point GIFs in Image.decode() to Animation.decode()

Author: matmen

CHANGELOG.md

@@ -36,6 +36,7 @@
     sizes in `renderText()` (which rendered an empty image); `maxPixels` that isn't positive in `Image.decode()` and
     `Animation.decode()` (which reported every image as too large); fractional loop counts in `new Animation()`.
 - `Animation.decode()` reports invalid `threads` and `maxPixels` as such, not as damaged image data.
+- `Image.decode()` refuses GIFs with a hint at `Animation.decode()` instead of "Unsupported image type".
 
 ## 3.13.2
 

src/image.ts

@@ -2295,6 +2295,7 @@ export class Image {
             if (ImageType.isPNM(dataView)) return netpbm.decode(data, maxPixels, toneMapping);
             if (ImageType.isHDR(dataView)) return hdr.decode(data, maxPixels, toneMapping);
             if (ImageType.isTGA(dataView)) return tga.decode(data, maxPixels);
+            if (ImageType.isGIF(dataView)) throw new Error('GIFs have to be decoded with Animation.decode() (or decode(), which returns an image or an animation)');
             throw new Error('Unsupported image type');
         });
 

tests/option-checks.js

@@ -61,6 +61,10 @@ const rejects = async (name, fn, Type, pattern) => {
     }
     await rejects('Animation.decode threads 0', () => Animation.decode(png, {threads: 0}), RangeError, /threads must be/);
 
+    // GIFs are refused by Image.decode() with a hint at Animation.decode()
+    const gif = await new Animation([new Frame(4, 4).fill(0xff0000ff)]).encodeGIF();
+    await rejects('Image.decode GIF', () => Image.decode(gif), Error, /Animation\.decode\(\)/);
+
     // valid values keep working
     for (const effort of [0, 1, 2]) await image.encodeAVIF({effort});
     for (const subsampling of ['4:4:4', '4:2:0']) await image.encodeAVIF({quality: 50, subsampling});