overlayWith improvements: diff sizes/formats, gravity, buffer input

docs/api.md

@@ -365,13 +365,18 @@ The output image will still be web-friendly sRGB and contain three (identical) c
 
 Enhance output image contrast by stretching its luminance to cover the full dynamic range. This typically reduces performance by 30%.
 
-#### overlayWith(path)
+#### overlayWith(image, [options])
 
-_Experimental_
+Overlay (composite) a image containing an alpha channel over the processed (resized, extracted etc.) image.
 
-Alpha composite image at `path` over the processed (resized, extracted) image. The dimensions of the two images must match.
+`image` is one of the following, and must be the same size or smaller than the processed image:
 
-* `path` is a String containing the path to an image file with an alpha channel.
+* Buffer containing PNG, WebP, GIF or SVG image data, or
+* String containing the path to an image file, with most major transparency formats supported.
+
+`options`, if present, is an Object with the following optional attributes:
+
+* `gravity` is a String or an attribute of the `sharp.gravity` Object e.g. `sharp.gravity.north` at which to place the overlay, defaulting to `center`/`centre`.
 
 ```javascript
 sharp('input.png')
@@ -379,7 +384,7 @@ sharp('input.png')
   .resize(300)
   .flatten()
   .background('#ff6600')
-  .overlayWith('overlay.png')
+  .overlayWith('overlay.png', { gravity: sharp.gravity.southeast } )
   .sharpen()
   .withMetadata()
   .quality(90)
@@ -387,8 +392,8 @@ sharp('input.png')
   .toBuffer()
   .then(function(outputBuffer) {
     // outputBuffer contains upside down, 300px wide, alpha channel flattened
-    // onto orange background, composited with overlay.png, sharpened,
-    // with metadata, 90% quality WebP image data. Phew!
+    // onto orange background, composited with overlay.png with SE gravity,
+    // sharpened, with metadata, 90% quality WebP image data. Phew!
   });
 ```
 

docs/changelog.md

@@ -1,5 +1,11 @@
 # Changelog
 
+### v0.14 - "*needle*"
+
+* Improvements to overlayWith: differing sizes/formats, gravity, buffer input.
+  [#239](https://github.com/lovell/sharp/issues/239)
+  [@chrisriley](https://github.com/chrisriley)
+
 ### v0.13 - "*mind*"
 
 #### v0.13.1 - 27<sup>th</sup> February 2016

index.js

@@ -84,7 +84,9 @@ var Sharp = function(input, options) {
     greyscale: false,
     normalize: 0,
     // overlay
-    overlayPath: '',
+    overlayFileIn: '',
+    overlayBufferIn: null,
+    overlayGravity: 0,
     // output options
     formatOut: 'input',
     fileOut: '',
@@ -106,13 +108,13 @@ var Sharp = function(input, options) {
       module.exports.queue.emit('change', queueLength);
     }
   };
-  if (typeof input === 'string') {
+  if (isString(input)) {
     // input=file
     this.options.fileIn = input;
-  } else if (typeof input === 'object' && input instanceof Buffer) {
+  } else if (isBuffer(input)) {
     // input=buffer
     this.options.bufferIn = input;
-  } else if (typeof input === 'undefined' || input === null) {
+  } else if (!isDefined(input)) {
     // input=stream
     this.options.streamIn = true;
   } else {
@@ -148,6 +150,12 @@ var isDefined = function(val) {
 var isObject = function(val) {
   return typeof val === 'object';
 };
+var isBuffer = function(val) {
+  return typeof val === 'object' && val instanceof Buffer;
+};
+var isString = function(val) {
+  return typeof val === 'string' && val.length > 0;
+};
 var isInteger = function(val) {
   return typeof val === 'number' && !Number.isNaN(val) && val % 1 === 0;
 };
@@ -232,11 +240,11 @@ module.exports.gravity = {
 
