export: cache the static background + bilinear video, add render profiling
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.
This commit is contained in:
Skyler Lehmkuhl
parent
7525a604f2
commit
aa7d3a3bf4
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@ -0,0 +1,102 @@
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# GPU-resident video decode + dynamic decode resolution
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## Context
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Profiling the zero-copy H.264 export (single Group[Video, Audio] clip, `LB_RENDER_PROFILE=1`)
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broke the per-frame CPU "render" bucket down as:
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| Cost (ms/frame) | 1080p | 4K | What it is |
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|-------------------------|-------|-------|-----------------------------------------------------|
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| decode | 3.1 | 19.0 | software ffmpeg decode (`video.rs::get_frame`) |
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| background re-render | 3.6 | 7.5 | static background pushed through Vello *every frame* |
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| video upload + blit | 4.1 | 4.2 | per-frame transient texture alloc + `write_texture` |
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| srgb | 0.4 | 0.4 | linear→sRGB pass |
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The video correctly takes the GPU Video-instance path (not Vello-baked) — `LB_LAYER_DEBUG=1`
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shows `Video (1 instance)`. So the cost is **the video frame itself**: software decode, then an
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8 MB `write_texture` upload of the decoded RGBA every frame. At 4K, software decode (19 ms)
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dominates everything.
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### Two correctness problems found alongside the perf issue
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1. **Decode resolution is frozen to document size at import.** `load_video(clip, src, doc_w, doc_h)`
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(`main.rs:4302`) sizes the decoder's swscale output to the document, capped to never upscale
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(`video.rs:149`). Export *reuses that decoder*, so exporting **above** document resolution yields
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video that was decoded to ≤document res and then GPU-**up**scaled — real source detail thrown away.
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2. **It can't follow the consumer or a document resize.** Preview wants small/fast frames; export
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wants full res; changing the document size should re-target the decode. None of that works with a
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size frozen at import.
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## Goal
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Decouple **decode resolution** from import/document size: the renderer requests a frame *at a target
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resolution*, and the decode path produces it. Hardware-decode H.264 (and later HEVC/AV1) into a GPU
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surface and keep it GPU-resident through composite into the encoder — no CPU frame copy in either
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direction. Software decode stays a **first-class** path (codecs/platforms without HW support), decoding
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at the requested target res. This fixes the 4K decode wall, the 8 MB upload, *and* the resolution bugs.
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## Design principles
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- **Decode native, scale to the consumer's target.**
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- *Hardware path:* decode into a native VAAPI surface → import as a wgpu texture (reuse the
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`gpu-video-encoder` `dmabuf.rs` / `vk_device.rs` plumbing, read direction) → the GPU blit that
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already composites the Video instance scales native→target for free. Handles any target res and
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document resizes inherently; the cached frame is a native GPU texture.
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- *Software path:* decode native → `swscale` to the requested target (the reusable scaler is keyed
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on input format/size **and** output size — rebuilt when the target changes). Preview requests
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preview res (cheap); export requests export res (full quality).
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- **`VideoManager::get_frame` takes a target `(w, h)`** instead of relying on a frozen output size.
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The frame cache is keyed to handle multiple live targets (preview + export) — either cache native
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frames and scale on demand, or key by `(clip, ts, target)`; decide in Stage 2 by measuring cache
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hit/scale tradeoff.
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- **Software is not optional.** Hardware decode is an acceleration of the same `get_frame` contract,
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selected per source when the codec/driver supports it; everything falls back to software cleanly.
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## Approach (staged; each stage compiles + is independently useful)
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### Stage 0 — independent quick wins (not blocked on decode)
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- **Cache the static background** (`composite_document_to_hdr`): render once, reuse via a persistent
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HDR texture (copy-in each frame) instead of a full Vello render + 2 passes/submits every frame.
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Recovers ~3.6 ms (1080p) / ~7.5 ms (4K) per frame on *every* export. (In flight.)
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### Stage 1 — software: decode at the requested target res (testable; fixes the quality bug now)
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- Change `VideoManager::get_frame(clip, ts)` → `get_frame(clip, ts, target_w, target_h)`; thread the
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target from the renderer (preview = current doc/preview res, export = export res). Cap at native.
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- Rework `VideoDecoder` so output size is per-request, not frozen at construction; cache the swscale
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context per output size (already cached per stream — extend the key). Adjust the frame cache key.
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- Result: software exports are full-quality at any export res, and document resizes re-target decode.
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No hardware needed; this is the correctness fix for the codecs HW can't handle anyway.
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### Stage 2 — hardware decode primitive (headless-testable here, like the 8 encode tests)
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- In `gpu-video-encoder` (rename → `gpu-video-codec`): `h264_vaapi`-style **decode** → VAAPI surface →
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export DMA-BUF → import as a wgpu texture. Hardware test: decode a known file, verify dims/contents.
