SPIRV-Cross/README.md

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.

Building

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

Linux and macOS

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

Using shaders generated from C++ backend

Please see samples/cpp where some GLSL shaders are compiled to SPIR-V, decompiled to C++ and run with test data. Reading through the samples should explain how to use the C++ interface. A simple Makefile is included to build all shaders in the directory.

Using SPIRV-Cross to output GLSL shaders from glslang HLSL

Entry point

When using SPIR-V shaders compiled from HLSL, there are some extra things you need to take care of. First make sure that the entry point is used correctly. If you forget to set the entry point correctly in glslangValidator (-e MyFancyEntryPoint), you will likely encounter this error message:

Cannot end a function before ending the current block.
Likely cause: If this SPIR-V was created from glslang HLSL, make sure the entry point is valid.

Separate image samplers

Another thing you need to remember is when using samplers and textures in HLSL these are separable, and not directly compatible with GLSL. If you need to use this with desktop GL/GLES, you need to call Compiler::build_combined_image_samplers first before calling Compiler::compile, or you will get an exception.

// From main.cpp
// Builds a mapping for all combinations of images and samplers.
compiler->build_combined_image_samplers();

// Give the remapped combined samplers new names.
// Here you can also set up decorations if you want (binding = #N).
for (auto &remap : compiler->get_combined_image_samplers())
{
   compiler->set_name(remap.combined_id, join("SPIRV_Cross_Combined", compiler->get_name(remap.image_id),
            compiler->get_name(remap.sampler_id)));
}

If your target is Vulkan GLSL, --vulkan-semantics will emit separate image samplers as you'd expect. The command line client does this automatically, but if you're calling the library, you'll need to do this yourself.

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 as well as SPIRV-Tools 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.

Formatting

SPIRV-Cross uses clang-format to automatically format code. Please use clang-format with the style sheet found in .clang-format to automatically format code before submitting a pull request.

To make things easy, the format_all.sh script can be used to format all source files in the library. In this directory, run the following from the command line:

./format_all.sh

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.