Allow for negative top/left offsets in composite overlays

A top or left offset value of -1 will no longer mean that the
value is not set, but will now be an actual offset of -1.

INT_MIN for left & top will mean that the values are not set.

Co-authored-by: Christian Flintrup <chr@gigahost.dk>

docs/changelog.md

@@ -10,6 +10,10 @@ Requires libvips v8.10.5
 
 * Remove experimental status from `heif` output, defaults are now AVIF-centric.
 
+* Allow negative top/left offsets for composite operation.
+  [#2391](https://github.com/lovell/sharp/pull/2391)
+  [@CurosMJ](https://github.com/CurosMJ)
+
 * Ensure all platforms use fontconfig for font rendering.
   [#2399](https://github.com/lovell/sharp/issues/2399)
 

lib/composite.js

@@ -105,8 +105,9 @@ function composite (images) {
       input: this._createInputDescriptor(image.input, inputOptions, { allowStream: false }),
       blend: 'over',
       tile: false,
-      left: -1,
-      top: -1,
+      left: 0,
+      top: 0,
+      hasOffset: false,
       gravity: 0,
       premultiplied: false
     };
@@ -125,21 +126,23 @@ function composite (images) {
       }
     }
     if (is.defined(image.left)) {
-      if (is.integer(image.left) && image.left >= 0) {
+      if (is.integer(image.left)) {
         composite.left = image.left;
       } else {
-        throw is.invalidParameterError('left', 'positive integer', image.left);
+        throw is.invalidParameterError('left', 'integer', image.left);
       }
     }
     if (is.defined(image.top)) {
-      if (is.integer(image.top) && image.top >= 0) {
+      if (is.integer(image.top)) {
         composite.top = image.top;
       } else {
-        throw is.invalidParameterError('top', 'positive integer', image.top);
+        throw is.invalidParameterError('top', 'integer', image.top);
       }
     }
-    if (composite.left !== composite.top && Math.min(composite.left, composite.top) === -1) {
+    if (is.defined(image.top) !== is.defined(image.left)) {
       throw new Error('Expected both left and top to be set');
+    } else {
+      composite.hasOffset = is.integer(image.top) && is.integer(image.left);
     }
     if (is.defined(image.gravity)) {
       if (is.integer(image.gravity) && is.inRange(image.gravity, 0, 8)) {

package.json

@@ -70,7 +70,9 @@
     "Roman Malieiev <aromaleev@gmail.com>",
     "Tomas Szabo <tomas.szabo@deftomat.com>",
     "Robert O'Rourke <robert@o-rourke.org>",
-    "Guillermo Alfonso Varela Chouciño <guillevch@gmail.com>"
+    "Guillermo Alfonso Varela Chouciño <guillevch@gmail.com>",
+    "Christian Flintrup <chr@gigahost.dk>",
+    "Manan Jadhav <manan@motionden.com>"
   ],
   "scripts": {
     "install": "(node install/libvips && node install/dll-copy && prebuild-install) || (node-gyp rebuild && node install/dll-copy)",

src/common.cc

@@ -658,26 +658,18 @@ namespace sharp {
     int top = 0;
 
     // assign only if valid
-    if (x >= 0 && x < (inWidth - outWidth)) {
+    if (x < (inWidth - outWidth)) {
       left = x;
     } else if (x >= (inWidth - outWidth)) {
       left = inWidth - outWidth;
     }
 
-    if (y >= 0 && y < (inHeight - outHeight)) {
+    if (y < (inHeight - outHeight)) {
       top = y;
     } else if (y >= (inHeight - outHeight)) {
       top = inHeight - outHeight;
     }
 