 Sharp.prototype.crop = function(gravity) {
   this.options.canvas = 'crop';
-  if (typeof gravity === 'undefined') {
+  if (!isDefined(gravity)) {
     this.options.gravity = module.exports.gravity.center;
-  } else if (typeof gravity === 'number' && !Number.isNaN(gravity) && gravity >= 0 && gravity <= 8) {
+  } else if (isInteger(gravity) && inRange(gravity, 0, 8)) {
     this.options.gravity = gravity;
-  } else if (typeof gravity === 'string' && typeof module.exports.gravity[gravity] === 'number') {
+  } else if (isString(gravity) && isInteger(module.exports.gravity[gravity])) {
     this.options.gravity = module.exports.gravity[gravity];
   } else {
     throw new Error('Unsupported crop gravity ' + gravity);
@@ -316,14 +324,26 @@ Sharp.prototype.negate = function(negate) {
   return this;
 };
 
-Sharp.prototype.overlayWith = function(overlayPath) {
-  if (typeof overlayPath !== 'string') {
-    throw new Error('The overlay path must be a string');
+/*
+  Overlay with another image, using an optional gravity
+*/
+Sharp.prototype.overlayWith = function(overlay, options) {
+  if (isString(overlay)) {
+    this.options.overlayFileIn = overlay;
+  } else if (isBuffer(overlay)) {
+    this.options.overlayBufferIn = overlay;
+  } else {
+    throw new Error('Unsupported overlay ' + typeof overlay);
+  }
+  if (isObject(options)) {
+    if (isInteger(options.gravity) && inRange(options.gravity, 0, 8)) {
+      this.options.overlayGravity = options.gravity;
+    } else if (isString(options.gravity) && isInteger(module.exports.gravity[options.gravity])) {
+      this.options.overlayGravity = module.exports.gravity[options.gravity];
+    } else if (isDefined(options.gravity)) {
+      throw new Error('Unsupported overlay gravity ' + options.gravity);
     }
-  if (overlayPath === '') {
-    throw new Error('The overlay path cannot be empty');
   }
-  this.options.overlayPath = overlayPath;
   return this;
 };
 

package.json

@@ -1,6 +1,6 @@
 {
   "name": "sharp",
-  "version": "0.13.1",
+  "version": "0.14.0",
   "author": "Lovell Fuller <npm@lovell.info>",
   "contributors": [
     "Pierre Inglebert <pierre.inglebert@gmail.com>",

src/common.cc

@@ -185,4 +185,45 @@ namespace sharp {
     }
   }
 
+  /*
+    Calculate the (left, top) coordinates of the output image
+    within the input image, applying the given gravity.
+  */
+  std::tuple<int, int> CalculateCrop(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;
+      case 5: // Northeast
+        left = inWidth - outWidth;
+        break;
+      case 6: // Southeast
+        left = inWidth - outWidth;
+        top = inHeight - outHeight;
+      case 7: // Southwest
+        top = inHeight - outHeight;
+      case 8: // Northwest
+        break;
+      default: // Centre
+        left = (inWidth - outWidth + 1) / 2;
+        top = (inHeight - outHeight + 1) / 2;
+    }
+    return std::make_tuple(left, top);
+  }
+
 } // namespace sharp

src/common.h

@@ -2,6 +2,8 @@
 #define SRC_COMMON_H_
 
 #include <string>
+#include <tuple>
+
 #include <vips/vips8>
 
 using vips::VImage;
@@ -80,6 +82,13 @@ namespace sharp {
   */
   void FreeCallback(char* data, void* hint);
 
+  /*
+    Calculate the (left, top) coordinates of the output image
+    within the input image, applying the given gravity.
+  */
+  std::tuple<int, int> CalculateCrop(int const inWidth, int const inHeight,
+    int const outWidth, int const outHeight, int const gravity);
+
 }  // namespace sharp
 
 #endif  // SRC_COMMON_H_

src/operations.cc

@@ -4,34 +4,49 @@
 #include "operations.h"
 
 using vips::VImage;
+using vips::VError;
 
 namespace sharp {
 
   /*
-    Alpha composite src over dst
-    Assumes alpha channels are already premultiplied and will be unpremultiplied after
+    Alpha composite src over dst with given gravity.
+    Assumes alpha channels are already premultiplied and will be unpremultiplied after.
    */
-  VImage Composite(VImage src, VImage dst) {
+  VImage Composite(VImage src, VImage dst, const int gravity) {
+    using sharp::CalculateCrop;
     using sharp::HasAlpha;
 