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### Stage 3 — wire hardware decode into `get_frame` (blind; user-verifies)
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- When the source codec/driver is HW-decodable, `get_frame` returns a **GPU texture** (native res)
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instead of `Arc<Vec<u8>>`; the compositor uses it directly (no `write_texture`), GPU-scaling to the
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target. For the zero-copy export the frame never leaves the GPU: **decode → composite → encode** on
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one device. Software path is the fallback for everything else.
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## Critical files
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- `lightningbeam-core/src/video.rs` — `VideoDecoder` (per-request output size, scaler cache),
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`VideoManager::get_frame` (target param, cache key).
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- `lightningbeam-core/src/renderer.rs` — pass the render target res into the video-instance build.
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- `lightningbeam-editor/src/export/video_exporter.rs` — background cache (Stage 0); consume a GPU
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texture instead of uploading RGBA (Stage 3).
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- `gpu-video-encoder/` (→ `gpu-video-codec`) — `dmabuf.rs`/`vk_device.rs` reused for the decode import.
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## Risks
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- **Codec coverage** — only some codecs are HW-decodable per GPU/driver; software must stay correct
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and well-tested. Selection must probe support per source, not assume.
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- **Cache memory** — native-res GPU textures (esp. 4K) are large; the frame cache budget needs revisiting.
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- **Colorspace/format** — VAAPI decode surfaces are NV12/tiled; the existing import handles NV12, but
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10-bit/HDR sources (P010) need format handling.
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- **Preview vs export sharing** — two live targets (preview res + export res) from the same source; the
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cache/scaler design must serve both without thrashing.
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## Verification
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- Stage 0/1: visual — export above document res is now full-quality (not upscaled); profile shows
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background ≈ 0 and (Stage 1) software export correct at the chosen res.
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- Stage 2: headless hardware test in `gpu-video-codec` (decode → wgpu texture, ffprobe/byte checks).
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- Stage 3 (user): 1080p + 4K H.264 export — decode/upload buckets collapse; software fallback for a
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non-HW codec (e.g. ProRes) still produces correct full-res output.
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@ -83,6 +83,11 @@ pub struct ExportGpuResources {
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pub canvas_blit: crate::gpu_brush::CanvasBlitPipeline,
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/// Per-keyframe GPU texture cache for raster layers during export.
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pub raster_cache: std::collections::HashMap<uuid::Uuid, crate::gpu_brush::CanvasPair>,
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/// Cached HDR accumulator state after the (static) background is composited in. The document
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/// background doesn't change across an export, so it's rendered once and restored with a cheap
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/// texture copy each frame instead of a full Vello render + 2 passes/submits. `None` until the
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/// first frame; invalidated on resize.
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cached_bg_hdr: Option<wgpu::Texture>,
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}
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impl ExportGpuResources {
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@ -108,7 +113,8 @@ impl ExportGpuResources {
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format: HDR_FORMAT,
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usage: wgpu::TextureUsages::RENDER_ATTACHMENT
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| wgpu::TextureUsages::TEXTURE_BINDING
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| wgpu::TextureUsages::COPY_SRC,
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| wgpu::TextureUsages::COPY_SRC
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| wgpu::TextureUsages::COPY_DST, // restore cached background each frame
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view_formats: &[],
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});
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let hdr_texture_view = hdr_texture.create_view(&wgpu::TextureViewDescriptor::default());
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@ -261,6 +267,7 @@ impl ExportGpuResources {
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linear_to_srgb_sampler,
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canvas_blit,
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raster_cache: std::collections::HashMap::new(),
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cached_bg_hdr: None,
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}
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}
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@ -279,10 +286,12 @@ impl ExportGpuResources {
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format: HDR_FORMAT,
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usage: wgpu::TextureUsages::RENDER_ATTACHMENT
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| wgpu::TextureUsages::TEXTURE_BINDING
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| wgpu::TextureUsages::COPY_SRC,
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| wgpu::TextureUsages::COPY_SRC
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| wgpu::TextureUsages::COPY_DST,
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view_formats: &[],
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});
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self.hdr_texture_view = self.hdr_texture.create_view(&wgpu::TextureViewDescriptor::default());
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self.cached_bg_hdr = None; // dimensions changed — rebuild the background cache
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}
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}
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@ -748,7 +757,30 @@ fn composite_document_to_hdr(
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antialiasing_method: vello::AaConfig::Area,
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};
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// --- Background ---
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let prof = render_profile_enabled();
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let t_c0 = std::time::Instant::now();
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// --- Background (cached) ---
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// The document background is static across an export, so render it through Vello exactly once
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// (into the accumulator) and snapshot the result; every later frame restores it with a single
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// GPU texture copy instead of a Vello render + sRGB-convert + composite (+2 submits).
