Add resolution option for PNG format

[zbjornson]

It seems browsers also always set the PPI to 72
-- #766 (comment)

Edge, Firefox and Chrome don't specify a pHYs chunk, so I left default behavior unchanged to stay consistent with them. (The internets say that the resolution doesn't mean much for on-screen display anyway.)

Fixes #766
Fixes #716

Thanks for contributing!

• Have you updated CHANGELOG.md?

[LinusU]

Neat 👍

[LinusU]

😄

[KFoxder]

@zbjornson I do not see this working for me? Don't you need to update the parsePNGArgs method in this PR?

[zbjornson]

Hrm it looks like I lost the changes to canvas.cc that were supposed to be in this PR. The test passes because pHYs is omitted if resolution isn't specified. Will fix tonight. Thanks for pointing that out.

[KFoxder]

@zbjornson Awesome thanks! Much appreciated.

[mikehalmamoj]

Hrm it looks like I lost the changes to canvas.cc that were supposed to be in this PR. The test passes because pHYs is omitted if resolution isn't specified. Will fix tonight. Thanks for pointing that out.

Did this make it onto another PR? The resolution option for png appears to do nothing...

[zbjornson]

@mikehalmamoj yes, #1376.

As an ancillary chunk, readers are allowed to ignore pHYs. That might be why you don't see it doing anything. Above shows that the chunk is encoded in the file correctly though.

[mikehalmamoj]

Thanks for the quick reply @zbjornson. That's ever so strange because I don't see the resolution in the image info when generating from this lib but if I add a resolution with the pngcrush CLI then I see the that resolution. 🤷‍♂️ I'll have to do some more digging.

Thanks again!

[mikehalmamoj]

You're absolutely correct and it works fine - it seems the issue is the haphazard support for the pHYs chunk. Thanks again @zbjornson and keep up the good work! 😄