Update PyPatchMatch/Makefile

PyPatchMatch/Makefile

@@ -15,10 +15,22 @@ CXX = $(ENVIRONMENT_OPTIONS) g++
 CXXFLAGS = -std=c++14
 CXXFLAGS += -Ofast -ffast-math -w
 # CXXFLAGS += -g
-CXXFLAGS += $(shell pkg-config --cflags opencv) -fPIC
-CXXFLAGS += $(INCLUDE_DIR)
-LDFLAGS = $(shell pkg-config --cflags --libs opencv) -shared -fPIC
 
+PKG_CONFIG := $(shell pkg-config --exists opencv || echo "no")
+ifeq ($(PKG_CONFIG),no)
+    PKG_CONFIG := $(shell pkg-config --exists opencv4 || echo "no")
+    ifeq ($(PKG_CONFIG),no)
+        $(error "opencv or opencv4 not found, please install OpenCV and try again.")
+    else
+        CXXFLAGS += $(shell pkg-config --cflags opencv4) -fPIC
+        LDFLAGS = $(shell pkg-config --cflags --libs opencv4) -shared -fPIC
+    endif
+else
+    CXXFLAGS += $(shell pkg-config --cflags opencv) -fPIC
+    LDFLAGS = $(shell pkg-config --cflags --libs opencv) -shared -fPIC
+endif
+
+CXXFLAGS += $(INCLUDE_DIR)
 
 CXXSOURCES = $(shell find $(SRC_DIR)/ -name "*.cpp")
 OBJS = $(addprefix $(OBJ_DIR)/,$(CXXSOURCES:.cpp=.o))
@@ -28,6 +40,7 @@ DEPFILES = $(OBJS:.o=.d)
 
 all: $(LIB_TARGET)
 
+
 $(OBJ_DIR)/%.o: %.cpp
 	@echo "[CC] $< ..."
 	@$(CXX) -c $< $(CXXFLAGS) -o $@