Re: [CSSOM] Revisiting transforms and getBoundingClientRect()

Reviving this old thread...

What do people think about the following as the most general API?

"element.getQuads(relativeTo)" returns a QuadList which is a list of Quads.
Each Quad contains floats x0,y0,x1,y1,x2,y2,x3,y3, where each value is in
CSS pixels relative to the top-left of the border-box of the first CSS box
of the element relativeTo. If relativeTo has no CSS boxes or is somehow
incomparable to the element (e.g., in a different window), return a
zero-length list. Similar to getClientRects, there would be one quad per CSS
border-box for the element, in content order.

Add element.getContentQuads(relativeTo),
element.getPaddingQuads(relativeTo), and element.getMarginQuads(relativeTo)
to return the other kinds of boxes.

We could add getBoundingRect(relativeTo),
getBoundingContentRect(relativeTo), getBoundingPaddingRect(relativeTo), and
getBoundingMarginRect(relativeTo), returning ClientRect, if that's helpful.
Or we could add getBoundingQuad variants.

We could make relativeTo optional and default to the viewport, if that's
helpful.

Things you can't do with this API:
-- Get values relative to the content-box, padding-box or margin-box of
relativeTo. You can call relativeTo.get*Quads(relativeTo) to get offsets for
relativeTo's first box and then easily do the math.
-- Get values relative to any box of relativeTo other than the first box.
Working around that is hard given the possibility that boxes for the same
element might have different ancestor transforms (which is true with CSS
Regions I think). But I'm not sure if there's any need for such information.
To fix, we would need a way to refer to a particular box of an element, and
I have no idea how authors would want to do that.

Rob
-- 
"If we claim to be without sin, we deceive ourselves and the truth is not in
us. If we confess our sins, he is faithful and just and will forgive us our
sins and purify us from all unrighteousness. If we claim we have not sinned,
we make him out to be a liar and his word is not in us." [1 John 1:8-10]