-    // Split src into non-alpha and alpha
+    if (!HasAlpha(src)) {
+      throw VError("Overlay image must have an alpha channel");
+    }
+    if (!HasAlpha(dst)) {
+      throw VError("Image to be overlaid must have an alpha channel");
+    }
+    if (src.width() > dst.width() || src.height() > dst.height()) {
+      throw VError("Overlay image must have same dimensions or smaller");
+    }
+
+    // Enlarge overlay src, if required
+    if (src.width() < dst.width() || src.height() < dst.height()) {
+      // Calculate the (left, top) coordinates of the output image within the input image, applying the given gravity.
+      int left;
+      int top;
+      std::tie(left, top) = CalculateCrop(dst.width(), dst.height(), src.width(), src.height(), gravity);
+      // Embed onto transparent background
+      std::vector<double> background { 0.0, 0.0, 0.0, 0.0 };
+      src = src.embed(left, top, dst.width(), dst.height(), VImage::option()
+        ->set("extend", VIPS_EXTEND_BACKGROUND)
+        ->set("background", background)
+      );
+    }
+
+    // Split src into non-alpha and alpha channels
     VImage srcWithoutAlpha = src.extract_band(0, VImage::option()->set("n", src.bands() - 1));
     VImage srcAlpha = src[src.bands() - 1] * (1.0 / 255.0);
 
     // Split dst into non-alpha and alpha channels
-    VImage dstWithoutAlpha;
-    VImage dstAlpha;
-    if (HasAlpha(dst)) {
-      // Non-alpha: extract all-but-last channel
-      dstWithoutAlpha = dst.extract_band(0, VImage::option()->set("n", dst.bands() - 1));
-      // Alpha: Extract last channel
-      dstAlpha = dst[dst.bands() - 1] * (1.0 / 255.0);
-    } else {
-      // Non-alpha: Copy reference
-      dstWithoutAlpha = dst;
-      // Alpha: Use blank, opaque (0xFF) image
-      dstAlpha = VImage::black(dst.width(), dst.height()).invert();
-    }
+    VImage dstWithoutAlpha = dst.extract_band(0, VImage::option()->set("n", dst.bands() - 1));
+    VImage dstAlpha = dst[dst.bands() - 1] * (1.0 / 255.0);
 
     //
     // Compute normalized output alpha channel:

src/operations.h

@@ -8,10 +8,10 @@ using vips::VImage;
 namespace sharp {
 
   /*
-    Composite images `src` and `dst` with premultiplied alpha channel and output
-    image with premultiplied alpha.
+    Alpha composite src over dst with given gravity.
+    Assumes alpha channels are already premultiplied and will be unpremultiplied after.
    */
-  VImage Composite(VImage src, VImage dst);
+  VImage Composite(VImage src, VImage dst, const int gravity);
 
   /*
    * Stretch luminance to cover full dynamic range.

src/pipeline.cc

@@ -1,10 +1,12 @@
-#include <tuple>
 #include <algorithm>
-#include <utility>
 #include <cmath>
+#include <tuple>
+#include <utility>
+
+#include <vips/vips8>
+
 #include <node.h>
 #include <node_buffer.h>
-#include <vips/vips8>
 
 #include "nan.h"
 
@@ -62,133 +64,22 @@ using sharp::IsWebp;
 using sharp::IsTiff;
 using sharp::IsDz;
 using sharp::FreeCallback;
+using sharp::CalculateCrop;
 using sharp::counterProcess;
 using sharp::counterQueue;
 
