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offscreen: Render GPUI views into images on iOS and Android - #33
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…en` feature Ungate `WgpuHeadlessRenderer` from `test-support` / `bench-support`, add `WgpuHeadlessRenderer::with_instance` so iOS can pass a Metal instance (the default instance only enables Vulkan and GL), and inherent `render_to_image` / `sprite_atlas` / `max_texture_size` that do not need GPUI's test-only `PlatformHeadlessRenderer` trait. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
madcodelife
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offscreen windows that render GPUI views into images
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Oct 13, 2026
…ws (#37) ## Summary Follow-up to #33. - **Release GPU memory after captures.** The headless renderer is kept for the rest of the process, so after a capture it held the render target and the path intermediate / MSAA textures sized to the last frame (for a 1170×16000 image that is roughly 75 MB + 75 MB + 300 MB at 4× path MSAA), plus every glyph and image tile uploaded to the sprite atlas the offscreen windows share. GPUI only removes image tiles through `App::drop_image` on open windows, which never reaches that atlas once the window is gone, so image tiles accumulated for the life of the process. - The vendored `gpui-pre-wgpu` gains two `offscreen`-gated methods on `WgpuHeadlessRenderer`: `release_render_target` (render target + path intermediates) and `clear_sprite_atlas` (atlas tiles + the cached bind groups that keep their textures alive). The readback buffer was already a per-call local, so there is no staging buffer to release. - `offscreen` counts live offscreen platform windows and calls both when GPUI drops the last one (after its view tree), so no open window can hold a tile that gets cleared. The device and pipelines stay for the next capture. - **Close dropped windows.** Dropping an `OffscreenWindow` without `close` (for example when the task holding it is cancelled) used to leave the window and its view tree alive forever. It now keeps an `AsyncApp` and, on drop, spawns the close on the foreground executor, since `Drop` may run while the `App` is borrowed. `close` disarms it, so the window is never closed twice. - README and the `[patch.crates-io]` comment describe the new vendor methods and the release behaviour. While an offscreen window stays open, image tiles still accumulate the same way they do for on-screen windows; the instance buffer, which grows to the largest frame's instance data, is kept with the pipelines. ## Testing - `cargo check --features offscreen` for `aarch64-apple-ios`, `aarch64-apple-ios-sim` and `aarch64-linux-android` - `cargo check --all-targets`, `cargo test --lib`, `cargo fmt --all -- --check` - `cargo clippy --features offscreen` for iOS and Android: no new warnings - New vendor test `headless_renderer_releases_frame_textures` (Linux, like the other headless tests); also run locally on macOS against a Metal instance, where it passes --------- Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>
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Summary
Adds an
offscreenfeature for rendering GPUI views into images on iOS and Android — for share cards, long screenshots and similar exports.gpui_mobile::offscreen::OffscreenWindowopens an ordinary GPUI window whose platform side has no UIKit/NDK surface. Layout, text shaping and painting run exactly as on screen;render(size)forces one frame and reads its pixels back through wgpu's headless renderer (image::RgbaImage), andlayout(size)paints without reading back so views can measure their content first.max_size()reports the GPU texture limit in logical pixels.IosPlatform::open_window/AndroidPlatform::open_windowhand out the offscreen window whenOffscreenWindow::openasked for one (a thread-local pending slot, like Android's pending-window lookup).Why a vendored
gpui-pre-wgpuUpstream
gpui-pre-wgpu0.3.8 only buildsWgpuHeadlessRendererwithtest-support/bench-support(the latter turns on GPUI's per-frame profiler), and its device comes from a Vulkan + GL instance, which has no adapter on iOS.vendor/gpui-pre-wgpuis the unmodified 0.3.8 source (first commit) plus a small patch (second commit, ~100 lines):offscreenfeature;WgpuHeadlessRenderer::with_instance(wgpu::Instance)so iOS can pass a Metal instance;render_to_image/sprite_atlas/max_texture_size, which don't need GPUI's test-onlyPlatformHeadlessRenderertrait.Applications enabling
offscreenmust patchgpui-pre-wgputo this copy (see the README section). The longer-term fix is to offer the same in upstreamgpui_wgpu.Testing
cargo checkforaarch64-apple-ios,aarch64-apple-ios-simandaarch64-linux-androidwithoffscreen; hostcargo check --all-targets; clippy clean for the new module;cargo fmt --all -- --check.