Ramp Parameter VOP

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Ramp Parameter VOP

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The Ramp Parameter VOP creates a ramp parameter that is usually promoted to the SOP level whenever you're working with point, primitive, attribute, vertex, or volume vops.

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    In practice, the reason why you might want to use a ramp parameter is to get really nice control over the distribution of middle values for an attribute.  As an example, let's say that we have an attribute called "foo" which has a min value of 0, a max of 1 along with a bunch of values that are in-between.  With a ramp, we can have better control over those middle values by placing markers between the min/max and adjusting them.  Many users also prefer a ramp because it provides a visual way of adjusting values.

    Keep in mind that the ramp parameter goes from 0 (the left-hand side of the ramp) to 1 (the right-hand side of the ramp).  If values go less than 0 or more than 1, then they will clamp to the left or right side of the ramp.  In other words, a value of -0.23 would turn into 0.  A value of 2.3 would clamp to 1.  So it's usually worth normalizing your values (that is, converting them to a range of 0-1) before feeding that data into a ramp parameter.  To procedurally figure out the min/max, go back to sops, use an attribute promote, and then promote the min and max to the detail context as its own attribute.  Back in VOPs, you can then use a bind to bring in that min/max value and then feed those values into the fit vop's srcmin and srcmax inputs.

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Main Parameters:


--  In VOPs, you have the internal name and the label.  The internal name is the name that gets used for calculating stuff and its what everything else references when it tries to find this parameter.  The label is what the user sees in SOPs.  This "Name" is basically what the parameter should be internally understood as.


--  This adds text before the name.  To see what this does, look at the output of the node and notice how the Prefix happens before the name when determining the internal name of the parameter.  In practice, this might be useful for organizational purposes.


--  Same thing as "prefix" except that the text gets added to the end of the name.


--  This label is what the user sees in SOPs when the parameter gets promoted.

Ramp Type:

--  There are two kinds of ramps that you can make.  By default, you have a RGB ramp, and that's ideal for adjusting vector data (such as color).  However, even if the data isn't color, it gives you access to all three vector components in one ramp.  R = the first vector component, G = the second, and B = the third number of the vector. 

--  The other type of ramp is a Spline Ramp (float).  This is ideal for adjusting float data.

Color Type:

--  Only available when the ramp type is set to RGB ramp.  This applies a color-correction to the data that's being used by the ramp.  In most cases, the default of RGB ought to be fine.

Default Interpolation:

--  The "interpolation" of the ramp is saying how one value ought to blend into another.  There's different ways of calculating this, and changing these settings will change how ramp value blend into each other.  To see what this does visually, try going to sops, placing a marker somewhere in the middle of the ramp, change the interpolation method, and notice how the values in-between the markers change.  

Ramp Default:

--  This sets the default value for the ramp that will be promoted to SOPs.  Remember that you may need to turn on "Use This Node to Set Parameter Attributes" to see it affect the correct default values in SOPs.

Use This Node to Set Parameter Attributes:

-- When creating multiple bind nodes which reference the same attribute, only one is allowed to set the attribute inside of VOPs. The reason why this is the case is because it's sort of like defining @foo multiple times. In other words, only one bind will be responsible for actually bringing in attribute "foo." If another bind node tries to bring in "foo," then it will basically refer to the first bind that was used to bring in foo rather than going into sops and importing "foo" again.  

Show UI Controls By Default:

--  Whenever you add a marker to the ramp in sops, it will usually give you UI controls for that marker.  You can turn that off, however, by turning this checkbox off.

Disable When, Hide When, Callback Script:

--  For more information on how to use these sections, please visit the HDA video in Houdini For the New Artist II


-- The contents of the text field appear in the help browser when the user clicks the help button for a node of this operator type in the parameter editor.
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