Add FetchContent fallback for CImg

CMakeLists.txt

@@ -7,8 +7,6 @@ set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
 set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${PROJECT_SOURCE_DIR}/cmake/Modules/")
 
-set(USE_SYSTEM_CIMG ON CACHE BOOL "Set to OFF to use CImg library bundled in lib directory")
-
 # support for ccache
 # call CMake with -DUSE_CCACHE=ON to make use of it
 set(USE_CCACHE ON CACHE BOOL "")

cmake/Modules/FindCImg.cmake

@@ -1,34 +1,97 @@
-# required for PNG imported target
-cmake_minimum_required(VERSION 3.6)
+#[=======================================================================[.rst:
+FindCImg
+-------
 
-find_package(PkgConfig)
-pkg_check_modules(libpng REQUIRED IMPORTED_TARGET libpng)
-pkg_check_modules(libjpeg REQUIRED IMPORTED_TARGET libjpeg)
+Finds the CImg library.
 
-message(STATUS "Searching for CImg")
+Imported Targets
+^^^^^^^^^^^^^^^^
+
+This module provides the following imported targets, if found:
+
+``CImg``
+  The CImg library
+
+Result Variables
+^^^^^^^^^^^^^^^^
+
+This will define the following variables:
+
+``CImg_FOUND``
+  True if the system has the CImg library.
+``CImg_VERSION``
+  The version of the CImg library which was found.
+``CImg_INCLUDE_DIRS``
+  Include directories needed to use CImg.
+``CImg_LIBRARIES``
+  Libraries needed to link to CImg.
+
+Cache Variables
+^^^^^^^^^^^^^^^
+
+The following cache variables may also be set:
+
+``CImg_INCLUDE_DIR``
+  The directory containing ``CImg.h``.
+
+#]=======================================================================]
+
+# 3.6 required for PNG imported target
+# 3.9 required for CMAKE_MATCH_<n>
+cmake_minimum_required(VERSION 3.9)
 
 find_path(CIMG_H_DIR
     NAMES CImg.h
-    HINTS ${CMAKE_INSTALL_PREFIX}
+    HINTS ${CMAKE_INSTALL_PREFIX} ${CIMG_DIR}
     PATH_SUFFIXES include include/linux
 )
 
 if(NOT CIMG_H_DIR)
-    message(FATAL_ERROR "CImg.h not found")
-endif()
+    set(CImg_FOUND FALSE)
+else()
+    set(CImg_FOUND TRUE)
 
-set(PNG_INCLUDE_DIR ${libpng_INCLUDE_DIRS})
-set(PNG_INCLUDE_DIR ${libjpeg_INCLUDE_DIRS})
+    find_package(PkgConfig)
 
-if(NOT STATIC_BUILD)
-    set(PNG_LIBRARY ${libpng_LIBRARIES})
-    set(JPEG_LIBRARIES ${libjpeg_LIBRARIES})
-else()
-    set(PNG_LIBRARY ${libpng_STATIC_LIBRARIES})
-    set(JPEG_LIBRARIES ${libjpeg_STATIC_LIBRARIES})
+    pkg_check_modules(libpng REQUIRED libpng)
+    pkg_check_modules(libjpeg REQUIRED libjpeg)
+
+    set(PNG_INCLUDE_DIR ${libpng_INCLUDE_DIRS})
+    set(JPEG_INCLUDE_DIR ${libjpeg_INCLUDE_DIRS})
+
+    if(STATIC_BUILD)
+        set(PNG_LIBRARY ${libpng_STATIC_LIBRARIES})
+        set(JPEG_LIBRARIES ${libjpeg_STATIC_LIBRARIES})
+    else()
+        set(PNG_LIBRARY ${libpng_LIBRARIES})
+        set(JPEG_LIBRARIES ${libjpeg_LIBRARIES})
+    endif()
+
+    set(CImg_INCLUDE_DIR ${CIMG_H_DIR} CACHE STRING "")
+    set(CImg_INCLUDE_DIRS ${CImg_INCLUDE_DIR})
+    set(CImg_LIBRARIES "${PNG_LIBRARY};${JPEG_LIBRARIES}")
+    set(CImg_DEFINITIONS "cimg_display=0;cimg_use_png=1;cimg_use_jpeg=1")
+
+    file(READ "${CIMG_H_DIR}/CImg.h" header)
+    string(REGEX MATCH "#define cimg_version ([0-9a-zA-Z\.]+)" _ "${header}")
+    set(CImg_VERSION "${CMAKE_MATCH_1}")
+
+    # CImg_VERSION
+
+    if(NOT TARGET CImg)
+        add_library(CImg INTERFACE)
+        set_property(TARGET CImg PROPERTY INTERFACE_INCLUDE_DIRECTORIES "${CIMG_H_DIR};${PNG_INCLUDE_DIR};${JPEG_INCLUDE_DIR}")
+        set_property(TARGET CImg PROPERTY INTERFACE_LINK_LIBRARIES "${CImg_LIBRARIES}")
+        set_property(TARGET CImg PROPERTY INTERFACE_COMPILE_DEFINITIONS "${CImg_DEFINITIONS}")
+    endif()
 endif()
 
-add_library(CImg INTERFACE)
-set_property(TARGET CImg PROPERTY INTERFACE_INCLUDE_DIRECTORIES "${CIMG_H_DIR};${PNG_INCLUDE_DIR};${JPEG_INCLUDE_DIR}")
-set_property(TARGET CImg PROPERTY INTERFACE_LINK_LIBRARIES "${PNG_LIBRARY};${JPEG_LIBRARIES}")
-set_property(TARGET CImg PROPERTY INTERFACE_COMPILE_DEFINITIONS "cimg_display=0;cimg_use_png=1;cimg_use_jpeg=1")
+include(FindPackageHandleStandardArgs)
+find_package_handle_standard_args(CImg
+  FOUND_VAR CImg_FOUND
+  REQUIRED_VARS
+    CImg_INCLUDE_DIRS
+    CImg_LIBRARIES
+    CImg_DEFINITIONS
+  VERSION_VAR CImg_VERSION
+)

src/core/CMakeLists.txt

@@ -5,7 +5,28 @@ file(GLOB HEADERS ${PROJECT_SOURCE_DIR}/include/linuxdeploy/core/*.h)
 
 find_package(Threads)
 
-find_package(CImg REQUIRED)
+find_package(CImg)
+
+if(NOT CImg_FOUND)
+    message(STATUS "CImg not found, fetching from GitHub")
+
+    cmake_minimum_required(VERSION 3.14)
+
+    FetchContent_Declare(
+        CImg
+        GIT_REPOSITORY https://github.com/dtschump/CImg
+        GIT_TAG v.2.9.9
+    )
+
+    FetchContent_MakeAvailable(CImg)
+
+    # unfortunately there is no easy way to fetch the source dir with MakeAvailable
+    # FETCHCONTENT_SOURCE_DIR_CIMG is not set
+    # we can apparently predict the path from the base dir, though
+    # we'll have to see how reliable this is going to be
+    set(CIMG_DIR "${FETCHCONTENT_BASE_DIR}/cimg-src")
+    find_package(CImg REQUIRED)
+endif()
 
 message(STATUS "Generating excludelist")
 execute_process(