OpenEXR
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# Install

The OpenEXR library is available for download and installation in binary form via package managers on many Linux distributions. See https://pkgs.org/download/openexr for a complete list.

RHEL/CentOS:

    $ sudo yum makecache
    $ sudo yum install OpenEXR

Ubuntu:

    $ sudo apt-get update
    $ sudo apt-get install openexr

Beware that some distributions are out of date and only provide distributions of outdated releases OpenEXR. We recommend against using OpenEXR v2, and we strongly recommend against using OpenEXR v1.

On macOS, install via Homebrew:

    $ brew install openexr

We do not recommend installation via Macports because the distribution is out of date.

Also note that the official OpenEXR project does not provide supported python bindings. `pip install openexr` installs the openexrpython module, which is not affiliated with the OpenEXR project or the ASWF. Please direct questions there.

## Build from Source

OpenEXR builds on Linux, macOS, Microsoft Windows via CMake, and is cross-compilable on other systems.

Download the source from the GitHub releases page page, or clone the repo.

The `release` branch of the repo always points to the most advanced release.

### Prerequisites

Make sure these are installed on your system before building OpenEXR:

- OpenEXR requires CMake version 3.12 or newer

- C++ compiler that supports C++11

- zlib

- Imath (auto fetched by CMake if not found)

The instructions that follow describe building OpenEXR with CMake.

Note that as of OpenEXR 3, the Gnu autoconf bootstrap/configure build system is no longer supported.

### Linux/macOS

To build via CMake, you need to first identify three directories:

1. The source directory, i.e. the top-level directory of the downloaded source archive or cloned repo, referred to below as `$srcdir`

2. A temporary directory to hold the build artifacts, referred to below as `$builddir`

3. A destination directory into which to install the libraries and headers, referred to below as `$installdir`.

To build: .. code-block:

    $ cd $builddir
    $ cmake $srcdir --install-prefix $installdir
    $ cmake --build $builddir --target install --config Release

Note that the CMake configuration prefers to apply an out-of-tree build process, since there may be multiple build configurations (i.e. debug and release), one per folder, all pointing at once source tree, hence the `$builddir` noted above, referred to in CMake parlance as the build directory. You can place this directory wherever you like.

See the CMake Configuration Options section below for the most common configuration options especially the install directory. Note that with no arguments, as above, `make install` installs the header files in `/usr/local/include`, the object libraries in `/usr/local/lib`, and the executable programs in `/usr/local/bin`.

### Windows

Under Windows, if you are using a command line-based setup, such as cygwin, you can of course follow the above. For Visual Studio, cmake generators are “multiple configuration”, so you don’t even have to set the build type, although you will most likely need to specify the install location. Install Directory By default, `make install` installs the headers, libraries, and programs into `/usr/local`, but you can specify a local install directory to cmake via the `CMAKE_INSTALL_PREFIX` variable:

    $ cmake .. -DCMAKE_INSTALL_PREFIX=$openexr_install_directory

## Library Names

By default the installed libraries follow a pattern for how they are named. This is done to enable multiple versions of the library to be installed and targeted by different builds depending on the needs of the project. A simple example of this would be to have different versions of the library installed to allow for applications targeting different VFX Platform years to co-exist.

If you are building dynamic libraries, once you have configured, built, and installed the libraries, you should see the following pattern of symlinks and files in the install lib folder:

    libOpenEXR.so -> libOpenEXR-3_1.so
    libOpenEXR-3_1.so -> libOpenEXR-3_1.so.30
    libOpenEXR-3_1.so.30 -> libOpenEXR-3_1.so.30.3.0
    libOpenEXR-3_1.so.30.3.0 (the shared object file)

The `-3_1` suffix encodes the major and minor version, which can be configured via the `OPENEXR_LIB_SUFFIX` CMake setting. The `30` corresponds to the so version, or in `libtool` terminology the `current` shared object version; the 3 denotes the `libtool` `revision`, and the `0` denotes the `libtool` `age`. See the libtool documentation for more details.

