fix diff order bug (#1311)

Author: hipstersmoothie

packages/diff/src/index.test.ts

@@ -13,6 +13,7 @@ describe("Compare image difference", () => {
     Jimp.fromBitmap(makeTestImage("2468", "2468", "2468", "2468")),
     Jimp.fromBitmap(makeTestImage("2212", "4434", "6656", "8878")),
     Jimp.fromBitmap(makeTestImage("2232", "4454", "6676", "8898")),
+    Jimp.fromBitmap(makeTestImage("22322", "44544", "66766", "88988")),
   ] as const;
 
   test("images 0 and 1", () => {
@@ -46,4 +47,10 @@ describe("Compare image difference", () => {
       "threshold must be a number between 0 and 1"
     );
   });
+
+  test("should resize image before diffing", () => {
+    expect(diff(imgs[3], imgs[4]).percent).toStrictEqual(
+      diff(imgs[4], imgs[3]).percent
+    );
+  });
 });

packages/diff/src/index.ts

@@ -25,22 +25,22 @@ import pixelMatch from "pixelmatch";
  * ```
  */
 export function diff<I extends JimpClass>(img1: I, img2: I, threshold = 0.1) {
-  const bmp1 = img1.bitmap;
-  const bmp2 = img2.bitmap;
+  let bmp1 = img1.bitmap;
+  let bmp2 = img2.bitmap;
 
   if (bmp1.width !== bmp2.width || bmp1.height !== bmp2.height) {
     if (bmp1.width * bmp1.height > bmp2.width * bmp2.height) {
       // img1 is bigger
-      img1 = methods.resize(clone(img1), {
+      bmp1 = methods.resize(clone(img1), {
         w: bmp2.width,
         h: bmp2.height,
-      });
+      }).bitmap;
     } else {
       // img2 is bigger (or they are the same in area)
-      img2 = methods.resize(clone(img2), {
+      bmp2 = methods.resize(clone(img2), {
         w: bmp1.width,
         h: bmp1.height,
-      });
+      }).bitmap;
     }
   }