Extend: default missing edge props to zero #2578

docs/api-resize.md

@@ -137,10 +137,10 @@ This operation will always occur after resizing and extraction, if any.
 ### Parameters
 
 -   `extend` **([number][8] \| [Object][9])** single pixel count to add to all edges or an Object with per-edge counts
-    -   `extend.top` **[number][8]?** 
-    -   `extend.left` **[number][8]?** 
-    -   `extend.bottom` **[number][8]?** 
-    -   `extend.right` **[number][8]?** 
+    -   `extend.top` **[number][8]**  (optional, default `0`)
+    -   `extend.left` **[number][8]**  (optional, default `0`)
+    -   `extend.bottom` **[number][8]**  (optional, default `0`)
+    -   `extend.right` **[number][8]**  (optional, default `0`)
     -   `extend.background` **([String][10] \| [Object][9])** background colour, parsed by the [color][11] module, defaults to black without transparency. (optional, default `{r:0,g:0,b:0,alpha:1}`)
 
 ### Examples
@@ -160,6 +160,16 @@ sharp(input)
   ...
 ```
 
+```javascript
+// Add a row of 10 red pixels to the bottom
+sharp(input)
+  .extend({
+    bottom: 10,
+    background: 'red'
+  })
+  ...
+```
+
 -   Throws **[Error][13]** Invalid parameters
 
 Returns **Sharp** 

docs/changelog.md

@@ -16,6 +16,9 @@ Requires libvips v8.10.6
 
 * Reduce concurrency on glibc-based Linux when using the default memory allocator to help prevent fragmentation.
 
+* Default missing edge properties of extend operation to zero.
+  [#2578](https://github.com/lovell/sharp/issues/2578)
+
 * Ensure composite does not clip top and left offsets.
   [#2594](https://github.com/lovell/sharp/pull/2594)
   [@SHG42](https://github.com/SHG42)

lib/resize.js

@@ -302,11 +302,20 @@ function resize (width, height, options) {
  *   })
  *   ...
  *
+* @example
+ * // Add a row of 10 red pixels to the bottom
+ * sharp(input)
+ *   .extend({
+ *     bottom: 10,
+ *     background: 'red'
+ *   })
+ *   ...
+ *
  * @param {(number|Object)} extend - single pixel count to add to all edges or an Object with per-edge counts
- * @param {number} [extend.top]
- * @param {number} [extend.left]
- * @param {number} [extend.bottom]
- * @param {number} [extend.right]
+ * @param {number} [extend.top=0]
+ * @param {number} [extend.left=0]
+ * @param {number} [extend.bottom=0]
+ * @param {number} [extend.right=0]
  * @param {String|Object} [extend.background={r: 0, g: 0, b: 0, alpha: 1}] - background colour, parsed by the [color](https://www.npmjs.org/package/color) module, defaults to black without transparency.
  * @returns {Sharp}
  * @throws {Error} Invalid parameters
@@ -317,17 +326,35 @@ function extend (extend) {
     this.options.extendBottom = extend;
     this.options.extendLeft = extend;
     this.options.extendRight = extend;
-  } else if (
-    is.object(extend) &&
-    is.integer(extend.top) && extend.top >= 0 &&
-    is.integer(extend.bottom) && extend.bottom >= 0 &&
-    is.integer(extend.left) && extend.left >= 0 &&
-    is.integer(extend.right) && extend.right >= 0
-  ) {
-    this.options.extendTop = extend.top;
-    this.options.extendBottom = extend.bottom;
-    this.options.extendLeft = extend.left;
-    this.options.extendRight = extend.right;
+  } else if (is.object(extend)) {
+    if (is.defined(extend.top)) {
+      if (is.integer(extend.top) && extend.top >= 0) {
+        this.options.extendTop = extend.top;
+      } else {
+        throw is.invalidParameterError('top', 'positive integer', extend.top);
+      }
+    }
+    if (is.defined(extend.bottom)) {
+      if (is.integer(extend.bottom) && extend.bottom >= 0) {
+        this.options.extendBottom = extend.bottom;
+      } else {
+        throw is.invalidParameterError('bottom', 'positive integer', extend.bottom);
+      }
+    }
+    if (is.defined(extend.left)) {
+      if (is.integer(extend.left) && extend.left >= 0) {
+        this.options.extendLeft = extend.left;
+      } else {
+        throw is.invalidParameterError('left', 'positive integer', extend.left);
+      }
+    }
+    if (is.defined(extend.right)) {
+      if (is.integer(extend.right) && extend.right >= 0) {
+        this.options.extendRight = extend.right;
+      } else {
+        throw is.invalidParameterError('right', 'positive integer', extend.right);
+      }
+    }
     this._setBackgroundColourOption('extendBackground', extend.background);
   } else {
     throw is.invalidParameterError('extend', 'integer or object', extend);

test/unit/extend.js

@@ -41,7 +41,6 @@ describe('Extend', function () {
       .resize(120)
       .extend({
         top: 50,
-        bottom: 0,
         left: 10,
         right: 35,
         background: { r: 0, g: 0, b: 0, alpha: 0 }
@@ -64,18 +63,38 @@ describe('Extend', function () {
       sharp().extend(-1);
     });
   });
-  it('partial object fails', function () {
-    assert.throws(function () {
-      sharp().extend({ top: 1 });
-    });
+  it('invalid top fails', () => {
+    assert.throws(
+      () => sharp().extend({ top: 'fail' }),
+      /Expected positive integer for top but received fail of type string/
+    );
+  });
+  it('invalid bottom fails', () => {
+    assert.throws(
+      () => sharp().extend({ bottom: -1 }),
+      /Expected positive integer for bottom but received -1 of type number/
+    );
+  });
+  it('invalid left fails', () => {
+    assert.throws(
+      () => sharp().extend({ left: 0.1 }),
+      /Expected positive integer for left but received 0.1 of type number/
+    );
+  });
+  it('invalid right fails', () => {
+    assert.throws(
+      () => sharp().extend({ right: {} }),
+      /Expected positive integer for right but received \[object Object\] of type object/
+    );
+  });
+  it('can set all edges apart from right', () => {
+    assert.doesNotThrow(() => sharp().extend({ top: 1, left: 2, bottom: 3 }));
   });
 
   it('should add alpha channel before extending with a transparent Background', function (done) {
     sharp(fixtures.inputJpgWithLandscapeExif1)
       .extend({
-        top: 0,
         bottom: 10,
-        left: 0,
         right: 10,
         background: { r: 0, g: 0, b: 0, alpha: 0 }
       })
@@ -91,9 +110,7 @@ describe('Extend', function () {
   it('PNG with 2 channels', function (done) {
     sharp(fixtures.inputPngWithGreyAlpha)
       .extend({
-        top: 0,
         bottom: 20,
-        left: 0,
         right: 20,
         background: 'transparent'
       })