This Gist demonstrates how to integrate the compilation of Protocol Buffer files into your CMake project

protobuf.cmake

# Protobuf setup, these should be set to your project's directories, and currently assumes
# that everything is relative to CMAKE_SOURCE_DIR (the directory CMake is run from)
set (PROTO_IN_DIR       ${CMAKE_SOURCE_DIR}/proto)
set (PROTO_OUT_DIR      ${CMAKE_SOURCE_DIR}/build/proto)
set (PROTOC_BIN         ${CMAKE_SOURCE_DIR}/thirdparty/protobuf/bin/protoc)
set (PROTOC_INCLUDE_DIR ${CMAKE_SOURCE_DIR}/thirdparty/protobuf/include)
set (PROTOC_LIB_DIR     ${CMAKE_SOURCE_DIR}/thirdparty/protobuf/lib

# Protobuf files
set (PROTO_FILES
    ${PROTO_DIR}/common.proto
    ${PROTO_DIR}/packet.proto
    ${PROTO_DIR}/rpc.proto)

# Protobuf output files
foreach (PROTO_FILE ${PROTO_FILES})
    get_filename_component (PROTO_NAME ${PROTO_FILE} NAME_WE)
    set (PROTO_SRC_FILES ${PROTO_SRC_FILES}
        ${PROTOC_OUT_DIR}/${PROTO_NAME}.pb.cc)
    set (PROTO_INCLUDE_FILES ${PROTO_INCLUDE_FILES}
        ${PROTOC_OUT_DIR}/${PROTO_NAME}.pb.h)
endforeach (PROTO_FILE ${PROTO_FILES})

# Custom protobuf command
file (MAKE_DIRECTORY ${PROTOC_SRC_DIR})
add_custom_command (
    OUTPUT ${PROTO_SRC_FILES} ${PROTO_INCLUDE_FILES}
    COMMAND ${PROTOC_BIN} ${PROTO_FILES} 
        --proto_path=${PROTO_IN_DIR} 
        --cpp_out=${PROTOC_OUT_DIR}
    DEPENDS ${PROTO_FILES}
    WORKING_DIRECTORY ${PROTO_IN_DIR})

# Add Protobuf to compiler and linker command lines
include_directotries (${PROTOC_INCLUDE_DIR})
link_directories (${PROTOC_LIB_DIR})