fix gemini-testing#10 with the addition of a transparency option to…

… control the alpha of unchanged pixels

README.md

@@ -104,7 +104,8 @@ await looksSame.createDiff({
     current: '/path/to/current/image.png',
     diff: '/path/to/save/diff/to.png',
     highlightColor: '#ff00ff', // color to highlight the differences
-    strict: false, // strict comparsion
+    transparency: 255, //0-255, controls the alpha channel for unchanged pixels
+    strict: false, // strict comparison
     tolerance: 2.5,
     antialiasingTolerance: 0,
     ignoreAntialiasing: true, // ignore antialising by default

index.js

@@ -77,6 +77,7 @@ const buildDiffImage = async (img1, img2, options) => {
     const minHeight = Math.min(img1.height, img2.height);
 
     const highlightColor = options.highlightColor;
+    const alphaLevel = isNaN(options.transparency) ? 255 : options.transparency;
     const resultBuffer = Buffer.alloc(width * height * 3);
 
     const setPixel = (buf, x, y, {R, G, B}) => {
@@ -98,7 +99,7 @@ const buildDiffImage = async (img1, img2, options) => {
         if (!options.comparator({color1, color2, img1, img2, x, y, width, height})) {
             setPixel(resultBuffer, x, y, highlightColor);
         } else {
-            setPixel(resultBuffer, x, y, color1);
+            setPixel(resultBuffer, x, y, color1, alphaLevel);
         }
     });
 

lib/same-colors.js

@@ -6,5 +6,6 @@ module.exports = (data) => {
 
     return c1.R === c2.R
         && c1.G === c2.G
-        && c1.B === c2.B;
+        && c1.B === c2.B
+        && c1.A === c2.A;
 };

test/test.js

@@ -449,7 +449,37 @@ describe('createDiff', () => {
 
         expect(equal).to.equal(true);
     });
+    it('should apply full transparency to the diff if set to 0', (done) => {
+        const _this = this;
+        looksSame.createDiff({
+            reference: srcPath('ref.png'),
+            current: srcPath('different.png'),
+            diff: this.tempName,
+            highlightColor: '#ff00ff',
+            transparency: 0
+        }, () => {
+            looksSame(imagePath('diffs/different-0-alpha.png'), _this.tempName, {strict: true}, (error, equal) => {
+                expect(equal).to.equal(true);
+                done();
+            });
+        });
+    });
 
+    it('should support partial transparency in the diff', (done) => {
+        const _this = this;
+        looksSame.createDiff({
+            reference: srcPath('ref.png'),
+            current: srcPath('different.png'),
+            diff: this.tempName,
+            highlightColor: '#ff00ff',
+            transparency: 50
+        }, () => {
+            looksSame(imagePath('diffs/different-50-alpha.png'), _this.tempName, {strict: true}, (error, equal) => {
+                expect(equal).to.equal(true);
+                done();
+            });
+        });
+    });
     it('should allow to build diff for taller images', async () => {
         await looksSame.createDiff({
             reference: srcPath('ref.png'),