I'd like to make a passionate plea that the spec say
"implementations must
support negative widths and negative heights and draw the image
backward
effectively flipping the result".
We'd need to be fairly sure that such a change would not break
existing content -- this is a change that would result in
substantially different rendering in some scenarios.
Also, I'd like to suggest that a widths and heights of 0 for source
should be
valid as well as rectangles outside of the source also be valid and
that this
part of the spec.
"If the source rectangle is not entirely within the source image, or
if one of
the sw or sh arguments is zero, the implementation must raise an
INDEX_SIZE_ERR
exception."
be changed to reflect that.
The issues of when exceptions should be thrown in the canvas API have
been discussed repeatedly on this list, you should search the archives
and see if there are any arguments you can make that have not already
been made. (I note that i am also all for exceptions not being thrown
in many of these cases)
The next issue related to drawImage is that the spec does not
specify how to
filter an image when scaling it. Should it use bi-linear
interpolation? Nearest
Neighbor? Maybe that should stay implementation dependent?
Image scaling is implementation dependent everywhere else, why would
it be spec defined in the case of canvas?
--Oliver
