在我的 cmake 项目中将 freetype2 编译为依赖项

Question

我正在尝试从源代码编译 freetype2 并将其链接到我自己的项目中，但我遇到了 CMake 错误：

CMake Error: install(EXPORT "freetype-targets" ...) includes target "freetype" which requires target "zlib" that is not in any export set.

大概这意味着zlib 无法被freetype2 目标识别。

我在这个项目中编译和使用zlib 来处理其他事情（特别是libpng），所以我假设我只需要以某种方式使我编译的zlib 可用于freetype2 是否正确？我该怎么做呢？

这是我的 CMakeLists.txt 的全部内容：

cmake_minimum_required(VERSION 3.17)
project(zgl)

set(CMAKE_CXX_STANDARD 17)

set(SKIP_INSTALL_EXPORT TRUE)

# If this is built standalone, and not part of an embedded project, define the build directory.
string(COMPARE EQUAL ${CMAKE_CURRENT_SOURCE_DIR} ${CMAKE_SOURCE_DIR} IS_ROOT_PROJECT)

if(IS_ROOT_PROJECT)
    if(NOT DEFINED DEPS_INSTALL_PREFIX)
        set(DEPS_INSTALL_PREFIX "${CMAKE_BINARY_DIR}/build" CACHE STRING "Installation Prefix" FORCE)
    endif()
    get_property(CMAKE_INSTALL_PREFIX_DOCS DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR} PROPERTY CMAKE_INSTALL_PREFIX FULL_DOCS)
    set(CMAKE_INSTALL_PREFIX ${DEPS_INSTALL_PREFIX} CACHE STRING "${CMAKE_INSTALL_PREFIX_DOCS}" FORCE)
    set(CMAKE_ARCHIVE_OUTPUT_DIRECTORY ${CMAKE_INSTALL_PREFIX}/bin)
    set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_INSTALL_PREFIX}/bin)
    set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_INSTALL_PREFIX}/bin)
    set(CMAKE_PDB_OUTPUT_DIRECTORY ${CMAKE_INSTALL_PREFIX}/bin)
endif()

set(THIRD_PARTY_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/third-party)

set(ZLIB_DIRECTORY ${THIRD_PARTY_DIRECTORY}/zlib)
add_subdirectory(${ZLIB_DIRECTORY})

# Explicitly set the ZLIB_BUILD_DIRECTORY for libpng (?)
get_directory_property(ZLIB_BUILD_DIRECTORY DIRECTORY ${ZLIB_DIRECTORY} DEFINITION CMAKE_CURRENT_BINARY_DIR)

option(PNG_LINK_ZLIB_STATIC "Use a static zlib library for libpng builds" OFF)

get_directory_property(zlib DIRECTORY ${ZLIB_DIRECTORY} DEFINITION zlib)
get_directory_property(zlibstatic DIRECTORY ${ZLIB_DIRECTORY} DEFINITION zlibstatic)

if (PNG_LINK_ZLIB_STATIC)
    set(ZLIB_LIBRARY zlibstatic)
else()
    set(ZLIB_LIBRARY zlib)
endif()

set(ZLIB_INCLUDE_DIR ${ZLIB_DIRECTORY})
set(LIBPNG_DIRECTORY "${THIRD_PARTY_DIRECTORY}/libpng")

if (WIN32)
    file(TO_NATIVE_PATH ${LIBPNG_DIRECTORY}/scripts/pnglibconf.h.prebuilt PNGLIBCONF_PATH_SRC)
    file(TO_NATIVE_PATH ${LIBPNG_DIRECTORY}/pnglibconf.h PNGLIBCONF_PATH_DST)
    execute_process(COMMAND cmd /c copy ${PNGLIBCONF_PATH_SRC} ${PNGLIBCONF_PATH_DST})
endif(WIN32)

include_directories(${ZLIB_DIRECTORY} ${ZLIB_BUILD_DIRECTORY} ${LIBPNG_DIRECTORY} ${LIBPNG_BUILD_DIRECTORY})
add_subdirectory(${LIBPNG_DIRECTORY})

get_directory_property(LIBPNG_BUILD_DIRECTORY DIRECTORY ${LIBPNG_DIRECTORY} DEFINITION CMAKE_CURRENT_BINARY_DIR)
get_directory_property(LIBPNG_STATIC DIRECTORY ${LIBPNG_DIRECTORY} DEFINITION PNG_LIB_NAME_STATIC)
get_directory_property(LIBPNG_SHARED DIRECTORY ${LIBPNG_DIRECTORY} DEFINITION PNG_LIB_NAME)

