Add support to extend for extendWith, allows copy/mirror/repeat (#3556)

lib/constructor.js

@@ -197,6 +197,7 @@ const Sharp = function (input, options) {
     extendLeft: 0,
     extendRight: 0,
     extendBackground: [0, 0, 0, 255],
+    extendWith: 'background',
     withoutEnlargement: false,
     withoutReduction: false,
     affineMatrix: [],

lib/index.d.ts

@@ -755,7 +755,7 @@ declare namespace sharp {
         resize(options: ResizeOptions): Sharp;
 
         /**
-         * Extends/pads the edges of the image with the provided background colour.
+         * Extends/pads the edges of the image with either the provided background colour or pixels derived from the image.
          * This operation will always occur after resizing and extraction, if any.
          * @param extend single pixel count to add to all edges or an Object with per-edge counts
          * @throws {Error} Invalid parameters
@@ -1245,6 +1245,8 @@ declare namespace sharp {
         sigma?: number | undefined;
     }
 
+    type ExtendWith = 'background' | 'copy' | 'repeat' | 'mirror';
+
     interface ExtendOptions {
         /** single pixel count to top edge (optional, default 0) */
         top?: number | undefined;
@@ -1256,6 +1258,8 @@ declare namespace sharp {
         right?: number | undefined;
         /** background colour, parsed by the color module, defaults to black without transparency. (optional, default {r:0,g:0,b:0,alpha:1}) */
         background?: Color | undefined;
+        /** how the extension is done, one of: "background", "copy", "repeat", "mirror" (optional, default `'background'`) */
+        extendWith?: ExtendWith | undefined;
     }
 
     interface TrimOptions {

lib/resize.js

@@ -36,6 +36,18 @@ const position = {
   'left top': 8
 };
 
+/**
+ * How to extend the image.
+ * @member
+ * @private
+ */
+const extendWith = {
+  background: 'background',
+  copy: 'copy',
+  repeat: 'repeat',
+  mirror: 'mirror'
+};
+
 /**
  * Strategies for automagic cover behaviour.
  * @member
@@ -393,6 +405,13 @@ function extend (extend) {
       }
     }
     this._setBackgroundColourOption('extendBackground', extend.background);
+    if (is.defined(extend.extendWith)) {
+      if (is.string(extendWith[extend.extendWith])) {
+        this.options.extendWith = extendWith[extend.extendWith];
+      } else {
+        throw is.invalidParameterError('extendWith', 'valid value', extend.extendWith);
+      }
+    }
   } else {
     throw is.invalidParameterError('extend', 'integer or object', extend);
   }