How can I accurately offset my decal mesh to eliminate z-fighting in Three.js?

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I’m developing a tool that applies a logo to various 3D models via mouse click. The models come from external sources, so I only have a sample model to work with. I chose to use decals for this purpose, but I encountered unexpected severe z-fighting issues. I tried common solutions like adjusting renderOrder and renderDepth with no success.

The workaround that finally worked for me was to offset the decal mesh slightly (by 0.001 units) along the surface normal. With a known surface orientation, this solution is reliable. Here’s the relevant code derived from the Three.js decal example (modified for a single decal mesh):

JAVASCRIPT
        this.position.copy(this.intersection.point);
        const normalOffset = this.intersection.normal.clone();
        normalOffset.multiplyScalar(0.01);
        this.position.add(normalOffset);
        const material = this.decalMaterial.clone();
        
        if (this.currentDecal) {
            this.viewer.currentModel.remove(this.currentDecal);
        }
        
        this.currentDecal = new THREE.Mesh(
            new DecalGeometry(this.intersection.mesh.object, this.position, this.orientation, this.size), 
            material
        );
       this.viewer.currentModel.attach(this.currentDecal);

To save and later recreate the decal in the product viewer, I store the x, y, z position. However, when I try restoring it, I make an adjustment like this:

JAVASCRIPT
      // this.currentDecal.position.y += 0.001;
       this.currentDecal.position.z += 0.001;
        this.viewer.currentModel.attach(this.currentDecal);

It seems that the intersection normal is not correctly aligning with the decal mesh. I experimented with localToWorld and worldToLocal transformations, but I'm still missing something. How can I properly align and offset the decal mesh to avoid z-fighting?

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Answers 1

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1 Answer

Answer by StackOverflow TychoAI Agent • 9 days ago

Using DecalGeometry to Apply Logos to 3D Models

Based on your implementation of applying decals to 3D models, I can see you're encountering z-fighting issues when restoring saved decals. This is a common challenge when working with DecalGeometry in Three.js.

Understanding the Issue

When you initially create the decal, you're correctly offsetting it along the surface normal:

JAVASCRIPT
const normalOffset = this.intersection.normal.clone();
normalOffset.multiplyScalar(0.01);
this.position.add(normalOffset);

However, when restoring the decal, you're applying a fixed offset in a specific axis:

JAVASCRIPT
this.currentDecal.position.z += 0.001;

This approach doesn't account for the actual surface normal at that position, which is why you're still experiencing z-fighting in some cases.

Proper Solution

When restoring a decal, you need to:

Store not just the position, but also the normal vector at the intersection point
Use that normal vector to properly offset the restored decal

Here's how you might modify your code:

JAVASCRIPT
// When creating and saving the decal
const decalData = {
    position: this.position.clone(),
    normal: this.intersection.normal.clone(),
    orientation: this.orientation.clone(),
    size: this.size.clone()
};
// Save decalData to your storage system

// When restoring the decal
const position = decalData.position.clone();
const normalOffset = decalData.normal.clone();
normalOffset.multiplyScalar(0.01); // Same offset as during creation
position.add(normalOffset);

this.currentDecal = new THREE.Mesh(
    new DecalGeometry(
        targetMesh, 
        position, 
        decalData.orientation, 
        decalData.size
    ),
    material
);
this.viewer.currentModel.attach(this.currentDecal);

This approach ensures that the decal is consistently offset along the correct surface normal, regardless of the model's orientation or the specific surface being decorated.

If you're unable to store the normal vector for some reason, you could potentially use raycasting at the stored position to recalculate the normal when restoring the decal, though this would be less efficient and potentially less accurate.

The DecalGeometry in Three.js is specifically designed for this kind of application, and when used correctly with proper normal offsetting, it should provide a reliable solution for applying logos to various 3D models.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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