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C++20 named module documentation updates (#1767)

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* Named module updates
- Fix CMake instructions for the module
- Provided examples on module config
- Elaborated on the dynamic dispatcher

* Update README.md

- Rearranged warning
- Removed subdirectory from `BASE_DIRS` 
- Added subdirectory to `FILES`
- Added more information for dynamic loader CMake setup with module

* Add target_compile_features for VulkanHppModule

* Add minimum required Vulkan version check in the CMake module example

Add minimum required Vulkan version check in the CMake module example
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Sharadh Rajaraman 2024-01-08 16:53:59 +00:00 committed by GitHub
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@ -673,18 +673,16 @@ Some functions might provide information that depends on the vulkan version. As
- `VULKAN_HPP_CONSTEXPR_20 bool isPromotedExtension( std::string const & extension );` - `VULKAN_HPP_CONSTEXPR_20 bool isPromotedExtension( std::string const & extension );`
Returns `true` if the given extension is promoted to some other extension or vulkan version. Returns `true` if the given extension is promoted to some other extension or vulkan version.
### C++20 standard module ### C++20 named module
#### Note on MS Visual Studio 2022 > [!WARNING]
> The current version of Microsoft Visual Studio 2022 is not able to handle the vulkan.cppm module. A bug is filed (<https://developercommunity.visualstudio.com/t/On-building-a-C20-module:-fatal--error/10469799#T-ND10485943>). You can at least use this feature if you don't need or want to use `vk::UniqueHandle` or `vk::SharedHandle` by defining `VULKAN_HPP_NO_SMART_HANDLE`.
The current version of MS Visual Studio 2022 is not able to handle the vulkan.cppm module. A bug is filed (https://developercommunity.visualstudio.com/t/On-building-a-C20-module:-fatal--error/10469799#T-ND10485943). You can at least use this feature if you don't need or want to use `vk::UniqueHandle` or `vk::SharedHandle` by defining `VULKAN_HPP_NO_SMART_HANDLE`.
#### Overview #### Overview
<!-- todo: add a link to the file --> Vulkan-Hpp provides a [C++ named module](https://en.cppreference.com/w/cpp/language/modules), `vulkan_hpp` in [`vulkan.cppm`](vulkan/vulkan.cppm).
Vulkan-Hpp provides a [C++ standard module](https://en.cppreference.com/w/cpp/language/modules) in [`vulkan.cppm`](vulkan/vulkan.cppm). C++ modules are intended to supersede header files. Modules have potential to drastically improve compilation times for large projects, as declarations and definitions may be easily shared across translation units without repeatedly parsing headers.
C++ modules are intended to supersede headers so that declarations and definitions may be easily shared across translation units without repeatedly parsing headers; therefore, they can potentially drastically improve compile times for large projects. Vulkan-Hpp has some extremely long headers (e.g. [`vulkan_structs.hpp`](vulkan/vulkan_structs.hpp)), and the C++ module is likely to shorten compile times for projects currently using it.
In particular, Vulkan-Hpp has some extremely long headers (e.g. [`vulkan_structs.hpp`](vulkan/vulkan_structs.hpp)), and the C++ module will shorten compile times for projects currently using it.
#### Compiler support #### Compiler support
@ -695,41 +693,76 @@ This feature requires a recent compiler with complete C++20 support:
If you intend to use CMake's C++ module support (and possibly Ninja), then more recent tools are required: If you intend to use CMake's C++ module support (and possibly Ninja), then more recent tools are required:
* Visual Studio 17.4 or later (providing `cl.exe` 19.34 or later) * Visual Studio 2022 17.4 or later (providing `cl.exe` 19.34 or later)
* Clang 16.0.0 or later * Clang 17.0.0 or later
* GCC 14.0 or later
* CMake 3.28 or later * CMake 3.28 or later
* Ninja 1.10.2 or later * Ninja 1.10.2 or later
Either way, GCC does not completely support C++ modules, is therefore not recommended for use. > [!WARNING]
> The Vulkan-Hpp C++ named module is still experimental. Some suggested ways to use it in your projects are below. The long-term goal is to submit patches to the CMake [`FindVulkan`](https://cmake.org/cmake/help/latest/module/FindVulkan.html) module so that users may transparently configure the named module, without needing to declare it as an additional library in consumer CMake code.
##### Usage with CMake ##### Usage with CMake
CMake is recommended for use with the Vulkan C++ module, as it provides a convenient platform-agnostic way to configure your project. CMake is recommended for use with the Vulkan-Hpp named module, as it provides a convenient platform-agnostic way to configure your project.
CMake version 3.28 or later is required to support C++ modules. CMake version 3.28 or later is required to support C++ modules. Refer to the [CMake documentation](https://cmake.org/cmake/help/latest/manual/cmake-cxxmodules.7.html) on the topic.
CMake provides the [FindVulkan module](https://cmake.org/cmake/help/latest/module/FindVulkan.html), which may be used to source the Vulkan SDK and Vulkan headers on your system. CMake provides the [FindVulkan module](https://cmake.org/cmake/help/latest/module/FindVulkan.html), which may be used to source the Vulkan SDK and Vulkan headers on your system.
