Tried an approch for text case in pixelmatch

[Vaivaswat2244]

Resolves #7496

Changes:

Modified the checkMatch function in visualtest.js to be more tolerant of slight text position shifts while still catching meaningful changes. Key changes:

Added text detection using pixel pattern analysis:

• Looks for moderate density and high contrast transitions typical of text
• Helps identify regions where small shifts should be allowed

Implemented shift tolerance for text regions:

• Allows up to 2-pixel shifts for detected text areas
• Still fails on actual content changes
• Configurable via shiftThreshold parameter

Screenshots of the change:

PR Checklist

• npm run lint passes
• Inline reference is included / updated
• Unit tests are included / updated

[davepagurek]

Thanks @Vaivaswat2244, nice approach! I have a few questions that might help us determine how to get this across the finish line.

• Do you have a sense of how often isLikelyText returns true, and if this gets called on anything non-text? I wonder if maybe rather than trying to detect whether we think there is text, we can directly record when text is called. Since we pass in a p5 instance to the test case anyway, maybe we can do something like this to patch text() to record that it got called:

  let hasText = false
  const prevText = myp5.text
  myp5.text = function(...args) {
    hasText = true
    prevText.apply(this, args)
  }

• It looks like some tests are failing on CI now. Do you know if these look like (1) false positives that the checker needs to address, (2) cases where we need to regenerate the screenshots because the old ones were out of date but still passed on CI under the old pixel checker, or (3) are actual bugs in p5 that are surfaced now by using a better pixel checker?

[Vaivaswat2244]

yeah sure, the text() passing makes much more sense. I can implement that.
And regarding the tests getting failed. I think that these are the 2nd case as you described, failed the CI tests after regenerating on my machine but were not passed by the old checker (Although the previous one seemed fine). Also I'm not so sure how to move ahead from here. So ig for now I'll change the text case and will see how that works out.

[davepagurek]

Are you able to see the test output from CI on your PR by clicking the Details button here?

For a next step, I'd look at the test output, and try regenerating the failed screenshots locally and pushing those. We can see if that fixes it on CI, and also by looking at the new images in the Files Changed tab, whether we think the changed images are expected.

[Vaivaswat2244]

hey, so I just noticed that the files which I added in the earlier commit aren't the one which are failing the tests on CI, but they are other files which were not touched.

Now, I changed the files which were failing tests in CI, and tried the tests locally. The tests are now failing for different files in the typography and webgl cases. I guess there is a problem with my changes in the visualtest file.
So maybe I'll revert these changes and think of something else.

[davepagurek]

Just looking at the last failure in the test file:

Expected:

Received:

Diff:

...it looks like a few isolated pixels are off. I wonder if we can do something to augment pixelmatch and check if the difference exists just on a single pixel (so no surrounding pixels are also flagged) and then ignore those?