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let bg_cached = matches!(
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&gpu_resources.cached_bg_hdr,
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Some(t) if t.width() == width && t.height() == height
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);
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let copy_size = wgpu::Extent3d { width, height, depth_or_array_layers: 1 };
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if bg_cached {
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// Restore the cached background into the accumulator.
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let cached = gpu_resources.cached_bg_hdr.as_ref().unwrap();
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let mut enc = device.create_command_encoder(&wgpu::CommandEncoderDescriptor { label: Some("export_bg_restore") });
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enc.copy_texture_to_texture(
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wgpu::TexelCopyTextureInfo { texture: cached, mip_level: 0, origin: wgpu::Origin3d::ZERO, aspect: wgpu::TextureAspect::All },
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wgpu::TexelCopyTextureInfo { texture: &gpu_resources.hdr_texture, mip_level: 0, origin: wgpu::Origin3d::ZERO, aspect: wgpu::TextureAspect::All },
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copy_size,
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);
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queue.submit(Some(enc.finish()));
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} else {
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// First frame (or after a resize): full background render into the accumulator.
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let bg_srgb = gpu_resources.buffer_pool.acquire(device, layer_spec);
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let bg_hdr = gpu_resources.buffer_pool.acquire(device, hdr_spec);
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if let (Some(bg_srgb_view), Some(bg_hdr_view)) = (
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@ -772,6 +804,28 @@ fn composite_document_to_hdr(
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gpu_resources.buffer_pool.release(bg_srgb);
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gpu_resources.buffer_pool.release(bg_hdr);
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// Snapshot the composited background for reuse on subsequent frames.
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let cached = device.create_texture(&wgpu::TextureDescriptor {
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label: Some("export_cached_bg_hdr"),
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size: copy_size,
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mip_level_count: 1,
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sample_count: 1,
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dimension: wgpu::TextureDimension::D2,
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format: HDR_FORMAT,
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usage: wgpu::TextureUsages::COPY_SRC | wgpu::TextureUsages::COPY_DST,
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view_formats: &[],
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});
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let mut enc = device.create_command_encoder(&wgpu::CommandEncoderDescriptor { label: Some("export_bg_snapshot") });
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enc.copy_texture_to_texture(
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wgpu::TexelCopyTextureInfo { texture: &gpu_resources.hdr_texture, mip_level: 0, origin: wgpu::Origin3d::ZERO, aspect: wgpu::TextureAspect::All },
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wgpu::TexelCopyTextureInfo { texture: &cached, mip_level: 0, origin: wgpu::Origin3d::ZERO, aspect: wgpu::TextureAspect::All },
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copy_size,
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);
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queue.submit(Some(enc.finish()));
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gpu_resources.cached_bg_hdr = Some(cached);
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}
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let t_bg = std::time::Instant::now();
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// --- Layers ---
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for rendered_layer in &composite_result.layers {
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if !rendered_layer.has_content { continue; }
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@ -906,10 +960,33 @@ fn composite_document_to_hdr(
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}
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}
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if prof {
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record_composite_profile(t_bg.duration_since(t_c0), t_bg.elapsed());
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}
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gpu_resources.buffer_pool.next_frame();
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Ok(())
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}
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/// Split of `composite_document_to_hdr`: static-background re-render vs. the layer loop
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/// (video upload + blits). Prints a running average every 200 frames under LB_RENDER_PROFILE.
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fn record_composite_profile(background: std::time::Duration, layers: std::time::Duration) {
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use std::sync::atomic::{AtomicU64, Ordering};
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static BG_US: AtomicU64 = AtomicU64::new(0);
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static LAYERS_US: AtomicU64 = AtomicU64::new(0);
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static N: AtomicU64 = AtomicU64::new(0);
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BG_US.fetch_add(background.as_micros() as u64, Ordering::Relaxed);
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LAYERS_US.fetch_add(layers.as_micros() as u64, Ordering::Relaxed);
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let n = N.fetch_add(1, Ordering::Relaxed) + 1;
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if n % 200 == 0 {
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println!(
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"📊 [COMPOSITE PROFILE] {n} frames avg: background-render {:.2}ms | layers(video upload+blit) {:.2}ms",
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BG_US.load(Ordering::Relaxed) as f64 / n as f64 / 1000.0,
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LAYERS_US.load(Ordering::Relaxed) as f64 / n as f64 / 1000.0,
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);
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}
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}
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/// Upload `pixels` to a transient GPU texture (TEXTURE_BINDING | COPY_DST) in the
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/// given format. Use `Rgba8UnormSrgb` to upload raw sRGB bytes and let the GPU
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/// decode to linear on sample (no CPU conversion).
