If I recall correctly, damage rects are a raster-stage optimization that rerenders components only if they have changed ('dirtied') since the previous render. You could extend this concept of 'damage rect' to the next layer down, like React has pursued with the vdom/dom split. If you continue extending the analogy through every layer (raster, layout, scene graph, component hierarchy, data model, ...) all the way down to and including the application interaction model ("user has pressed the E key", "received IO result", ...) and then statically project every interaction model event back up through all the layers to derive a rerender box, then I think you could say damage rects are kinda like deltas. (I think this explanation is mostly reasonable.)
Yeah, I get it. Although in React's case the whole vDOM diffing thing is self-inflicted - it is only necessary because they insist on the UI being a "pure" function of state. Turns out that the only way to do this with an imperative API is some kind of tree diffing, so that you don't recreate expensive stuff from zero each frame.
