Do not download objects if they already exist

CMakeLists.txt

@@ -214,10 +214,15 @@ if (DOWNLOAD_TITLE_SEQUENCES)
         endif ()")
 endif ()
 if (DOWNLOAD_OBJECTS)
-    set(OBJECT_DIR "\$ENV{DESTDIR}${CMAKE_INSTALL_FULL_DATADIR}/${PROJECT}/object")
-    install(CODE "file(DOWNLOAD ${OBJECTS_URL} ${OBJECT_DIR}/objects.zip EXPECTED_HASH SHA1=${OBJECTS_SHA1} SHOW_PROGRESS)")
-    install(CODE "execute_process(COMMAND \"${CMAKE_COMMAND}\" -E chdir ${OBJECT_DIR}/ \"${CMAKE_COMMAND}\" -E tar xvf objects.zip)")
-    install(CODE "file(REMOVE ${OBJECT_DIR}/objects.zip)")
+    # If rct2.wtrcyan.json or data/object/ exists, assume all the objects are already present
+    install(CODE
+        "if (EXISTS \"\$ENV{DESTDIR}/${CMAKE_INSTALL_FULL_DATADIR}/${PROJECT}/object/rct2/water/rct2.wtrcyan.json\" OR EXISTS ${CMAKE_SOURCE_DIR}/data/object/)\n\
+            message(\"Using cached objects\")\n\
+        else () \n\
+            file(DOWNLOAD ${OBJECTS_URL} \$ENV{DESTDIR}/${CMAKE_INSTALL_FULL_DATADIR}/${PROJECT}/object/objects.zip EXPECTED_HASH SHA1=${OBJECTS_SHA1} SHOW_PROGRESS)\n\
+            execute_process(COMMAND \"${CMAKE_COMMAND}\" -E chdir \$ENV{DESTDIR}/${CMAKE_INSTALL_FULL_DATADIR}/${PROJECT}/object/ \"${CMAKE_COMMAND}\" -E tar xvf objects.zip)\n\
+            file(REMOVE \$ENV{DESTDIR}/${CMAKE_INSTALL_FULL_DATADIR}/${PROJECT}/object/objects.zip)\n\
+        endif ()")
 endif ()
 install(TARGETS "libopenrct2" LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}"
                               ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}")