Web Rendering in Iced: A Few Months On
A progress update on iced_webview. Blitz went GPU-native, HiDPI stopped fighting me, and Servo hit a version wall.
Back in February I wrote about rendering web content in Iced across four backends: litehtml, Blitz, Servo, and CEF. A few months of poking at iced_webview later, enough has changed that it’s worth a short update.
Blitz went GPU-native
The February post made a big deal of two rendering paths: an image-handle path (litehtml, Blitz) where the engine draws the whole document to a pixel buffer and the widget scrolls it, and a shader path (Servo, CEF) where the engine owns its viewport and hands frames to the GPU. That split is collapsing.
Blitz now rasterizes directly onto iced’s own wgpu device via a shared Vello renderer. No CPU readback, no viewport-sized buffer clone per frame — Vello draws straight into iced’s texture. It also owns its own scrolling now, applies :hover styles before paint, and does drag-selection. So Blitz moved from the “just a layout library” camp toward behaving like a real engine, while staying pure Rust. That’s the change I’m most happy about.
The catch is it only works on iced master (wgpu 29) paired with a Blitz alpha, so it lives on a separate branch (next) rather than the crates.io release. Bleeding edge, but it works:
[dependencies]
iced_webview_v2 = { git = "https://github.com/franzos/iced_webview_v2", branch = "next", default-features = false, features = ["blitz"] }
iced = { git = "https://github.com/iced-rs/iced", features = ["advanced", "image", "tokio", "lazy", "wgpu"] }
HiDPI stopped fighting me
On my machines the last post’s builds were subtly wrong on HiDPI displays: content stretched vertically by the scale factor, Servo rendering at 2x and upscaling (so everything was soft), text blitting through a bilinear resample instead of 1:1. I’d been papering over it with a manual set_scale_factor.
That’s all gone. The scale factor is auto-detected across every engine now, content blits 1:1 with the surface, and Servo paints a physical-resolution buffer. Text is crisp. It turns out most of “why does this look blurry” was me applying the display scale twice in different places.
A security and soundness pass
Remote HTML is hostile input, and I’d been treating the fetch pipeline like it wasn’t. So: download size limits are enforced while streaming instead of after buffering the whole body, images per page are capped, litehtml’s render height is clamped so a hostile page can’t exhaust memory, and a malformed @import at the end of a stylesheet no longer panics. The litehtml container access got reworked to raw-pointer provenance too, which closed an aliasing soundness hole that had been quietly sitting there. The SSRF exposure in the fetcher is documented rather than fixed, so treat that as a known edge for now.
Servo hit a version wall
I upgraded Servo from 0.1 to 0.3 and Blitz to its 0.3 alpha, and the two no longer coexist. Both depend on Stylo, and the versions Blitz-on-iced-master and Servo each need now conflict at the links level, so Cargo won’t build them together. On the GPU-Blitz branch, Servo is temporarily disabled until it catches up to the newer Stylo.
So the four-backend story from February is really “pick your tradeoff” right now: crates.io release with the stable set, or the next branch with GPU Blitz but no Servo.
A couple of people pitched in on this round, which I appreciate. Nico Burns, who works on Blitz and Taffy upstream, handled the Servo and Blitz version upgrades (and the earlier one) that the version wall above is all about. folknor fixed a scale-factor and a close-view panic.
It’s still early work and the dependencies underneath it are all moving, but it’s moving in the right direction. Repo’s on GitHub if you want to follow along.