How to use Material correctly in PPv2?

I want use Material because I want only expose few settings in PostProcessEffectSettings and tweak most properties in Material.
So I tried this :

Code (CSharp):

1.  
2. [Serializable]
3. [PostProcess(typeof(PostMaterialRender),PostProcessEvent.AfterStack,"Custom/PostMaterial")]
4. public sealed class PostMaterial : PostProcessEffectSettings {
5.     public MaterialParameter mat = new MaterialParameter() {value = null};
6. }
7. public sealed class PostMaterialRender : PostProcessEffectRenderer<PostMaterial> {
8.     public override void Render(PostProcessRenderContext context) {
9.         Material mat = settings.mat;
10.         context.command.Blit(context.source,context.destination,mat,0);
11.     }
12. }
13. [Serializable]
14. public sealed class MaterialParameter : ParameterOverride<Material>{}
15.  

Then I got this result.Only 1/4 of the screen rendered.So how to use Material correctly?



https://ibb.co/pPX3y0S
https://ibb.co/HpMcCNW
https://ibb.co/Q8Ct4xb