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The Matrix Field DOP creates a Matrix Field data that can be attached to simulation objects and manipulated by solvers. A Matrix Field is an axis-aligned box divided into individual voxels. Each voxel is giving a 3d matrix. The entries thus can encode an affine transformation, such as stretch, shear, or rotation.
One of the divisions of the voxel grid will be forced to one to create a two dimensional field.
If set to two dimensional, this plane determines which axes remain unaffected.
If non square, the specified size is divided into the given number of divisions of voxels. The sides of these voxels may not be equal, however, possibly leading to distorted simulations.
When an axis is specified, that axis is considered authoritative for determining the number of divisions. The chosen axis' size will be divided by the uniform divisions to yield the voxel size. The divisions for the other axes will then be adjusted to the closest integer multiple that fits in the required size.
Finally, the size along non-chosen axes will be changed to represent uniform voxel sizes. If the Max Axis option is chosen, the maximum sized axis is used.
When By Size is specified, the Division Size will be used to compute the number of voxels that fit in the given sized box.
The resolution of the key axis on the voxel grid. This allows one to control the overall resolution with one parameter and still preserve uniform voxels. The Uniform Voxels option specifies which axis should be used as the reference - it is usually safest to use the maximum axis.
The resolution of the voxel grid that will be used to calculate the smoke object. Higher resolutions allow for finer detail in both the appearance and in the resulting motion. However, doubling the divisions requires eight times the memory.
Since the substepping should be proportional to the voxel size, doubling the divisions may require double the substepping, resulting in sixteen times the simulation time.
The explicit size of the voxels. The number of voxels will be computed by fitting an integer number of voxels of this size into the given bounds.
The size of the voxel grid. The size of each voxel will be this divided by the divisions.
The position in world space of the center of the voxel grid.
The overall box will be divided into the specified number of small boxes, or voxels.
However, the question remains where on these voxels the field’s matrixs should be stored.
The matrix will be stored at the center of each voxel. The total number of samples thus matches the number of boxes.
The diagonal elements of the matrix are stored in the center of the cell, but the off diagonal will be stored on the corresponding edges.
The value will be stored on the corners of each voxel.
The number of samples will be one higher in each dimension than the division count to contain all the boundary values.
The behavior when the field is sampled outside of its defined box.
The initial value will be returned.
The field will wrap, returning values from the opposite side of the field.
The value at the edge of the field closest to the sample will be returned.
When first initialized, the matrix field will be set uniformly to this value.
The absolute tolerance to use for lossy compression of the matrix field.
This can reduce memory usage by detecting constant areas or using a lower bit-depth representation. A value of 0 only allows lossless compression.
Use 16bit Float
The tiles will be stored using a 16 bit float rather than 32 bit float. This uses half the memory, but at the cost of reduced precision and increased computation.
All computations are still done in 32 bit floats.
Which slice to use. Should be a number between 0 and the number of slices - 1.
Number of pieces to cut the volume into along each axis. The total number of pieces, or slices, created will be the product of these numbers. Ie, 2, 3, 4 will create 24 slices.
Overlap Voxels Negative, Positive
Adds a padding on the lower/upper side of the slices. The slices start by dividing space evenly, but then this overlap will cause them to overlap with their neighbors. The field exchange nodes use this overlap to determine what is communicated.
Position Data Path
The optional relative path for Position data. This will be used to
transform the fluid box, allowing for non-axis aligned fluid sims. A value
../Position will allow you to attach a Position DOP to your fluid object and thus reorient the fluid.
This optional input can be used to control which simulation objects are modified by this node. Any objects connected through this input and which match the Group parameter field will be modified.
If this input is not connected, this node can be used in conjunction with an Apply Data node, or can be used as an input to another data node.
All Other Inputs
If this node has more input connectors, other data nodes can be attached to act as modifiers for the data created by this node.
The specific types of subdata that are meaningful vary from node to node. Click an input connector to see a list of available data nodes that can be meaningfully attached.
The operation of this output depends on what inputs are connected to this node. If an object stream is input to this node, the output is also an object stream containing the same objects as the input (but with the data from this node attached).
If no object stream is connected to this node, the output is a data output. This data output can be connected to an Apply Data DOP, or connected directly to a data input of another data node, to attach the data from this node to an object or another piece of data.
This DOP node defines a local variable for each channel and parameter on the Data Options page, with the same name as the channel. So for example, the node may have channels for Position (positionx, positiony, positionz) and a parameter for an object name (objectname).
Then there will also be local variables with the names positionx, positiony, positionz, and objectname. These variables will evaluate to the previous value for that parameter.
