Adsk Contrib - OCIO cmake improvements (#1736)

* - Refactoring how OCIO search for minizip-ng. The first step is to search for an external minizip-ng. If not found, search for minizip-ng with MZ_COMPAT=ON (libminizip). If it is not found either, download and install minizip-ng with MZ_COMPAT=OFF.
- Removing the minizip-ng part for the includes for minizip-ng headers.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Update comments

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Improved find_package in Config mode (adding it back)
Added missing scripts to install minizip-ng and zlib for the analysis workflow

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Adding +x permissions for install_minizip_ng and zlib
Fixing path to find zlib in install_minizip-ng.sh

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Changing target name to match the one used by minizip-ng library (+ using the imported target instead of creating a new one when minizip-ng is found)

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* First pass for the OpenColorIOConfig.cmake file with the required dependencies only.
A few extra fixes for OpenEXR, ZLIB and Minizip-ng.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Adding a informative message when building static ocio instead of per module.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Adding an extra step to test the consumer app with static OpenColorIO for Windows, Linux and MacOS.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Re-using the same test instead of creating a new one by removing the condition on build-shared.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Fixing spacing, typo and adding back the NOT in the condition. (it was removed for debugging purpose)

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Changing directory where we share OCIO custom find modules (now in <install dir>/share/cmake/modules).
Adding a cmake macro when installing OCIO since it is needed by some custom find modules.
The find modules are only installed when building OCIO as a static library.
The config.cmake.in files now only looks for the dependency when OCIO was built as a static library.
Tentative (ci-workflow): Adding cmake-consumer test for static builds.
Overhaul of the Findzlib module to be more inline with the FindZLIB from cmake and to be more robust.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Adding missing backward slashes and saving the build path in an existing step instead of creating a new step.
Adding a check for CMake version for a section in Findzlib.cmake.
Re-phrasing some comments.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Prevent the download of the dependencies in the scenario where static OCIO is linked to a consumer project. Since OCIO_INSTALL_EXT_PACKAGES is not defined, our find module tries to download the dependencies, but we don't want that mecanism for consumer project.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Changing path where OCIO install its own custom find module.
Removing custom Findzlib and making modifications to use CMake FindZLIB.
Created a InstallZLIB module which does the download and install part if OCIO_INSTALL_EXT_PACAKGES is ALL or MISSING.
Tweaked config.cmake.in to use CMake FindZLIB.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Adding more details in comments

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Removing an extra "shell" property in CI workflow.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Fix issues discovered with the failing CI workflow:

Cmake-consumer test now prefer the static version of the dependencies.
Fix an issue where yaml-cpp is not found by a consumer app (variable spelled incorectly in Findyaml-cpp).
Fix an issue expat library is not found by a consumer app on Windows.
Adding support for OCIO's  <pkg_name>_STATIC_LIBRARY for ZLIB while supporting ZLIB_USE_STATIC_LIBS (CMake 3.24+) from CMake's FindZLIB.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Removing pystring_STATIC_LIBRARY does not exists in CI workflow.
Detecting if the build is Debug in the find module that OCIO installs since they can't rely on variables set by OCIO CMakefiles.
Fix issue with yaml-cpp library naming in debug.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Fix issues on Windows with expat and minizip-ng library naming when building static OCIO.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Added option for macOS CI job in order to get more info on a failed job. Will be reverted once the issue is found.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Fixing a issue on macOS.
Improving ZLIB usage comments.
Bumping minizip-ng to the latest version - 3.0.7.
Bumping ZLIB to the latest version 2.1.13 to fix a vulnerability (CVE-2022-37434)

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Proposing to remove Findminizip module since external minizip-ng build need to be done with the same option as the internal build.
Otherwise, linking and symbols issues are going to happend if the other libraries are not linked in correctly.
It is going to simplify the maintainability of OCIO.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

* Removing findminizip.cmake from the install since it does not exist anymore.

