Add background option to tile output operation (#1924)

docs/api-output.md

@@ -319,6 +319,7 @@ Warning: multiple sharp instances concurrently producing tile output can expose
     -   `options.size` **[Number][9]** tile size in pixels, a value between 1 and 8192. (optional, default `256`)
     -   `options.overlap` **[Number][9]** tile overlap in pixels, a value between 0 and 8192. (optional, default `0`)
     -   `options.angle` **[Number][9]** tile angle of rotation, must be a multiple of 90. (optional, default `0`)
+	-   `options.background` **([String][2] \| [Object][6])** background colour, parsed by the [color][10] module, defaults to white without transparency. (optional, default `{r:255,g:255,b:255,alpha:1}`)
     -   `options.depth` **[String][2]?** how deep to make the pyramid, possible values are `onepixel`, `onetile` or `one`, default based on layout.
     -   `options.skipBlanks` **[Number][9]** threshold to skip tile generation, a value 0 - 255 for 8-bit images or 0 - 65535 for 16-bit images (optional, default `-1`)
     -   `options.container` **[String][2]** tile container, with value `fs` (filesystem) or `zip` (compressed file). (optional, default `'fs'`)
@@ -359,3 +360,5 @@ Returns **Sharp**
 [8]: https://nodejs.org/api/buffer.html
 
 [9]: https://developer.mozilla.org/docs/Web/JavaScript/Reference/Global_Objects/Number
+
+[10]: https://www.npmjs.org/package/color

lib/constructor.js

@@ -213,6 +213,7 @@ const Sharp = function (input, options) {
     tileSize: 256,
     tileOverlap: 0,
     tileSkipBlanks: -1,
+    tileBackground: [255, 255, 255, 255],
     linearA: 1,
     linearB: 0,
     // Function to notify of libvips warnings

lib/output.js

@@ -551,6 +551,7 @@ function toFormat (format, options) {
  * @param {Number} [options.size=256] tile size in pixels, a value between 1 and 8192.
  * @param {Number} [options.overlap=0] tile overlap in pixels, a value between 0 and 8192.
  * @param {Number} [options.angle=0] tile angle of rotation, must be a multiple of 90.
+ * @param {String|Object} [options.background={r: 255, g: 255, b: 255, alpha: 1}] - background colour, parsed by the [color](https://www.npmjs.org/package/color) module, defaults to white without transparency.
  * @param {String} [options.depth] how deep to make the pyramid, possible values are `onepixel`, `onetile` or `one`, default based on layout.
  * @param {Number} [options.skipBlanks=-1] threshold to skip tile generation, a value 0 - 255 for 8-bit images or 0 - 65535 for 16-bit images
  * @param {String} [options.container='fs'] tile container, with value `fs` (filesystem) or `zip` (compressed file).
@@ -603,6 +604,8 @@ function tile (options) {
         throw is.invalidParameterError('angle', 'positive/negative multiple of 90', options.angle);
       }
     }
+    // Background colour
+    this._setBackgroundColourOption('tileBackground', options.background);
     // Depth of tiles
     if (is.defined(options.depth)) {
       if (is.string(options.depth) && is.inArray(options.depth, ['onepixel', 'onetile', 'one'])) {

package.json

@@ -62,7 +62,8 @@
     "Michael B. Klein <mbklein@gmail.com>",
     "Jordan Prudhomme <jordan@raboland.fr>",
     "Ilya Ovdin <iovdin@gmail.com>",
-    "Andargor <andargor@yahoo.com>"
+    "Andargor <andargor@yahoo.com>",
+    "Paul Neave <paul.neave@gmail.com>"
   ],
   "scripts": {
     "install": "(node install/libvips && node install/dll-copy && prebuild-install) || (node-gyp rebuild && node install/dll-copy)",

src/pipeline.cc

@@ -959,6 +959,11 @@ class PipelineWorker : public Nan::AsyncWorker {
             };
             suffix = AssembleSuffixString(extname, options);
           }
+
+          // Remove alpha channel from tile background if image does not contain an alpha channel
+          if (!HasAlpha(image)) {
+            baton->tileBackground.pop_back();
+          }
           // Write DZ to file
           vips::VOption *options = VImage::option()
                                        ->set("strip", !baton->withMetadata)
@@ -968,6 +973,7 @@ class PipelineWorker : public Nan::AsyncWorker {
                                        ->set("layout", baton->tileLayout)
                                        ->set("suffix", const_cast<char*>(suffix.data()))
                                        ->set("angle", CalculateAngleRotation(baton->tileAngle))
+                                       ->set("background", baton->tileBackground)
                                        ->set("skip_blanks", baton->tileSkipBlanks);
 
           // libvips chooses a default depth based on layout. Instead of replicating that logic here by
@@ -1374,6 +1380,7 @@ NAN_METHOD(pipeline) {
   baton->tileOverlap = AttrTo<uint32_t>(options, "tileOverlap");
   std::string tileContainer = AttrAsStr(options, "tileContainer");
   baton->tileAngle = AttrTo<int32_t>(options, "tileAngle");
+  baton->tileBackground = AttrAsRgba(options, "tileBackground");
   baton->tileSkipBlanks = AttrTo<int32_t>(options, "tileSkipBlanks");
   if (tileContainer == "zip") {
     baton->tileContainer = VIPS_FOREIGN_DZ_CONTAINER_ZIP;

src/pipeline.h

@@ -175,6 +175,7 @@ struct PipelineBaton {
   VipsForeignDzLayout tileLayout;
   std::string tileFormat;
   int tileAngle;
+  std::vector<double> tileBackground;
   int tileSkipBlanks;
   VipsForeignDzDepth tileDepth;
   std::unique_ptr<double[]> recombMatrix;
@@ -280,6 +281,7 @@ struct PipelineBaton {
     tileContainer(VIPS_FOREIGN_DZ_CONTAINER_FS),
     tileLayout(VIPS_FOREIGN_DZ_LAYOUT_DZ),
     tileAngle(0),
+    tileBackground{ 255.0, 255.0, 255.0, 255.0 },
     tileSkipBlanks(-1),
     tileDepth(VIPS_FOREIGN_DZ_DEPTH_LAST) {}
 };