Blog about shadertoys

Author: LegNeato

blog/2025-04-10-shadertoys.md

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+---
+title: "Shadertoys ported to Rust GPU"
+authors: [LegNeato]
+tags: ["demo"]
+---
+
+# Porting Shadertoys to Rust with Rust GPU
+
+We ported a few popular [Shadertoy](https://www.shadertoy.com/) shaders over to Rust
+using [Rust GPU](https://github.com/Rust-GPU/rust-gpu/). The process was straightforward
+and we want to share some highlights.
+
+<!-- truncate -->
+
+The code is available on [GitHub](https://github.com/Rust-GPU/rust-gpu-shadertoys).
+
+![Shadertoy screenshot](/img/shadertoys.png)
+
+## What is Rust GPU?
+
+[Rust GPU](https://rust-gpu.github.io/) is a project that allows you to write code for
+GPUs using the Rust programming language. GPUs are typically programmed using
+specialized languages like [WGSL](https://www.w3.org/TR/WGSL/),
+[GLSL](https://developer.mozilla.org/en-US/docs/Games/Techniques/3D_on_the_web/GLSL_Shaders),
+[MSL](https://developer.apple.com/documentation/metal/performing_calculations_on_a_gpu),
+or
+[HLSL](https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl).
+Rust GPU changes this by letting you use Rust to write GPU programs (often called
+"shaders" or "kernels").
+
+These Rust GPU programs are then compiled into [SPIR-V](https://www.khronos.org/spir/),
+a low-level format that [most GPUs understand](https://vulkan.gpuinfo.org/). Since
+SPIR-V is the format [Vulkan](https://www.vulkan.org/) uses, Rust GPU makes it possible
+to integrate Rust-based GPU programs into any Vulkan-compatible workflow.
+
+For more details, check out the [Rust GPU website](http://rust-gpu.github.io/) or the
+[GitHub repository](https://github.com/rust-gpu/rust-gpu).
+
+## Shared code between CPU and GPU
+
+Sharing data between the CPU and GPU is common in shader programming. This often
+requires special tooling or manual effort. Using Rust on both sides made this seamless:
+
+```rust
+#[repr(C)]
+#[derive(Copy, Clone, Pod, Zeroable)]
+pub struct ShaderConstants {
+    pub width: u32,
+    pub height: u32,
+    pub time: f32,
+    pub cursor_x: f32,
+    pub cursor_y: f32,
+    pub drag_start_x: f32,
+    pub drag_start_y: f32,
+    pub drag_end_x: f32,
+    pub drag_end_y: f32,
+    pub mouse_left_pressed: u32,
+    pub mouse_left_clicked: u32,
+}
+```
+
+Note that on both the CPU and the GPU we are using the
+[`bytemuck`](https://github.com/Lokathor/bytemuck) crate for the `Pod` and `Zeroable`
+derives. This crate is unmodified and integrated directly from
+[crates.io](https://crates.io/crates/bytemuck). Many `no_std` + no `alloc` Rust crates
+work on the GPU!
+
+## Traits, generics, and macros
+
+Rust GPU supports traits. We used traits to encapsulate shader-specific operations in
+reusable ergonomic abstractions:
+
+```rust
+pub trait FloatExt {
+    fn gl_fract(self) -> Self;
+    fn rem_euclid(self, rhs: Self) -> Self;
+    fn gl_sign(self) -> Self;
+    fn deg_to_radians(self) -> Self;
+    fn step(self, x: Self) -> Self;
+}
+```
+
+While there are still some rough edges, generics mostly work as expected. We used them
+to support multiple channel types without duplicating logic:
+
+```rust
+pub struct State<C0, C1> {
+    inputs: Inputs<C0, C1>,
+    cam_point_at: Vec3,
+    cam_origin: Vec3,
+    time: f32,
+    ldir: Vec3,
+}
+```
+
+Rust macros also function normally. Using macros allowed us to reduce repetitive code
+further.
+
+```rust
+macro_rules! deriv_impl {
+    ($ty:ty) => {
+        impl Derivative for $ty {
+            deriv_fn!(ddx, OpDPdx, false);
+            deriv_fn!(ddx_fine, OpDPdxFine, true);
+            deriv_fn!(ddx_coarse, OpDPdxCoarse, true);
+            deriv_fn!(ddy, OpDPdy, false);
+            deriv_fn!(ddy_fine, OpDPdyFine, true);
+            deriv_fn!(ddy_coarse, OpDPdyCoarse, true);
+            deriv_fn!(fwidth, OpFwidth, false);
+            deriv_fn!(fwidth_fine, OpFwidthFine, true);
+            deriv_fn!(fwidth_coarse, OpFwidthCoarse, true);
+        }
+    };
+}
+
+// Applied easily to multiple types:
+deriv_impl!(f32);
+deriv_impl!(Vec2);
+deriv_impl!(Vec3A);
+deriv_impl!(Vec4);
+```
+
+## Standard Rust tools
+
+Want to typecheck the shaders? `cargo check`. Build them? `cargo build`. Run in release
+mode? `cargo run --release`. Gate code at compile time? Use
+[features](https://doc.rust-lang.org/cargo/reference/features.html).
+
+If you run `clippy` on the shaders, you'll see it complains about many things as we
+intentionally kept the Rust versions of shaders similar to their original GLSL versions.
+
+This is one of Rust GPU's big advantages: you can use all the Rust tools you're already
+familiar with.
+
+## Improving the Rust ecosystem
+
+While porting shaders, we also contributed back to the ecosystem by identifying and
+fixing several issues in [`wgpu` and `naga`](https://github.com/gfx-rs/wgpu):
+
+- [Fixed a panic while processing SPIR-V](https://github.com/gfx-rs/wgpu/pull/7397)
+- [Fixed incorrect translation of certain shader literals when targeting
+  Metal](https://github.com/gfx-rs/wgpu/pull/7437)
+- [Fixed a regression making it impossible to include raw
+  SPIR-V](https://github.com/gfx-rs/wgpu/pull/7503)
+
+These fixes help everyone using `wgpu` and `naga`, not just users of Rust GPU.
+
+## Come join us!
+
+While we hit some sharp edges, porting Shadertoy shaders to Rust with Rust GPU was
+reasonably straightforward. Rust GPU is definitely ready for shader experimentation.
+
+We're eager to add more users and contributors! We will be working on revamping the
+onboarding and documentation soon. To follow along or get involved, check out the
+[`rust-gpu` repo on GitHub](https://github.com/rust-gpu/rust-gpu).