Compare current depth with older depth

Questions
1

We have a scene rendered to a WebGLRenderTarget with a depth texture which is being passed to a ShaderMaterial in a different scene as tDepth. Following is the fragment shader for that ShaderMaterial. It does a depth check and then renders onto the canvas. (I can just disable autoclear of depth and have it working, but I want a custom depth function, hence the code).

varying vec2 vUv;
uniform sampler2D tDepth;
uniform float width;
uniform float height;
void main() {
  vec2 clipCoord = vec2(gl_FragCoord.x / width , gl_FragCoord.y / height)
  float oldDepth = texture2D(tDepth, clipCoord).r; // Gets wrong value.
  float currentDepth = gl_FragCoord.z;
  if (oldDepth > currentDepth) {
    gl_FragColor = vec4(1,0,0,0);
  } else {
    discard;
  }
}

Instead of using clipCoord, if I just use vUv it works only when the other scene is a full screen quad with ortho camera. How do I get the correct value of oldDepth in case of other scenes?

2

Do you mind providing a live demo?

BTW: Instead of using two uniforms width and height, i suggest you use vec2 resolution. The variable name clipCoord is wrong. You are not calculating clip coordinates but normalized pixel coordinates (with values from 0 to 1).

3

Crossposting:

4

The problem that I’m trying to solve is the losing anti aliasing the moment we render to WebGLRenderTarget. Edges look really bad without AA.

The idea is I draw the main object first, then do the post processing using EffectComposer (I need to use outline_pass for somethings), then draw the edges directly to the canvas so that I don’t lose AA.

To be honest, when I posted this question I wasn’t getting the right value for tDepth, but when I tried to make the code simpler, I got the right values :slight_smile:. I was seeing edges on the other side as well.

However, there’s still a problem: the lines are jagged which shouldn’t be the case.
02%20AM

5

That’s because the cube itself is not smoothed via antialiasing.

6

Okay, I tried not rendering the cube at all:

I still see the jagged lines.

7

I’ve refactored your codepen so the actual depth texture is rendered. You can still see the effect similar to missing antialiasing. You could try to blur the depth texture a bit. Maybe this helps to smooth your lines…