-enum class Canvas {
-  CROP,
-  EMBED,
-  MAX,
-  MIN,
-  IGNORE_ASPECT
-};
-
-struct PipelineBaton {
-  std::string fileIn;
-  char *bufferIn;
-  size_t bufferInLength;
-  std::string iccProfilePath;
-  int limitInputPixels;
-  std::string density;
-  int rawWidth;
-  int rawHeight;
-  int rawChannels;
-  std::string formatOut;
-  std::string fileOut;
-  void *bufferOut;
-  size_t bufferOutLength;
-  int topOffsetPre;
-  int leftOffsetPre;
-  int widthPre;
-  int heightPre;
-  int topOffsetPost;
-  int leftOffsetPost;
-  int widthPost;
-  int heightPost;
-  int width;
-  int height;
-  int channels;
-  Canvas canvas;
-  int gravity;
-  std::string interpolator;
-  double background[4];
-  bool flatten;
-  bool negate;
-  double blurSigma;
-  int sharpenRadius;
-  double sharpenFlat;
-  double sharpenJagged;
-  int threshold;
-  std::string overlayPath;
-  double gamma;
-  bool greyscale;
-  bool normalize;
-  int angle;
-  bool rotateBeforePreExtract;
-  bool flip;
-  bool flop;
-  bool progressive;
-  bool withoutEnlargement;
-  VipsAccess accessMethod;
-  int quality;
-  int compressionLevel;
-  bool withoutAdaptiveFiltering;
-  bool withoutChromaSubsampling;
-  bool trellisQuantisation;
-  bool overshootDeringing;
-  bool optimiseScans;
-  std::string err;
-  bool withMetadata;
-  int withMetadataOrientation;
-  int tileSize;
-  int tileOverlap;
-
-  PipelineBaton():
-    bufferInLength(0),
-    limitInputPixels(0),
-    density(""),
-    rawWidth(0),
-    rawHeight(0),
-    rawChannels(0),
-    formatOut(""),
-    fileOut(""),
-    bufferOutLength(0),
-    topOffsetPre(-1),
-    topOffsetPost(-1),
-    channels(0),
-    canvas(Canvas::CROP),
-    gravity(0),
-    flatten(false),
-    negate(false),
-    blurSigma(0.0),
-    sharpenRadius(0),
-    sharpenFlat(1.0),
-    sharpenJagged(2.0),
-    threshold(0),
-    gamma(0.0),
-    greyscale(false),
-    normalize(false),
-    angle(0),
-    flip(false),
-    flop(false),
-    progressive(false),
-    withoutEnlargement(false),
-    quality(80),
-    compressionLevel(6),
-    withoutAdaptiveFiltering(false),
-    withoutChromaSubsampling(false),
-    trellisQuantisation(false),
-    overshootDeringing(false),
-    optimiseScans(false),
-    withMetadata(false),
-    withMetadataOrientation(-1),
-    tileSize(256),
-    tileOverlap(0) {
-      background[0] = 0.0;
-      background[1] = 0.0;
-      background[2] = 0.0;
-      background[3] = 255.0;
-    }
-};
-
 class PipelineWorker : public AsyncWorker {
 
  public:
-  PipelineWorker(Callback *callback, PipelineBaton *baton, Callback *queueListener, const Local<Object> &bufferIn) :
+  PipelineWorker(Callback *callback, PipelineBaton *baton, Callback *queueListener,
+    const Local<Object> &bufferIn, const Local<Object> &overlayBufferIn) :
     AsyncWorker(callback), baton(baton), queueListener(queueListener) {
       if (baton->bufferInLength > 0) {
         SaveToPersistent("bufferIn", bufferIn);
       }
+      if (baton->overlayBufferInLength > 0) {
+        SaveToPersistent("overlayBufferIn", overlayBufferIn);
+      }
     }
   ~PipelineWorker() {}
 
@@ -508,11 +399,19 @@ class PipelineWorker : public AsyncWorker {
         }
       }
 
+      // Ensure image has an alpha channel when there is an overlay
+      bool hasOverlay = baton->overlayBufferInLength > 0 || !baton->overlayFileIn.empty();
+      if (hasOverlay && !HasAlpha(image)) {
+        double multiplier = (image.interpretation() == VIPS_INTERPRETATION_RGB16) ? 256.0 : 1.0;
+        image = image.bandjoin(
+          VImage::new_matrix(image.width(), image.height()).new_from_image(255 * multiplier)
+        );
+      }
+
       bool shouldAffineTransform = xresidual != 0.0 || yresidual != 0.0;
       bool shouldBlur = baton->blurSigma != 0.0;
       bool shouldSharpen = baton->sharpenRadius != 0;
       bool shouldThreshold = baton->threshold != 0;
-      bool hasOverlay = !baton->overlayPath.empty();
       bool shouldPremultiplyAlpha = HasAlpha(image) &&
         (shouldAffineTransform || shouldBlur || shouldSharpen || hasOverlay);
 
