[whatwg] createImageData

Maciej Stachowiak mjs at apple.com
Tue May 13 16:49:01 PDT 2008

On May 13, 2008, at 4:28 PM, Vladimir Vukicevic wrote:

> On May 13, 2008, at 4:10 PM, Oliver Hunt wrote:
>> I think we need a list of use cases for ImageData, off the top of  
>> my head i can think of:
>> * filters -- in general a single write per pixel, potentially  
>> multiple reads
>> * Generated images -- still arguably single write per pixel
>> * I'm not sure what to call this -- but things like http://jsmsxdemo.googlepages.com/jsmsx.html
>> I honestly can't think of something that would (sanely) expect to  
>> be writing multiple times to the same pixel between blits, but i  
>> should note i haven't actively spent any significant time trying to  
>> come up with these.  That said in all of the above cases the cost  
>> of immediate clamping is technically the same as delaying the  
>> clamp, although it also has the benefit of allowing reduced memory  
>> usage.
> Yeah, those are all good use cases -- it just seems like requiring  
> immediate clamping is basically specifying for a specific  
> implementation, when the overall goal is "checking for invalid  
> data".  Specifying that the error should come from putImageData  
> would give implementations more flexibility, without limiting error  
> checking.

Wouldn't delaying clamping and error checking make it hard to use a  
native pixel data array as the ImageData backing store? In fact it  
would make it pretty much impossible unless you at least clamp/round/ 
throw when reading the data from JS. And even then, such an ImageData  
implementation would have to taint itself to record whether an error  
had occurred.


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