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The Blend CHOP combines two or more chops in input 2, 3 and so on, by using a set of blending channels in input 1. The blending channels cause different strengths of the chops to contribute to the output of the chop. It works like the Blend SOP.
Input 1 acts as the control input, which contains the blend weight channels for the rest of the inputs. There is one channel in it for each of the blended chops coming in on input 2, 3 and so on.
The first channel in input 1 is input 2's blend weight, the second channel in input 1 is the input 3's blend weight, and so on. There should be as many blend channels in input 1 as there are inputs, excluding input 1.
The interval of the output of the chop is the interval of input 1 (the blend channels).
If input 2 onwards are just poses, it’s acceptable, as the chop blends between poses by using extend conditions.
Advantages of Difference Method
Each blend input affects the result without reducing the effect of the others. You can exaggerate beyond each of the inputs by setting their Blend > 1, and you can also use negative values. When all blend channels are 0, you get smooth transitions as any of the blend channels ease out of zero.
The blend method.
Each blend source contributes to the result according to its blend weight. If the blend weights do not add up to one, they are scaled so that they do.
The input 2 is always the "base", which is the default behavior of the Blend CHOP. There are blend channels for all the other inputs, and when they are all zero, you get base. If any one blend channel is 1 and the others are zero, then your output is the same as the input that corresponds to that blend channel.
Omit First Weight Channel
The weight channel for the base input has no effect when using the Differencing method. So, the channel is omitted if this option is on.
Rotation channels typically don’t blend well when treated as Euler angles, and straight linear blending can result in flips and odd rotations. Instead, shortest path blending can be used to properly blend orientations represented by Euler rotation angles.
Rotation channels are blended like any other channel.
Shortest Path (Linear)
Two inputs are blended using shortest path rotation blending. If more than two blend inputs are connected, use Fast Linear.
Shortest Path (Fast Linear)
Multiple inputs are blended together using shortest path rotation blending.
Use Rotation Hint
When rotation blending is set to Shortest Path, a rotation hint can be specified when recreating the Euler angles. This hint will modify the starting values of the Euler angles so that they are close to the rotation hint. When off, the hint is ignored and the Euler angles will not be altered from their computed values.
This can be useful if many CHOPs in the same network are working with rotations, then all these CHOPs can have their rotation hints set to the same values to keep the Euler angles similar.
Some of these parameters may not be available on all CHOP nodes.
To determine which channels get affected, some CHOPs have a scope string. Patterns can be used in the scope, for example
* (match all), and
? (match single character).
The following are examples of possible channel name matching options:
Matches a single channel name.
chan3 tx ty tz
Matches four channel names, separated by spaces.
Matches each channel that starts with
Matches each channel that has
foot in it.
? matches a single character.
t? matches two-character channels starting with t.
Matches number ranges giving
[xyz]matches three characters, giving channels
Sample Rate Match
The Sample Rate Match Options handle cases where multiple input CHOPs’ sample rates are different.
Resample At First Input’s Rate
Use rate of first input to resample others.
Resample At Maximum Rate
Resample to highest sample rate.
Resample At Minimum Rate
Resample to the lowest sample rate.
Error if Rates Differ
Does not accept conflicting sample rates.
The units for which time parameters are specified.
For example, you can specify the amount of time a lag should last for in seconds (default), frames (at the Houdini FPS), or samples (in the CHOP’s sample rate).
When you change the Units parameter, it does not convert the existing parameters to the new units.
Time Slicing is a feature which boosts cooking performance and reduces memory usage. Traditionally, CHOPs calculate the channel over its entire frame range. If the channel does need to be evaluated every frame, then cooking the entire range of the channel is unnecessary. It is more efficient to calculate only the fraction of the channel that is needed. This fraction is known as a Time Slice.
Causes the memory consumed by a CHOP to be released after it is cooked and the data passed to the next CHOP.
The Export prefix is prepended to CHOP channel names to determine where to export to.
For example, if the CHOP channel was named
geo1:tx, and the prefix was
/obj, the channel would be exported to
You can leave the Export Prefix blank, but then your CHOP track names need to be absolute paths, such as
Every CHOP has this option. Each CHOP gets a default color assigned for display in the Graph port, but you can override the color in the Common page under Graph Color. There are 36 RGB color combinations in the Palette.
Graph Color Step
When the graph displays the animation curves and a CHOP has two or more channels, this defines the difference in color from one channel to the next, giving a rainbow spectrum of colors.
This example demonstrates how the Blend CHOP combines several channels together using an interpolated blend weight control.
The following examples include this node.