Switch to libvips' resize, make fastShrinkOnLoad optional (#977)

test/fixtures/index.js

@@ -67,6 +67,7 @@ module.exports = {
   inputJpg320x240: getPath('320x240.jpg'), // http://www.andrewault.net/2010/01/26/create-a-test-pattern-video-with-perl/
   inputJpgOverlayLayer2: getPath('alpha-layer-2-ink.jpg'),
   inputJpgTruncated: getPath('truncated.jpg'), // head -c 10000 2569067123_aca715a2ee_o.jpg > truncated.jpg
+  inputJpgCenteredImage: getPath('centered_image.jpeg'),
 
   inputPng: getPath('50020484-00001.png'), // http://c.searspartsdirect.com/lis_png/PLDM/50020484-00001.png
   inputPngWithTransparency: getPath('blackbug.png'), // public domain

test/unit/extract.js

@@ -98,6 +98,7 @@ describe('Partial image extraction', function () {
     sharp(fixtures.inputPngWithGreyAlpha)
       .extract({ left: 20, top: 10, width: 380, height: 280 })
       .rotate(90)
+      .jpeg()
       .toBuffer(function (err, data, info) {
         if (err) throw err;
         assert.strictEqual(280, info.width);

test/unit/gamma.js

@@ -48,11 +48,12 @@ describe('Gamma correction', function () {
     sharp(fixtures.inputPngOverlayLayer1)
       .resize(320)
       .gamma()
+      .jpeg()
       .toBuffer(function (err, data, info) {
         if (err) throw err;
-        assert.strictEqual('png', info.format);
+        assert.strictEqual('jpeg', info.format);
         assert.strictEqual(320, info.width);
-        fixtures.assertSimilar(fixtures.expected('gamma-alpha.jpg'), data, { threshold: 20 }, done);
+        fixtures.assertSimilar(fixtures.expected('gamma-alpha.jpg'), data, done);
       });
   });
 

test/unit/resize.js

@@ -448,4 +448,34 @@ describe('Resize dimensions', function () {
           });
       });
   });
+
+  it('fastShrinkOnLoad: false ensures image is not shifted', function (done) {
+    return sharp(fixtures.inputJpgCenteredImage)
+      .resize(9, 8, {
+        fastShrinkOnLoad: false,
+        centreSampling: true
+      })
+      .png()
+      .toBuffer(function (err, data, info) {
+        if (err) throw err;
+        assert.strictEqual(9, info.width);
+        assert.strictEqual(8, info.height);
+        // higher threshold makes it pass for both jpeg and jpeg-turbo libs
+        fixtures.assertSimilar(fixtures.expected('fast-shrink-on-load-false.png'), data, { threshold: 7 }, done);
+      });
+  });
+
+  it('fastShrinkOnLoad: true (default) might result in shifted image', function (done) {
+    return sharp(fixtures.inputJpgCenteredImage)
+    .resize(9, 8, {
+      centreSampling: true
+    })
+    .png()
+    .toBuffer(function (err, data, info) {
+      if (err) throw err;
+      assert.strictEqual(9, info.width);
+      assert.strictEqual(8, info.height);
+      fixtures.assertSimilar(fixtures.expected('fast-shrink-on-load-true.png'), data, done);
+    });
+  });
 });