Screencasting requires every frame be rendered twice

[Daniel van Vugt]

Screencasting requires every frame be rendered twice. Once to go on the physical screen and again to export to the screencast client.

[Kevin DuBois (kdub)]

(been poking in this area with screencast-to-buffer work lately... Changing this system isn't in that line of work, but worth evaluating)

In my estimation (didn't design it initially, but have been tinkering), its a good design for screenshotting, or a good design if you have a 120hz/60hz display, but are happy with a 25hz video.
It also lets us isolate the generally-more problematic GL code (glReadPixels) from the display output code.

[Daniel van Vugt (vanvugt)]

glReadPixels is not problematic if you do it after your swap (which on ES requires an FBO I think). Then the only requirement is that it completes within a few milliseconds to make way for the next frame. That's certainly less CPU intensive than rendering every frame twice, and more accurate too, since you will get the actual pixels that went to screen instead of an estimation of them.

[Michał Sawicz (saviq)]

Syncing task from Mir.