Getting world position from vertex shader

Hello,

I’m trying to implement a custom pass in a postprocessing pipeline, but I can’t find a way to get the world positions of my scene.

I use this very simple shader as a base, which works on threejs default composer : https://jsfiddle.net/4nzkwesg/1/

vert :

    varying vec3 vColor;

    void main()
    {
        vec4 worldPosition = modelMatrix * vec4(position, 1.0);
        vColor = normalize(abs(worldPosition.xyz));
        gl_Position = projectionMatrix * viewMatrix * worldPosition;
    }

frag :

    precision mediump float;

    varying vec3 vColor;

    void main()
    {
        gl_FragColor = vec4(vColor, 1.0);
    }

But I can’t make it work on postprocessing because (it seems) I get screen space positions :

I’m calling this pass just after the renderPass.

What would be the correct way to port this shader to postprocessing ? Should I pass the geometries as attributes somewhere ? Or is there another way to access it from the vertex shader ?

Thank you very much.

[risq]

Thank you very much, it works perfectly ! I now understand better how the pipeline works and the difference between effects and passes. Blend function seems to be very powerful too !

Thanks again for your time, this is really appreciated 😃

[vanruesc]

For that you’d make an Effect. For example: https://codesandbox.io/s/gallant-dew-9zog6?runonclick=1&file=/src/FogEffect.js

The strategy is this: render the scene colors (RenderPass) and the world position data (WorldPositionPass) into two separate buffers and then use those buffers in a fullscreen shader to render the desired effect. The scene colors are already available to Effect shaders via the inputColor argument, but you can just render the fog factor out and then use the blend function mechanism to handle blending.

An optimal pipeline would make use of multiple render targets (MRT) to render the geometry buffers but three.js doesn’t support that yet.