Add support for GIF output using cgif in prebuilt binaries

lib/constructor.js

@@ -13,7 +13,7 @@ const debuglog = util.debuglog('sharp');
 /**
  * Constructor factory to create an instance of `sharp`, to which further methods are chained.
  *
- * JPEG, PNG, WebP, AVIF or TIFF format image data can be streamed out from this object.
+ * JPEG, PNG, WebP, GIF, AVIF or TIFF format image data can be streamed out from this object.
  * When using Stream based output, derived attributes are available from the `info` event.
  *
  * Non-critical problems encountered during processing are emitted as `warning` events.
@@ -246,6 +246,9 @@ const Sharp = function (input, options) {
     webpNearLossless: false,
     webpSmartSubsample: false,
     webpReductionEffort: 4,
+    gifBitdepth: 8,
+    gifEffort: 7,
+    gifDither: 1,
     tiffQuality: 80,
     tiffCompression: 'jpeg',
     tiffPredictor: 'horizontal',

lib/output.js

@@ -22,14 +22,15 @@ const formats = new Map([
   ['j2c', 'jp2']
 ]);
 
-const errMagickSave = new Error('GIF output requires libvips with support for ImageMagick');
 const errJp2Save = new Error('JP2 output requires libvips with support for OpenJPEG');
 
+const bitdepthFromColourCount = (colours) => 1 << 31 - Math.clz32(Math.ceil(Math.log2(colours)));
+
 /**
  * Write output image data to a file.
  *
  * If an explicit output format is not selected, it will be inferred from the extension,
- * with JPEG, PNG, WebP, AVIF, TIFF, DZI, and libvips' V format supported.
+ * with JPEG, PNG, WebP, AVIF, TIFF, GIF, DZI, and libvips' V format supported.
  * Note that raw pixel data is only supported for buffer output.
  *
  * By default all metadata will be removed, which includes EXIF-based orientation.
@@ -63,8 +64,6 @@ function toFile (fileOut, callback) {
     err = new Error('Missing output file path');
   } else if (is.string(this.options.input.file) && path.resolve(this.options.input.file) === path.resolve(fileOut)) {
     err = new Error('Cannot use same file for input and output');
-  } else if (this.options.formatOut === 'input' && fileOut.toLowerCase().endsWith('.gif') && !this.constructor.format.magick.output.file) {
-    err = errMagickSave;
   }
   if (err) {
     if (is.fn(callback)) {
@@ -81,9 +80,9 @@ function toFile (fileOut, callback) {
 
 /**
  * Write output to a Buffer.
- * JPEG, PNG, WebP, AVIF, TIFF and raw pixel data output are supported.
+ * JPEG, PNG, WebP, AVIF, TIFF, GIF and raw pixel data output are supported.
  *
- * If no explicit format is set, the output format will match the input image, except GIF and SVG input which become PNG output.
+ * If no explicit format is set, the output format will match the input image, except SVG input which becomes PNG output.
  *
  * By default all metadata will be removed, which includes EXIF-based orientation.
  * See {@link withMetadata} for control over this.
@@ -412,7 +411,7 @@ function png (options) {
       const colours = options.colours || options.colors;
       if (is.defined(colours)) {
         if (is.integer(colours) && is.inRange(colours, 2, 256)) {
-          this.options.pngBitdepth = 1 << 31 - Math.clz32(Math.ceil(Math.log2(colours)));
+          this.options.pngBitdepth = bitdepthFromColourCount(colours);
         } else {
           throw is.invalidParameterError('colours', 'integer between 2 and 256', colours);
         }
@@ -495,13 +494,40 @@ function webp (options) {
 }
 
 /**
- * Use these GIF options for output image.
+ * Use these GIF options for the output image.
  *
- * Requires libvips compiled with support for ImageMagick or GraphicsMagick.
- * The prebuilt binaries do not include this - see
- * {@link https://sharp.pixelplumbing.com/install#custom-libvips installing a custom libvips}.
+ * The first entry in the palette is reserved for transparency.
+ *
+ * @example
+ * // Convert PNG to GIF
+ * await sharp(pngBuffer)
+ *   .gif()
+ *   .toBuffer());
+ *
+ * @example
+ * // Convert animated WebP to animated GIF
+ * await sharp('animated.webp', { animated: true })
+ *   .toFile('animated.gif');
+ *
+ * @example
+ * // Create 128x128, non-dithered thumbnail of an animated GIF
+ * const { pages } = await sharp('animated.gif').metadata();
+ * const gif = await sharp('animated.gif', { animated: true })
+ *   .resize({
+ *     width: 128,
+ *     height: 128 * pages
+ *   })
+ *   .gif({
+ *     pageHeight: 128,
+ *     dither: 0
+ *   })
+ *   .toBuffer();
  *
  * @param {Object} [options] - output options
+ * @param {number} [options.colours=256] - maximum number of palette entries, including transparency, between 2 and 256
+ * @param {number} [options.colors=256] - alternative spelling of `options.colours`
+ * @param {number} [options.effort=7] - CPU effort, between 1 (fastest) and 10 (slowest)
+ * @param {number} [options.dither=1.0] - level of Floyd-Steinberg error diffusion, between 0 (least) and 1 (most)
  * @param {number} [options.pageHeight] - page height for animated output
  * @param {number} [options.loop=0] - number of animation iterations, use 0 for infinite animation
  * @param {number[]} [options.delay] - list of delays between animation frames (in milliseconds)
@@ -509,10 +535,30 @@ function webp (options) {
  * @returns {Sharp}
  * @throws {Error} Invalid options
  */
-/* istanbul ignore next */
 function gif (options) {
-  if (!this.constructor.format.magick.output.buffer) {
-    throw errMagickSave;
+  if (is.object(options)) {
+    const colours = options.colours || options.colors;
+    if (is.defined(colours)) {
+      if (is.integer(colours) && is.inRange(colours, 2, 256)) {
+        this.options.gifBitdepth = bitdepthFromColourCount(colours);
+      } else {
+        throw is.invalidParameterError('colours', 'integer between 2 and 256', colours);
+      }
+    }
+    if (is.defined(options.effort)) {
+      if (is.number(options.effort) && is.inRange(options.effort, 1, 10)) {
+        this.options.gifEffort = options.effort;
+      } else {
+        throw is.invalidParameterError('effort', 'integer between 1 and 10', options.effort);
+      }
+    }
+    if (is.defined(options.dither)) {
+      if (is.number(options.dither) && is.inRange(options.dither, 0, 1)) {
+        this.options.gifDither = options.dither;
+      } else {
+        throw is.invalidParameterError('dither', 'number between 0.0 and 1.0', options.dither);
+      }
+    }
   }
   trySetAnimationOptions(options, this.options);
   return this._updateFormatOut('gif', options);