[whatwg] ImageData constructor questions

2014-03-23 Thread Dirk Schulze 
Hi, 

I was reading the spec part about ImageData [1].

1) 
I noticed that createImageData() is explicit that it represent a transparent 
black rectangle. The constructor for ImageData is not that explicit.

2)
The last step of the 2nd constructor that takes an Uint8ClampedArray says:
   • Return a new ImageData object whose width is sw, whose height is 
height, and whose data is source.”

Is data a reference to the original source or a copy of source? For the former, 
there might be two ImageData objects referencing the same ByteArray. How would 
that be useful?

Greetings,
Dirk

[1] 
http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dfnReturnLink-7
 (4.12.4.2.16 Pixel manipulation)

Re: [whatwg] ImageData constructor questions

2014-03-23 Thread Rik Cabanier 
On Sat, Mar 22, 2014 at 11:31 PM, Dirk Schulze dschu...@adobe.com wrote:

 Hi,

 I was reading the spec part about ImageData [1].

 1)
 I noticed that createImageData() is explicit that it represent a
 transparent black rectangle. The constructor for ImageData is not that
 explicit.


Yes, that seems like an oversight.


 2)
 The last step of the 2nd constructor that takes an Uint8ClampedArray says:
* Return a new ImageData object whose width is sw, whose height is
 height, and whose data is source.

 Is data a reference to the original source or a copy of source?


It is the original source. The spec does not say anything about creating a
new array and copying the bits over.


 For the former, there might be two ImageData objects referencing the same
 ByteArray. How would that be useful?


You *could* use the API that way but I don't see why there has to be a way
to prevent that from happening. Is there an implementation issue if 2
different imageData object point to the same dataarray/



 [1]
 http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#dfnReturnLink-7(4.12.4.2.16
  Pixel manipulation)


Correct link is:
http://www.whatwg.org/specs/web-apps/current-work/multipage/the-canvas-element.html#pixel-manipulation