How to apply post processing effects to specified camera ?

[Aqaao]

I modifyed "post_process" example to 2d, and I had multiple cameras. When I add "PostProcessSettings" component to one of cameras, the effect will apply to the texture in other cameras of lower order.

  let mut camera_1: Camera2dBundle = Camera2dBundle::default();
  camera_1.camera.order = 1;
  commands.spawn((
      camera_1,
      RenderLayers::layer(1),
  ));

  let mut camera_2: Camera2dBundle = Camera2dBundle::default();
  camera_2.camera.order = 2;
  commands.spawn((
      camera_2,
      RenderLayers::layer(2),
      PostProcessSettings {
          intensity: 0.01,
          ..default()
      },
  ));

Any sprites in camara_1 will had postprocess effect, but if change camera_2's order to "0", effect in camera_2 only.
How to apply post processing in high order camera only?
I‘m sorry that I have little if any knowledge of render pipeline.

This is test project. test_pp.zip

[Aqaao]

I spent a couple days trying to figure out bevy's rendering. Eventually, I solved it. Just add a render node before Node2d::MsaaWriteback, clear view_target.main_texture_view() in node.

But I still can't figure out the rest of the render graph. Why pass main_texture between cameras? Would it cause any trouble for each camera to do its own rendering and then write the texture to view_target.out_texture()?