返回资源后处理器的版本。
重新编译脚本时，如果检测到版本变化，系统将重新导入与此资源后处理器关联的资源。
class TexturePostProcessor : AssetPostprocessor
{
// Bump this number to make textures reimport after modifying the post processor below.
private uint m_Version = 0;
public override uint GetVersion() {return m_Version;}
public void OnPostprocessTexture(Texture2D tex)
{
Color[] pix = tex.GetPixels();
for (int i = 0; i < pix.Length; i++)
{
pix[i] = pix[i] * 0.5f;
}
tex.SetPixels(pix);
tex.Apply(true, true);
}
}