add imgui cpp minimal example

Author: RobertJN64

.gitmodules

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+[submodule "UI/imgui"]
+	path = UI/imgui
+	url = https://github.com/ocornut/imgui
+	branch = docking
+
+[submodule "UI/implot"]
+	path = UI/implot
+	url = https://github.com/epezent/implot

UI/.gitignore

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+*.o
+*.ini
+*.exe

UI/Makefile

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+CXX      := g++
+CXXFLAGS := -Iimgui -Iimgui/backends -Iimplot
+LDFLAGS  := -luser32 -lgdi32 -ld3d11 -ldxgi -ld3dcompiler -ldwmapi
+
+# Sources
+IMGUI_SRC := imgui/imgui.cpp \
+             imgui/imgui_draw.cpp \
+             imgui/imgui_widgets.cpp \
+             imgui/imgui_tables.cpp \
+             imgui/backends/imgui_impl_win32.cpp \
+             imgui/backends/imgui_impl_dx11.cpp \
+             implot/implot.cpp \
+             implot/implot_items.cpp
+
+APP_SRC   := main.cpp ui.cpp
+SRC       := $(APP_SRC) $(IMGUI_SRC)
+
+# Objects
+OBJ       := $(SRC:.cpp=.o)
+
+# Output
+TARGET    := app.exe
+
+all: $(TARGET)
+
+# Link step
+$(TARGET): $(OBJ)
+	$(CXX) $^ -o $@ $(LDFLAGS)
+
+# Compile step
+%.o: %.cpp
+	$(CXX) $(CXXFLAGS) -c $< -o $@
+
+clean:
+	del /Q $(OBJ) $(TARGET) 2>nul || true