2D mapping parameters
3D mapping/subdivision parameters
Displacement mapping is a technique for adding detail to your scene geometry without having to model it first. The concept is very similar to bump mapping. However, bump mapping is a shading effect that only changes the appearance of a surface, while displacement mapping actually modifies the surface. In Softimage the V-Ray Displacement controls are added by selecting the object and selecting the VRayDisplacementProperty from Get>Property>.
Use globals - when this option is disabled the settings in the Default Displacement roll up will be overridden for the current object.
Displacement Type - the method used to apply displacement mapping:
2D displacement - this method bases the displacement on a texture map that is known in advance. The displaced surface is rendered as a warped height-field based on that texture map. The actual raytracing of the displaced surface is done in texture space, and the result is mapped back into 3d space. The advantage of this method is that it preserves all the details in the displacement map. However, it requires that the object has valid texture coordinates. You cannot use this method for 3d procedural textures or other textures that use object or world coordinates. The displacement map can take any values (as opposed to normal displacement, which will ignore values outside the 0.0-1.0 or black to white range).
Normal displacement - this is a general method which takes the original surface geometry and subdivides its triangles into smaller sub-triangles which are then displaced. It can be applied for arbitrary displacement maps with any kind of mapping.
Subdivision - this method is similar to the 3D mapping method, with the difference that it will apply a subdivision scheme to the object. For triangular portions of a mesh, the Loop subdivision scheme is used. For quadrangular portions, the Catmull-Clark scheme is used. Other polygons are first converted to triangles.
Vector displacement (signed) - If you have a displacement texture that is not grayscale V-Ray will convert it to grayscale before rendering the displaced geometry. When this option is enabled it allows V-Ray to use the Red, Green and Blue channels of the displacement texture to displace the geometry in the U and V directions in addition to the normal of the face
Note: To use a vector displacement texture, open the Render Tree for the object to which you have applied the VRayDisplacementProperty. Then connect a texture node to the "Displacement" port of your object material. A "Color To Scalar" node will automatically appear between them. V-Ray will ignore the "Color To Scalar" node and will take the vector values directly from the texture. This is a workaround for Softimage's lack of a color displacement port.
Which method to use? In previous V-Ray versions, there was a great difference between the performance of the two methods, with the 2D mapping being faster in many cases. With the introduction of dynamic geometry handling in V-Ray 1.45.xx, 3d displacement has become a lot faster for similar or better quality compared to the 2d mapping. Still, for large displaced surfaces like oceans or mountains, the 2d mapping method might work better.
Also the 2D mapping method keeps the displacement map in a precompiled state in memory. Large displacement maps can take a lot of RAM. It may be more efficient to use 3D mapping in that case, since it can recycle the memory used for the displaced geometry.
Amount - the amount of displacement. A value of 0.0 means the object will appear unchanged (or simply smoothed, if you use the Subdivision method). Higher values produce a greater displacement effect. This can also be negative, in which case the displacement will push geometry inside the object.
Shift - this specifies a constant, which will be added to the displacement map values, effectively shifting the displaced surface up and down along the normals. This can be either positive or negative.
Enable water level - allows you to enable and disable the Water level option
Water level - this will clip the surface geometry in places where the displacement map value is below the specified threshold. This can be used for clip mapping a displacement map value below which geometry will be clipped.
Tight bounds - when this is on, V-Ray will try to compute the exact bounding volume of the displaced triangles from the original mesh. This requires pre-sampling of the displacement texture, but the rendering will be faster, if the texture has large black or white areas. However, if the displacement texture is slow to evaluate and varies a lot between full black and white, if may be faster to turn this option off. When it is off, V-Ray will assume worst-case bounding volumes, and will not presample the texture. Note that this affects only the 2d displacement and Normal displacement modes; with the Subdivision method V-Ray will always compute the exact bounding volume and this parameter is ignored.
2D displacement parameters
Resolution - this determines the resolution of the displacement texture used by V-Ray. If the texture map is a bitmap, it would be best to match this resolution to the size of the bitmap. For procedural 2d maps, the resolution is determined by the desired quality and detail in the displacement. Note that V-Ray will also automatically generate a normals map based on the displacement map, to compensate for details not captured by the actual displaced surface.
Precision - this parameter is related to the curvature of the displaced surface; flat surfaces can do with a lower precision (for a perfectly flat plane you can use 1), more curved surfaces require higher values. If the precision is not high enough you can get dark spots ("surface acne") on the displacement. Lower values compute faster.
Filter texture - if this is on, the texture map will be filtered.
Filter Blur - this is the strength of the blur filter that will be applied
3D mapping/subdivision parameters
Edge length - this determines the quality of the displacement. Each triangle of the original mesh is subdivided into a number of sub triangles. More sub triangles mean more detail in the displacement, slower rendering times and more RAM usage. Less sub triangles mean less detail, faster rendering and less RAM. The meaning of Edge length depends on the View-dependent parameter below.
View-dependent - when this is on, Edge length determines the maximum length of a sub triangle edge, in pixels. A value of 1.0 means that the longest edge of each sub triangle will be about one pixel long when projected on the screen. When View-dependent is off, Edge length is the maximum sub triangle edge length in world units.
Max. subdivs - this controls the maximum sub triangles generated from any triangle of the original mesh. The value is in fact the square root of the maximum number of sub triangles. For example, a value of 256 means that at most 256 x 256 = 65536 sub triangles will be generated for any given original triangle. It is not a good idea to keep this value very high. If you need to use higher values, it will be better to tessellate the original mesh itself into smaller triangles instead. From build 1.45.20 onward, the actual subdivisions for a triangle are rounded up to the nearest power of two (this makes it easier to avoid gaps because of different tessellation on neighboring triangles).
Use bounds - when using a texture that has color values beyond the standard 0-1 you can enable this check box and manually specify the value range of the texture. If you don't do that the colors in the texture will be automatically clipped to 0 and 1
Min bound - a boundary for the smallest color value in the texture used for displacement
Max bound - a boundary for the largest color value in the texture used for displacement
Keep continuity - using this will try to produce a connected surface, without splits, when you have faces from different smoothing groups and/or material IDs. Note that using material IDs is not a very good way to combine displacement maps since V-Ray cannot always guarantee the surface continuity. Use other methods (vertex colors, masks etc) to blend different displacement maps.
Smooth UVs At borders - allows you to choose whether or not the UVs of the object will be subdivided at the borders.
Smooth UVs - enables or disables the subdividing of the objects UVs