[vtk-developers] VTK image error 0 despite differences - false pass

[Marcus D. Hanwell]

On Fri, May 4, 2018 at 9:34 AM, Marcus D. Hanwell <
marcus.hanwell at kitware.com> wrote:

> Hi,
>
> A while ago I opened issue https://gitlab.kitware.com/vtk/vtk/issues/17201
> that talked about a bug on Windows where setting the precision to 0
> resulted in 6 precision on Windows. There was a test, but it was passing
> even on Windows, this week we had a new employee start and I thought it
> would be a good first bug to create a failing test, and then make it pass
> by addressing the issue.
>
> I thought that TestAxes was a little crowded, and that had perhaps been
> enough to throw the image diff off. So he wrote a test that just had this
> axis in, made a baseline for what was expected, and then changed it so that
> we could see the test fail. Changing to 6 or 8 is still showing passing
> test:
>
>
>
> This looks like a good difference to me (not sure if we are allowed
> attachments, but I tried). The ImageError is being shown as 0. We could
> make the text bigger, but there are a few chart tests where we use text of
> this size and I thought they would fail with extra numbers like this.
>

Digging into this for anyone following, I can change vtkTesting.cxx to use
'rtId->SetAllowShift(0);' which removes the single pixel shift logic, and I
get a diff showing my extra digits, as I would expect. We likely have this
on for a reason, and the text is pretty tiny, so I could see a nearest
neighbor search turning up no difference for every character added.

As the docs say this is not symmetric - the testing does shoe a diff if the
image on the right is the baseline, and the characters get removed.
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