Add gravity support to crop #45

README.md

@@ -95,7 +95,7 @@ sharp('input.jpg').resize(300, 200).toFile('output.jpg', function(err) {
 ```
 
 ```javascript
-var transformer = sharp().resize(300, 200);
+var transformer = sharp().resize(300, 200).crop(sharp.gravity.north);
 readableStream.pipe(transformer).pipe(writableStream);
 // Read image data from readableStream, resize and write image data to writableStream
 ```
@@ -183,10 +183,14 @@ Scale output to `width` x `height`. By default, the resized image is cropped to
 
 `height` is the Number of pixels high the resultant image should be. Use `null` or `undefined` to auto-scale the height to match the width.
 
-#### crop()
+#### crop([gravity])
 
 Crop the resized image to the exact size specified, the default behaviour.
 
+`gravity`, if present, is an attribute of the `sharp.gravity` Object e.g. `sharp.gravity.north`.
+
+Possible values are `north`, `east`, `south`, `west`, `center` and `centre`. The default gravity is `center`/`centre`.
+
 #### max()
 
 Preserving aspect ratio, resize the image to the maximum width or height specified.

binding.gyp

@@ -13,9 +13,9 @@
       '<!(node -e "require(\'nan\')")'
     ],
     'cflags': ['-fexceptions', '-Wall', '-O3'],
-    'cflags_cc': ['-fexceptions', '-Wall', '-O3'],
+    'cflags_cc': ['-std=c++0x', '-fexceptions', '-Wall', '-O3'],
     'xcode_settings': {
-      'OTHER_CFLAGS': ['-fexceptions', '-Wall', '-O3']
+      'OTHER_CFLAGS': ['-std=c++11', '-fexceptions', '-Wall', '-O3']
     }
   }]
 }

index.js

@@ -15,6 +15,7 @@ var Sharp = function(input) {
     width: -1,
     height: -1,
     canvas: 'c',
+    gravity: 0,
     angle: 0,
     withoutEnlargement: false,
     sharpen: false,
@@ -72,8 +73,19 @@ Sharp.prototype._write = function(chunk, encoding, callback) {
   }
 };
 
-Sharp.prototype.crop = function() {
+// Crop this part of the resized image (Center/Centre, North, East, South, West)
+module.exports.gravity = {'center': 0, 'centre': 0, 'north': 1, 'east': 2, 'south': 3, 'west': 4};
+
+Sharp.prototype.crop = function(gravity) {
   this.options.canvas = 'c';
+  if (typeof gravity !== 'undefined') {
+    // Is this a supported gravity?
+    if (!Number.isNaN(gravity) && gravity >= 0 && gravity <= 4) {
+      this.options.gravity = gravity;
+    } else {
+      throw new Error('Unsupported crop gravity ' + gravity);
+    }
+  }
   return this;
 };
 

src/sharp.cc

@@ -3,6 +3,7 @@
 #include <math.h>
 #include <string>
 #include <string.h>
+#include <tuple>
 #include <vips/vips.h>
 
 #include "nan.h"
@@ -20,6 +21,7 @@ struct resize_baton {
   int width;
   int height;
   bool crop;
+  int gravity;
   bool max;
   VipsExtend extend;
   bool sharpen;
@@ -36,6 +38,7 @@ struct resize_baton {
     buffer_in_len(0),
     buffer_out_len(0),
     crop(false),
+    gravity(0),
     max(false),
     sharpen(false),
     progressive(false),
@@ -94,7 +97,8 @@ static void resize_error(resize_baton *baton, VipsImage *unref) {
    2. Use input image EXIF Orientation header (does not support mirroring)
    3. Otherwise default to zero, i.e. no rotation
 */
-static VipsAngle calc_rotation(int const angle, VipsImage const *input) {
+static VipsAngle
+sharp_calc_rotation(int const angle, VipsImage const *input) {
   VipsAngle rotate = VIPS_ANGLE_0;
   if (angle == -1) {
     const char *exif;
@@ -119,6 +123,36 @@ static VipsAngle calc_rotation(int const angle, VipsImage const *input) {
   return rotate;
 }
 
+/*
+  Calculate the (left, top) coordinates of the output image
+  within the input image, applying the given gravity.
+*/
+static std::tuple<int, int>
+sharp_calc_crop(int const inWidth, int const inHeight, int const outWidth, int const outHeight, int const gravity) {
+  int left = 0;
+  int top = 0;
+  switch (gravity) {
+    case 1: // North
+      left = (inWidth - outWidth + 1) / 2;
+      break;
+    case 2: // East
+      left = inWidth - outWidth;
+      top = (inHeight - outHeight + 1) / 2;
+      break;
+    case 3: // South
+      left = (inWidth - outWidth + 1) / 2;
+      top = inHeight - outHeight;
+      break;
+    case 4: // West
+      top = (inHeight - outHeight + 1) / 2;
+      break;