@@ -634,38 +533,41 @@ class PipelineWorker : public AsyncWorker {
       // Composite with overlay, if present
       if (hasOverlay) {
         VImage overlayImage;
-        ImageType overlayImageType = DetermineImageType(baton->overlayPath.data());
+        ImageType overlayImageType = ImageType::UNKNOWN;
+        if (baton->overlayBufferInLength > 0) {
+          // Overlay with image from buffer
+          overlayImageType = DetermineImageType(baton->overlayBufferIn, baton->overlayBufferInLength);
           if (overlayImageType != ImageType::UNKNOWN) {
-          overlayImage = VImage::new_from_file(
-            baton->overlayPath.data(),
-            VImage::option()->set("access", baton->accessMethod)
-          );
+            try {
+              overlayImage = VImage::new_from_buffer(baton->overlayBufferIn, baton->overlayBufferInLength,
+                nullptr, VImage::option()->set("access", baton->accessMethod));
+            } catch (...) {
+              (baton->err).append("Overlay buffer has corrupt header");
+              overlayImageType = ImageType::UNKNOWN;
+            }
           } else {
-          (baton->err).append("Overlay image is of an unsupported image format");
+            (baton->err).append("Overlay buffer contains unsupported image format");
+          }
+        } else {
+          // Overlay with image from file
+          overlayImageType = DetermineImageType(baton->overlayFileIn.data());
+          if (overlayImageType != ImageType::UNKNOWN) {
+            try {
+              overlayImage = VImage::new_from_file(baton->overlayFileIn.data(),
+                VImage::option()->set("access", baton->accessMethod));
+            } catch (...) {
+              (baton->err).append("Overlay file has corrupt header");
+              overlayImageType = ImageType::UNKNOWN;
+            }
+          }
+        }
+        if (overlayImageType == ImageType::UNKNOWN) {
           return Error();
         }
-        if (image.format() != VIPS_FORMAT_UCHAR && image.format() != VIPS_FORMAT_FLOAT) {
-          (baton->err).append("Expected image band format to be uchar or float: ");
-          (baton->err).append(vips_enum_nick(VIPS_TYPE_BAND_FORMAT, image.format()));
-          return Error();
-        }
-        if (overlayImage.format() != VIPS_FORMAT_UCHAR && overlayImage.format() != VIPS_FORMAT_FLOAT) {
-          (baton->err).append("Expected overlay image band format to be uchar or float: ");
-          (baton->err).append(vips_enum_nick(VIPS_TYPE_BAND_FORMAT, overlayImage.format()));
-          return Error();
-        }
-        if (!HasAlpha(overlayImage)) {
-          (baton->err).append("Overlay image must have an alpha channel");
-          return Error();
-        }
-        if (overlayImage.width() != image.width() && overlayImage.height() != image.height()) {
-          (baton->err).append("Overlay image must have same dimensions as resized image");
-          return Error();
-        }
-        // Ensure overlay is sRGB and premutiplied
+        // Ensure overlay is premultiplied sRGB
         overlayImage = overlayImage.colourspace(VIPS_INTERPRETATION_sRGB).premultiply();
-
-        image = Composite(overlayImage, image);
+        // Composite images with given gravity
+        image = Composite(overlayImage, image, baton->overlayGravity);
       }
 
       // Reverse premultiplication after all transformations:
@@ -708,6 +610,9 @@ class PipelineWorker : public AsyncWorker {
         SetExifOrientation(image, baton->withMetadataOrientation);
       }
 
