fix a crash in getImageDate if the rectangle is outside the canvas

CHANGELOG.md

@@ -10,6 +10,7 @@ project adheres to [Semantic Versioning](http://semver.org/).
 ### Changed
 ### Added
 ### Fixed
+* Fix a crash in `getImageData` when the rectangle is entirely outside the canvas. ([#2024](https://github.com/Automattic/node-canvas/issues/2024))
 
 2.10.2
 ==================

src/CanvasRenderingContext2d.cc

@@ -986,10 +986,6 @@ NAN_METHOD(Context2d::GetImageData) {
  if (sx + sw > width) sw = width - sx;
  if (sy + sh > height) sh = height - sy;
 
- // WebKit/moz functionality. node-canvas used to return in either case.
- if (sw <= 0) sw = 1;
- if (sh <= 0) sh = 1;
-
  // Non-compliant. "Pixels outside the canvas must be returned as transparent
  // black." This instead clips the returned array to the canvas area.
  if (sx < 0) {
@@ -1001,6 +997,10 @@ NAN_METHOD(Context2d::GetImageData) {
  sy = 0;
  }
 
+ // WebKit/moz functionality. node-canvas used to return in either case.
+ if (sw <= 0) sw = 1;
+ if (sh <= 0) sh = 1;
+
  int srcStride = canvas->stride();
  int bpp = srcStride / width;
  int size = sw * sh * bpp;

test/canvas.test.js

@@ -1242,6 +1242,18 @@ describe('Canvas', function () {
  ctx.getImageData(0, 0, 3, 6)
  })
  })
+
+ it('does not throw if rectangle is outside the canvas (#2024)', () => {
+ const canvas = createCanvas(200, 200)
+ const ctx = canvas.getContext('2d')
+
+ ctx.rect(0, 0, 100, 100);
+ ctx.fill();
+
+ const imageData = ctx.getImageData(0, -11, 10, 10);
+ assert.equal(10, imageData.width)
+ assert.equal(1, imageData.height)
+ })
  })
 
  it('Context2d#createPattern(Canvas)', function () {