Skip shrink-on-load when trimming (#887) (#888)

src/pipeline.cc

@@ -220,12 +220,12 @@ class PipelineWorker : public Nan::AsyncWorker {
       }
 
       // If integral x and y shrink are equal, try to use shrink-on-load for JPEG and WebP,
-      // but not when applying gamma correction or pre-resize extract
+      // but not when applying gamma correction, pre-resize extract or trim
       int shrink_on_load = 1;
       if (
         xshrink == yshrink && xshrink >= 2 &&
         (inputImageType == ImageType::JPEG || inputImageType == ImageType::WEBP) &&
-        baton->gamma == 0 && baton->topOffsetPre == -1
+        baton->gamma == 0 && baton->topOffsetPre == -1 && baton->trimTolerance == 0
       ) {
         if (xshrink >= 8) {
           xfactor = xfactor / 8;

test/fixtures/index.js

@@ -65,6 +65,7 @@ module.exports = {
   inputJpgWithLowContrast: getPath('low-contrast.jpg'), // http://www.flickr.com/photos/grizdave/2569067123/
   inputJpgLarge: getPath('giant-image.jpg'),
   inputJpg320x240: getPath('320x240.jpg'), // http://www.andrewault.net/2010/01/26/create-a-test-pattern-video-with-perl/
+  inputJpgOverlayLayer2: getPath('alpha-layer-2-ink.jpg'),
 
   inputPng: getPath('50020484-00001.png'), // http://c.searspartsdirect.com/lis_png/PLDM/50020484-00001.png
   inputPngWithTransparency: getPath('blackbug.png'), // public domain

test/unit/trim.js

@@ -20,6 +20,20 @@ describe('Trim borders', function () {
       });
   });
 
+  it('Skip shrink-on-load', function (done) {
+    const expected = fixtures.expected('alpha-layer-2-trim-resize.jpg');
+    sharp(fixtures.inputJpgOverlayLayer2)
+      .trim()
+      .resize(300)
+      .toBuffer(function (err, data, info) {
+        if (err) throw err;
+        assert.strictEqual('jpeg', info.format);
+        assert.strictEqual(300, info.width);
+        assert.strictEqual(300, info.height);
+        fixtures.assertSimilar(expected, data, done);
+      });
+  });
+
   it('16-bit PNG with alpha channel', function (done) {
     sharp(fixtures.inputPngWithTransparency16bit)
       .resize(32, 32)