-    // the resulting left and top could have been outside the image after calculation from bottom/right edges
-    if (left < 0) {
-      left = 0;
-    }
-    if (top < 0) {
-      top = 0;
-    }
-
     return std::make_tuple(left, top);
   }
 

src/pipeline.cc

@@ -570,7 +570,7 @@ class PipelineWorker : public Napi::AsyncWorker {
               int left;
               int top;
               compositeImage = compositeImage.replicate(across, down);
-              if (composite->left >= 0 && composite->top >= 0) {
+              if (composite->hasOffset) {
                 std::tie(left, top) = sharp::CalculateCrop(
                   compositeImage.width(), compositeImage.height(), image.width(), image.height(),
                   composite->left, composite->top);
@@ -592,7 +592,7 @@ class PipelineWorker : public Napi::AsyncWorker {
           // Calculate position
           int left;
           int top;
-          if (composite->left >= 0 && composite->top >= 0) {
+          if (composite->hasOffset) {
             // Composite image at given offsets
             std::tie(left, top) = sharp::CalculateCrop(image.width(), image.height(),
               compositeImage.width(), compositeImage.height(), composite->left, composite->top);
@@ -1253,6 +1253,7 @@ Napi::Value pipeline(const Napi::CallbackInfo& info) {
     composite->gravity = sharp::AttrAsUint32(compositeObject, "gravity");
     composite->left = sharp::AttrAsInt32(compositeObject, "left");
     composite->top = sharp::AttrAsInt32(compositeObject, "top");
+    composite->hasOffset = sharp::AttrAsBool(compositeObject, "hasOffset");
     composite->tile = sharp::AttrAsBool(compositeObject, "tile");
     composite->premultiplied = sharp::AttrAsBool(compositeObject, "premultiplied");
     baton->composite.push_back(composite);

src/pipeline.h

@@ -40,6 +40,7 @@ struct Composite {
   int gravity;
   int left;
   int top;
+  bool hasOffset;
   bool tile;
   bool premultiplied;
 
@@ -47,8 +48,9 @@ struct Composite {
     input(nullptr),
     mode(VIPS_BLEND_MODE_OVER),
     gravity(0),
-    left(-1),
-    top(-1),
+    left(0),
+    top(0),
+    hasOffset(false),
     tile(false),
     premultiplied(false) {}
 };

test/unit/composite.js

@@ -172,6 +172,24 @@ describe('composite', () => {
       });
   });
 
+  it('negative offset and gravity', done => {
+    sharp(fixtures.inputJpg)
+      .resize(400)
+      .composite([{
+        input: fixtures.inputPngWithTransparency16bit,
+        left: -10,
+        top: -10,
+        gravity: 4
+      }])
+      .toBuffer((err, data, info) => {
+        if (err) throw err;
+        assert.strictEqual('jpeg', info.format);
+        assert.strictEqual(3, info.channels);
+        fixtures.assertSimilar(
+          fixtures.expected('overlay-negative-offset-with-gravity.jpg'), data, done);
+      });
+  });
+
   it('offset, gravity and tile', done => {
     sharp(fixtures.inputJpg)
       .resize(80)
@@ -333,13 +351,25 @@ describe('composite', () => {
     it('invalid left', () => {
       assert.throws(() => {
         sharp().composite([{ input: 'test', left: 0.5 }]);
-      }, /Expected positive integer for left but received 0.5 of type number/);
+      }, /Expected integer for left but received 0.5 of type number/);
+      assert.throws(() => {
+        sharp().composite([{ input: 'test', left: 'invalid' }]);
+      }, /Expected integer for left but received invalid of type string/);
+      assert.throws(() => {
+        sharp().composite([{ input: 'test', left: 'invalid', top: 10 }]);
+      }, /Expected integer for left but received invalid of type string/);
     });
 
     it('invalid top', () => {
       assert.throws(() => {
-        sharp().composite([{ input: 'test', top: -1 }]);
-      }, /Expected positive integer for top but received -1 of type number/);
+        sharp().composite([{ input: 'test', top: 0.5 }]);
+      }, /Expected integer for top but received 0.5 of type number/);
+      assert.throws(() => {
+        sharp().composite([{ input: 'test', top: 'invalid' }]);
+      }, /Expected integer for top but received invalid of type string/);
+      assert.throws(() => {
+        sharp().composite([{ input: 'test', top: 'invalid', left: 10 }]);
+      }, /Expected integer for top but received invalid of type string/);
     });
 
     it('left but no top', () => {