Dxgi tearing support (#2601)

* present tearing support

* use existing syncInterval variable

src/dxgi.cpp

@@ -122,6 +122,7 @@ namespace bgfx
 		, m_factory(NULL)
 		, m_adapter(NULL)
 		, m_output(NULL)
+		, m_tearingSupported(false)
 	{
 	}
 
@@ -389,6 +390,8 @@ namespace bgfx
 				: 0
 				;
 
+			m_tearingSupported = allowTearing;
+
 			DX_RELEASE_I(factory5);
 		}
 
@@ -785,6 +788,11 @@ namespace bgfx
 #endif // BX_PLATFORM_WINDOWS || BX_PLATFORM_WINRT
 	}
 
+	bool Dxgi::tearingSupported()
+	{
+		return m_tearingSupported;
+	}
+
 } // namespace bgfx
 
 #endif // BGFX_CONFIG_RENDERER_DIRECT3D11 || BGFX_CONFIG_RENDERER_DIRECT3D12