[whatwg] More random comments on the putImageData definition

[Oliver Hunt]

>
> If, 5 years from now, most Web developers have 200dpi screens so  
> browsers are using at least a 2:1 ratio for their canvas backing  
> stores, then putImageData and getImageData could be safely  
> introduced with the current spec, because an assumption that device  
> pixels are the same as canvas units would break immediately in  
> testing.
The problem is that you couldn't, if you waited for 5 years, you'd get  
5 years of people developing on the assumption that there's a 1:1  
ratio -- at that point you could no longer change the ratio as you  
would break 5 years of sites, even those sites made by developers with  
hidpi screens who had been trying to be correct -- because they would  
not be able to test.

An example of this effect in html5 is the behaviour of transforms  
during path transforms -- having path construction not be effected by  
transforms would arguably be better than what html5 has ended up  
doing, and the reason html5 does it the way it does is because firefox  
and webkit have both been doing it that way for a number of years, and  
there's already content that breaks if we change behaviour.  (Ideally  
there would be a distinct Path object that was not tied to the canvas,  
the resolving this issue)

--Oliver

>
>
> Rob
> --
> "He was pierced for our transgressions, he was crushed for our  
> iniquities; the punishment that brought us peace was upon him, and  
> by his wounds we are healed. We all, like sheep, have gone astray,  
> each of us has turned to his own way; and the LORD has laid on him  
> the iniquity of us all." [Isaiah 53:5-6]