Keep shrink-on-load logic DRY. Ensure canvas option (crop vs embed) is always as requested.

binding.gyp

@@ -7,6 +7,8 @@
       '<!@(PKG_CONFIG_PATH="/usr/lib/pkgconfig" pkg-config --libs vips)'
     ],
     'include_dirs': [
+      '/usr/local/include/glib-2.0',
+      '/usr/local/lib/glib-2.0/include',
       '/usr/include/glib-2.0',
       '/usr/lib/glib-2.0/include',
       '/usr/lib/x86_64-linux-gnu/glib-2.0/include'

package.json

@@ -1,6 +1,6 @@
 {
   "name": "sharp",
-  "version": "0.1.1",
+  "version": "0.1.3",
   "author": "Lovell Fuller",
   "description": "High performance module to resize JPEG and PNG images using the libvips image processing library",
   "scripts": {

src/sharp.cc

@@ -98,22 +98,21 @@ void resize_async(uv_work_t *work) {
   int shrink_on_load = 1;
   if (inputImageType == JPEG) {
     if (shrink >= 8) {
-      factor = residual * shrink / 8;
+      factor = factor / 8;
       shrink_on_load = 8;
-      shrink = floor(factor);
-      residual = shrink / factor;
     } else if (shrink >= 4) {
-      factor = residual * shrink / 4;
+      factor = factor / 4;
       shrink_on_load = 4;
-      shrink = floor(factor);
-      residual = shrink / factor;
     } else if (shrink >= 2) {
-      factor = residual * shrink / 2;
+      factor = factor / 2;
       shrink_on_load = 2;
-      shrink = floor(factor);
-      residual = shrink / factor;
     }
     if (shrink_on_load > 1) {
+      // Recalculate integral shrink and double residual
+      factor = std::max(factor, 1.0);
+      shrink = floor(factor);
+      residual = shrink / factor;
+      // Reload input using shrink-on-load 
       g_object_unref(in);
       in = vips_image_new();
       if (baton->buffer_in_len > 1) {
@@ -151,8 +150,8 @@ void resize_async(uv_work_t *work) {
   g_object_unref(shrunk);
 
   VipsImage *canvased = vips_image_new();
-  if (affined->Xsize != baton->width && affined->Ysize != baton->height) {
+  if (affined->Xsize != baton->width || affined->Ysize != baton->height) {
-    if (baton->crop && affined->Xsize != baton->width && affined->Ysize != baton->height) {
+    if (baton->crop) {
       // Crop
       int width = std::min(affined->Xsize, baton->width);
       int height = std::min(affined->Ysize, baton->height);

tests/parallel.js

@@ -0,0 +1,29 @@
+var sharp = require("../index");
+var fs = require("fs");
+var assert = require("assert");
+var async = require("async");
+
+var inputJpg = __dirname + "/2569067123_aca715a2ee_o.jpg"; // http://www.flickr.com/photos/grizdave/2569067123/
+var width = 720;
+var height = 480;
+
+async.mapSeries([1, 1, 2, 4, 8, 16, 32, 64, 128], function(parallelism, next) {
+  var start = new Date().getTime();
+  async.times(parallelism,
+    function(id, callback) {
+      sharp.resize(inputJpg, sharp.buffer.jpeg, width, height, function(err, buffer) {
+        buffer = null;
+        callback(err, new Date().getTime() - start);
+      });
+    },
+    function(err, ids) {
+      assert(!err);
+      assert(ids.length === parallelism);
+      var mean = ids.reduce(function(a, b) {
+        return a + b;
+      }) / ids.length;
+      console.log(parallelism + " parallel calls: fastest=" + ids[0] + "ms slowest=" + ids[ids.length - 1] + "ms mean=" + mean + "ms");
+      next();
+    }
+  );
+}, function() {});