ExportTarget

For an offline render, which composites and encodes frames itself and has nothing to stream to. acquire is this plus a stream; keeping them separate means the offline path never creates a MediaStream it would only have to stop.

Asked before rendering, so the render loop can skip a frame the recorder would only throw away — see FramePacer.due for why that is a correctness matter and not merely a saving.

Call this once per animation frame, drawing or not. The instant is kept and reused when the frame is handed over, so the schedule is queried and advanced on one clock. It used to take a second reading at the end of the render pass, which put the pacer's grid a whole render ahead of the frames arriving and cost most of the rate: target 60 fps on a 60 Hz display captured 59.5 when a frame cost 4 ms, 40 at 6 ms and 30 at 12 ms, and an export-size frame always costs more than 6 ms.

Must be called at the end of the render pass, in the same task: a WebGL drawing buffer is only guaranteed readable until the browser composites the page, so copying it from a timer produces black frames on some drivers.

Takes no instant on purpose — it uses the one captureDue was given for this frame. There is no second clock to get wrong.

Returns true when the frame was captured, so a caller can count.

Also the still-image path: a downloadable frame is the cheapest shareable artefact there is, and it must carry the same mark as the clip.

Draws unconditionally, even when duplicateFrame is about to say the source has not changed. Deciding what to do with a repeated frame — drop it, hold the last one longer, encode it anyway — is a policy choice about the file being produced, and this class produces composites rather than files; see presentedFrames on ExportTargetOptions for where that decision gets the information it needs to make it.