**Note that this module does not yet provide an IMPORTED target for the Vulkan C++ module, so you must set it up manually.**
To use CMake with C++ modules, you must first set up `vulkan.cppm` as the source for a library target with `FILE_SET` configured `TYPE = CXX_MODULES`, and then link it into your project.
```cmake ```cmake
# find Vulkan SDK # find Vulkan SDK
find_package( Vulkan REQUIRED ) find_package( Vulkan REQUIRED )
# set up Vulkan C++ module # Require Vulkan version ≥ 1.3.256 (earliest version when the Vulkan module was available)
add_library(VulkanCppModule) if( ${Vulkan_VERSION} VERSION_LESS "1.3.256" )
target_sources(VulkanCppModule PRIVATE message( FATAL_ERROR "Minimum required Vulkan version for C++ modules is 1.3.256. "
FILE_SET CXX_MODULES "Found ${Vulkan_VERSION}."
FILES ${Vulkan_INCLUDE_DIR}/vulkan.cppm
) )
endif()
# set up Vulkan C++ module as a library
add_library( VulkanHppModule )
target_sources( VulkanHppModule PRIVATE
FILE_SET CXX_MODULES
BASE_DIRS ${Vulkan_INCLUDE_DIR}
FILES ${Vulkan_INCLUDE_DIR}/vulkan/vulkan.cppm
)
target_compile_features( VulkanHppModule PUBLIC cxx_std_20 )
target_link_libraries( VulkanHppModule PUBLIC Vulkan::Vulkan )
# link Vulkan C++ module into your project # link Vulkan C++ module into your project
add_executable( YourProject main.cpp ) add_executable( YourProject main.cpp )
target_link_libraries(YourProject VulkanCppModule) target_link_libraries( YourProject PRIVATE VulkanHppModule )
``` ```
It is important here, that you need to have `VULKAN_HPP_DISPATCH_LOADER_DYNAMIC` defined equally for both, the module and your importing project. If you want to use the dynamic dispatcher, set it to `1`, otherwise to `0`. Configuring the named module is straightforward; add any required Vulkan-Hpp feature macros (listed in [Configuration Options](#configuration-options)) to `target_compile_definitions`. For instance:
If you're using the dynamic dispatcher, you need to have the macro `VULKAN_HPP_DEFAULT_DISPATCH_LOADER_DYNAMIC_STORAGE` exactly once in your source code, just as in the non-module case. In order to have that macro available, you need to include `<vulkan/vulkan_hpp_macros.hpp>`, a lightweight header providing all the Vulkan-Hpp related macros and defines. And as explained above, you need to initialize that dispatcher in two or three steps:
```cmake
# Disable exceptions, disable smart handles, disable constructors
target_compile_definitions( VulkanHppModule PRIVATE
VULKAN_HPP_NO_EXCEPTIONS
VULKAN_HPP_NO_SMART_HANDLE
VULKAN_HPP_NO_CONSTRUCTORS
)
```
It is important to have `VULKAN_HPP_DISPATCH_LOADER_DYNAMIC` defined equally for both the module and an importing project. To use the [dynamic dispatcher](#extensions--per-device-function-pointers), set it to `1`; otherwise, leave it undefined or set it to `0`. In CMake, do this in a single line with `target_compile_definitions` and the `PUBLIC` scope:
```cmake
target_compile_definitions( VulkanHppModule PUBLIC
VULKAN_HPP_DISPATCH_LOADER_DYNAMIC=1
)
# ...
target_link_libraries( YourProject PRIVATE VulkanHppModule )
```
Furthermore, you may also prefer linking `VulkanHppModule` to just the `Vulkan::Headers` target with the `PUBLIC` scope instead of `Vulkan::Vulkan`, so that the `vulkan-1` library is not linked in, and the Vulkan headers are available to your consuming project, as detailed further below.
```cmake
target_link_libraries( VulkanHppModule PUBLIC Vulkan::Headers )
```
Finally, supply the macro `VULKAN_HPP_DEFAULT_DISPATCH_LOADER_DYNAMIC_STORAGE` exactly once in your source code, just as in the non-module case. In order to have that macro available, include `<vulkan/vulkan_hpp_macros.hpp>`, a lightweight header providing all Vulkan-Hpp related macros and defines. And as explained above, you need to initialize that dispatcher in two or three steps:
```cpp ```cpp
import vulkan_hpp; import vulkan_hpp;
@ -757,14 +790,13 @@ An example is provided in [`tests/Cpp20Modules/Cpp20Modules.cpp`](tests/Cpp20Mod
Finally, you can configure and build your project as usual. Finally, you can configure and build your project as usual.
Note that CMake currently only supports the Ninja and Visual Studio generators for C++ modules. Note that CMake currently only supports the Ninja and Visual Studio generators for C++ modules.
##### Command-line usage ##### Command-line usage
If you want to use the Vulkan-Hpp C++ module without CMake, you must first pre-compile it, and then import it into your project. If you want to use the Vulkan-Hpp C++ module without CMake, you must first pre-compile it, and then import it into your project.
You will also need to define any macros that control various features of Vulkan-Hpp, such as `VULKAN_HPP_NO_EXCEPTIONS` and `VULKAN_HPP_NO_SMART_HANDLE`. You will also need to define any macros that control various features of Vulkan-Hpp, such as `VULKAN_HPP_NO_EXCEPTIONS` and `VULKAN_HPP_NO_SMART_HANDLE`.
Different compilers have different command-lines for module pre-compilation; however, for initial use, some examples are provided below, assuming the same `main.cpp` consumer as above. Different compilers have different command-lines for module pre-compilation; however, for initial use, some examples are provided below, assuming the same `main.cpp` consumer as above.
For MSVC, source `vcvars64.bat` or use a Developer Command Prompt/PowerShell instance, and run the following: For MSVC, source `vcvars64.bat` or use a Developer Command Prompt/Developer PowerShell instance, and run the following:
```cmd ```cmd
cl.exe /std:c++20 /interface /TP <path-to-vulkan-hpp>\vulkan.cppm cl.exe /std:c++20 /interface /TP <path-to-vulkan-hpp>\vulkan.cppm