Pixel by pixel comparison with high zoom can't reach the same precision level as diff demo

Product: PDFTron WebViewer

Product Version: 8.3

Please give a brief summary of your issue:


We integrated your pixel by pixel comparison feature using the related documentation, and we face a performance issue related to the accuracy in the middle generated instance once we zoom a lot, in comparison to what you propose in your demo:

It seems that our generated middle instance comparison loads, but at some point it has zoom rerender capacity limits (like blurred) and it doesn’t load more anymore, while for your demo it is more powerful.

If it may help, we have multiple errors in the Console:

It seems you also have the “Cannot cancel callback undefined” in your demo, but in addition, on our side, we have the “functions-to-override.js:1005 Uncaught (in promise) TypeError: Cannot read properties of undefined (reading ‘polygon’)”.

And this occures multiple times each time we zoom.

Could you please explain us why do we have such a limitation, and if some specific code could tackle that, please?

Thanks in advance for your time.

Best Regards,


Hi alex.plt,

Thank you for contacting WebViewer forums,

I tested the diff sample for versions from 8.3 to 8.9, and 8.9 has the fix without the console error message.
The sample on the demo site is also on 8.9:

Could you update your WebViewer version to 8.9 or later to see if the issue has been fixed?

Here is a guide on updating WebViewer:

Thank you in advance.

Best Regards,
Kevin Kim