On Fri, 29 Jan 2021 00:05:57 GMT, Kevin Rushforth <k...@openjdk.org> wrote:
> As indicated in the JBS bug, using a `PixelReader` to read a scaled image in > HiDPI mode, for example an `@2x` image, to read more than one pixel will read > data from the wrong location in the image, usually leading to an IOOBE. > > The bug is in the `getPixelAccessor` method of Prism Image. The method > correctly creates a new `Accessor` if one hasn't already been created, but > then it unconditionally wraps the current `Accessor` in a > `ScaledPixelAccessor` if the scale is > 1. So the second time this method is > called, it created another `ScaledPixelAccessor` that wraps the first > `ScaledPixelAccessor`, meaning that the indexes into the pixel array are > multiplied by 4. This continues for each new call to this method. > > The fix is to only wrap an `Accessor` in a `ScaledPixelAccessor` the first > time, when it is created. > > I added a test, which is run for both scaled and unscaled images, to ensure > that we get the right value when reading a pixel, and that reading it a > second time returns the same result. Without the fix, the new test will fail > with IOOBE when the scale factor is two. Related to this, I initially > commented out the wrapping in a `ScaledPixelAccessor` entirely, just to see > what would happen, and none of the existing tests caught it. The new test > will catch this. +1 Test and sanity check looks good. ------------- Marked as reviewed by arapte (Reviewer). PR: https://git.openjdk.java.net/jfx/pull/389