+      // Number of channels used in output image
+      baton->channels = image.bands();
+
       // Output
       if (baton->fileOut == "") {
         // Buffer output
@@ -728,6 +633,7 @@ class PipelineWorker : public AsyncWorker {
           area->free_fn = nullptr;
           vips_area_unref(area);
           baton->formatOut = "jpeg";
+          baton->channels = std::min(baton->channels, 3);
         } else if (baton->formatOut == "png" || (baton->formatOut == "input" && inputImageType == ImageType::PNG)) {
           // Write PNG to buffer
           VipsArea *area = VIPS_AREA(image.pngsave_buffer(VImage::option()
@@ -800,6 +706,7 @@ class PipelineWorker : public AsyncWorker {
             ->set("interlace", baton->progressive)
           );
           baton->formatOut = "jpeg";
+          baton->channels = std::min(baton->channels, 3);
         } else if (baton->formatOut == "png" || isPng || (matchInput && inputImageType == ImageType::PNG)) {
           // Write PNG to file
           image.pngsave(const_cast<char*>(baton->fileOut.data()), VImage::option()
@@ -824,6 +731,7 @@ class PipelineWorker : public AsyncWorker {
             ->set("compression", VIPS_FOREIGN_TIFF_COMPRESSION_JPEG)
           );
           baton->formatOut = "tiff";
+          baton->channels = std::min(baton->channels, 3);
         } else if (baton->formatOut == "dz" || IsDz(baton->fileOut)) {
           // Write DZ to file
           image.dzsave(const_cast<char*>(baton->fileOut.data()), VImage::option()
@@ -838,8 +746,6 @@ class PipelineWorker : public AsyncWorker {
           return Error();
         }
       }
-      // Number of channels used in output image
-      baton->channels = image.bands();
     } catch (VError const &err) {
       (baton->err).append(err.what());
     }
@@ -890,10 +796,13 @@ class PipelineWorker : public AsyncWorker {
       }
     }
 
-    // Dispose of Persistent wrapper around input Buffer so it can be garbage collected
+    // Dispose of Persistent wrapper around input Buffers so they can be garbage collected
     if (baton->bufferInLength > 0) {
       GetFromPersistent("bufferIn");
     }
+    if (baton->overlayBufferInLength > 0) {
+      GetFromPersistent("overlayBufferIn");
+    }
     delete baton;
 
     // Decrement processing task counter
@@ -944,46 +853,6 @@ class PipelineWorker : public AsyncWorker {
     return std::make_tuple(rotate, flip, flop);
   }
 
-  /*
-    Calculate the (left, top) coordinates of the output image
-    within the input image, applying the given gravity.
-  */
-  std::tuple<int, int>
-  CalculateCrop(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;
-      case 5: // Northeast
-        left = inWidth - outWidth;
-        break;
-      case 6: // Southeast
-        left = inWidth - outWidth;
-        top = inHeight - outHeight;
-      case 7: // Southwest
-        top = inHeight - outHeight;
-      case 8: // Northwest
-        break;
-      default: // Centre
-        left = (inWidth - outWidth + 1) / 2;
-        top = (inHeight - outHeight + 1) / 2;
-    }
-    return std::make_tuple(left, top);
-  }
-
   /*
     Calculate integral shrink given factor and interpolator window size
   */
@@ -1088,7 +957,14 @@ NAN_METHOD(pipeline) {
     baton->background[i] = To<int32_t>(Get(background, i).ToLocalChecked()).FromJust();
   }
   // Overlay options
-  baton->overlayPath = attrAsStr(options, "overlayPath");
+  baton->overlayFileIn = attrAsStr(options, "overlayFileIn");
+  Local<Object> overlayBufferIn;
+  if (node::Buffer::HasInstance(Get(options, New("overlayBufferIn").ToLocalChecked()).ToLocalChecked())) {
+    overlayBufferIn = Get(options, New("overlayBufferIn").ToLocalChecked()).ToLocalChecked().As<Object>();
+    baton->overlayBufferInLength = node::Buffer::Length(overlayBufferIn);
+    baton->overlayBufferIn = node::Buffer::Data(overlayBufferIn);
+  }
+  baton->overlayGravity = attrAs<int32_t>(options, "overlayGravity");
   // Resize options
   baton->withoutEnlargement = attrAs<bool>(options, "withoutEnlargement");
   baton->gravity = attrAs<int32_t>(options, "gravity");
@@ -1131,7 +1007,7 @@ NAN_METHOD(pipeline) {
 
