RealFlow's Hybrido solver is able to process many millions (even hundreds of millions) of particles and this huge amount has to be handled during several procedures: exporting, displaying and meshing. It is a real challenge to create high-quality meshes from a hundred million (or more!) particles within a reasonable time frame. Our new “Hybrido Mesh” engine uses state-of-the-art algorithms and powerful techniques to exceed your expectations in terms of speed, quality and file size. The “Hybrido Mesh” tool catches even the finest structures and splashes with a minimum of parameters and settings.
Experienced users will find a set of new parameters under the mesh node's “Filter” panel. Basically, these settings can be split into two main parts. The parameters of the first part are used to adjust the grid fluid's splashes. Please note that here, we are really talking about the splashes of the grid fluid, not the secondary HySPH particles. These elements are rendered either as particles or treated with the “Particle Mesh” tool. With the splash-related parameters of the “Hybrido Mesh” engine you can create ultra-realistic structures with thin borders. In the second part you will find parameters to reduce the “rounded borders” effect in the main fluid body.
The well-known relaxation and tension filters are still available, but we recommend using the splash- and core-related parameters only, because they are highly optimized for Hybrido grid fluids and produce accurate results.
To get you off to a good start we have added a comprehensive description about how these parameters work, which dependencies they have, and how they finally affect the mesh. We also want to encourage you to perform some tests to become familiar with the filter's mode of operation. It will certainly take a few attempts to understand the principle behind these settings, but once you got it, you will be able to create stunning results.
How to Configure the “Hybrido Mesh” Engine
For most cases, there is a standard workflow that can be used to define the initial main parameters. These values can be used for further tests and for fine-tuning the mesh. The “Filters” parameters, in particular “Core smoothing” and Splash thinning”, play a very important role here. The “Hybrido Mesh” engine can detect which areas of the fluid are considered the main body of the fluid (also called core fluid) and which parts are splashes. Based on this differentiation, it is possible to apply separate filters on the mesh and treat these parts individually.
“Core smoothing”
Let's start with “Core smoothing”. Each vertex of the mesh has a certain property that ranges between 0 and 1. A value of 0 (or close to 0) means that a vertex does not have any core characteristics, while 1 tells the engine that it has full core attributes. This value acts like a scale factor which is eventually responsible for the smooth transitions between the mesh's different core areas. With the “@ core threshold” value it is possible to control this transition, because it determines when the smoothing process will start:
If you enter a threshold of 0.4, for example, all vertices with values greater than 0.4 will be taking into account. The “Core smoothing” filter will be only applied to vertices with values between 0.4 and 1.0. One of the key features is that these candidates will not simply receive the same amount of smoothing, but each vertex will be treated individually to create clean transitions. Good starting values for “@ core threshold” range between 0.2 and 0.4.
Finally, there is “@ smoothing steps”. The value determines how of the “Core smoothing” filter will be applied to the mesh. It is important to know that this parameter is resolution-dependant. For high-resolution meshes, values between 100 and 150 should work. With increasing quality, the number of steps has to be raised as well.
“Splash thinning”
The “Splash thinning” filter, on the other hand, is very important to increase the mesh's level of detail and to create a realistic look. The idea behind this filter is actually the same as with “Core smoothing”: each vertex carries a value between 0 (no splash) and 1 (full splash characteristics). Again, the associated “@ splash threshold” parameter determines when the thinning effect should start and creates a smooth transition. Vertices with a value smaller than the threshold will not be filtered, while vertices with values between “@ splash threshold” and 1.0 will receive an appropriate amount of filtering/thinning. Good values range between 0.8 and 1.0.
“@ thinning size” tells the engine how much you finally want to thin out the splashes and is used to avoid rounded borders. Technically, the mesh engine “pushes” the mesh's vertices closer to the fluid particles. Since the position of the vertices also define the edges of the mesh's triangles you have to be careful with high values close to 1.0, because you might see flipped polygons or intersecting areas. Good initial values are between 0.5 and 0.6.
There is a simple rule you can follow: a “@ thinning size” value of 0.0 represents a particle radius of 0, while 1.0 exactly matches the radius. Or: the maximum thinning size equals the particle’s radius. The current thinning size is calculated as:
Total thinning size = @ thinning size * particle radius
How to Adjust the Mesh's Polygon Size?
If you do not want to use the “Hybrido Mesh” engine's “Auto polygon size” feature (it can be found under the “Mesh” panel) then there is often the problem of which starting value you should use? To avoid guessing, there is an easy formula to calculate the mesh's polygon size. The result can be used as a starting point to decrease the size of the triangles. For this calculation the particle radius rp is required:
Polygon size <= rp / sqr( 3 )
Please bear in mind that “@ polygon size” should never be greater than the particle radius. The particle radius can be calculated with this formula – the “Cell size” and “Particle sampling” parameters are properties of the “HY_Domain” node:
rp = sqr( 3 ) * ( Cell size / 2 * Particle sampling )