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>

Signed-off-by: Cédrik Fuoco <cedrik.fuoco@autodesk.com>
Signed-off-by: Cédrik Fuoco <105517825+cedrik-fuoco-adsk@users.noreply.github.com>

Author: cedrik-fuoco-adsk

.github/workflows/ci_workflow.yml

@@ -287,11 +287,12 @@ jobs:
                 --target install \
                 --config ${{ matrix.build-type }} \
                 -- -j$(nproc)
+          echo "ocio_build_path=$(pwd)" >> $GITHUB_ENV
         working-directory: _build
       - name: Test
         run: ctest -V -C ${{ matrix.build-type }}
         working-directory: _build
-      - name: Test CMake Consumer
+      - name: Test CMake Consumer with shared OCIO
         if: matrix.build-shared == 'ON'
         run: |
           cmake . \
@@ -301,6 +302,34 @@ jobs:
                 --config ${{ matrix.build-type }}
           ./consumer
         working-directory: _build/tests/cmake-consumer-dist
+      - name: Test CMake Consumer with static OCIO
+        if: matrix.build-shared == 'OFF'
+        # The yaml-cpp_VERSION is set below because Findyaml-cpp.cmake needs it but is unable to 
+        # extract it from the headers, like the other modules.
+        #
+        # Prefer the static version of each dependencies by using <pkg>_STATIC_LIBRARY. 
+        # Alternatively, this can be done by setting <pkg>_LIBRARY and <pkg>_INCLUDE_DIR to 
+        # the static version of the package.
+        run: |
+          cmake . \
+                -DCMAKE_PREFIX_PATH=../../../_install \
+                -DCMAKE_BUILD_TYPE=${{ matrix.build-type }} \
+                -Dexpat_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -Dexpat_STATIC_LIBRARY=ON \
+                -DImath_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -DImath_STATIC_LIBRARY=ON \
+                -Dpystring_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -Dyaml-cpp_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -Dyaml-cpp_STATIC_LIBRARY=ON \
+                -Dyaml-cpp_VERSION=0.7.0 \
+                -DZLIB_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -DZLIB_STATIC_LIBRARY=ON \
+                -Dminizip-ng_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -Dminizip-ng_STATIC_LIBRARY=ON
+          cmake --build . \
+                --config ${{ matrix.build-type }}
+          ./consumer
+        working-directory: _build/tests/cmake-consumer-dist
 
   # ---------------------------------------------------------------------------
   # macOS
@@ -424,11 +453,12 @@ jobs:
                 --target install \
                 --config ${{ matrix.build-type }} \
                 -- -j$(sysctl -n hw.ncpu)
+          echo "ocio_build_path=$(pwd)" >> $GITHUB_ENV
         working-directory: _build
       - name: Test
         run: ctest -V -C ${{ matrix.build-type }}
         working-directory: _build
-      - name: Test CMake Consumer
+      - name: Test CMake Consumer with shared OCIO
         if: matrix.build-shared == 'ON'
         run: |
           cmake . \
@@ -438,6 +468,34 @@ jobs:
                 --config ${{ matrix.build-type }}
           ./consumer
         working-directory: _build/tests/cmake-consumer-dist
+      - name: Test CMake Consumer with static OCIO
+        if: matrix.build-shared == 'OFF'
+        # The yaml-cpp_VERSION is set below because Findyaml-cpp.cmake needs it but is unable to 
+        # extract it from the headers, like the other modules.
+        #
+        # Prefer the static version of each dependencies by using <pkg>_STATIC_LIBRARY. 
+        # Alternatively, this can be done by setting <pkg>_LIBRARY and <pkg>_INCLUDE_DIR to 
+        # the static version of the package.       
+        run: |
+          cmake . \
+                -DCMAKE_PREFIX_PATH=../../../_install \
+                -DCMAKE_BUILD_TYPE=${{ matrix.build-type }} \
+                -Dexpat_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -Dexpat_STATIC_LIBRARY=ON \
+                -DImath_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -DImath_STATIC_LIBRARY=ON \
+                -Dpystring_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -Dyaml-cpp_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -Dyaml-cpp_STATIC_LIBRARY=ON \
+                -Dyaml-cpp_VERSION=0.7.0 \
+                -DZLIB_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -DZLIB_STATIC_LIBRARY=ON \
+                -Dminizip-ng_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -Dminizip-ng_STATIC_LIBRARY=ON
+          cmake --build . \
+                --config ${{ matrix.build-type }}
+          ./consumer
+        working-directory: _build/tests/cmake-consumer-dist
 
