Consider this example:
<svg xmlns="
http://www.w3.org/2000/svg">
<filter id="f1" x="0" y="0" width="20" height="10" filterUnits="userSpaceOnUse">
<feFlood flood-color="green" x="-10" y="0" width="20" height="10"/>
<feTile x="0" y="0" width="20" height="10"/>
</filter>
<rect x="0" y="0" width="20" height="10" filter="url(#f1)"/>
</svg>
I see two possible renderings:
1) the filter primitive subregion for the feFlood is the rectangle (-10,0)-(10,10). The output is a green rectangle at (0,0)-(10,10). (The rectangle (10,0)-(10,10) is filled with the left half of the feFlood filter primitive subregion, which is presumably transparent since it's outside the filter region.)
2) the filter primitive subregion for the feFlood is clamped to the filter effects region, i.e. (0,0)-(10,10). The output is a green rectangle at (0,0)-(20,10) since we get two full copies of the tile.
IMHO the spec is much too vague on the exact definition of the filter primitive subregion:
http://www.w3.org/TR/SVG/filters.html#FilterPrimitiveSubRegion
All intermediate offscreens are defined to not exceed the
intersection of x, y,
width and height with the filter
region. The
filter region and any of the x,
y, width and
height subregions are to be set up such that
all offscreens are made big enough to accommodate any pixels
which even partly intersect with either the filter region or
the x,y,width,height subregions.
I interpret this discussion of "intermediate offscreens" as an implementation note that does not affect the actual definition of the "filter primitive subregion", in which case rendering #1 would be correct. But if this is supposed to affect the filter primitive subregion rectangle that feTile uses, then rendering #2 would be correct. Please write a clear definition of "filter primitive subregion" into the spec. I also suggest removing all language about "intermediate offscreens" or else making it into a clearly identified "implementation note".
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]
