ビルトインシェーダーのかわりにカスタムシェーダーを使用する。
This is useful for implementing custom functionality. For example, by default deferred shading does shading calculations
that match the Standard shader lighting model. But if you'd want to use a different BRDF, or use a custom deferred G-buffer
layout, then you'd need to override BuiltinShaderType.DeferredShading with your own custom shader.
See Also: GraphicsSettings.SetShaderMode, GraphicsSettings.SetCustomMode, BuiltinShaderType, Graphics Settings.