--- title: Testing WebGPU data layouts with Facet | daily.dev description: A Rust developer shares a technique for catching WebGPU data layout mismatches between Rust structs and WGSL shader structs before they cause GPU hangs. After... canonical: https://daily.dev/posts/testing-webgpu-data-layouts-with-facet-wgh7iqcr3 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: Testing WebGPU data layouts with Facet | daily.dev og:description: A Rust developer shares a technique for catching WebGPU data layout mismatches between Rust structs and WGSL shader structs before they cause GPU hangs. After... og:url: https://daily.dev/posts/testing-webgpu-data-layouts-with-facet-wgh7iqcr3 og:image: https://api.daily.dev/og/posts/WgH7iqCr3.png og:image:alt: Testing WebGPU data layouts with Facet og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # Testing WebGPU data layouts with Facet **[Matt Keeter](https://daily.dev/sources/mattkeeter)** · 7 min read · 1 upvotes · 0 comments ## Summary A Rust developer shares a technique for catching WebGPU data layout mismatches between Rust structs and WGSL shader structs before they cause GPU hangs. After hand-writing offset checks using the naga crate to parse WGSL and compare field offsets against Rust's std::mem::offset_of!, the author builds a more robust generic solution using the facet crate's runtime reflection. The resulting compare_struct_layout function automatically checks struct sizes, field offsets, and field sizes between Rust and WGSL definitions, and confirms no fields are missing on either side, including special handling for runtime-sized trailing arrays. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### why does my WGSL mat3x3 struct field have a different byte offset than my Rust struct field WGSL pads each row of a mat3x3f to 16 bytes, making the matrix 48 bytes total, while a Rust [[f32; 3]; 3] is tightly packed at 36 bytes. This 12-byte discrepancy shifts the offset of any field placed after the matrix, which is exactly the kind of layout mismatch that silently corrupts GPU buffer data. _daily.dev surfaces posts like this for developers chasing subtle WebGPU buffer layout bugs._ ### how can I automatically test that my Rust struct layout matches my WGSL struct layout Derive facet::Facet on the Rust struct (conditionally, for tests only) and use naga to parse the WGSL source, then write a generic function that cross-checks each field's offset and size using facet's runtime SHAPE reflection data against naga's parsed struct members, including handling for trailing runtime-sized arrays. _Developers building CPU-GPU interchange layers track testing patterns like this on daily.dev._ ## Similar posts on daily.dev - [Introducing wgsl-rs](https://daily.dev/posts/introducing-wgsl-rs-ny7e7ryhk) · Lobsters · 4 upvotes · 1 comments - [Cache-Conscious Data Layout in Rust: Field Zoning, False Sharing, and the 128-Byte Rule](https://daily.dev/posts/cache-conscious-data-layout-in-rust-field-zoning-false-sharing-and-the-128-byte-rule-47ojtsopq) · Hacker News · 0 upvotes · 0 comments - [Offloading Rust To GPUs Proves Capable Of High Performance With Memory Safety](https://daily.dev/posts/offloading-rust-to-gpus-proves-capable-of-high-performance-with-memory-safety-6ojskq9d9) · Phoronix · 0 upvotes · 0 comments - [Where Your Bytes Live: Memory Layout in Rust and Java](https://daily.dev/posts/where-your-bytes-live-memory-layout-in-rust-and-java-tjqya8qqa) · Medium · 4 upvotes · 1 comments --- Tags: [#testing](https://daily.dev/tags/testing), [#rust](https://daily.dev/tags/rust), [#webgpu](https://daily.dev/tags/webgpu) [View this post on daily.dev](https://daily.dev/posts/testing-webgpu-data-layouts-with-facet-wgh7iqcr3) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"Testing WebGPU data layouts with Facet","url":"https://daily.dev/posts/testing-webgpu-data-layouts-with-facet-wgh7iqcr3","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/testing-webgpu-data-layouts-with-facet-wgh7iqcr3"},"datePublished":"2026-08-23T13:10:26.198Z","dateModified":"2026-09-14T07:31:49.832Z","description":"A Rust developer shares a technique for catching WebGPU data layout mismatches between Rust structs and WGSL shader structs before they cause GPU hangs. 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