add_executable(zgl src/main.cpp src/resources/images/Image.cpp src/Game.cpp src/Game.h src/platform/Platform.cpp src/platform/Platform.h src/platform/Window.cpp src/platform/Window.h src/components/GameComponent.cpp src/components/GameComponent.h src/input/InputEvent.h src/input/Joystick.cpp src/input/Joystick.h src/utilities/StringUtilities.cpp src/utilities/StringUtilities.h src/input/InputEvent.cpp src/Actor.cpp src/Actor.h src/Scene.cpp src/Scene.h src/math/Range.h src/components/CameraComponent.cpp src/components/CameraComponent.h src/components/GameComponentCollection.h src/FreeCamera.cpp src/FreeCamera.h src/input/InputManager.cpp src/input/InputManager.h src/math/Rectangle.h src/input/InputSubscription.cpp src/input/InputSubscription.h src/Application.cpp src/Application.h src/math/Interpolation.h src/graphics/Texture.cpp src/graphics/Texture.h src/graphics/Gpu.cpp src/graphics/Gpu.h src/graphics/ColorType.h src/graphics/TextureFormat.h src/input/InputSubscriber.cpp src/input/InputSubscriber.h src/graphics/ColorType.cpp src/resources/images/formats/ImageFormatPng.cpp src/resources/images/formats/ImageFormatPng.h src/resources/ResourceManager.cpp src/resources/ResourceManager.h src/resources/images/formats/ImageFormat.cpp src/resources/images/formats/ImageFormat.h src/resources/Resource.cpp src/resources/Resource.h src/graphics/FrameBuffer.cpp src/graphics/FrameBuffer.h src/graphics/GpuTypes.h src/graphics/GpuProgram.cpp src/graphics/GpuProgram.h src/input/joysticks/XboxController.h src/input/InputAction.cpp src/input/InputAction.h src/utilities/FlagMacros.h src/input/Pointer.cpp src/input/Pointer.h src/input/Keyboard.cpp src/input/Keyboard.h src/input/KeyboardKey.cpp src/input/KeyboardKey.h src/components/FreeCameraControllerComponent.cpp src/components/FreeCameraControllerComponent.h src/components/GameComponentRegistry.cpp src/components/GameComponentRegistry.h src/platform/Cursor.cpp src/platform/Cursor.h src/graphics/GpuBuffer.cpp src/graphics/GpuBuffer.h src/graphics/GpuIndexBuffer.h src/components/MeshComponent.cpp src/components/MeshComponent.h src/graphics/GpuVertexBuffer.h src/resources/mesh/Mesh.cpp src/resources/mesh/Mesh.h src/ActorDefinition.cpp src/ActorDefinition.h src/graphics/CameraParameters.h)

# Compiling GLEW requires CYGWIN to be installed on Windows!

#glew
set(GLEW_DIRECTORY "${THIRD_PARTY_DIRECTORY}/glew-cmake")
message("${GLEW_DIRECTORY}")
add_subdirectory(${GLEW_DIRECTORY})
include_directories(${GLEW_DIRECTORY}/include)
target_link_libraries(zgl libglew_static)

#glfw
set(GLFW_DIRECTORY "${THIRD_PARTY_DIRECTORY}/glfw")
add_subdirectory(${GLFW_DIRECTORY})
include_directories(${GLFW_DIRECTORY}/include)

#opengl
find_package(OpenGL REQUIRED)
include_directories(${OPENGL_INCLUDE_DIRS})

#freetype
set(FREETYPE_DIRECTORY "${THIRD_PARTY_DIRECTORY}/freetype2")
add_subdirectory(${FREETYPE_DIRECTORY})
include_directories(${FREETYPE_DIRECTORY}/include)

#glm
set(GLM_DIRECTORY "${THIRD_PARTY_DIRECTORY}/glm")
include_directories(${GLM_DIRECTORY})

#yaml-cpp
set(YAML_DIRECTORY "${THIRD_PARTY_DIRECTORY}/yaml-cpp")
add_subdirectory(${YAML_DIRECTORY})
set(YAML_LIBRARIES yaml-cpp)
include_directories(${YAML_DIRECTORY}/include)

#magic_enum
set(MAGIC_ENUM_DIRECTORY "${THIRD_PARTY_DIRECTORY}/magic_enum")
include_directories(${MAGIC_ENUM_DIRECTORY}/include)

#zgl
set(ZGL_SRC_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/src")
include_directories(${ZGL_SRC_DIRECTORY})

target_link_libraries(zgl ${OPENGL_LIBRARIES})
target_link_libraries(zgl ${ZLIB_LIBRARY})
target_link_libraries(zgl ${FREETYPE_LIBRARY})
target_link_libraries(zgl ${LIBPNG_STATIC})
target_link_libraries(zgl glfw ${GLFW_LIBRARIES})
target_link_libraries(zgl ${BULLET3_LIRRARIES})
target_link_libraries(zgl ${YAML_LIBRARIES})

target_include_directories(zgl PUBLIC ${ZLIB_DIRECTORY})
target_include_directories(zgl PUBLIC ${LIBPNG_DIRECTORY})

Answer 1

错误信息

CMake Error: install(EXPORT "freetype-targets" ...) includes target "freetype" which requires target "zlib" that is not in any export set.

指行

  install(
    TARGETS freetype
      EXPORT freetype-targets
      <...>)

在freetype2的CMakeLists.txt中。

这些行标记freetype 安装目标并将此目标添加到导出集，以便可以通过find_package 找到安装。

目标freetype 与目标zlib 链接，因为您指定了

set(ZLIB_LIBRARY zlib)

这里是 CMake 指向的问题：

虽然zlib 目标已安装，但它不属于任何导出集。

由于 CMake 在安装后不知道如何翻译 freetype 和 zlib 的链接，因此 CMake 无法为 freetype 安装生成配置文件。

为了克服错误，您可以告诉 CMake 将 freetype 与 ALIAS 库链接：

add_library(ZLIB::ZLIB ALIAS zlib)
set(ZLIB_LIBRARY ZLIB::ZLIB)

CMake 知道永远不会安装 ALIAS 目标，并且不会发出错误。

---

注意，虽然使用 ALIAS 目标，错误将消失，find_package 仍然无法用于已安装的 freetype2。但否则安装将是正确且可用的。