This previous value is always stored as part of the data attached to the object being processed. This is essentially a shortcut for a dopfield expression like:
dopfield($DOPNET, $OBJID, dataName, "Options", 0, channelname)
If the data does not already exist, then a value of zero or an empty string will be returned.
This value is the simulation time (see variable ST) at which the current data was created. This value may not be the same as the current simulation time if this node is modifying existing data, rather than creating new data.
This value is the simulation frame (see variable SF) at which the current data was created. This value may not be the same as the current simulation frame if this node is modifying existing data, rather than creating new data.
In this case, this value is set to the name of the relationship the data to which the data is being attached.
In this case, this value is set to a string that is a space separated list of the object identifiers for all the Affected Objects of the relationship to which the data is being attached.
In this case, this value is set to a string that is a space separated list of the names of all the Affected Objects of the relationship to which the data is being attached.
In this case, this value is set to a string that is a space separated list of the object identifiers for all the Affector Objects of the relationship to which the data is being attached.
In this case, this value is set to a string that is a space separated list of the names of all the Affector Objects of the relationship to which the data is being attached.
This value is the simulation time for which the node is being evaluated.
This value may not be equal to the current Houdini time represented by the variable T, depending on the settings of the DOP Network Offset Time and Time Scale parameters.
This value is guaranteed to have a value of zero at the
start of a simulation, so when testing for the first timestep of a
simulation, it is best to use a test like
$ST == 0 rather than
$T == 0 or
$FF == 1.
This value is the simulation frame (or more accurately, the simulation time step number) for which the node is being evaluated.
This value may not be equal to the current Houdini frame number represented by the variable F, depending on the settings of the DOP Network parameters. Instead, this value is equal to the simulation time (ST) divided by the simulation timestep size (TIMESTEP).
This value is the size of a simulation timestep. This value is useful to scale values that are expressed in units per second, but are applied on each timestep.
This value is the inverse of the TIMESTEP value. It is the number of timesteps per second of simulation time.
This is the number of objects in the simulation. For nodes that create objects such as the Empty Object node, this value will increase for each object that is evaluated.
A good way to guarantee unique object names is to use an expression
This value is the number of objects that will be evaluated by the current node during this timestep. This value will often be different from SNOBJ, as many nodes do not process all the objects in a simulation.
This value may return 0 if the node does not process each object sequentially (such as the Group DOP).
This value is the index of the specific object being processed by the node. This value will always run from zero to NOBJ-1 in a given timestep. This value does not identify the current object within the simulation like OBJID or OBJNAME, just the object’s position in the current order of processing.
This value is useful for generating a random number for each object, or simply splitting the objects into two or more groups to be processed in different ways. This value will be -1 if the node does not process objects sequentially (such as the Group DOP).
This is the unique object identifier for the object being processed. Every object is assigned an integer value that is unique among all objects in the simulation for all time. Even if an object is deleted, its identifier is never reused.
The object identifier can always be used to uniquely identify a given object. This makes this variable very useful in situations where each object needs to be treated differently. It can be used to produce a unique random number for each object, for example.
This value is also the best way to look up information on an object using the dopfield expression function. This value will be -1 if the node does not process objects sequentially (such as the Group DOP).
This string contains a space separated list of the unique object identifiers for every object being processed by the current node.
This string contains a space separated list of the names of every object being processed by the current node.
This value is the simulation time (see variable ST) at which the current object was created.
Therefore, to check if an object was created
on the current timestep, the expression
$ST == $OBJCT should
always be used. This value will be zero if the node does not process
objects sequentially (such as the Group DOP).
This value is the simulation frame (see variable SF) at which the current object was created.
This value is equivalent to using the dopsttoframe expression on the OBJCT variable. This value will be zero if the node does not process objects sequentially (such as the Group DOP).
This is a string value containing the name of the object being processed.
Object names are not guaranteed to be unique within a simulation. However, if you name your objects carefully so that they are unique, the object name can be a much easier way to identify an object than the unique object identifier, OBJID.
The object name can
also be used to treat a number of similar objects (with the same
name) as a virtual group. If there are 20 objects named "myobject",
strcmp($OBJNAME, "myobject") == 0 in the activation field
of a DOP will cause that DOP to operate only on those 20 objects. This
value will be the empty string if the node does not process objects
sequentially (such as the Group DOP).
This is a string value containing the full path of the current DOP Network. This value is most useful in DOP subnet digital assets where you want to know the path to the DOP Network that contains the node.
Most dynamics nodes have local variables with the same names as the node’s parameters. For example, in a Position node, you could write the expression:
$tx + 0.1
…to make the object move 0.1 units along the X axis at each timestep.