DecalGeometry Stretching Issues

Based on the information you've provided about stretching issues with DecalGeometry, this does sound like it could be related to UV mapping, but there are several potential causes to consider.

DecalGeometry in Three.js creates a new geometry that projects a texture onto an existing mesh. The stretching you're observing could be caused by:

1. UV Mapping Issues: DecalGeometry generates its own UV coordinates based on the projection. If the projection angle or orientation doesn't align well with the surface geometry, stretching can occur.

2. Normal Direction Inconsistencies: If the normals of your mesh aren't consistent or properly calculated, this can affect how the decal is projected onto the surface.

3. Projection Parameters: The parameters you're using for the DecalGeometry constructor (position, orientation, size) might need adjustment to better fit the surface.

4. Mesh Geometry Quality: Even on seemingly flat surfaces, if there are subtle variations in the geometry or polygon distribution, it can affect how the decal is applied.

To troubleshoot this issue, you might try:

• Checking the normals of your mesh to ensure they're consistent
• Adjusting the size and orientation parameters of your DecalGeometry
• Ensuring your base mesh has adequate polygon density in areas where decals are applied
• Experimenting with different projection directions

Without seeing the specific code and models you're using, it's difficult to pinpoint the exact cause, but these are common issues that can lead to the stretching behavior you're describing with DecalGeometry.