Occlusion-Aware Outlines in Three.js

Based on your issue with outlines appearing on top of other objects even when the mesh should be occluded, I can suggest a few approaches to achieve occlusion-aware outlines.

Depth Testing Approach

The main issue appears to be that your outline shader is rendering on top of other objects regardless of depth. To make the outline respect occlusion:

1. Ensure your outline material has proper depth testing enabled:

JAVASCRIPTCopied
outlineMaterial.depthTest = true;
outlineMaterial.depthWrite = true;

2. If you're using a post-processing approach, you'll need to compare the depth of your outlined object with the scene depth.

Multi-Pass Rendering Technique

A common approach for occlusion-aware outlines is to use a multi-pass technique:

1. First pass: Render your object slightly scaled up with a solid color (outline color)
2. Second pass: Render the original object on top
3. Use proper depth testing to ensure occlusion works correctly

JAVASCRIPTCopied
// Create outline mesh (slightly larger than original)
const outlineMesh = new THREE.Mesh(
  originalGeometry.clone(),
  new THREE.MeshBasicMaterial({ 
    color: outlineColor,
    side: THREE.BackSide,
    depthTest: true,
    depthWrite: true
  })
);
outlineMesh.scale.multiplyScalar(1.05); // Scale up slightly
scene.add(outlineMesh);

// Ensure original mesh renders on top of outline
originalMesh.renderOrder = 1;
outlineMesh.renderOrder = 0;

Custom Depth Material Approach

Since you're already working with custom shaders, you could modify your approach to:

1. Use a custom depth material for your outline object
2. Compare this depth with the scene depth in your shader
3. Only render the outline where it's not occluded

This would involve creating a custom depth render target and comparing depth values in your fragment shader.

Using MeshDepthMaterial

You might also consider using Three.js's built-in MeshDepthMaterial as part of your solution:

JAVASCRIPTCopied
const depthMaterial = new THREE.MeshDepthMaterial({
  depthPacking: THREE.RGBADepthPacking,
  alphaTest: 0.5
});

// Render to a depth texture
// Then use this in your outline shader to check for occlusion

If you'd like more specific guidance on implementing any of these approaches with your existing code, please share more details about your current shader implementation.