Platform/GFX/Surfaces/Use cases

Use cases for surfaces in Gecko. (Parenthetical list items are optional, but future-looking)

WebGL

Production by Content:

(Producible in workers)
(Backbuffer is allocated lazily on any draw/read/query of the backbuffer)
(Wait on Fence that prevents early writes to an in-use buffer)
Backbuffer is read/writeable at any time during JS execution.
'Present' events cause us to detach the backbuffer frame, create a Fence, and submit it towards the consumer.

Consumption in Compositor:

Request the most recently submitted frame (from the producer), and Wait on the Fence to establish frame completeness.
(Ability to, instead: Request the most-recently-complete frame, likely polling for frame completion)
If new frame retrieved, recycle old frame.
(Fence before recycle, so we're sure we're done reading before we begin writing)
Frame is considered read-only.
Avoid unnecessary readbacks and uploads.
Consumed frame persists until overridden by a newer frame. (WebGL can stop producing at any time)

Consumption in Content: