Huge canvases are not rendered

[Rob--W]

PDF.js seems to assume that the canvas size is unlimited.

As demonstrated by #6385, this is not true. In that bug, a specific system using IE11 with HWA enabled supported canvases of at most 2048x2048 (#6385 (comment)).

Other browsers / systems have more generous limits, but there are probably images (e.g. high-res scans?) that exceeds these boundaries. In these cases, we should still be able to display the image in some way.

Slicing the canvas seems a solution, but that might be a bit tricky with gradients.

In IE, feature detection seems possible using canvas.toDataURL & img.naturalWidth & img.naturalHeight. In Chrome, toDataURL. I haven't checked Firefox or Safari yet, but detection can probably be done in a similar way.

So, how should we tackle big canvases?

[timvandermeij]

Yury talked about canvas tiling a while ago, but nobody has further investigated or implemented that. I think the idea is to split the one large canvas into multiple smaller canvases, though I would not really have an idea on how to implement that properly.

/cc @yurydelendik (who can probably add more to this issue than I can)

[yurydelendik]

Blocked by #6419