Add top/left offset support to overlayWith operation (#473)

test/unit/overlay.js

@@ -264,6 +264,164 @@ describe('Overlays', function() {
     });
   });
 
+  describe("Overlay with top-left offsets", function() {
+    it('Overlay with 10px top & 10px left offsets', function(done) {
+      var expected = fixtures.expected('overlay-valid-offsets-10-10.jpg');
+      sharp(fixtures.inputJpg)
+        .resize(400)
+        .overlayWith(fixtures.inputPngWithTransparency16bit, {
+          top: 10,
+          left: 10
+        })
+        .toBuffer(function(err, data, info) {
+          if (err) throw err;
+          assert.strictEqual('jpeg', info.format);
+          assert.strictEqual(3, info.channels);
+          fixtures.assertSimilar(expected, data, done);
+        });
+      
+    });
+
+    it('Overlay with 100px top & 300px left offsets', function(done) {
+      var expected = fixtures.expected('overlay-valid-offsets-100-300.jpg');
+      sharp(fixtures.inputJpg)
+        .resize(400)
+        .overlayWith(fixtures.inputPngWithTransparency16bit, {
+          top: 100,
+          left: 300
+        })
+        .toBuffer(function(err, data, info) {
+          if (err) throw err;
+          assert.strictEqual('jpeg', info.format);
+          assert.strictEqual(3, info.channels);
+          fixtures.assertSimilar(expected, data, done);
+        });
+      
+    });
+
+    it('Overlay with only top offset', function() {
+      assert.throws(function() {
+        sharp(fixtures.inputJpg)
+          .resize(400)
+          .overlayWith(fixtures.inputPngWithTransparency16bit, {
+            top: 1000
+          });
+      });
+    });
+
+    it('Overlay with only left offset', function() {
+      assert.throws(function() {
+        sharp(fixtures.inputJpg)
+          .resize(400)
+          .overlayWith(fixtures.inputPngWithTransparency16bit, {
+            left: 1000
+          });
+        });
+    });
+
+    it('Overlay with negative offsets', function() {
+      assert.throws(function() {
+        sharp(fixtures.inputJpg)
+          .resize(400)
+          .overlayWith(fixtures.inputPngWithTransparency16bit, {
+            top: -1000,
+            left: -1000
+          });
+        });     
+    });
+
+    it('Overlay with 0 offset', function(done) {
+      var expected = fixtures.expected('overlay-offset-0.jpg');
+      sharp(fixtures.inputJpg)
+        .resize(400)
+        .overlayWith(fixtures.inputPngWithTransparency16bit, {
+          top: 0,
+          left: 0
+        })
+        .toBuffer(function(err, data, info) {
+          if (err) throw err;
+          assert.strictEqual('jpeg', info.format);
+          assert.strictEqual(3, info.channels);
+          fixtures.assertSimilar(expected, data, done);
+        });
+      
+    });
+
+    it('Overlay with offset and gravity', function(done) {
+      var expected = fixtures.expected('overlay-offset-with-gravity.jpg');
+      sharp(fixtures.inputJpg)
+        .resize(400)
+        .overlayWith(fixtures.inputPngWithTransparency16bit, {
+          left: 10,
+          top: 10,
+          gravity : 4
+          
+        })
+        .toBuffer(function(err, data, info) {
+          if (err) throw err;
+          assert.strictEqual('jpeg', info.format);
+          assert.strictEqual(3, info.channels);
+          fixtures.assertSimilar(expected, data, done);
+        });
+      
+    });
+
+    it('Overlay with offset and gravity and tile', function(done) {
+      var expected = fixtures.expected('overlay-offset-with-gravity-tile.jpg');
+      sharp(fixtures.inputJpg)
+        .resize(400)
+        .overlayWith(fixtures.inputPngWithTransparency16bit, {
+          left: 10,
+          top: 10,
+          gravity : 4,
+          tile: true
+        })
+        .toBuffer(function(err, data, info) {
+          if (err) throw err;
+          assert.strictEqual('jpeg', info.format);
+          assert.strictEqual(3, info.channels);
+          fixtures.assertSimilar(expected, data, done);
+        });
+      
+    });
+
+    it('Overlay with offset and tile', function(done) {
+      var expected = fixtures.expected('overlay-offset-with-tile.jpg');
+      sharp(fixtures.inputJpg)
+        .resize(400)
+        .overlayWith(fixtures.inputPngWithTransparency16bit, {
+          left: 10,
+          top: 10,
+          tile: true
+        })
+        .toBuffer(function(err, data, info) {
+          if (err) throw err;
+          assert.strictEqual('jpeg', info.format);
+          assert.strictEqual(3, info.channels);
+          fixtures.assertSimilar(expected, data, done);
+        });
+      
+    });
+
+
+    it('Overlay with very large offset', function(done) {
+      var expected = fixtures.expected('overlay-very-large-offset.jpg');
+      sharp(fixtures.inputJpg)
+        .resize(400)
+        .overlayWith(fixtures.inputPngWithTransparency16bit, {
+          left: 1000000,
+          top: 100000
+        })
+        .toBuffer(function(err, data, info) {
+          if (err) throw err;
+          assert.strictEqual('jpeg', info.format);
+          assert.strictEqual(3, info.channels);
+          fixtures.assertSimilar(expected, data, done);
+        });
+      
+    });
+  });
+
   it('With tile enabled and image rotated 90 degrees', function(done) {
     var expected = fixtures.expected('overlay-tile-rotated90.jpg');
     sharp(fixtures.inputJpg)