   # ---------------------------------------------------------------------------
   # Windows
@@ -567,13 +625,14 @@ jobs:
           cmake --build . \
                 --target install \
                 --config ${{ matrix.build-type }}
+          echo "ocio_build_path=$(pwd)" >> $GITHUB_ENV
         shell: bash
         working-directory: _build
       - name: Test
         run: ctest -V -C ${{ matrix.build-type }}
         shell: bash
         working-directory: _build
-      - name: Test CMake Consumer
+      - name: Test CMake Consumer with shared OCIO
         if: matrix.build-shared == 'ON'
         run: |
           cmake . \
@@ -585,3 +644,33 @@ jobs:
           ./${{ matrix.build-type }}/consumer
         shell: bash
         working-directory: _build/tests/cmake-consumer-dist
+      - name: Test CMake Consumer with static OCIO
+        if: matrix.build-shared == 'OFF'
+        # The yaml-cpp_VERSION is set below because Findyaml-cpp.cmake needs it but is unable to 
+        # extract it from the headers, like the other modules.
+        #
+        # Prefer the static version of each dependencies by using <pkg>_STATIC_LIBRARY. 
+        # Alternatively, this can be done by setting <pkg>_LIBRARY and <pkg>_INCLUDE_DIR to 
+        # the static version of the package.
+        run: |
+          cmake . \
+                -DCMAKE_PREFIX_PATH=../../../_install \
+                -DCMAKE_BUILD_TYPE=${{ matrix.build-type }} \
+                -Dexpat_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -Dexpat_STATIC_LIBRARY=ON \
+                -DImath_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -DImath_STATIC_LIBRARY=ON \
+                -Dpystring_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -Dyaml-cpp_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -Dyaml-cpp_STATIC_LIBRARY=ON \
+                -Dyaml-cpp_VERSION=0.7.0 \
+                -DZLIB_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -DZLIB_STATIC_LIBRARY=ON \
+                -Dminizip-ng_ROOT=${{ env.ocio_build_path }}/ext/dist \
+                -Dminizip-ng_STATIC_LIBRARY=ON
+          cmake --build . \
+                --config ${{ matrix.build-type }}
+          export PATH=../../../_install/bin:$PATH
+          ./${{ matrix.build-type }}/consumer
+        shell: bash
+        working-directory: _build/tests/cmake-consumer-dist

CMakeLists.txt

@@ -251,6 +251,15 @@ if(OCIO_BUILD_STATIC)
 	endif()
 endif()
 
+if (NOT BUILD_SHARED_LIBS AND NOT OCIO_INSTALL_EXT_PACKAGES STREQUAL NONE)
+   message(STATUS "Note that building the static version of OpenColorIO does not embed the dependencies\  
+   into the library file. The needed dependencies must be linked to the consumer
+   application or shared library that uses static OpenColorIO.
+
+   The following mandatory dependencies MUST be linked to the consumer application or shared library:
+   expat, yaml-cpp, Imath, pystring, minizip-ng and ZLIB")
+endif()
+
 
 ###############################################################################
 # Find or install external dependencies
@@ -299,6 +308,8 @@ set(OCIO_TARGETS_EXPORT_NAME "${PROJECT_NAME}Targets.cmake")
 set(OCIO_VERSION_CONFIG "${CMAKE_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake")
 set(OCIO_PROJECT_CONFIG "${CMAKE_BINARY_DIR}/${PROJECT_NAME}Config.cmake")
 set(OCIO_CONFIG_INSTALL_DIR "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}")
+set(OCIO_CUSTOM_FIND_MODULE_DIR "${CMAKE_INSTALL_PREFIX}/share/OpenColorIO/cmake/modules")
+set(OCIO_CUSTOM_MACROS_MODULE_DIR "${CMAKE_INSTALL_PREFIX}/share/OpenColorIO/cmake/macros")
 