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@ -1224,6 +1301,12 @@ pub fn render_frame_to_gpu_rgba(
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) -> Result<wgpu::CommandEncoder, String> {
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use vello::kurbo::Affine;
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// One-shot profiling of the render-bucket split (LB_RENDER_PROFILE=1): how much of the
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// per-frame CPU "render" is document build (incl. video decode) vs. composite-command
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// recording (incl. the frame texture upload) vs. the sRGB pass. Prints a running average.
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let prof = render_profile_enabled();
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let t0 = std::time::Instant::now();
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// Set document time to the frame timestamp
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document.current_time = timestamp;
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@ -1256,8 +1339,10 @@ pub fn render_frame_to_gpu_rgba(
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floating_selection,
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false, // No checkerboard in export
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);
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let t_build = std::time::Instant::now();
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composite_document_to_hdr(&composite_result, document, device, queue, renderer, gpu_resources, width, height, allow_transparency)?;
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let t_composite = std::time::Instant::now();
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// Convert HDR to sRGB (linear → sRGB), render directly to external RGBA texture
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let output_view = rgba_texture_view;
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@ -1302,11 +1387,49 @@ pub fn render_frame_to_gpu_rgba(
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render_pass.draw(0..4, 0..1);
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}
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if prof {
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record_render_profile(
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t_build.duration_since(t0),
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t_composite.duration_since(t_build),
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t_composite.elapsed(),
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);
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}
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// Return encoder for caller to submit (ReadbackPipeline will handle submission and async readback)
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// Frame is already rendered to external RGBA texture, no GPU YUV conversion needed
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Ok(encoder)
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}
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/// `LB_RENDER_PROFILE` gate, checked once.
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fn render_profile_enabled() -> bool {
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static V: std::sync::OnceLock<bool> = std::sync::OnceLock::new();
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*V.get_or_init(|| std::env::var("LB_RENDER_PROFILE").is_ok())
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}
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/// Accumulate the per-frame render split and print a running average every 200 frames.
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/// `build` = document build incl. video decode; `composite` = composite-command recording
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/// incl. the frame texture upload; `srgb` = the linear→sRGB pass.
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fn record_render_profile(build: std::time::Duration, composite: std::time::Duration, srgb: std::time::Duration) {
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use std::sync::atomic::{AtomicU64, Ordering};
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static BUILD_US: AtomicU64 = AtomicU64::new(0);
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static COMPOSITE_US: AtomicU64 = AtomicU64::new(0);
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static SRGB_US: AtomicU64 = AtomicU64::new(0);
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static N: AtomicU64 = AtomicU64::new(0);
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BUILD_US.fetch_add(build.as_micros() as u64, Ordering::Relaxed);
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COMPOSITE_US.fetch_add(composite.as_micros() as u64, Ordering::Relaxed);
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SRGB_US.fetch_add(srgb.as_micros() as u64, Ordering::Relaxed);
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let n = N.fetch_add(1, Ordering::Relaxed) + 1;
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if n % 200 == 0 {
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let (b, c, s) = (BUILD_US.load(Ordering::Relaxed), COMPOSITE_US.load(Ordering::Relaxed), SRGB_US.load(Ordering::Relaxed));
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println!(
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"📊 [RENDER PROFILE] {n} frames avg: build(+decode) {:.2}ms | composite(+upload) {:.2}ms | srgb {:.2}ms",
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b as f64 / n as f64 / 1000.0,
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c as f64 / n as f64 / 1000.0,
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s as f64 / n as f64 / 1000.0,
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);
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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|
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@ -2238,6 +2238,8 @@ impl CanvasBlitPipeline {
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/// Blit a **straight-alpha** source (e.g. a video frame uploaded to an
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/// `Rgba8UnormSrgb` texture, hardware-decoded to linear on sample). Uses the
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/// `fs_main_straight` pipeline, which skips the unpremultiply that `blit` does.
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/// Bilinear-sampled: video frames are scaled to the output size (document→export, or any
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/// non-1:1 transform), and nearest sampling makes that look blocky.
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pub fn blit_straight(
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&self,
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device: &wgpu::Device,
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@ -2247,7 +2249,7 @@ impl CanvasBlitPipeline {
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transform: &BlitTransform,
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mask_view: Option<&wgpu::TextureView>,
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) {
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self.blit_with(device, queue, canvas_view, target_view, transform, mask_view, &self.sampler, &self.pipeline_straight);
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self.blit_with(device, queue, canvas_view, target_view, transform, mask_view, &self.linear_sampler, &self.pipeline_straight);
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}
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#[allow(clippy::too_many_arguments)]
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|
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Loading…
Reference in New Issue