[Public WebGL] getContext multiple context language
Fri Jan 22 17:45:54 PST 2010
Here's the language for getContext() -- let me know of any suggestions
before I send it off to hixie:
object getContext(in DOMString contextId, in optional object attributes)
'contextId' must be a string naming a canvas rendering context to be
returned. This specification only defines one context, with the
name "2d". If getContext() is called with that exact string for its
'contextId' argument, then the UA must return a reference to an
object implementing CanvasRenderingContext2D. Other specifications
may define their own contexts, which would return different objects.
The optional 'attributes' parameter must be either null, or an
object specific to the context being requested. A null or
unspecified value for the 'attributes' parameter is equivalent to
requesting default attributes for the given context.
If getContext() is called multiple times on the same canvas with the
same context ID, it must return the same resulting context object
provided that the attributes are identical to all previous requests
for that context ID. If the attributes are not identical,
getContext() must raise an INVALID_STATE_ERR exception. (XXX is
INVALID_STATE the right thing here? or is SYNTAX_ERR better?)
If getContext() is called with a context ID different from the
context IDs given to any previous successful calls to getContext(),
it may either return a new canvas context that can be used
simultaneously with all previously obtained contexts, or return null
to indicate that the newly requested context cannot be used with the
previously obtained contexts.
If multiple rendering contexts are active, they all render to the
same canvas; they are not layered or otherwise isolated. Changes
made to the canvas with one context must be immediately visible to
any other active contexts on the canvas. It is up to the
implementation to manage synchronization issues associated with
rendering with different contexts to the same canvas.
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