   // Join queue for worker thread
   Callback *callback = new Callback(info[1].As<Function>());
-  AsyncQueueWorker(new PipelineWorker(callback, baton, queueListener, bufferIn));
+  AsyncQueueWorker(new PipelineWorker(callback, baton, queueListener, bufferIn, overlayBufferIn));
 
   // Increment queued task counter
   g_atomic_int_inc(&counterQueue);

src/pipeline.h

@@ -5,4 +5,125 @@
 
 NAN_METHOD(pipeline);
 
+enum class Canvas {
+  CROP,
+  EMBED,
+  MAX,
+  MIN,
+  IGNORE_ASPECT
+};
+
+struct PipelineBaton {
+  std::string fileIn;
+  char *bufferIn;
+  size_t bufferInLength;
+  std::string iccProfilePath;
+  int limitInputPixels;
+  std::string density;
+  int rawWidth;
+  int rawHeight;
+  int rawChannels;
+  std::string formatOut;
+  std::string fileOut;
+  void *bufferOut;
+  size_t bufferOutLength;
+  std::string overlayFileIn;
+  char *overlayBufferIn;
+  size_t overlayBufferInLength;
+  int overlayGravity;
+  int topOffsetPre;
+  int leftOffsetPre;
+  int widthPre;
+  int heightPre;
+  int topOffsetPost;
+  int leftOffsetPost;
+  int widthPost;
+  int heightPost;
+  int width;
+  int height;
+  int channels;
+  Canvas canvas;
+  int gravity;
+  std::string interpolator;
+  double background[4];
+  bool flatten;
+  bool negate;
+  double blurSigma;
+  int sharpenRadius;
+  double sharpenFlat;
+  double sharpenJagged;
+  int threshold;
+  double gamma;
+  bool greyscale;
+  bool normalize;
+  int angle;
+  bool rotateBeforePreExtract;
+  bool flip;
+  bool flop;
+  bool progressive;
+  bool withoutEnlargement;
+  VipsAccess accessMethod;
+  int quality;
+  int compressionLevel;
+  bool withoutAdaptiveFiltering;
+  bool withoutChromaSubsampling;
+  bool trellisQuantisation;
+  bool overshootDeringing;
+  bool optimiseScans;
+  std::string err;
+  bool withMetadata;
+  int withMetadataOrientation;
+  int tileSize;
+  int tileOverlap;
+
+  PipelineBaton():
+    bufferInLength(0),
+    limitInputPixels(0),
+    density(""),
+    rawWidth(0),
+    rawHeight(0),
+    rawChannels(0),
+    formatOut(""),
+    fileOut(""),
+    bufferOutLength(0),
+    overlayBufferInLength(0),
+    overlayGravity(0),
+    topOffsetPre(-1),
+    topOffsetPost(-1),
+    channels(0),
+    canvas(Canvas::CROP),
+    gravity(0),
+    flatten(false),
+    negate(false),
+    blurSigma(0.0),
+    sharpenRadius(0),
+    sharpenFlat(1.0),
+    sharpenJagged(2.0),
+    threshold(0),
+    gamma(0.0),
+    greyscale(false),
+    normalize(false),
+    angle(0),
+    flip(false),
+    flop(false),
+    progressive(false),
+    withoutEnlargement(false),
+    quality(80),
+    compressionLevel(6),
+    withoutAdaptiveFiltering(false),
+    withoutChromaSubsampling(false),
+    trellisQuantisation(false),
+    overshootDeringing(false),
+    optimiseScans(false),
+    withMetadata(false),
+    withMetadataOrientation(-1),
+    tileSize(256),
+    tileOverlap(0) {
+      background[0] = 0.0;
+      background[1] = 0.0;
+      background[2] = 0.0;
+      background[3] = 255.0;
+    }
+};
+
 #endif  // SRC_PIPELINE_H_

test/unit/overlay.js

@@ -1,5 +1,6 @@
 'use strict';
 
+var fs = require('fs');
 var assert = require('assert');
 var fixtures = require('../fixtures');
 var sharp = require('../../index');
@@ -17,7 +18,7 @@ var getPaths = function(baseName, extension) {
 
