Edit Invalidation: User:SOFTowaha

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The Invalidation Problem

Gecko:Invalidation_Handling describes some rules about what should be invalidated, and when. This page is about a separate problem: *how* to implement invalidation, when views have been removed.

Invalidation must be fast, because we sometimes invalidate a lot.
We'd like to accumulate invalidation in regions, not just take the bounding rect of everything.
We need to handle cases like foreignObject where the area to be invalidated must be transformed in interesting ways.

Current Status

nsIFrame::Invalidate calls nsIFrame::InvalidateInternal, which is virtual
the standard nsIFrame implementation just computes the offset from this frame to its parent, adds it to rect (or region/offset pair), and calls its parent
nsHTML/XULScrollFrame::InvalidateInternal clips the invalidation before they pass it up
nsSVGForeignObjectFrame transforms the invalidation and pass it through the SVG invalidation mechanism
Invalidation goes all the way up to the root frame of the root document, where we invalidate widgets. Eventually there will only be one top-level widget to invalidate.

That's nice and simple, and it doesn't seem to be a problem for performance at the moment, with invalidation batching in place.

Summary:

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