>>> Displacement mapping >>>
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.
Type - the method used to apply displacement mapping:
2D mapping (landscape) - 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 3D mapping, which will ignore values outside the 0.0-1.0 or black to white range).
3D mapping - 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. This method can also use the displacement map specified in the object's material. Note that with 3d mapping the displacement map's range of values must be within the 0.0-1.0 range (black to white). Values outside of this range will be clipped.
Subdivision - this method is similar to the 3D mapping method, with the difference that it will apply a subdivision scheme to the object, similarly to a MeshSmooth modifier. 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. If just want to smooth the object, without applying a displacement map, set the Amount parameter to 0.0.
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.
Texmap - the displacement map. This can be any texture map - a bitmap, procedural map, 2d or 3d map etc. Note that you can only use textures with explicit UV mapping with 2D displacement, while with 3D displacement any texture can be used. The texture map is ignored if the Use object mtl option is turned on.
Texture chan - the UVW channel that will be used for displacement mapping. This must match the texture channel specified in the texture map itself, if it uses explicit UVW mapping. This is ignored if the Use object mtl option is on.
Filter texmap - if this is on, the texture map will be filtered. This is ignored if the Use object mtl option is on.
Filter Blur -
Amount - the amount of displacement. A value of 0.0 means the object will apear 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.
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.
2D mapping 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.
Tight bounds - this parameter will cause V-Ray to compute more precise bounding volumes for the displaced triangles, leading to slightly better rendering times.
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 subtriangles. More subtriangles mean more detail in the displacement, slower rendering times and more RAM usage. Less subtriangles 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 subtriangle edge, in pixels. A value of 1.0 means that the longest edge of each subtriangle will be about one pixel long when projected on the screen. When View-dependent is off, Edge length is the maximum subtriangle edge length in world units.
Max. subdivs - this controls the maximum subtriangles generated from any triangle of the original mesh. The value is in fact the square root of the maximum number of subtriangles. For example, a value of 256 means that at most 256 x 256 = 65536 subtriangles 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 tesselate 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 tesselation on neighboring triangles).
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 mapping and 3d mapping modes; with the Subdivision method V-Ray will always compute the exact bounding volume and this parameter is ignored.
Use object mtl - this will cause the displacement map to be taken from the object's material instead of the map selected in VRayDisplacementMod.
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.
Edge thresh - when Keep continuity is checked, this controls the extent to which maps on faces with different material IDs will be blended. Note that V-Ray can only guarantee edge continuity, but not vertex continuity (meaning that the surface will not have gaps along edges, but there may be splits around vertices). For this reason you should keep this value small.
Vector Displacement - 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 enabaled 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
Split Method - determines the method which is going to be used to subdivide the faces of the geometry. For better understanding check the Examples section.
Tex. map min/max - these two options allow you to specify custom bounderies for the displaced geometry (Examples). By default is limited to values between 0 and 1.