Add attention_x and attention_y as output to attention based crop

lib/output.js

@@ -61,6 +61,7 @@ const bitdepthFromColourCount = (colours) => 1 << 31 - Math.clz32(Math.ceil(Math
  * `info` contains the output image `format`, `size` (bytes), `width`, `height`,
  * `channels` and `premultiplied` (indicating if premultiplication was used).
  * When using a crop strategy also contains `cropOffsetLeft` and `cropOffsetTop`.
+ * When using attention as crop strategy also contains the center of the cropped region in the fields `attentionX` and `attentionY`.
  * May also contain `textAutofitDpi` (dpi the font was rendered at) if image was created from text.
  * @returns {Promise<Object>} - when no callback is provided
  * @throws {Error} Invalid parameters

src/pipeline.cc

@@ -456,6 +456,7 @@ class PipelineWorker : public Napi::AsyncWorker {
             // Gravity-based crop
             int left;
             int top;
+
             std::tie(left, top) = sharp::CalculateCrop(
               inputWidth, inputHeight, baton->width, baton->height, baton->position);
             int width = std::min(inputWidth, baton->width);
@@ -466,16 +467,25 @@ class PipelineWorker : public Napi::AsyncWorker {
                   left, top, width, height, nPages, &targetPageHeight)
               : image.extract_area(left, top, width, height);
           } else {
+            int attention_x;
+            int attention_y;
+
             // Attention-based or Entropy-based crop
             MultiPageUnsupported(nPages, "Resize strategy");
             image = image.tilecache(VImage::option()
               ->set("access", VIPS_ACCESS_RANDOM)
               ->set("threaded", TRUE));
+
             image = image.smartcrop(baton->width, baton->height, VImage::option()
-              ->set("interesting", baton->position == 16 ? VIPS_INTERESTING_ENTROPY : VIPS_INTERESTING_ATTENTION));
+              ->set("interesting", baton->position == 16 ? VIPS_INTERESTING_ENTROPY : VIPS_INTERESTING_ATTENTION)
+              ->set("attention_x", &attention_x)
+              ->set("attention_y", &attention_y));
             baton->hasCropOffset = true;
             baton->cropOffsetLeft = static_cast<int>(image.xoffset());
             baton->cropOffsetTop = static_cast<int>(image.yoffset());
+            baton->hasAttentionCenter = true;
+            baton->attentionX = static_cast<int>(attention_x * jpegShrinkOnLoad / scale);
+            baton->attentionY = static_cast<int>(attention_y * jpegShrinkOnLoad / scale);
           }
         }
       }
@@ -1198,6 +1208,10 @@ class PipelineWorker : public Napi::AsyncWorker {
         info.Set("cropOffsetLeft", static_cast<int32_t>(baton->cropOffsetLeft));
         info.Set("cropOffsetTop", static_cast<int32_t>(baton->cropOffsetTop));
       }
+      if (baton->hasAttentionCenter) {
+        info.Set("attentionX", static_cast<int32_t>(baton->attentionX));
+        info.Set("attentionY", static_cast<int32_t>(baton->attentionY));
+      }
       if (baton->trimThreshold > 0.0) {
         info.Set("trimOffsetLeft", static_cast<int32_t>(baton->trimOffsetLeft));
         info.Set("trimOffsetTop", static_cast<int32_t>(baton->trimOffsetTop));

src/pipeline.h

@@ -74,6 +74,9 @@ struct PipelineBaton {
   bool hasCropOffset;
   int cropOffsetLeft;
   int cropOffsetTop;
+  bool hasAttentionCenter;
+  int attentionX;
+  int attentionY;
   bool premultiplied;
   bool tileCentre;
   bool fastShrinkOnLoad;
@@ -236,6 +239,9 @@ struct PipelineBaton {
     hasCropOffset(false),
     cropOffsetLeft(0),
     cropOffsetTop(0),
+    hasAttentionCenter(false),
+    attentionX(0),
+    attentionY(0),
     premultiplied(false),
     tintA(128.0),
     tintB(128.0),

test/unit/resize-cover.js

@@ -376,6 +376,8 @@ describe('Resize fit=cover', function () {
           assert.strictEqual(320, info.height);
           assert.strictEqual(-107, info.cropOffsetLeft);
           assert.strictEqual(0, info.cropOffsetTop);
+          assert.strictEqual(588, info.attentionX);
+          assert.strictEqual(640, info.attentionY);
           fixtures.assertSimilar(fixtures.expected('crop-strategy-attention.jpg'), data, done);
         });
     });
@@ -394,10 +396,32 @@ describe('Resize fit=cover', function () {
           assert.strictEqual(80, info.height);
           assert.strictEqual(0, info.cropOffsetLeft);
           assert.strictEqual(0, info.cropOffsetTop);
+          assert.strictEqual(0, info.attentionX);
+          assert.strictEqual(0, info.attentionY);
           fixtures.assertSimilar(fixtures.expected('crop-strategy.png'), data, done);
         });
     });
 
+    it('WebP', function (done) {
+      sharp(fixtures.inputWebP)
+        .resize(320, 80, {
+          fit: 'cover',
+          position: sharp.strategy.attention
+        })
+        .toBuffer(function (err, data, info) {
+          if (err) throw err;
+          assert.strictEqual('webp', info.format);
+          assert.strictEqual(3, info.channels);
+          assert.strictEqual(320, info.width);
+          assert.strictEqual(80, info.height);
+          assert.strictEqual(0, info.cropOffsetLeft);
+          assert.strictEqual(-161, info.cropOffsetTop);
+          assert.strictEqual(288, info.attentionX);
+          assert.strictEqual(745, info.attentionY);
+          fixtures.assertSimilar(fixtures.expected('crop-strategy.webp'), data, done);
+        });
+    });
+
     it('supports the strategy passed as a string', function (done) {
       sharp(fixtures.inputPngWithTransparency)
         .resize(320, 80, {