 # Version fetched from the top level project()
 write_basic_package_version_file(
@@ -321,6 +332,24 @@ install(
     FILE ${OCIO_TARGETS_EXPORT_NAME}
 )
 
+if (NOT BUILD_SHARED_LIBS)
+    # Install custom macros used in the find modules.
+    install(FILES
+        ${CMAKE_CURRENT_LIST_DIR}/share/cmake/macros/VersionUtils.cmake
+        DESTINATION ${OCIO_CUSTOM_MACROS_MODULE_DIR}
+    )
+
+    # Install custom Find modules.
+    install(FILES
+        ${CMAKE_CURRENT_LIST_DIR}/share/cmake/modules/Findexpat.cmake
+        ${CMAKE_CURRENT_LIST_DIR}/share/cmake/modules/FindImath.cmake
+        ${CMAKE_CURRENT_LIST_DIR}/share/cmake/modules/Findpystring.cmake
+        ${CMAKE_CURRENT_LIST_DIR}/share/cmake/modules/Findminizip-ng.cmake
+        ${CMAKE_CURRENT_LIST_DIR}/share/cmake/modules/Findyaml-cpp.cmake
+        DESTINATION ${OCIO_CUSTOM_FIND_MODULE_DIR}
+    )
+endif()
+
 install(
     FILES "${OCIO_PROJECT_CONFIG}" "${OCIO_VERSION_CONFIG}"
     DESTINATION "${OCIO_CONFIG_INSTALL_DIR}"

share/cmake/modules/FindExtPackages.cmake

@@ -21,6 +21,17 @@ set(CMAKE_FIND_PACKAGE_NO_PACKAGE_REGISTRY ON CACHE BOOL
 set(CMAKE_FIND_PACKAGE_NO_SYSTEM_PACKAGE_REGISTRY ON CACHE BOOL
     "Disable CMake System Package Registry when finding packages")
 
+if (APPLE)
+    # Store the previous value of CMAKE_FIND_FRAMEWORK and CMAKE_FIND_APPBUNDLE.
+    set(_PREVIOUS_CMAKE_FIND_FRAMEWORK ${CMAKE_FIND_FRAMEWORK})
+    set(_PREVIOUS_CMAKE_FIND_APPBUNDLE ${CMAKE_FIND_APPBUNDLE})
+
+    # Prioritize other paths before Frameworks and Appbundle for find_path, find_library and 
+    # find_package.
+    set(CMAKE_FIND_FRAMEWORK LAST)
+    set(CMAKE_FIND_APPBUNDLE LAST)
+endif()
+
 ###############################################################################
 ### Packages and versions ###
 
@@ -41,14 +52,93 @@ find_package(pystring 1.1.3 REQUIRED)
 set(_Imath_ExternalProject_VERSION "3.1.5")
 find_package(Imath 3.0 REQUIRED)
 
