# How to Build

## Python v3.6+ required

Certain source files are generated at build time from the `xr.xml` file, utilizing 
python scripts. The scripts make use of the python `pathlib` module, which is 
fully supported in python version 3.6 or later.

You will also need the python `jinja2` package, available from your package
manager or with something like `pip3 install jinja2`.

## Windows

Building the OpenXR components in this tree on Windows is supported using
Visual Studio 2013 and newer.  Before beginning, make sure the appropriate
"msbuild.exe" is in your PATH.  Also, when generating the solutions/projects
using CMake, be sure to use the correct compiler version number.  The
following table is provided to help you:

| Visual Studio        | Version Number |
| -------------------- |:--------------:|
| Visual Studio 2013   |       12       |
| Visual Studio 2015   |       14       |
| Visual Studio 2017   |       15       |

### Windows 64-bit

First, generate the 64-bit solution and project files using CMake:

```
mkdir build\win64
cd build\win64
cmake -G "Visual Studio [Version Number] Win64" ../..
```

Finally, open the build\win64\OPENXR.sln in the Visual Studio to build the samples.

### Windows 32-bit

First, generate the 32-bit solution and project files using CMake:

```
mkdir build\win32
cd build\win32
cmake -G "Visual Studio [Version Number]" ../..
```

Open the build\win32\OPENXR.sln in the Visual Studio to build the samples.

## Linux

The following set of packages provides all required libs for building for xlib or xcb with OpenGL and Vulkan support.
 - build-essential
 - cmake (of _somewhat_ recent vintage, 3.10+ known working)
 - libgl1-mesa-dev
 - libvulkan-dev
 - libx11-xcb-dev
 - libxcb-dri2-0-dev
 - libxcb-glx0-dev
 - libxcb-icccm4-dev
 - libxcb-keysyms1-dev
 - libxcb-randr0-dev
 - libxrandr-dev
 - libxxf86vm-dev
 - mesa-common-dev

### Linux Debug

```
mkdir -p build/linux_debug
cd build/linux_debug
cmake -DCMAKE_BUILD_TYPE=Debug ../..
make
```

### Linux Release

```
mkdir -p build/linux_release
cd build/linux_release
cmake -DCMAKE_BUILD_TYPE=Release ../..
make
```

## (Optional) Building the OpenXR Loader as a DLL  

The OpenXR loader is built as a static library by default. To instead build as a dynamic link library, define
the cmake option `DYNAMIC_LOADER=ON`.  e.g. for Win64, replace the cmake line shown above with:

```
cmake -DDYNAMIC_LOADER=ON -G "Visual Studio [Version Number] Win64" ../..
```

# Running the HELLO_XR sample

## OpenXR runtime installation

An OpenXR _runtime_ must first be installed before running the hello_xr sample. The runtime is an
implementation of the OpenXR API, typically tailed to a specific device and distributed by the
device manufacturer. To allow experimentation with the API in the absence of a specific device runtime, 
several organizations have made available prototype OpenXR runtimes, linked from the main OpenXR landing 
page at https://www.khronos.org/openxr

## Configuring the OpenXR Loader
### XR\_RUNTIME\_JSON environment variable

The OpenXR loader looks in system-specific locations for the JSON file `active_runtime.json`, which describes the
default installed OpenXR runtime. To override the default selection, you may define an environment variable 
`XR_RUNTIME_JSON` to select a different runtime, or a runtime which has not been installed in the default
location.

For example, you might set XR\_RUNTIME\_JSON to `<build_dir>/test/runtime/my_custom_runtime.json` to select
an OpenXR runtime described by JSON file `my_custom_runtime.json`.

## Running the Hello_XR Test

The binary for the hello_xr application is written to the `<build_dir>/src/tests/hello_xr` directory.
Set your working directory to this directory and execute the hello_xr binary.

### Hello_XR with a dynamic loader (Windows)

When building a DLL version of the loader, the Visual Studio projects generated by CMake will copy the loader
DLLs to the test application's (hello_xr) binary directory. This makes it unnecessary to copy these files to someplace like `Windows\System32`.

