Ensure animated GIF to WebP conversion retains loop #3394

Author: lovell

docs/src/content/docs/changelog.md

@@ -8,6 +8,9 @@ Requires libvips v8.16.1
 
 ### v0.34.2 - TBD
 
+* Ensure animated GIF to WebP conversion retains loop (regression in 0.34.0).
+  [#3394](https://github.com/lovell/sharp/issues/3394)
+
 * Ensure `pdfBackground` constructor property is used.
   [#4207](https://github.com/lovell/sharp/pull/4207)
 

lib/constructor.js

@@ -298,7 +298,7 @@ const Sharp = function (input, options) {
     withExif: {},
     withExifMerge: true,
     resolveWithObject: false,
-    loop: 1,
+    loop: -1,
     delay: [],
     // output format
     jpegQuality: 80,

src/common.cc

@@ -651,22 +651,21 @@ namespace sharp {
   */
   VImage SetAnimationProperties(VImage image, int nPages, int pageHeight, std::vector<int> delay, int loop) {
     bool hasDelay = !delay.empty();
-
-    // Avoid a copy if none of the animation properties are needed.
-    if (nPages == 1 && !hasDelay && loop == -1) return image;
-
-    if (delay.size() == 1) {
-      // We have just one delay, repeat that value for all frames.
-      delay.insert(delay.end(), nPages - 1, delay[0]);
-    }
-
-    // Attaching metadata, need to copy the image.
     VImage copy = image.copy();
 
     // Only set page-height if we have more than one page, or this could
     // accidentally turn into an animated image later.
     if (nPages > 1) copy.set(VIPS_META_PAGE_HEIGHT, pageHeight);
-    if (hasDelay) copy.set("delay", delay);
+    if (hasDelay) {
+      if (delay.size() == 1) {
+        // We have just one delay, repeat that value for all frames.
+        delay.insert(delay.end(), nPages - 1, delay[0]);
+      }
+      copy.set("delay", delay);
+    }
+    if (nPages == 1 && !hasDelay && loop == -1) {
+      loop = 1;
+    }
     if (loop != -1) copy.set("loop", loop);
 
     return copy;

src/pipeline.h

@@ -384,7 +384,7 @@ struct PipelineBaton {
     ensureAlpha(-1.0),
     colourspacePipeline(VIPS_INTERPRETATION_LAST),
     colourspace(VIPS_INTERPRETATION_LAST),
-    loop(1),
+    loop(-1),
     tileSize(256),
     tileOverlap(0),
     tileContainer(VIPS_FOREIGN_DZ_CONTAINER_FS),

test/unit/gif.js

@@ -238,4 +238,15 @@ describe('GIF input', () => {
       assert.strictEqual(1, loop);
     }
   });
+
+  it('Animated GIF to animated WebP merges identical frames', async () => {
+    const webp = await sharp(fixtures.inputGifAnimated, { animated: true })
+      .webp()
+      .toBuffer();
+
+    const { delay, loop, pages } = await sharp(webp).metadata();
+    assert.deepStrictEqual([120, 120, 90, 120, 120, 90, 120, 90, 30], delay);
+    assert.strictEqual(0, loop);
+    assert.strictEqual(9, pages);
+  });
 });