docs(roadmap): the platform-parity tier described a Windows-only engine

It still called the compositor "Direct3D 11", listed MP4 export on macOS and
Linux as unstarted, and framed "porting it off Windows" as the biggest open
item — while v1.8.0-rc.5 was already publishing DMGs and Linux packages built
on the Metal and WGSL backends. #18 (software encoder fallback) shipped with
them too, as an automatically-selected CPU backend rather than the encoder flag
the entry anticipated.

Marked all three shipped, and replaced them with the two gaps that are actually
open: Linux export is software-encoded (the capture helper has a hardware H.264
encoder, the export pipeline does not), and every performance number on record
still comes from one passive-iGPU laptop, so nothing is measured on the hardware
most users have.

Author: EtienneLescot

ROADMAP.md

@@ -34,12 +34,18 @@ Still open on this axis:
 - [ ] **Sanctioned ChatGPT / GitHub Copilot sign-in** — both were removed in 1.8.0: reaching a user's subscription meant shipping GitHub's and OpenAI's own client IDs and an editor `User-Agent` against endpoints reserved for first-party clients, from inside a signed installer. They come back on the vendors' sanctioned surfaces — GitHub's Copilot SDK (we register our own OAuth App) and `codex app-server` (drives the user's own `codex login`, no client ID shipped at all). Separate integrations, not a header swap.
 
 ## 🖥️ Rendering & platform parity
-The live preview and MP4 export run on one native Rust + Direct3D 11 compositor: demux → decode → composite → hardware encode → mux, GPU-resident, no CPU readback between stages. Both consume the same scene description, so the frame you see in the editor is the frame the export writes — there is no second renderer that can drift.
+The live preview and MP4 export run on one native Rust compositor: demux → decode → composite → hardware encode → mux, GPU-resident, no CPU readback between stages. Both consume the same scene description, so the frame you see in the editor is the frame the export writes — there is no second renderer that can drift.
 
-That engine is **Windows-only today**, which makes this the largest gap on the roadmap:
+That engine ran on Direct3D 11 only until 1.8.0, which made this the largest gap on the roadmap. It now has three backends behind the same scene contract:
 
-- [ ] **MP4 export on macOS and Linux** — needs a Metal and a Vulkan backend behind the same scene contract. Recording, editing, transcription and GIF export already work on all three platforms; MP4 export does not.
-- [ ] **Feature:** software H.264 fallback when no GPU encoder is available — [#18](../../issues/18). Critical for VMs, broken-driver machines, and headless environments.
+- [x] **MP4 export on macOS** — Metal render pipeline with VideoToolbox decode and encode, a CoreText text rasterizer, and audio muxed into the output. All nine shader entry points are ported to MSL, so annotations, the cursor and its trail, the 3D tilt zoom and the dual-Kawase blur all render there.
+- [x] **MP4 export on Linux** — wgpu/WGSL pipeline with software H.264 encode, MP4 mux and AAC audio.
+- [x] **Feature:** software fallback when no GPU encoder is available — [#18](../../issues/18). A CPU backend (software render + decode) is selected automatically and surfaced in the UI, and reaches the export encoder like any other backend. Direct3D 11 now fails legibly rather than silently degrading to WARP.
+
+Still open on this axis:
+
+- [ ] **Hardware encode on Linux** — the export path is correct but software-encoded, so it is slower than the Windows and macOS ones. The capture helper already uses a hardware H.264 encoder; the export pipeline does not.
+- [ ] **A discrete-GPU and Intel QSV measurement.** Every number in [rendering-performance.md](technical-documentation/engineering/rendering-performance.md) comes from one passive-iGPU laptop, deliberately chosen as the weak case. Nothing is measured on the hardware most users have.
 
 ## 🛠️ Stability & quality (what we're actually shipping)
 Pulled from real user bug reports on getopenscreen/openscreen. This is the queue for the next release window.
@@ -71,4 +77,4 @@ Anything not on this list yet? Open an issue and tag it `roadmap` — we'll tria
 - **2026-06-24** — initial draft. Stability items pulled from open issues / PRs on getopenscreen/openscreen. AI section presented as opt-in / off by default. Whisper entry updated to reflect existing caption feature.
 - **2026-06-25** — added "Site & documentation" tier: Docusaurus + GitHub Pages. Cleaned smoke-test noise from the changelog (internal CI sync validation, not user-facing).
 - **2026-07-06** — added blur regions to the stability & quality tier. Confirmed upstream deprecated the feature in v1.5.0 without an explicit reason; the renderer code carried over to the fork, so the work is unblocking the export guard + adding coverage. Tracked via #76.
-- **2026-07-27** — reconciled the roadmap with the code. The AI Edition tier moved from "a direction, not a sprint plan" to shipped: on-device transcription, transcript-driven editing, captions as a derived layer with translation, the chat agent, and `.openscreen` projects are all in. Provider list corrected — ChatGPT and GitHub Copilot were removed in 1.8.0 and are now blocked on the vendors' sanctioned surfaces, and MiniMax was missing. New "Rendering & platform parity" tier: preview and MP4 export share one native D3D11 compositor, and porting it off Windows is now the biggest open item; #18 moved there since it's an encoder concern. Blur (#76) marked shipped — as an annotation type, not a region kind, so the old note pointing at `src/lib/exporter/videoExporter.ts` was doubly stale (that file was deleted with the web export pipeline). Copy/paste (#24) split: the shortcuts shipped, the right-click menu didn't. Docusaurus site marked shipped.
+- **2026-07-27** — reconciled the roadmap with the code. The AI Edition tier moved from "a direction, not a sprint plan" to shipped: on-device transcription, transcript-driven editing, captions as a derived layer with translation, the chat agent, and `.openscreen` projects are all in. Provider list corrected — ChatGPT and GitHub Copilot were removed in 1.8.0 and are now blocked on the vendors' sanctioned surfaces, and MiniMax was missing. New "Rendering & platform parity" tier: preview and MP4 export share one native D3D11 compositor, and porting it off Windows is now the biggest open item; #18 moved there since it's an encoder concern. Blur (#76) marked shipped — as an annotation type, not a region kind, so the old note pointing at `src/lib/exporter/videoExporter.ts` was doubly stale (that file was deleted with the web export pipeline). Copy/paste (#24) split: the shortcuts shipped, the right-click menu didn't. Docusaurus site marked shipped.- **2026-08-01** — the platform-parity tier was the stalest thing on this page: it still described the compositor as Direct3D 11 and listed MP4 export on macOS and Linux as unstarted, while v1.8.0-rc.5 was already publishing DMGs and Linux packages built on the Metal and WGSL backends. #18 (software encoder fallback) shipped with them, as an automatically-selected CPU backend rather than an encoder flag. Two real gaps replace them: Linux export is software-encoded, and every performance number on record still comes from one passive-iGPU laptop. Also corrected the framing that produced this drift — the tier was written as "porting it off Windows is the biggest open item", which stayed true in the text long after it stopped being true in the tree.