SPIRV-Cross

SPIRV-Cross is a tool designed for parsing and converting SPIR-V to other shader languages.

Features

• Convert SPIR-V to readable, usable and efficient GLSL
• Convert SPIR-V to readable, usable and efficient Metal Shading Language (MSL) [EXPERIMENTAL]
• Convert SPIR-V to debuggable C++ [EXPERIMENTAL]
• Reflection API to simplify the creation of Vulkan pipeline layouts
• Reflection API to modify and tweak OpDecorations
• Supports "all" of vertex, fragment, tessellation, geometry and compute shaders.

SPIRV-Cross tries hard to emit readable and clean output from the SPIR-V. The goal is to emit GLSL or MSL that looks like it was written by a human and not awkward IR/assembly-like code.

NOTE: Individual features are expected to be mostly complete, but it is possible that certain obscure GLSL features are not yet supported. However, most missing features are expected to be "trivial" improvements at this stage.

Occasionally, missing features is due to glslangValidator's lack of proper support for that feature making testing hard.

Building

SPIRV-Cross has been tested on Linux, OSX and Windows.

Linux and OSX

Just run make on the command line. A recent GCC (4.8+) or Clang (3.x+) compiler is required as SPIRV-Cross uses C++11 extensively.

Windows

MinGW-w64 based compilation works with make, and an MSVC 2013 solution is also included.

Usage

Using the C++ API

To perform reflection and convert to other shader languages you can use the SPIRV-Cross API. For example:

#include "spirv_glsl.hpp"
#include <vector>
#include <utility>

extern std::vector<uint32_t> load_spirv_file();

int main()
{
	// Read SPIR-V from disk or similar.
	std::vector<uint32_t> spirv_binary = load_spirv_file();

	spirv_cross::CompilerGLSL glsl(std::move(spirv_binary));

	// The SPIR-V is now parsed, and we can perform reflection on it.
	spirv_cross::ShaderResources resources = glsl.get_shader_resources();

	// Get all sampled images in the shader.
	for (auto &resource : resources.sampled_images)
	{
		unsigned set = glsl.get_decoration(resource.id, spv::DecorationDescriptorSet);
		unsigned binding = glsl.get_decoration(resource.id, spv::DecorationBinding);
		printf("Image %s at set = %u, binding = %u\n", resource.name.c_str(), set, binding);

		// Modify the decoration to prepare it for GLSL.
		glsl.unset_decoration(resource.id, spv::DecorationDescriptorSet);

		// Some arbitrary remapping if we want.
		glsl.set_decoration(resource.id, spv::DecorationBinding, set * 16 + binding);
	}

	// Set some options.
	spirv_cross::CompilerGLSL::Options options;
	options.version = 310;
	options.es = true;
	glsl.set_options(options);

	// Compile to GLSL, ready to give to GL driver.
	std::string source = glsl.compile();
}

Integrating SPIRV-Cross in a custom build system

To add SPIRV-Cross to your own codebase, just copy the source and header files from root directory and build the relevant .cpp files you need. Make sure to build with C++11 support, e.g. -std=c++11 in GCC and Clang. Alternatively, the Makefile generates a libspirv-cross.a static library during build that can be linked in.

Creating a SPIR-V file from GLSL with glslang

glslangValidator -H -V -o test.spv test.frag

Converting a SPIR-V file to GLSL ES

glslangValidator -H -V -o test.spv shaders/comp/basic.comp
./spirv-cross --version 310 --es test.spv

Converting to desktop GLSL

glslangValidator -H -V -o test.spv shaders/comp/basic.comp
./spirv-cross --version 330 test.spv --output test.comp

Disable prettifying optimizations

glslangValidator -H -V -o test.spv shaders/comp/basic.comp
./spirv-cross --version 310 --es test.spv --output test.comp --force-temporary

Contributing

Contributions to SPIRV-Cross are welcome. See Testing and Licensing sections for details.

Testing

SPIRV-Cross maintains a test suite of shaders with reference output of how the output looks after going through a roundtrip through glslangValidator then back through SPIRV-Cross again. The reference files are stored inside the repository in order to be able to track regressions.

All pull requests should ensure that test output does not change unexpectedly. This can be tested with ./test_shaders.py shaders. However, when improving SPIRV-Cross there are of course legitimate cases where reference output should change. In these cases, run ./test_shaders.py shaders --update to update the reference files and include these changes as part of the pull request. Always make sure you are running up to date glslangValidator when updating reference files.

In short, the master branch should always be able to run ./test_shaders.py shaders without failure.

When adding support for new features to SPIRV-Cross, a new shader and reference file should be added which covers usage of the new shader features in question.

Licensing

Contributors of new files should add a copyright header at the top of every new source code file with their copyright along with the Apache 2.0 licensing stub.

ABI concerns

SPIR-V headers

The current repository uses the latest SPIR-V and GLSL.std.450 headers. SPIR-V files created from older headers could have ABI issues.

Regression testing

In shaders/ a collection of shaders are maintained for purposes of regression testing. The current reference output is contained in reference/. ./test_shaders.py shaders can be run to perform regression testing.

See ./test_shaders.py --help for more.

Updating regression tests

When legitimate changes are found, use --update flag to update regression files. Otherwise, ./test_shaders.py will fail with error code.

Mali Offline Compiler cycle counts

To obtain a CSV of static shader cycle counts before and after going through spirv-cross, add --malisc flag to ./test_shaders. This requires the Mali Offline Compiler to be installed in PATH.