WebSurfaceFrame::from_parts was unconditionally calling
Arc::new(RenderImage::new([image::Frame::new(image_buffer)])) on
every live frame, even when the underlying bytes were
byte-for-byte identical to the previous frame. At 60 fps on a 1080p
canvas that was ~960 MB/s of host-side cloning plus a fresh GPUI
texture allocation on every tick — the bottleneck Linus + Karpathy
+ Jony flagged as the next material step after dropping the
file-system pixel pipe (a80d039).
A thread_local single-slot cache in web_surface_frame.rs now keys
on a 64-bit DefaultHasher of the raw RGBA bytes. On a cache hit
the existing Arc<RenderImage> is reused; on a miss the buffer is
built once, stored, and returned. Steady-state idle pages stop
churning the GPUI texture pool entirely. Hash collisions are
1 in 2^64 — if that ever becomes a real worry, the cache key can
be widened to length + a sample of bytes before paying the full
memcmp; not worth doing today.
The T10 red guard
(identical_live_frames_share_render_image_arc) drops its
#[ignore] attribute outright per the contract it documented.
The T7 red guard (user_click_in_rendered_web_canvas_reaches_input_pipeline)
remains ignored — it's a separate diagnosis tracked under T13.
cargo test --bin ely_app: 113 passed, 0 failed, 1 ignored
(was 112+2, T10 guard went green).
cargo test --bin ely_app -- --ignored: 1 failed (only T7 click
pipeline remains red).
Follow-ups (left for the endgame T10 IOSurface path):
* a per-tab cache would prevent multi-tab switching from
thrashing the single slot; defer until a real multi-tab
scroll benchmark shows it matters.
* the endgame is OffscreenRenderingContext + IOSurface so the
GPU texture itself is the source of truth and the host-side
Vec<u8> + ImageBuffer + RenderImage allocation chain
disappears entirely.
ZacharyZhang-NY
7f3b8b42b3