ncnn/docs/webgpu-native-support.md

• WebGPU Native Support for NCNN
• • Key Features
  • Usage
  • Shader Transformation Example
  • Implementation Details
  • Files Modified
  • Building

WebGPU Native Support for NCNN

This implementation adds WebGPU native support to NCNN, allowing the reuse of existing Vulkan compute shaders with automatic conversion to WebGPU-compatible format.

Key Features

1. Push Constant to Uniform Binding Conversion: Automatically transforms Vulkan push constants to WebGPU uniform bindings
2. Modified psc Macro: Updated to use float(x)==0 for WebGPU compatibility instead of x==0
3. Seamless Integration: Reuses existing Vulkan shader infrastructure with minimal changes

Usage

WebGPU support is automatically enabled when compiling to WebAssembly (wasm) target with emscripten and Vulkan support is enabled:

# Use emscripten toolchain with Vulkan enabled
emcmake cmake .. -DNCNN_VULKAN=ON

This will automatically:

• Enable WebGPU when targeting emscripten + vulkan
• Transform all ~300+ compute shaders for WebGPU compatibility
• Apply the correct psc macro definition

Shader Transformation Example

Vulkan (original):

layout (push_constant) uniform parameter
{
    int dims;
    int w;
    int h;
    int c;
    int cstep;
} p;

WebGPU (transformed):

struct parameter
{
    int dims;
    int w;
    int h;
    int c;
    int cstep;
};
layout (binding = 1) uniform parameter_blob { parameter p; };

Implementation Details

The implementation addresses the SPIR-V compilation issues mentioned in the GitHub issue:

1. Error: unknown SPIR-V storage class: 9 - Fixed by converting push constants to uniform bindings
2. Error: unhandled expression for ID 33 - Fixed by changing psc macro to use float(x)==0

Files Modified

• CMakeLists.txt: Automatic WebGPU detection for emscripten + vulkan
• src/gpu.cpp: Updated psc macro for WebGPU compatibility
• cmake/ncnn_add_shader.cmake: Added WebGPU shader preprocessing path
• cmake/ncnn_generate_webgpu_shader_header.cmake: New shader transformation logic

Building

# Standard build with WebGPU support using emscripten
mkdir build && cd build
emcmake cmake .. -DNCNN_VULKAN=ON -DNCNN_BUILD_TESTS=ON
emmake make -j$(nproc)

All 300+ compute shaders will be automatically transformed during the build process when targeting emscripten with vulkan enabled.