+    default: // Centre
+      left = (inWidth - outWidth + 1) / 2;
+      top = (inHeight - outHeight + 1) / 2;
+  }
+  return std::make_tuple(left, top);
+}
+
 class ResizeWorker : public NanAsyncWorker {
  public:
   ResizeWorker(NanCallback *callback, resize_baton *baton)
@@ -189,7 +223,7 @@ class ResizeWorker : public NanAsyncWorker {
     int inputHeight = in->Ysize;
 
     // Calculate angle of rotation, to be carried out later
-    VipsAngle rotation = calc_rotation(baton->angle, in);
+    VipsAngle rotation = sharp_calc_rotation(baton->angle, in);
     if (rotation == VIPS_ANGLE_90 || rotation == VIPS_ANGLE_270) {
       // Swap input output width and height when rotating by 90 or 270 degrees
       int swap = inputWidth;
@@ -337,10 +371,11 @@ class ResizeWorker : public NanAsyncWorker {
     if (rotated->Xsize != baton->width || rotated->Ysize != baton->height) {
       if (baton->crop || baton->max) {
         // Crop/max
+        int left;
+        int top;
+        std::tie(left, top) = sharp_calc_crop(rotated->Xsize, rotated->Ysize, baton->width, baton->height, baton->gravity);
         int width = std::min(rotated->Xsize, baton->width);
         int height = std::min(rotated->Ysize, baton->height);
-        int left = (rotated->Xsize - width + 1) / 2;
-        int top = (rotated->Ysize - height + 1) / 2;
         if (vips_extract_area(rotated, &canvased, left, top, width, height, NULL)) {
           return resize_error(baton, rotated);
         }
@@ -507,6 +542,7 @@ NAN_METHOD(resize) {
     baton->max = true;
   }
   // Other options
+  baton->gravity = options->Get(NanNew<String>("gravity"))->Int32Value();
   baton->sharpen = options->Get(NanNew<String>("sharpen"))->BooleanValue();
   baton->interpolator = *String::Utf8Value(options->Get(NanNew<String>("interpolator"))->ToString());
   baton->progressive = options->Get(NanNew<String>("progressive"))->BooleanValue();

tests/unit.js

@@ -344,6 +344,60 @@ async.series([
     var pipeline = sharp().resize(320, 240);
     readable.pipe(pipeline).pipe(writable)
   },
+  // Crop, gravity=north
+  function(done) {
+    sharp(inputJpg).resize(320, 80).crop(sharp.gravity.north).toFile(path.join(fixturesPath, 'output.gravity-north.jpg'), function(err, info) {
+      if (err) throw err;
+      assert.strictEqual(320, info.width);
+      assert.strictEqual(80, info.height);
+      done();
+    });
+  },
+  // Crop, gravity=east
+  function(done) {
+    sharp(inputJpg).resize(80, 320).crop(sharp.gravity.east).toFile(path.join(fixturesPath, 'output.gravity-east.jpg'), function(err, info) {
+      if (err) throw err;
+      assert.strictEqual(80, info.width);
+      assert.strictEqual(320, info.height);
+      done();
+    });
+  },
+  // Crop, gravity=south
+  function(done) {
+    sharp(inputJpg).resize(320, 80).crop(sharp.gravity.south).toFile(path.join(fixturesPath, 'output.gravity-south.jpg'), function(err, info) {
+      if (err) throw err;
+      assert.strictEqual(320, info.width);
+      assert.strictEqual(80, info.height);
+      done();
+    });
+  },
+  // Crop, gravity=west
+  function(done) {
+    sharp(inputJpg).resize(80, 320).crop(sharp.gravity.west).toFile(path.join(fixturesPath, 'output.gravity-west.jpg'), function(err, info) {
+      if (err) throw err;
+      assert.strictEqual(80, info.width);
+      assert.strictEqual(320, info.height);
+      done();
+    });
+  },
+  // Crop, gravity=center
+  function(done) {
+    sharp(inputJpg).resize(320, 80).crop(sharp.gravity.center).toFile(path.join(fixturesPath, 'output.gravity-center.jpg'), function(err, info) {
+      if (err) throw err;
+      assert.strictEqual(320, info.width);
+      assert.strictEqual(80, info.height);
+      done();
+    });
+  },
+  // Crop, gravity=centre
+  function(done) {
+    sharp(inputJpg).resize(80, 320).crop(sharp.gravity.centre).toFile(path.join(fixturesPath, 'output.gravity-centre.jpg'), function(err, info) {
+      if (err) throw err;
+      assert.strictEqual(80, info.width);
+      assert.strictEqual(320, info.height);
+      done();
+    });
+  },
   // Verify internal counters
   function(done) {
     var counters = sharp.counters();