Slang on Raspberry Pico 2 W

This is a proof-of-concept of compiling and running Slang and GLSL code on a microcontroller. It is able to run Shadertoy shaders on the microcontroller! Although, performance is measured in seconds per frame.

The program running "A Dead Planet of Silicon Dreams" by mrange

NOTE that none of the code in the shaders folder is mine; they're just example shaders from Shadertoy that work with this program! Their respective licenses are found at the beginning of the shader files. You can add more shaders in that directory and they will automatically be compiled into the program.

What's special about this?

Slang (in its current form) is a shading language. This means that it's usually used to write code to run on GPUs. The "special" part of this project is running that GPU code on something it's absolutely not meant to be run on: an underpowered microcontroller, without any operating system or interpreter!

slangc, the Slang compiler, also supports compiling GLSL and HLSL code; this means that in addition to Slang, it is possible to compile GLSL and HLSL into CPU programs on bare metal now.

This is not a simple transpiler hack - the Slang/GLSL code is never compiled into C or C++ or any other high-level language. Instead, the new LLVM emitter of slangc is used to directly emit object code for the microcontroller.

Several, now merged PRs to Slang were necessary to make this work: 9491, 9492, 9493, and 9501.

Build

To test this out, use the v2026.1 release of Slang and place slangc in PATH.

This has only been tested on a single setup:

• Host: OpenSUSE Tumbleweed, x86_64
• Microcontroller: Raspberry Pico 2 W

The GCC 15 toolchain is used for pico-sdk, and the Slang compiler is using LLVM 21. The PICO_SDK_PATH environment variable must be defined to point to pico-sdk. Other than that, there shouldn't be anything special.

The pico.slang bindings to pico-sdk have been generated with this binding generator. It has been generated using flags that are specifically correct for the Pico 2 W, so this project only works on that device currently.

With all this in place, you should be able to just:

cmake -S . -B build -DCMAKE_BUILD_TYPE=Release [-DOVERCLOCK]
cmake --build build
cp build/picotoy.uf2 /run/media/username/RP2350

If you connect the USB to your Linux PC, you can observe the printfs with:

screen /dev/ttyACM0 115200

The program prints some basic performance metrics for each frame.

Hardware

• Raspberry Pi Pico 2 W
  • Using the Cortex M33 CPU, no RISC-V support yet
• Adafruit 2.0" 240x320 IPS TFT LCD
  • Display SPI pins connected to Pico's SPI0
  • D/C in GPIO 21, RESET in GPIO 20
• Two push buttons to cycle between shaders
  • They connect GPIO 14 & 15 to ground when connected
  • Internal pull-up resistors are used, you don't need external resistors

Gallery / Performance

Timings are measured using -DOVERCLOCK (overclocks the Pico to 532 MHz) and both Cortex M33 cores, using a release build. The performance results are averaged over 10 frames and reported in SPF (Seconds Per Frame).

setup.mp4

The overall setup (pre-overclock)

"A Dead Planet of Silicon Dreams" by mrange, 11.1 SPF

"Cable nest v2" by mrange, 4.8 SPF

"Let's self reflect" by mrange, 2.2 SPF

starry_planes.mp4

"Starry planes" by mrange, 0.37 SPF (2.7 FPS, whoa!)

"Synthwave canyon" by mrange, 2.2 SPF