-# ZLIB
-# https://github.com/madler/zlib
-set(_zlib_ExternalProject_VERSION "1.2.12")
-find_package(zlib REQUIRED)
+###############################################################################
+### ZLIB (https://github.com/madler/zlib)
+###
+### The following variables can be set:
+### ZLIB_ROOT               Location of ZLIB library file and includes folder.
+###                         Alternatively, ZLIB_LIBRARY and ZLIB_INCLUDE_DIR can be used.
+###
+### ZLIB_LIBRARY            Location of ZLIB library file.
+### ZLIB_INCLUDE_DIR        Location of ZLIB includes folder.
+###
+### ZLIB_VERSION            ZLIB Version (CMake 3.26+)
+### ZLIB_VERSION_STRING     ZLIB Version (CMake < 3.26)
+###
+###############################################################################
+# ZLIB 1.2.13 is used since it fixes a critical vulnerability.
+# See https://nvd.nist.gov/vuln/detail/CVE-2022-37434
+# See https://github.com/madler/zlib/releases/tag/v1.2.13
+set(_ZLIB_FIND_VERSION "1.2.13")
+set(_ZLIB_ExternalProject_VERSION ${_ZLIB_FIND_VERSION})
+
+if(NOT OCIO_INSTALL_EXT_PACKAGES STREQUAL ALL)
+    # ZLIB_USE_STATIC_LIBS is supported only from CMake 3.24+.
+    if(${CMAKE_VERSION} VERSION_GREATER_EQUAL "3.24.0") 
+        if (ZLIB_STATIC_LIBRARY)
+            set(ZLIB_USE_STATIC_LIBS "${ZLIB_STATIC_LIBRARY}")
+        endif()
+    else() # For CMake < 3.24 since ZLIB_USE_STATIC_LIBS is not available.
+        if(NOT ZLIB_LIBRARY)
+            if(DEFINED CMAKE_FIND_LIBRARY_PREFIXES)
+                set(_ZLIB_ORIG_CMAKE_FIND_LIBRARY_PREFIXES "${CMAKE_FIND_LIBRARY_PREFIXES}")
+            else()
+                set(_ZLIB_ORIG_CMAKE_FIND_LIBRARY_PREFIXES)
+            endif()
+
+            if(DEFINED CMAKE_FIND_LIBRARY_SUFFIXES)
+                set(_ZLIB_ORIG_CMAKE_FIND_LIBRARY_SUFFIXES "${CMAKE_FIND_LIBRARY_SUFFIXES}")
+            else()
+                set(_ZLIB_ORIG_CMAKE_FIND_LIBRARY_SUFFIXES)
+            endif()
+
+            # Prefix/suffix for windows.
+            if(WIN32)
+                list(APPEND CMAKE_FIND_LIBRARY_PREFIXES "" "lib")
+                list(APPEND CMAKE_FIND_LIBRARY_SUFFIXES ".dll.a")
+            endif()
+
+            # Check if static lib is preferred.
+            if(ZLIB_STATIC_LIBRARY OR ZLIB_USE_STATIC_LIBS)
+                if(WIN32)
+                    set(CMAKE_FIND_LIBRARY_SUFFIXES .lib .a ${CMAKE_FIND_LIBRARY_SUFFIXES})
+                else()
+                    set(CMAKE_FIND_LIBRARY_SUFFIXES .a)
+                endif()
+            endif()
+        endif()
+    endif()
+
+    set(_ZLIB_REQUIRED REQUIRED)
+    # Override REQUIRED if package can be installed
+    if(OCIO_INSTALL_EXT_PACKAGES STREQUAL MISSING)
+        set(_ZLIB_REQUIRED "")
+    endif()
+
+    find_package(ZLIB ${_ZLIB_FIND_VERSION} ${_ZLIB_REQUIRED})
+
+    # Restore the original find library ordering
+    if(DEFINED _ZLIB_ORIG_CMAKE_FIND_LIBRARY_SUFFIXES)
+        set(CMAKE_FIND_LIBRARY_SUFFIXES "${_ZLIB_ORIG_CMAKE_FIND_LIBRARY_SUFFIXES}")
+    else()
+        set(CMAKE_FIND_LIBRARY_SUFFIXES)
+    endif()
+
+    if(DEFINED _ZLIB_ORIG_CMAKE_FIND_LIBRARY_PREFIXES)
+        set(CMAKE_FIND_LIBRARY_PREFIXES "${_ZLIB_ORIG_CMAKE_FIND_LIBRARY_PREFIXES}")
+    else()
+        set(CMAKE_FIND_LIBRARY_PREFIXES)
+    endif()
+endif()
+
+if(NOT ZLIB_FOUND AND OCIO_INSTALL_EXT_PACKAGES AND NOT OCIO_INSTALL_EXT_PACKAGES STREQUAL NONE)
+    include(InstallZLIB)
+endif()
+###############################################################################
 
 # minizip-ng
 # https://github.com/zlib-ng/minizip-ng
-find_package(minizip-ng 3.0.6 REQUIRED)
+find_package(minizip-ng 3.0.7 REQUIRED)
 
 if(OCIO_BUILD_APPS)
 
