[SigmundA]

You can't convert a bitmap back into vectors (well maybe image recognition of some sort). Once you render to canvas its a bitmap and stays that way all the way to printer.

SVG is turned into the appropriate PS/PDF vector drawing command by the browser print engine, canvas just gets sent as a bitmap in the printer language since that all that's left.

I believe pdf.js incorporated and modified https://github.com/gliffy/canvas2svg which implements the canvas api but instead creates an SVG dom.

[leni536]

Yeah, ok, so we have essentially PDF -> SVG -> PDF/PS because of too many abstractions. It would make sense to expose some internal printing API to the embedded PDF reader so all this nonsense wouldn't be necessary.

[SigmundA]

Firefox tried to with mozPrintCallback specifically for pdf.js, then went away from that. Not sure what happened behind the scenes exactly as they wanted to get it standardized for canvas printing.

Printing is a forgotten corner on the web, would be nice if a mainstream browser implemented the full css print spec too so we could create page perfect output without relying on PrinceXml...