From 7c631c0787915416e20a567a039516e99c81c42d Mon Sep 17 00:00:00 2001
From: Lovell Fuller <github@lovell.info>
Date: Thu, 3 Jan 2019 12:01:55 +0000
Subject: [PATCH] Ensure shortest resized edge is >= 1px #1003

---
 docs/changelog.md   |  3 +++
 src/pipeline.cc     |  9 +++++++++
 test/unit/resize.js | 34 ++++++++++++++++++++++++++++++++++
 3 files changed, 46 insertions(+)

diff --git a/docs/changelog.md b/docs/changelog.md
index d43613a0..3d0d1637 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -6,6 +6,9 @@ Requires libvips v8.7.0.
 
 #### v0.21.2 - TBD
 
+* Ensure shortest edge is at least one pixel after resizing.
+  [#1003](https://github.com/lovell/sharp/issues/1003)
+
 * Expose `pages` and `pageHeight` metadata for multi-page input images.
   [#1205](https://github.com/lovell/sharp/issues/1205)
 
diff --git a/src/pipeline.cc b/src/pipeline.cc
index c3008126..029943b6 100644
--- a/src/pipeline.cc
+++ b/src/pipeline.cc
@@ -385,6 +385,15 @@ class PipelineWorker : public Nan::AsyncWorker {
         ) {
           throw vips::VError("Unknown kernel");
         }
+        // Ensure shortest edge is at least 1 pixel
+        if (image.width() / xfactor < 0.5) {
+          xfactor = 2 * image.width();
+          baton->width = 1;
+        }
+        if (image.height() / yfactor < 0.5) {
+          yfactor = 2 * image.height();
+          baton->height = 1;
+        }
         image = image.resize(1.0 / xfactor, VImage::option()
           ->set("vscale", 1.0 / yfactor)
           ->set("kernel", kernel));
diff --git a/test/unit/resize.js b/test/unit/resize.js
index fc5cbaf9..ee6ed639 100644
--- a/test/unit/resize.js
+++ b/test/unit/resize.js
@@ -525,6 +525,40 @@ describe('Resize dimensions', function () {
       });
   });
 
+  it('Ensure shortest edge (height) is at least 1 pixel', function () {
+    return sharp({
+      create: {
+        width: 10,
+        height: 2,
+        channels: 3,
+        background: 'red'
+      }
+    })
+      .resize(2)
+      .toBuffer({ resolveWithObject: true })
+      .then(function (output) {
+        assert.strictEqual(2, output.info.width);
+        assert.strictEqual(1, output.info.height);
+      });
+  });
+
+  it('Ensure shortest edge (width) is at least 1 pixel', function () {
+    return sharp({
+      create: {
+        width: 2,
+        height: 10,
+        channels: 3,
+        background: 'red'
+      }
+    })
+      .resize(null, 2)
+      .toBuffer({ resolveWithObject: true })
+      .then(function (output) {
+        assert.strictEqual(1, output.info.width);
+        assert.strictEqual(2, output.info.height);
+      });
+  });
+
   it('unknown kernel throws', function () {
     assert.throws(function () {
       sharp().resize(null, null, { kernel: 'unknown' });