[whatwg] Responsive images and printing/zooming

[Markus Ernst]

Hello

I try to follow the actual discussion with much interest and, I admit, 
not full understanding. If my inputs are inappropriate, please feel free 
to ignore this message.

I read the current spec and huge parts of today's discussions to find 
out how images with multiple sources are intended to behave when 
printed, or when the page is zoomed, but I found no hints. I think some 
words on this might be useful in the spec, regardless of what the final 
syntax will be.

1. Print
When a page is printed (or also converted to PDF or whatever), both 
"viewport" width and pixel ratio change. Are UAs expected to load the 
appropriate sources then? This could result in increased bandwidth, 
delayed printing, and IMHO a disturbed user experience, as the image may 
differ from the one seen on screen. Thus, I suggest to always use the 
resource actually shown on screen for printing.

2. Zoom
On mobile devices, web pages are often zoomed out to fit the viewport 
width by default, the user is supposed to manually zoom in and scroll in 
order to read parts of pages. I understand that the whole thing about 
responsive design is to make this kind of zooming unnecessary, but in 
practice there will be all kinds of partly responsive designs using 
responsive images.
Specially in cases where separate sources are given to match device 
pixel densities, zooming might matter, as for a zoomed-out page the low 
res image might be more than sufficient, but after zooming in the higher 
resolution might be appropriate. Which OTOH can disturb the user 
experience, when the images differ.