Get vertex position on a postprocessing custom shaderPass

[ventoline]

I am trying to get the world / local position of a vertex but I only get the screenSpace value, what I am missing?

 vertexShader: /* glsl */ `

	varying vec2 vUv;
        uniform float opacity;
        varying vec3 p;

		void main() {
			vUv = uv;
                p = modelView * vec4(position, 1.0);
			gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );

		}`,