The code in hlsl but I can’t use it.
Unity says “sampler2D object does not have methods”
Here are the detail about Object.SampleGrad SampleGrad (DirectX HLSL Texture Object) - Win32 apps | Microsoft Learn
The article that related to http://www.gamedev.net/page/resources/_/technical/graphics-programming-and-theory/a-closer-look-at-parallax-occlusion-mapping-r3262