See if we can use Config.cmake approach to find_package for zlib and …

…png.

Depends on the bext zlib CMake logic being patched to provide the
necessary files.  Once this proves out, we should be able to avoid
patching a lot of bext dependency builds to add custom FindZLIB.cmake
and FindPNG.cmake modules - instead we can just make sure
CMAKE_FIND_PACKAGE_PREFER_CONFIG is set to ON.

misc/CMake/BRLCAD_ExternalDeps.cmake

@@ -930,6 +930,9 @@ endfunction(brlcad_process_ext)
 # it's more complicated.
 #####################################################################
 
+# Prefer the Config.cmake file, if it can be found
+set(CMAKE_FIND_PACKAGE_PREFER_CONFIG ON)
+
 # Not all packages will define all of these, but it shouldn't matter -
 # an unset of an unused variable shouldn't be harmful
 function(find_package_reset pname trigger_var)
@@ -969,11 +972,29 @@ macro(find_package_zlib)
   else()
     find_package(ZLIB)
   endif()
-  list(GET ZLIB_LIBRARIES 0 ZLIB_FILE)
-  is_subpath("${CMAKE_BINARY_DIR}" "${ZLIB_FILE}" ZLIB_LOCAL_TEST)
-  if(ZLIB_LOCAL_TEST)
-    set(Z_PREFIX_STR "brl_" CACHE STRING "Using local zlib" FORCE)
-  endif(ZLIB_LOCAL_TEST)
+
+  if (TARGET ZLIB::ZLIB)
+    get_target_property(ZLIB_FILE ZLIB::ZLIB LOCATION)
+    if (NOT ZLIB_FILE)
+      get_target_property(llibs ZLIB::ZLIB INTERFACE_LINK_LIBRARIES)
+      foreach(ll ${llibs})
+	if("${ll}" MATCHES "zlib::.*")
+	  if (NOT ZLIB_FILE)
+	    get_target_property(ZLIB_FILE ${ll} LOCATION)
+	  endif()
+	endif()
+      endforeach(ll ${llibs})
+    endif()
+    is_subpath("${CMAKE_BINARY_DIR}" "${ZLIB_FILE}" ZLIB_LOCAL_TEST)
+    if(ZLIB_LOCAL_TEST)
+      set(Z_PREFIX_STR "brl_" CACHE STRING "Using local zlib" FORCE)
+      set(ZLIB_STATUS "Bundled" CACHE STRING "zlib is bundled" FORCE)
+    else(ZLIB_LOCAL_TEST)
+      set(ZLIB_STATUS "System" CACHE STRING "zlib is system" FORCE)
+    endif(ZLIB_LOCAL_TEST)
+  else()
+    set(ZLIB_STATUS "NotFound" CACHE STRING "zlib is not found" FORCE)
+  endif()
 endmacro(find_package_zlib)
 
 # Eigen - linear algebra library

misc/CMake/BRLCAD_Find_Package.cmake

@@ -54,6 +54,9 @@
 macro(BRLCAD_Find_Package pkg_name)
   cmake_parse_arguments(F "REQUIRED;NOINSTALL" "SYSPATTERN" "" ${ARGN})
 
+  # Prefer the Config.cmake file, if it can be found.
+  set(CMAKE_FIND_PACKAGE_PREFER_CONFIG ON)
+
   # If we have a bundled copy of this package, always use that.  Packages we
   # are not going to install are not copied to CMAKE_BINARY_DIR, so set the
   # *_ROOT variable accordingly

misc/CMake/BRLCAD_Summary.cmake

@@ -278,7 +278,7 @@ function(BRLCAD_Summary)
   ext_report("Tcl" TCL_LIBRARY REQUIRED_VARS "BRLCAD_ENABLE_TCL")
   ext_report("Tk" TK_LIBRARY REQUIRED_VARS "BRLCAD_ENABLE_TCL")
   ext_report("UtahRLE" UTAHRLE_STATUS)
-  ext_report("Zlib" ZLIB_LIBRARY)
+  ext_report("Zlib" ZLIB_STATUS)
 
   # Find the maximum label length
   set(LABEL_LENGTH 0)

misc/CMake/CMakeLists.txt

@@ -52,7 +52,6 @@ set(
   FindOpenVDB.cmake
   FindPERPLEX.cmake
   FindPkgMacros.cmake
-  FindPNG.cmake
   FindPROJ4.cmake
   FindRE2C.cmake
   FindREGEX.cmake
@@ -67,7 +66,6 @@ set(
   FindWix.cmake
   FindXMLLINT.cmake
   FindXSLTPROC.cmake
-  FindZLIB.cmake
   NSIS.template.in
   NSIS_silent.template.in
   OpenVDBUtils.cmake