meshops_bake

Baker

The baker, meshopsOpBake(), generates displacement distances to transform a base mesh into a given reference mesh (after tessellation). The tessellation scheme is specific to micromeshes. Base triangles are subdivided to a given level into micro-triangles. The baker then raytraces from the micro-vertices along per-triangle direction vectors until an intersection with the reference mesh is found. VK_KHR_acceleration_structure is required for this. The distances, relative to the direction vector length, are written to a BaryData object. These are typically then compressed into a .bary file.

Distances will always be in the unit range, 0 to 1. If per-vertex direction bounds do not exist, the BaryGroup's bias and scale is used to define their range. This is uncommon as per-vertex bounds are required for micromeshes to perform well.

It is common to use meshops_remesher to generate the base mesh. In such cases, textures may only exist for the reference mesh. These cannot simply be applied to the base mesh even though the texture coordinates may be similar, especially in the case of normal maps where tangent space changes dramatically. Resampling textures uses the same reference geometry and can be performed at the same time as baking.

Bounds fitting

Direction bounds are a per-vertex bias and scale pair affecting the displacement start and direction. These form a minimum and maximum shell that any displacement must be within. A tight shell will result in better raytracing performance.

The baker can generate direction bounds. This is currently implemented in two passes. The first computes per-triangle displacement ranges and the second re-computes displacement distances after using those displacement ranges as direction bounds. A final global fitting is performed as the second pass may still produce displacements outside the unit range.

Note that changing the direction bounds can actually change the micro-vertex displacement direction vector due to interpolation across the triangle. This is why bounds fitting must be iterative. It also has an effect on texture sampling, which is why resampling is encouraged.

Heightmaps

Providing a heightmap for the reference mesh will result in tessellation and displacement of the reference mesh before tracing. This can result in a significant amount of geometry, in which case baking can happen in batches.

Enabling PN Triangle interpolation will smooth the reference mesh tessellation while applying heightmap displacement.

Resampler

Texture resampling happens during baking, to take advantage of the reference geometry existing at the same time, particularly when it is generated on the fly with heightmap displacement. The mesh is rendered in UV space over the output texture and a ray is traced to the reference mesh for each pixel. The values written depend on the texture type:

• Generic - E.g. color/diffuse texture.
• Normal map - Resample direction vectors based on the change in tangent space from one mesh to the other.

Textures may also be generated from scratch:

• Offset map - a texture that stores the same texture space offsets used to resample Generic textures. This can be used to access the original non-resampled textures at runtime by offsetting the texture coordinates prior to lookup.
• Quaternion map - a texture of quaternion rotations representing the change of basis used when resampling Normal textures. Similar to the offset map, but for normal maps.
• Height map - displacements to the reference mesh. This is similar to a micromap but at texel frequency rather than micro-vertex. Experimental as it conflicts with bounds fitting and has no scale support.

Note that the resampler operates using the same per-vertex displacement directions and direction bounds, which means they are only valid after applying them to the original mesh.