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Paint Holding - reducing the flash of white on same-origin navigations

For a while now, Chrome has eagerly cleared the screen when transitioning to a new page to give users the reassurance that the page is loading. This "flash of white" is this brief moment during which the browser shows a white paint while loading a page. This can be distracting in-between navigations, especially when the page is reasonably fast in reaching a more interesting state.

But for pages that load lightning fast, this approach is actually detrimental to the user experience. In the following animation, you see an example of what this looks like today.

We are big fans of this website and it kills us that their quality experience has a flash of white, and we wanted to fix it. We did so with a new behavior that we're calling Paint Holding, where the browser waits briefly before starting to paint, especially if the page is fast enough. This ensures that the page renders as a whole delivering a truly instant experience.

The way this works is that we defer compositor commits until a given page load signal (PLS) (e.g. first contentful paint / fixed timeout) is reached. We distinguish between main-thread rendering work and commit to the impl thread (only the latter is deferred). Waiting until a PLS occurs reduces likelihood of flashes of white/solid-color.

Our goal with this work was for navigations in Chrome between two pages that are of the same origin to be seamless and thus deliver a fast default navigation experience with no flashes of white/solid-color background between old and new content.

Try Paint Holding in Chrome Canary (Chrome 76) and let us know what you think. Developers shouldn't have to worry about making any modifications to their pages to take advantage of it.

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