Add centre/center option to tile-based output (#2397)

docs/api-output.md

@@ -372,6 +372,7 @@ Warning: multiple sharp instances concurrently producing tile output can expose
     -   `options.skipBlanks` **[number][9]** threshold to skip tile generation, a value 0 - 255 for 8-bit images or 0 - 65535 for 16-bit images (optional, default `-1`)
     -   `options.container` **[string][2]** tile container, with value `fs` (filesystem) or `zip` (compressed file). (optional, default `'fs'`)
     -   `options.layout` **[string][2]** filesystem layout, possible values are `dz`, `iiif`, `zoomify` or `google`. (optional, default `'dz'`)
+    -   `options.centre|center` **[boolean][7]** center image in tile (optional, default `false`)
 
 ### Examples
 

lib/constructor.js

@@ -238,6 +238,7 @@ const Sharp = function (input, options) {
     tileAngle: 0,
     tileSkipBlanks: -1,
     tileBackground: [255, 255, 255, 255],
+    tileCentre: false,
     linearA: 1,
     linearB: 0,
     // Function to notify of libvips warnings

lib/output.js

@@ -658,6 +658,7 @@ function raw () {
  * @param {number} [options.skipBlanks=-1] threshold to skip tile generation, a value 0 - 255 for 8-bit images or 0 - 65535 for 16-bit images
  * @param {string} [options.container='fs'] tile container, with value `fs` (filesystem) or `zip` (compressed file).
  * @param {string} [options.layout='dz'] filesystem layout, possible values are `dz`, `iiif`, `zoomify` or `google`.
+ * @param {boolean} [options.centre=false] center image in tile.
  * @returns {Sharp}
  * @throws {Error} Invalid parameters
  */
@@ -726,6 +727,10 @@ function tile (options) {
     } else if (is.defined(options.layout) && options.layout === 'google') {
       this.options.tileSkipBlanks = 5;
     }
+    // Center image in tile
+    if (is.defined(options.centre) || is.defined(options.center)) {
+      this._setBooleanOption('tileCentre', options.centre || options.center);
+    }
   }
   // Format
   if (is.inArray(this.options.formatOut, ['jpeg', 'png', 'webp'])) {

src/pipeline.cc

@@ -1014,6 +1014,7 @@ class PipelineWorker : public Napi::AsyncWorker {
             ->set("suffix", const_cast<char*>(suffix.data()))
             ->set("angle", CalculateAngleRotation(baton->tileAngle))
             ->set("background", baton->tileBackground)
+            ->set("centre", baton->tileCentre)
             ->set("skip_blanks", baton->tileSkipBlanks);
           // libvips chooses a default depth based on layout. Instead of replicating that logic here by
           // not passing anything - libvips will handle choice
@@ -1403,6 +1404,7 @@ Napi::Value pipeline(const Napi::CallbackInfo& info) {
   baton->tileDepth = static_cast<VipsForeignDzDepth>(
     vips_enum_from_nick(nullptr, VIPS_TYPE_FOREIGN_DZ_DEPTH,
     sharp::AttrAsStr(options, "tileDepth").data()));
+  baton->tileCentre = sharp::AttrAsBool(options, "tileCentre");
 
   // Force random access for certain operations
   if (baton->input->access == VIPS_ACCESS_SEQUENTIAL) {

src/pipeline.h

@@ -79,6 +79,7 @@ struct PipelineBaton {
   int cropOffsetLeft;
   int cropOffsetTop;
   bool premultiplied;
+  bool tileCentre;
   std::string kernel;
   bool fastShrinkOnLoad;
   double tintA;

test/unit/tile.js

@@ -289,6 +289,14 @@ describe('Tile', function () {
     });
   });
 
+  it('Invalid center parameter value fail', function () {
+    assert.throws(function () {
+      sharp().tile({
+        center: 'true'
+      });
+    });
+  });
+
   it('Deep Zoom layout', function (done) {
     const directory = fixtures.path('output.dzi_files');
     rimraf(directory, function () {
@@ -765,6 +773,46 @@ describe('Tile', function () {
     });
   });
 
+  it('Google layout with center image in tile', function (done) {
+    const directory = fixtures.path('output.google_center.dzi');
+    rimraf(directory, function () {
+      sharp(fixtures.inputJpg)
+        .tile({
+          center: true,
+          layout: 'google'
+        })
+        .toFile(directory, function (err, info) {
+          if (err) throw err;
+          assert.strictEqual('dz', info.format);
+          assert.strictEqual(2725, info.width);
+          assert.strictEqual(2225, info.height);
+          assert.strictEqual(3, info.channels);
+          assert.strictEqual('number', typeof info.size);
+          fixtures.assertSimilar(fixtures.expected('tile_centered.jpg'), fs.readFileSync(path.join(directory, '0', '0', '0.jpg')), done);
+        });
+    });
+  });
+
+  it('Google layout with center image in tile centre', function (done) {
+    const directory = fixtures.path('output.google_center.dzi');
+    rimraf(directory, function () {
+      sharp(fixtures.inputJpg)
+        .tile({
+          centre: true,
+          layout: 'google'
+        })
+        .toFile(directory, function (err, info) {
+          if (err) throw err;
+          assert.strictEqual('dz', info.format);
+          assert.strictEqual(2725, info.width);
+          assert.strictEqual(2225, info.height);
+          assert.strictEqual(3, info.channels);
+          assert.strictEqual('number', typeof info.size);
+          fixtures.assertSimilar(fixtures.expected('tile_centered.jpg'), fs.readFileSync(path.join(directory, '0', '0', '0.jpg')), done);
+        });
+    });
+  });
+
   it('IIIF layout', function (done) {
     const directory = fixtures.path('output.iiif.info');
     rimraf(directory, function () {