## Imath Dependency

OpenEXR depends on Imath. If a suitable installation of Imath cannot be found, CMake will automatically download it at configuration time. To link against an existing installation of Imath, add the Imath directory to the `CMAKE_PREFIX_PATH` setting:

    $ mkdir $build_directory
    $ cd $build_directory
    $ cmake -DCMAKE_PREFIX_PATH=$imath_install_directory \
            -DCMAKE_INSTALL_PREFIX=$openexr_install_destination \
            $openexr_source_directory
    $ cmake --build . --target install --config Release

Alternatively, you can specify the `Imath_DIR` variable:

    $ mkdir $build_directory
    $ cd $build_directory
    $ cmake -DImath_DIR=$imath_config_directory \
            -DCMAKE_INSTALL_PREFIX=$openexr_install_destination \
            $openexr_source_directory
    $ cmake --build . --target install --config Release

Note that `Imath_DIR` should point to the directory that includes the `ImathConfig.cmake` file, which is typically the `lib/cmake/Imath` folder of the root install directory where Imath is installed.

See below for other customization options.

## Porting Applications from OpenEXR v2 to v3

See the OpenEXR/Imath 2.x to 3.x Porting Guide for details about differences from previous releases and how to address them. Also refer to the porting guide for details about changes to Imath.

## Building the Documentation

The OpenEXR technical documentation at https://openexr.readthedocs.io is generated via Sphinx with the Breathe extension using information extracted from header comments by Doxygen.

To build the documentation locally from the source headers and `.rst` files, set the CMake option `BUILD_DOCS=ON`. This adds `Doxygen` and `Sphinx` CMake targets and enables building the docs by default. generation is off by default.

Building the documentation requires that `sphinx`, `breathe`, and `doxygen` are installed. It further requires the sphinx-press-theme, as indicated in the requirements.txt file.

See the doxygen downloads page for how to install it. Binary distributions are available for many systems, so you likely do not need to build from source. On Debian/Ubuntu, for example:

    $ sudo apt-get install doxygen

Similarly, see the sphinx installation page for how to install it. On Debian/Ubuntu:

    $ sudo apt-get install python3-sphinx

And to install sphinx-press-theme:

    $ pip3 install sphinx_press_theme

Note that the https://openexr.readthedocs.io documentation takes the place of the formerly distributed .pdf documents in the `docs` folder, although readthedocs supports downloading of documentation in pdf format, for those who prefer it that way.

## CMake Build-time Configuration Options

The default CMake configuration options are stored in `cmake/OpenEXRSetup.cmake`. To see a complete set of option variables, run:

    $ cmake -LAH $openexr_source_directory

You can customize these options three ways:

1. Modify the `.cmake` files in place.

2. Use the UI `cmake-gui` or `ccmake`.

3. Specify them as command-line arguments when you invoke cmake.

### Library Naming Options

- `OPENEXR_LIB_SUFFIX`

  Append the given string to the end of all the OpenEXR libraries. Default is `-<major>_<minor>` version string. Please see the section on library names

### Imath Dependency

- `CMAKE_PREFIX_PATH`

  The standard CMake path in which to search for dependencies, Imath in particular. A comma-separated path. Add the root directory where Imath is installed.

- `Imath_DIR`

  The config directory where Imath is installed. An alternative to using `CMAKE_PREFIX_PATH`. Note that `Imath_DIR` should be set to the directory that includes the `ImathConfig.cmake` file, which is typically the `lib/cmake/Imath` folder of the root install directory.

### Namespace Options

- `OPENEXR_IMF_NAMESPACE`

  Public namespace alias for OpenEXR. Default is `Imf`.

- `OPENEXR_INTERNAL_IMF_NAMESPACE`

  Real namespace for OpenEXR that will end up in compiled symbols. Default is `Imf_<major>_<minor>`.

- `OPENEXR_NAMESPACE_CUSTOM`

  Whether the namespace has been customized (so external users know)

- `IEX_NAMESPACE`

  Public namespace alias for Iex. Default is `Iex`.

