column: -1, row: 1 },
+];
+test('stack of 2 images', () => {
+  const stack = new Stack([image1, image2]);
+  const absTranslations = absoluteTranslations.slice(0, 2);
+
+  const commonArea = findCommonArea(stack, absTranslations);
+
+  const result = computeCropOrigins(stack, commonArea, absTranslations);
+
+  expect(result).toStrictEqual([
+    { column: 2, row: 0 },
+    { column: 0, row: 2 },
+  ]);
+});
+
+test('stack of 3 images', () => {
+  const stack = new Stack([image1, image2, image3]);
+  const absTranslations = absoluteTranslations.slice(0, 3);
+
+  const commonArea = findCommonArea(stack, absTranslations);
+
+  const result = computeCropOrigins(stack, commonArea, absTranslations);
+
+  expect(result).toStrictEqual([
+    { column: 2, row: 1 },
+    { column: 0, row: 3 },
+    { column: 1, row: 0 },
+  ]);
+});
+
+test('stack of 4 images', () => {
+  const stack = new Stack([image1, image2, image3, image4]);
+  const absTranslations = absoluteTranslations.slice(0, 4);
+
+  const commonArea = findCommonArea(stack, absTranslations);
+
+  const result = computeCropOrigins(stack, commonArea, absTranslations);
+
+  expect(result).toStrictEqual([
+    { column: 2, row: 1 },
+    { column: 0, row: 3 },
+    { column: 1, row: 0 },
+    { column: 3, row: 0 },
+  ]);
+});

src/stack/align/utils/computeCropOrigins.ts

@@ -1,13 +1,29 @@
+import { Stack } from '../../../Stack';
+import { Point } from '../../../geometry';
+import { difference } from '../../../utils/geometry/points';
+
 import { CommonArea } from './findCommonArea';
 
 /**
  * Compute the origins of the crops relative to the top left corner of each image in order
  * to crop the common area of each of the images of an aligned stack.
  * @param stack - Stack to process.
  * @param commonArea - The data of the common area of the stack.
+ * @param absoluteTranslations - The absolute translations of the images of the stack (relative to the first image).
  * @returns The origins of the crops.
  */
 export function computeCropOrigins(
   stack: Stack,
   commonArea: CommonArea,
-): Point[] {}
+  absoluteTranslations: Point[],
+): Point[] {
+  const cropOrigins: Point[] = [];
+  let currentCropOrigin = commonArea.origin;
+  cropOrigins.push(currentCropOrigin);
+  for (let i = 1; i < stack.size; i++) {
+    currentCropOrigin = difference(commonArea.origin, absoluteTranslations[i]);
+    cropOrigins.push(currentCropOrigin);
+  }
+
+  return cropOrigins;
+}