tc_curvature v1.0

Calculate from:

- Surface Derivaives (NURBS)
Select this option when working with NURBS surfaces. Curvature is calculated from the derivatives in the state->derivs array. If you choose this method with polys and some sub-div surfaces, you'll just get black.

- Tesselation
Curvature is calculated by comparing the face normal to the vertex normals. This is suitable for any kind of geometry. This only works with 'softened' normals. Any hard normals will not show curvature. This method has the downside that the curvature value is 'per face', so with low poly geometry, you will get noticable steps in the output. (see example below)

- Normal Sampling
Curvature is calculated by arbitrarily sampling the normals around the current surface point. This has the benefit that you should get a smooth output no matter how coarsly tesselated the geometry is.

Method:

- Average
The presented curvature is the average of the principal curvatures (NURBS), the average of the vertex curvatures (Tesselation) or the average of the sampled points (Normal Sampling).

- Gaussian
This is the product of the curvatures. Generaly highlights only sharper curvatures compared to average.

- Barycentric Interpolation (Tesselation derived curvatures only)
This interpolates the vertex curvatures depending on where you are on the face. Has the effect of softening Tesselation based curvature, though sometimes it gives a 'fish scale' like effect. .

Range:

- Full (only usefull for NURBS surfaces)
Negative (concave) curvature is clipped at 'Concave Max' and scaled to the output range between 0 -> 0.5. Positive curvature (convex) is clipped at 'Convex Max' and scaled to the output range between 0.5 -> 1.0. No curvature = 0.5.

- Convex only (+ve)
Negative curvature is ignored, and the range betweeen flat (0) and 'Convex Max' is scaled to the output range 0 -> 1.0. This setting is the most usefull for poly geom.

- Concave only (-ve)
Positive curvature is ignored, and the range betweeen flat (0) and 'Concave Max' is scaled to the output range 0 -> 1.0. Only usefull with NURBS surfaces.

Convex max:

The 'upper clipping' value for positive curvature. This will usualy need quite a bit of tweaking from the default as curvature seems to vary quite a lot from surfce to surface.

Concave max:

As above, but for negative curvature.

Threshold:

When using the 'Convex only' or 'Concave only' range setting, this value sets a 'low clip' value, so you can trim away small curvature values from the lower end of the scale.

Smooth Result:

When enabled, applies cardinal spline interpolation of the curvature between 0 and 1.0.

Smooth gamma:

Moves the mid-point of the spline used for interpolation. Works a little bit like a gamma control. NOTE: at the moment, extreme settings can cause vaules above 1.0 and below 0.0 - got to sort that out.

Samples:

The number of samples per point in 'Normal Sampling' mode.

Focus:

The focus of the sample rays cast. Higher values samples over a smaller area. Use for more precise curvature calculation. Kind of a backwards 'ray spread'.

NURBS

with nurbs objects the shader has the option to calculate curvature based on the surface derivatives. This is a nice method as it easlity allows us to know wether the surface is convex or concaved.

the images below are a few quick examples showing the different options:

full range output

convex only output

concave only output

Polygon geometry

there are two options for recovering curvature from poly meshes (or tesalated nurbs - see below). The first - 'tesselation' gives per-face curvature. Youll notice this has an obvious problem with big faces. An alternative is 'normal sampling' which samples the surface normals independently of tesselation, which gives smoother results. With the current inplementation, poly geometry only ever gives +ve curvature output.

tesselation

tesselation with barycentric interp.

nomal sampling.