@@ -157,3 +247,9 @@ if(OCIO_BUILD_TESTS)
         message(WARNING "Could NOT find OpenImageIO. Skipping build of the OSL unit tests.")
     endif()
 endif()
+
+if (APPLE)
+    # Restore CMAKE_FIND_FRAMEWORK and CMAKE_FIND_APPBUNDLE values.
+    set(CMAKE_FIND_FRAMEWORK ${_PREVIOUS_CMAKE_FIND_FRAMEWORK})
+    set(CMAKE_FIND_APPBUNDLE ${_PREVIOUS_CMAKE_FIND_APPBUNDLE})
+endif()

share/cmake/modules/FindImath.cmake

@@ -25,6 +25,15 @@
 ###############################################################################
 ### Try to find package ###
 
+# BUILD_TYPE_DEBUG variable is currently set in one of the OCIO's CMake files. 
+# Now that some OCIO's find module are installed with the library itself (with static build), 
+# a consumer app don't have access to the variables set by an OCIO's CMake files. Therefore, some 
+# OCIO's find modules must detect the build type by itselves. 
+set(BUILD_TYPE_DEBUG OFF)
+if(CMAKE_BUILD_TYPE MATCHES "[Dd][Ee][Bb][Uu][Gg]")
+   set(BUILD_TYPE_DEBUG ON)
+endif()
+
 if(NOT OCIO_INSTALL_EXT_PACKAGES STREQUAL ALL)
     set(_Imath_REQUIRED_VARS Imath_LIBRARY)
     set(_Imath_LIB_VER "${Imath_FIND_VERSION_MAJOR}_${Imath_FIND_VERSION_MINOR}")
@@ -131,7 +140,7 @@ endif()
 ###############################################################################
 ### Install package from source ###
 
-if(NOT Imath_FOUND AND NOT OCIO_INSTALL_EXT_PACKAGES STREQUAL NONE)
+if(NOT Imath_FOUND AND OCIO_INSTALL_EXT_PACKAGES AND NOT OCIO_INSTALL_EXT_PACKAGES STREQUAL NONE)
     include(ExternalProject)
     include(GNUInstallDirs)
 

share/cmake/modules/FindOpenEXR.cmake

@@ -45,6 +45,10 @@ if(NOT OCIO_INSTALL_EXT_PACKAGES STREQUAL ALL)
     if(OpenEXR_FOUND)
         get_target_property(OpenEXR_LIBRARY OpenEXR::OpenEXR LOCATION)
         get_target_property(OpenEXR_INCLUDE_DIR OpenEXR::OpenEXR INTERFACE_INCLUDE_DIRECTORIES)
+        
+        # IMPORTED_GLOBAL property must be set to TRUE since alisasing a non-global imported target
+        # is not possible until CMake 3.18+.
+        set_target_properties(OpenEXR::OpenEXR PROPERTIES IMPORTED_GLOBAL TRUE)
     endif()
 
     # Override REQUIRED if package can be installed
@@ -77,21 +81,22 @@ macro(set_target_location target_name)
     endif()
 endmacro()
 
-if(NOT OpenEXR_FOUND AND NOT OCIO_INSTALL_EXT_PACKAGES STREQUAL NONE)
+if(NOT OpenEXR_FOUND AND OCIO_INSTALL_EXT_PACKAGES AND NOT OCIO_INSTALL_EXT_PACKAGES STREQUAL NONE)
     include(ExternalProject)
     include(GNUInstallDirs)
 
     set(_EXT_DIST_ROOT "${CMAKE_BINARY_DIR}/ext/dist")
     set(_EXT_BUILD_ROOT "${CMAKE_BINARY_DIR}/ext/build")
 
     # Required dependency
-    # OCIO custom module to find ZLIB. (Findzlib)
-    find_package(zlib)
     if(NOT ZLIB_FOUND)
-        message(STATUS "ZLib is required to build OpenEXR.")
-        return()
+        find_package(ZLIB)
+        if(NOT ZLIB_FOUND)
+            message(STATUS "ZLib is required to build OpenEXR.")
+            return()
+        endif()
     endif()
-
+    
     find_package(Threads)
     if(NOT Threads_FOUND)
         message(STATUS "Threads is required to build OpenEXR.")