allow to use a perfetto library already built (#10)

README.md

@@ -55,6 +55,7 @@ For a real life examples, have a look at:
 * `PERFETTO_TRACE_PROCESSOR_LIB` (REQUIRED): path to `libtrace_processor.a` produces by a perfetto build.
 * `PERFETTO_INTERNAL_INCLUDE_PATH` (REQUIRED): path to perfetto internal include directory (`<perfetto>/include`), or where it is installed.
 * OPTIONAL:
+  * `PERFETTO_LIBRARY`: name of a perfetto library already available (avoid having to compile `perfetto.cc`).
   * `PERFETTO_GEN_INCLUDE_PATH`: path to a a perfetto build (if not installed) `<perfetto>/out/release/gen/build_config`.
   * `PERFETTO_CXX_CONFIG_INCLUDE_PATH`: path to perfetto buildtools config `<perfetto>/buildtools/libcxx_config`.
   * `PERFETTO_CXX_SYSTEM_INCLUDE_PATH`: path to perfetto buildtools include `<perfetto>/buildtools/libcxx/include`.

layer/CMakeLists.txt

@@ -12,9 +12,15 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-add_library (vulkan-shader-profiler MODULE layer.cpp ${PERFETTO_SDK_PATH}/perfetto.cc)
+if (NOT PERFETTO_LIBRARY)
+  add_library(perfetto STATIC ${PERFETTO_SDK_PATH}/perfetto.cc)
+  set_target_properties(perfetto PROPERTIES POSITION_INDEPENDENT_CODE ON)
+  set(PERFETTO_LIBRARY perfetto)
+endif()
+
+add_library (vulkan-shader-profiler MODULE layer.cpp)
 target_include_directories(vulkan-shader-profiler PUBLIC ${Vulkan_INCLUDE_DIRS} ${PERFETTO_SDK_PATH} ${SPIRV-Tools-opt_INCLUDE_DIRS})
-target_link_libraries (vulkan-shader-profiler ${SPIRV-Tools-opt_LIBRARIES})
+target_link_libraries (vulkan-shader-profiler ${SPIRV-Tools-opt_LIBRARIES} ${PERFETTO_LIBRARY})
 
 set(BACKEND "InProcess"
   CACHE STRING "Select perfetto backend")