The export render bucket was dominated by re-rendering the static document
background through Vello every frame and by nearest-sampling the video on
upscale.
- Background cache: render the (static) background through Vello once, snapshot
the composited HDR accumulator, and restore it with a single texture copy on
every later frame instead of a Vello render + sRGB-convert + composite (+2
submits). Invalidated on resize. background-render 3.6ms -> 0.56ms (1080p),
7.5ms -> ~0.5ms (4K).
- blit_straight now uses the bilinear sampler — video frames are scaled to the
output size, and nearest made that blocky. Fixes export and live preview.
- LB_RENDER_PROFILE: gated per-frame timing split (build/decode vs composite/
upload vs srgb, and background vs layers) used to find all of the above. Kept
as a debug aid for the remaining decode stages.
Net: export render ~12.8ms -> ~7.4ms/frame on a 1080p video clip.
Skyler Lehmkuhl