Support minimal dependency linux build.

src/graphics/CMakeLists.txt

@@ -3,32 +3,29 @@ set(platform_INCLUDE_DIRS "")
 set(platform_HEADERS "")
 set(platform_LIBS "")
 
-if (UNIX)
-list(APPEND platform_LIBSs
-	GL
-)
-else()
-list(APPEND platform_LIBS
-	OpenGL32.lib
-)
-endif()
-
 list(APPEND graphics_LIB_INCLUDES 
     DrawingContext.cpp
     DrawingManager.cpp
     DrawingSurface.cpp
     Rasterizer.cpp
-    opengl/OpenGlInterface.cpp
-	${platform_LIB_INCLUDES}
+    ${platform_LIB_INCLUDES}
 )
     
 list(APPEND graphics_HEADERS 
-    opengl/OpenGlInterface.h
     ${platform_HEADERS}
     Rasterizer.h
     INativeDrawingSurface.h
-    INativeDrawingContext.h)
+    INativeDrawingContext.h
+    )
 
+find_package(OpenGL QUIET)
+if (OpenGL_FOUND)
+    list(APPEND platform_LIBS OpenGL::GL)
+    list(APPEND graphics_LIB_INCLUDES opengl/OpenGlInterface.cpp)
+    list(APPEND graphics_HEADERS opengl/OpenGlInterface.h)
+else()
+    message(STATUS "OpenGL headers not found - skipping OpenGL support")
+endif()
 
 add_library(graphics SHARED 
     ${graphics_LIB_INCLUDES}