Merge pull request #40 from happo/no-array-destructuring

Remove array destructuring in colorDelta, add colorDeltaChannels, deprecate colorDelta

src/__tests__/colorDelta-test.js

@@ -1,43 +1,76 @@
-const colorDelta = require('../colorDelta');
+const colorDelta = require("../colorDelta");
+const { colorDeltaChannels } = require("../colorDelta");
 
-it('is large when comparing black and white', () => {
-  expect(colorDelta([0, 0, 0, 255], [255, 255, 255, 255])).toBeGreaterThan(
-    0.92,
+describe("colorDelta", () => {
+  it("produces the same results as colorDeltaChannels", () => {
+    const pixels = [
+      [0, 0, 0, 255],
+      [255, 255, 255, 255],
+      [0, 0, 0, 0],
+      [1, 1, 1, 1],
+      [1, 46, 250, 0],
+      [1, 42, 250, 4],
+    ];
+
+    for (let i = 0; i < pixels.length; i++) {
+      for (let j = 0; j < pixels.length; j++) {
+        expect(colorDelta(pixels[i], pixels[j])).toEqual(
+          colorDeltaChannels(
+            pixels[i][0],
+            pixels[i][1],
+            pixels[i][2],
+            pixels[i][3],
+            pixels[j][0],
+            pixels[j][1],
+            pixels[j][2],
+            pixels[j][3]
+          )
+        );
+      }
+    }
+  });
+});
+
+it("is large when comparing black and white", () => {
+  expect(colorDeltaChannels(0, 0, 0, 255, 255, 255, 255, 255)).toBeGreaterThan(
+    0.92
   );
 });
 
-it('is small when comparing black and very dark grey', () => {
-  expect(colorDelta([0, 0, 0, 255], [10, 10, 10, 255])).toBeLessThan(0.02);
+it("is small when comparing black and very dark grey", () => {
+  expect(colorDeltaChannels(0, 0, 0, 255, 10, 10, 10, 255)).toBeLessThan(0.02);
 });
 
-it('is medium when comparing black and medium grey', () => {
-  const delta = colorDelta([0, 0, 0, 255], [127, 127, 127, 255]);
+it("is medium when comparing black and medium grey", () => {
+  const delta = colorDeltaChannels(0, 0, 0, 255, 127, 127, 127, 255);
   expect(delta).toBeGreaterThan(0.21);
   expect(delta).toBeLessThan(0.24);
 });
 
-it('is medium when comparing red and blue', () => {
-  const delta = colorDelta([255, 0, 0, 255], [0, 0, 255, 255]);
+it("is medium when comparing red and blue", () => {
+  const delta = colorDeltaChannels(255, 0, 0, 255, 0, 0, 255, 255);
   expect(delta).toBeGreaterThan(0.5);
   expect(delta).toBeLessThan(0.51);
 });
 
-it('is one when comparing filler pixel and white', () => {
-  expect(colorDelta([1, 1, 1, 1], [255, 255, 255, 255])).toEqual(1);
+it("is one when comparing filler pixel and white", () => {
+  expect(colorDeltaChannels(1, 1, 1, 1, 255, 255, 255, 255)).toEqual(1);
 });
 
-it('is large when comparing transparent and black', () => {
-  expect(colorDelta([0, 0, 0, 0], [0, 0, 0, 255])).toBeGreaterThan(0.92);
+it("is large when comparing transparent and black", () => {
+  expect(colorDeltaChannels(0, 0, 0, 0, 0, 0, 0, 255)).toBeGreaterThan(0.92);
 });
 
-it('is large when comparing white and filler pixel', () => {
-  expect(colorDelta([255, 255, 255, 255], [1, 1, 1, 1])).toBeGreaterThan(0.92);
+it("is large when comparing white and filler pixel", () => {
+  expect(colorDeltaChannels(255, 255, 255, 255, 1, 1, 1, 1)).toBeGreaterThan(
+    0.92
+  );
 });
 
-it('is one when comparing filler pixel and some other color', () => {
-  expect(colorDelta([1, 1, 1, 1], [33, 33, 33, 10])).toEqual(1);
+it("is one when comparing filler pixel and some other color", () => {
+  expect(colorDeltaChannels(1, 1, 1, 1, 33, 33, 33, 10)).toEqual(1);
 });
 
-it('is small when comparing transparent and similar color', () => {
-  expect(colorDelta([1, 46, 250, 0], [1, 42, 250, 4])).toBeLessThan(0.05);
+it("is small when comparing transparent and similar color", () => {
+  expect(colorDeltaChannels(1, 46, 250, 0, 1, 42, 250, 4)).toBeLessThan(0.05);
 });

src/colorDelta.js

@@ -17,26 +17,27 @@ function blend(color, alpha) {
   return 255 + (color - 255) * alpha;
 }
 
-function isFillerPixel([r, g, b, a]) {
+function isFillerPixel(r, g, b, a) {
   return r === 1 && g === 1 && b === 1 && a === 1;
 }
 
-// calculate color difference according to the paper "Measuring perceived color
-// difference using YIQ NTSC transmission color space in mobile applications" by
-// Y. Kotsarenko and F. Ramos
-//
-// Modified from https://github.com/mapbox/pixelmatch
-module.exports = function colorDelta(previousPixel, currentPixel) {
-  let [r1, g1, b1, a1] = previousPixel;
-  let [r2, g2, b2, a2] = currentPixel;
-
+/**
+ * Calculate color difference between two pixels
+ *
+ * The difference is calculated according to the paper "Measuring perceived
+ * color difference using YIQ NTSC transmission color space in mobile
+ * applications" by Y. Kotsarenko and F. Ramos.
+ *
+ * Modified from https://github.com/mapbox/pixelmatch
+ */
+function colorDeltaChannels(r1, g1, b1, a1, r2, g2, b2, a2) {
   if (r1 === r2 && g1 === g2 && b1 === b2 && a1 === a2) {
     return 0;
   }
 
   if (
-    (isFillerPixel(currentPixel) && a1 > 0) ||
-    (isFillerPixel(previousPixel) && a2 > 0)
+    (isFillerPixel(r1, g1, b1, a1) && a1 > 0) ||
+    (isFillerPixel(r2, g2, b2, a2) && a2 > 0)
   ) {
     return 1;
   }
@@ -60,4 +61,31 @@ module.exports = function colorDelta(previousPixel, currentPixel) {
   const q = rgb2q(r1, g1, b1) - rgb2q(r2, g2, b2);
 
   return (0.5053 * y * y + 0.299 * i * i + 0.1957 * q * q) / MAX_YIQ_DIFFERENCE;
-};
+}
+
+/**
+ * Calculate color difference between two pixels
+ *
+ * The difference is calculated according to the paper "Measuring perceived
+ * color difference using YIQ NTSC transmission color space in mobile
+ * applications" by Y. Kotsarenko and F. Ramos.
+ *
+ * Modified from https://github.com/mapbox/pixelmatch
+ *
+ * @deprecated use `colorDeltaChannels` instead
+ */
+function colorDelta(previousPixel, currentPixel) {
+  return colorDeltaChannels(
+    previousPixel[0],
+    previousPixel[1],
+    previousPixel[2],
+    previousPixel[3],
+    currentPixel[0],
+    currentPixel[1],
+    currentPixel[2],
+    currentPixel[3]
+  );
+}
+
+module.exports = colorDelta;
+module.exports.colorDeltaChannels = colorDeltaChannels;