The remesher prepares high resolution meshes for use with micromeshes. It currently decimates the input mesh and outputs target micromesh subdivision levels and displacement bounds. This information can then be used by the micromesh baker to generate a lightweight, micromesh-enabled model. The remesher fully executes on graphics hardware for interactive performance: the model below has been decimated in 700 ms using an NVIDIA GeForce RTX 3090Ti.
The parameters described below can be found in the OpRemesh_input structure.
| Original 2M triangles | Decimated 20K triangles |
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- Edge collapse decimation
- Parallel execution
- Preservation of attributes discontinuities
- Outputs micromesh metadata to drive micromesh bakers
The remesher collapses all edges until such collapsed incur a maximum error. This error is a mixture of resulting edge length, a user-defined, per-vertex importance metric, the resulting vertex valence and a maximum decimation level.
The maximum error value can be directly specified using this parameter. This value is dependent on the scale of the scene.
A simpler stopping criterion is a target triangle count for the decimated mesh. In practice this will gradually increase the error threshold until reaching the maximum triangle count. Note that due to the massively parallel nature of the underlying algorithms the resulting triangle count may be significantly lower than this maximum value.
| Original 2M triangles | Target 500K → 355K | Target 50K → 40K | Target 5K → 4.5K | Target 1.5K → 1.4K |
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The decision to collapse an edge is not only based on the above error metric, but also uses local criteria to determine whether the edge can be collapsed.
An edge can be collapsed only if the resulting triangles would not cover more than 4^maxSubdivLevel triangles in the original mesh.
If provided along with the texture coordinate index heightmapTextureCoord this extends the principle of maxSubdivLevel to the UV domain: an edge collapse will be blocked if it would result in triangles covering more than 4^maxSubdivLevel texels.
Limits the valence of the vertices resulting from an edge collapse, which helps avoiding large triangle fans in the final result. Note this will not reduce the valence of the input vertices even if their valence exceeds this threshold.
| Vertex Valence | Original Mesh | Unlimited valence | Max valence 11 |
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The remesher supports per-vertex importance, whose value is integrated in the error calculation. The higher the importance value (between 0 and 1) of the vertices of an edge, the higher the collapse error metric. The per-vertex importance is provided as part of the ResizableMeshView, and can be generated automatically.
The importanceWeight parameter defines the weight of the per-vertex importance in the estimate of the error incurred by edge collapse operations.
| Importance Weight | 0.05 | 0.1 | 0.2 |
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If defined, importanceThreshold forbids edge collapses involving a vertex whose importance exceeds this threshold. This can be particularly useful to enforce the preservation of fine features.
| Vertex Importance | Original Mesh | No Max | Max 0.9 |
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The preservedVertexAttributeFlags value defines which vertex attributes discontinuities are preserved by the remeshing process. This typically allows preservation of UV islands, so the textures designed for the input mesh can still be used on the decimated mesh.
This parameter supports combinations of a subset of MeshAttributeFlagBits: eMeshAttributeVertexNormalBit, eMeshAttributeVertexTangentBit,
eMeshAttributeVertexDirectionBit, and eMeshAttributeVertexTexcoordBit.
| Texture Map | Original 100K triangles | Decimated 20K triangles |
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During decimation the remesher gathers information linking the input and decimated meshes, such as the input vertices covered by each decimated triangle and the size of the shell encompassing the input triangles. This data is then used to deduce a target subdivision level and displacement bounds for micromeshes.
| Original Mesh | Decimated Result | Target Subdivision Level | Displacement Bounds |
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The generated shell may bound the original mesh very tightly. To ensure a successfull micromesh baking the directionBoundsFactor may be used to enlarge the displacement bounds, avoiding floating-point approximation artifacts.
This metadata export can be enabled and disabled using the generateMicromeshInfo parameter.
The input mesh is expected to have manifold topology. Topological issues such as T-junctions, overlapping triangles, or edges connected to more than 2 triangles will result in undefined behavior.
Distinct connected components will be remeshed independently, even though they visually appear connected (e.g. assembled mechanical parts). After remeshing some visible gaps may appear between those connected components.
By default the remesher attempts to preserve the volume of the input mesh by offsetting the position of the vertices along their displacement direction. While this reduces shrinking, decimating a mesh to a very low triangle count may result in excessive offsets. If needed this mechanism can be disabled by setting fitToOriginalSurface to false.
The displacement bounds approximation may underestimate the required displacement, especially when the number of triangles in the decimated mesh is close to the one of the original mesh. Adjusting directionBoundsFactor accordingly works around this limitation.
The remesher fully operates on graphics hardware, and requires some scratch memory. Decimating large meshes can therefore fail due to insufficient memory. In our tests we could decimate meshes up to 70M triangles on a 24GB RTX 3090Ti.
The per-vertex importance used by the remesher can be either computed externally and provided in the input ResizableMeshView, or generated using meshopsOpGenerateImportance, whose parameters are defined in OpGenerateImportance_modified.
The importance generation is based either on a local curvature metric obtained by tracing rays above and below each vertex, or using an input importance map.
The world-space tracing distance defines the scale of the features preserved during decimation.
| Tracing Distance | 0.05 | 0.1 | 0.2 |
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The power value is applied to the curvature values obtained by ray tracing, allowing for fine adjustment of the curvature contrast.
| Curvature Power | 0.5 | 1.0 | 5.0 |
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This texture object is an external importance source, mapped using the texture coordinates indicated by importanceTextureCoord. If non-null, this importance map supersedes the curvature estimation.
| Importance Map | Per-Vertex Importance | Decimated Result |
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The models shown in this page are under Creative Commons licence. The "Plastic Dragon" and "Dark Finger Reef Crab" models are available on Three D Scans. The "Panulirus Longpipes" model is available on The Smithsonian 3D Digitization.