- `IEX_INTERNAL_NAMESPACE`

  Real namespace for Iex that will end up in compiled symbols. Default is `Iex_<major>_<minor>`.

- `IEX_NAMESPACE_CUSTOM`

  Whether the namespace has been customized (so external users know)

- `ILMTHREAD_NAMESPACE`

  Public namespace alias for IlmThread. Default is `IlmThread`.

- `ILMTHREAD_INTERNAL_NAMESPACE`

  Real namespace for IlmThread that will end up in compiled symbols. Default is `IlmThread_<major>_<minor>`.

- `ILMTHREAD_NAMESPACE_CUSTOM`

  Whether the namespace has been customized (so external users know)

### Component Options

- `BUILD_TESTING`

  Build the testing tree. Default is `ON`. Note that this causes the test suite to be compiled, but it is not executed. To execute the suite, run “make test”.

- `OPENEXR_RUN_FUZZ_TESTS`

  Controls whether to include the fuzz tests (very slow). Default is `OFF`.

- `OPENEXR_BUILD_TOOLS`

  Build and install the binary programs (exrheader, exrinfo, exrmakepreview, etc). Default is `ON`.

- `OPENEXR_INSTALL_EXAMPLES`

  Build and install the example code. Default is `ON`.

### Additional CMake Options

See the CMake documentation for more information (https://cmake.org/cmake/help/v3.12/).

- `CMAKE_BUILD_TYPE`

  For builds when not using a multi-configuration generator. Available values: `Debug`, `Release`, `RelWithDebInfo`, `MinSizeRel`

- `BUILD_SHARED_LIBS`

  This is the primary control whether to build static libraries or shared libraries / dlls (side note: technically a convention, hence not an official `CMAKE_` variable, it is defined within cmake and used everywhere to control this static / shared behavior)

- `OPENEXR_CXX_STANDARD`

  C++ standard to compile against. This obeys the global `CMAKE_CXX_STANDARD` but doesn’t force the global setting to enable sub-project inclusion. Default is `14`.

- `CMAKE_CXX_COMPILER`

  The C++ compiler.

- `CMAKE_C_COMPILER`

  The C compiler.

- `CMAKE_INSTALL_RPATH`

  For non-standard install locations where you don’t want to have to set `LD_LIBRARY_PATH` to use them

- `CMAKE_EXPORT_COMPILE_COMMANDS`

  Enable/Disable output of compile commands during generation. Default is `OFF`.

- `CMAKE_VERBOSE_MAKEFILE`

  Echo all compile commands during make. Default is `OFF`.

## Cross Compiling / Specifying Specific Compilers

When trying to either cross-compile for a different platform, or for tasks such as specifying a compiler set to match the VFX reference platform, cmake provides the idea of a toolchain which may be useful instead of having to remember a chain of configuration options. It also means that platform-specific compiler names and options are out of the main cmake file, providing better isolation.

A toolchain file is simply just a cmake script that sets all the compiler and related flags and is run very early in the configuration step to be able to set all the compiler options and such for the discovery that cmake performs automatically. These options can be set on the command line still if that is clearer, but a theoretical toolchain file for compiling for VFX Platform 2015 is provided in the source tree at `cmake/Toolchain-Linux-VFX_Platform15.cmake` which will hopefully provide a guide how this might work.

For cross-compiling for additional platforms, there is also an included sample script in `cmake/Toolchain-mingw.cmake` which shows how cross compiling from Linux for Windows may work. The compiler names and paths may need to be changed for your environment.

More documentation:

- Toolchains: https://cmake.org/cmake/help/v3.12/manual/cmake-toolchains.7.html

- Cross compiling: https://gitlab.kitware.com/cmake/community/wikis/doc/cmake/

## Ninja

If you have Ninja installed, it is faster than make. You can generate ninja files using cmake when doing the initial generation:

    $ cmake -G “Ninja” ..

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