Expose libvips affine operation (#2336)

lib/operation.js

@@ -1,5 +1,6 @@
 'use strict';
 
+const { flatten: flattenArray } = require('array-flatten');
 const color = require('color');
 const is = require('./is');
 
@@ -82,6 +83,103 @@ function flop (flop) {
   return this;
 }
 
+/**
+ * Perform an affine transform on an image. This operation will always occur after resizing, extraction and rotation, if any.
+ *
+ * You must provide an array of length 4 or a 2x2 affine transformation matrix.
+ * By default, new pixels are filled with a black background. You can provide a background color with the `background` option.
+ * A particular interpolator may also be specified. Set the `interpolator` option to an attribute of the `sharp.interpolator` Object e.g. `sharp.interpolator.nohalo`.
+ *
+ * In the case of a 2x2 matrix, the transform is:
+ * - X = `matrix[0, 0]` \* (x + `idx`) + `matrix[0, 1]` \* (y + `idy`) + `odx`
+ * - Y = `matrix[1, 0]` \* (x + `idx`) + `matrix[1, 1]` \* (y + `idy`) + `ody`
+ *
+ * where:
+ * - x and y are the coordinates in input image.
+ * - X and Y are the coordinates in output image.
+ * - (0,0) is the upper left corner.
+ *
+ * @since 0.27.0
+ *
+ * @example
+ * const pipeline = sharp()
+ *   .affine([[1, 0.3], [0.1, 0.7]], {
+ *      background: 'white',
+ *      interpolate: sharp.interpolators.nohalo
+ *   })
+ *   .toBuffer((err, outputBuffer, info) => {
+ *      // outputBuffer contains the transformed image
+ *      // info.width and info.height contain the new dimensions
+ *   });
+ *
+ * inputStream
+ *   .pipe(pipeline);
+ *
+ * @param {Array<Array<number>>|Array<number>} matrix - affine transformation matrix
+ * @param {Object} [options] - if present, is an Object with optional attributes.
+ * @param {String|Object} [options.background="#000000"] - parsed by the [color](https://www.npmjs.org/package/color) module to extract values for red, green, blue and alpha.
+ * @param {Number} [options.idx=0] - input horizontal offset
+ * @param {Number} [options.idy=0] - input vertical offset
+ * @param {Number} [options.odx=0] - output horizontal offset
+ * @param {Number} [options.ody=0] - output vertical offset
+ * @param {String} [options.interpolator=sharp.interpolators.bicubic] - interpolator
+ * @returns {Sharp}
+ * @throws {Error} Invalid parameters
+ */
+function affine (matrix, options) {
+  const flatMatrix = flattenArray(matrix);
+  if (flatMatrix.length === 4 && flatMatrix.every(is.number)) {
+    this.options.affineMatrix = flatMatrix;
+  } else {
+    throw is.invalidParameterError('matrix', '1x4 or 2x2 array', matrix);
+  }
+
+  if (is.defined(options)) {
+    if (is.object(options)) {
+      this._setBackgroundColourOption('affineBackground', options.background);
+      if (is.defined(options.idx)) {
+        if (is.number(options.idx)) {
+          this.options.affineIdx = options.idx;
+        } else {
+          throw is.invalidParameterError('options.idx', 'number', options.idx);
+        }
+      }
+      if (is.defined(options.idy)) {
+        if (is.number(options.idy)) {
+          this.options.affineIdy = options.idy;
+        } else {
+          throw is.invalidParameterError('options.idy', 'number', options.idy);
+        }
+      }
+      if (is.defined(options.odx)) {
+        if (is.number(options.odx)) {
+          this.options.affineOdx = options.odx;
+        } else {
+          throw is.invalidParameterError('options.odx', 'number', options.odx);
+        }
+      }
+      if (is.defined(options.ody)) {
+        if (is.number(options.ody)) {
+          this.options.affineOdy = options.ody;
+        } else {
+          throw is.invalidParameterError('options.ody', 'number', options.ody);
+        }
+      }
+      if (is.defined(options.interpolator)) {
+        if (is.inArray(options.interpolator, Object.values(this.constructor.interpolators))) {
+          this.options.affineInterpolator = options.interpolator;
+        } else {
+          throw is.invalidParameterError('options.interpolator', 'valid interpolator name', options.interpolator);
+        }
+      }
+    } else {
+      throw is.invalidParameterError('options', 'object', options);
+    }
+  }
+
+  return this;
+}
+
 /**
  * Sharpen the image.
  * When used without parameters, performs a fast, mild sharpen of the output image.
@@ -482,6 +580,7 @@ module.exports = function (Sharp) {
     rotate,
     flip,
     flop,
+    affine,
     sharpen,
     median,
     blur,