 // Test
 describe('Overlays', function() {
-  it('Overlay transparent PNG on solid background', function(done) {
+  it('Overlay transparent PNG file on solid background', function(done) {
     var paths = getPaths('alpha-layer-01');
 
     sharp(fixtures.inputPngOverlayLayer0)
@@ -29,6 +30,18 @@ describe('Overlays', function() {
       });
   });
 
+  it('Overlay transparent PNG Buffer on solid background', function(done) {
+    var paths = getPaths('alpha-layer-01');
+
+    sharp(fixtures.inputPngOverlayLayer0)
+      .overlayWith(fs.readFileSync(fixtures.inputPngOverlayLayer1))
+      .toFile(paths.actual, function (error) {
+        if (error) return done(error);
+        fixtures.assertMaxColourDistance(paths.actual, paths.expected);
+        done();
+      });
+  });
+
   it('Overlay low-alpha transparent PNG on solid background', function(done) {
     var paths = getPaths('alpha-layer-01-low-alpha');
 
@@ -141,18 +154,19 @@ describe('Overlays', function() {
     });
   }
 
-  it('Fail when compositing images with different dimensions', function(done) {
-    sharp(fixtures.inputJpg)
-      .overlayWith(fixtures.inputPngWithGreyAlpha)
+  it('Fail when overlay does not contain alpha channel', function(done) {
+    sharp(fixtures.inputPngOverlayLayer1)
+      .overlayWith(fixtures.inputJpg)
       .toBuffer(function(error) {
         assert.strictEqual(true, error instanceof Error);
         done();
       });
   });
 
-  it('Fail when compositing non-PNG image', function(done) {
-    sharp(fixtures.inputPngOverlayLayer1)
-      .overlayWith(fixtures.inputJpg)
+  it('Fail when overlay is larger', function(done) {
+    sharp(fixtures.inputJpg)
+      .resize(320)
+      .overlayWith(fixtures.inputPngOverlayLayer1)
       .toBuffer(function(error) {
         assert.strictEqual(true, error instanceof Error);
         done();
@@ -170,4 +184,62 @@ describe('Overlays', function() {
       sharp().overlayWith(1);
     });
   });
+
+  it('Fail with unsupported gravity', function() {
+    assert.throws(function() {
+      sharp()
+        .overlayWith(fixtures.inputPngOverlayLayer1, {
+          gravity: 9
+        });
+    });
+  });
+
+  it('Empty options', function() {
+    assert.doesNotThrow(function() {
+      sharp().overlayWith(fixtures.inputPngOverlayLayer1, {});
+    });
+  });
+
+  describe('Overlay with numeric gravity', function() {
+    Object.keys(sharp.gravity).forEach(function(gravity) {
+      it(gravity, function(done) {
+        var expected = fixtures.expected('overlay-gravity-' + gravity + '.jpg');
+        sharp(fixtures.inputJpg)
+          .resize(80)
+          .overlayWith(fixtures.inputPngWithTransparency16bit, {
+            gravity: gravity
+          })
+          .toBuffer(function(err, data, info) {
+            if (err) throw err;
+            assert.strictEqual('jpeg', info.format);
+            assert.strictEqual(80, info.width);
+            assert.strictEqual(65, info.height);
+            assert.strictEqual(3, info.channels);
+            fixtures.assertSimilar(expected, data, done);
+          });
+      });
+    });
+  });
+
+  describe('Overlay with string-based gravity', function() {
+    Object.keys(sharp.gravity).forEach(function(gravity) {
+      it(gravity, function(done) {
+        var expected = fixtures.expected('overlay-gravity-' + gravity + '.jpg');
+        sharp(fixtures.inputJpg)
+          .resize(80)
+          .overlayWith(fixtures.inputPngWithTransparency16bit, {
+            gravity: sharp.gravity[gravity]
+          })
+          .toBuffer(function(err, data, info) {
+            if (err) throw err;
+            assert.strictEqual('jpeg', info.format);
+            assert.strictEqual(80, info.width);
+            assert.strictEqual(65, info.height);
+            assert.strictEqual(3, info.channels);
+            fixtures.assertSimilar(expected, data, done);
+          });
+      });
+    });
+  });
+
 });