Pyro Burst Source

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Pyro Burst Source

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The pyro burst source sop can be used to generate particles which describe the shape of something that you'd like to make within your pyro simulation.  These particles also have attributes, and these attribute values can eventually be converted into voxel values by using the Volume Rasterize Attribute SOP.  The idea here is that you setup the shape you want with particles, convert it into VDB volumes, and then feed that into the pyro solver to get the pyro effect that you're after.
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Summary:

    In practice, the pyro burst sop can be used in a wide variety of ways.  This SOP will give you particles that are shaped as spikes.  So, for pyro effects that take on the shape of spikes, this node can be an easy way of getting those shapes.  It also features a nice collection of animation/retiming options, the ability to randomize various parameters when determining the behavior and/or shape of the spikes, the option to add noise to the attribute values on the particles, and controls for changing the particle's attribute values over time and/or along the length of the spear shapes.

    The input of this node expects points.  If you feed points into this input, then it will use those point locations for determining where the pyro burst happens.  Attributes assigned to any points can also be used for controlling various parameters on this node.

    You'll notice that this node has a dropdown menu and a dice icon next to most parameters.  The dropdown gives you three options:  Set Uniform, Set Varying, Use Attribute, and Scale Attribute.  These options are asking you how you'd like to control the value for that parameter. 

    "Set Uniform" means that you want to just use the slider as it is by default on the node.

    "Set Varying" will add two additional settings - variation and seed.  The variation will add and/or subtract randomly from the base value by this amount.  The seed offers a different version of the values. 

    "Use Attribute" will allow the pyro burst shape to read an incoming attribute when determining the value of something.  The attribute it reads needs to be a point attribute, it must belong to points that you plug into this node, and the naming needs to line up with the internal name used for the parameter.  An easy way to see what internal name the parameter needs is by hovering over the text of the parameter name.  As an example, if you hover your cursor over "Initial Size," it tells you that the internal name is "size" in the section that says, "Parameter: size"

    "Scale Attribute" works just like the "Use Attribute" except that it also gives you the option to multiply the incoming attribute values by a certain amount.  

    Last but not least, the dice icon will generate a node called "Attribute Adjust ____"  which is basically like a whole node designed for randomizing attribute values.  If the above dropdown parameters aren't enough to give you the randomization you're looking for, then the options found here ought to work instead.

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General Parameters:

Group:

--  When reading points along the input, you can specify which points you'd like to read from by specifying their group here.  For more on groups, be sure to check out the Group SOP.

Guide Display:

-- This gives you the option to change how you'd like to preview your burst shape.  By default, it will show you particles.  But you can also specify "proxy shape."  This can be helpful when determining the shape of the silhouette of the particle burst. 

Additional Guides:


--  If you're also using a "pryo tail path" node, then this will overlay the direction of those paths.

Quick Setups & Initialize:

--  These parameters are useful for times when you want a preset or want to change the settings for every parameter along the node.  The Node Bible will not cover what each preset does, so it's best to explore for yourself what these do by clicking on them and examining the changes in various settings.

Randomization By:

--  When the pyro burst sources goes to create the spikes based on incoming points, it determines what variation it uses by the point number.  If the point number changes on the incoming points, the spikes will change their shape.  If you don't want to rely on point number, you can specify a seed attribute instead.  That seed attribute can then be used to determine the shape of the spikes.  In practice, if you notice your spikes changing shape over time, it's probably because the point number is changing on the incoming points.  To get around that, use an attribute instead so that the shapes remain consistent.  

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Burst Shape:

Initial Size:

--  This determines the overall scale of the burst shape.

Direction:

-- Multiple spears are generated going on this direction.  As an example, a value of 0,1,0 will have the spikes shooting in the Y direction.  If you want the burst shape to face in the direction of a terrain's normal, you can specify that normal's value here and that will change the direction of the spikey burst.

Spread Angle:


--  The spikes will randomly spread outwards from the direction (as described above) by this many degrees.  180 means that you have spikes shooting in all directions.

Roundness:

--  The roundness will change the overall shape of the silhouette.  A high roundness makes a very spherical shape with the spears, and less roundness creates more defined shapes in certain directions.

Shape Offset:

--  The Shape Offset can be used as a seed to the pyro burst shape.  If you don't like the shape that you're getting, try changing the offset and selecting a version that you like better instead.

Number of Trailings:

--  How many spikes to generate

Trailing Separation:

-- This determines how many points are used to represent each spike.  Lower separation means more particles.  Higher separation means less particles.

Trailing Length:


--  The trailing length gives you control over where particles are cut off.  A lower trailing length will give you short, stubby looking spikes.  A longer length reaches back to the position where where the spikes originally came from.

Trailing Thickness:

--  This controls how chunky and/or skinny the spikes are. 

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Burst Animation:

Start Frame:

--  This determines when the burst will start its animation.  Note that the pyro burst source will spawn a burst on frame 1 at the origin if there are no incoming points detected at frame 1.  This is important to recognize if, lets say, you're trying to do a missile simulation which does not feature any sourced points on frame 1.

Frame Duration:

-- This determines how long each burst animation will last.

Outward Expansion:


--  This will scale up the burst uniformly as the animation progresses.

Directional Expansion:

--  This will scale up the burst based on its shape.  Smaller spikes which are closer to the sourced position will scale up more slowly than spikes which are originally larger and further outwards.

Expansion Over Duration Ramp:

--  This controls how much the burst will scale up or down over the duration specified above in the frame duration parameter.


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Burst Components:

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The Burst Components section is used to control the attribute values on points generated by the pyro burst source.
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Default Value:

--  The default value is the starting value of each attribute.  The default value of 1 is good for most situations.

Scale Over Duration:

-- This allows you to scale down the attribute value over the duration of the burst.  If you check this on, then a ramp will appear, and that ramp describes how the attribute value changes over time.  

Scale Along Trailing:


--  This gives you the option to scale down the attribute value along the length of each spike.

Number of Sources:

--  These tabs represent different attributes that you can create.  As you add attributes, more particles will be spawned which contain those attribute values.  The various attributes are also color-coded.

Attribute:

--  This selects which attribute you'd like to create.  As of writing, there is no option for creating "flame" or "fuel."  If you ever want to change the name of something after the pyro burst source, it's easy to do with a primitive wrangle and saying @name = "foo"; for those particular particles.  There is a dice icon next to this field, however, I've found that it's better to add variety by using the noise parameters below or by using an attribute randomize after the pyro burst source sop.  Adding variety here only makes sense if you want to have multiple bursts which feature different starting values.  This can also be achieved with the "Source Value Scale" parameter that's described below.

Prefix Attribute Name:

--  This parameter is only useful if you're also using the Pyro Trail Path SOP.  It creates a prefix called "burst_" so that you can tell separate density values made by the pyro burst source from the density values made by the pyro trail path sop.

Source Value Scale:

--  This scales the overall values of the burst.  Clicking the +/- button will allow to to randomly add or subtract by a certain amount for each burst.

Enable Noise:


--  Reveals parameters for adjusting noise.  The noise travels along with the animation of the spikes.

Start Frame:

--  This burst override will offset the starting frame of this group of particles.  In practice, this is useful if you want something to come after or before other sources.  As an example, if you want density to show up first, and then burn to show up 3 frames after, you can make those adjustments here.

Expansion Scale:

--  Makes this group of particles expand further than the default behavior set in the burst animation tab.

Seed Offset:

--  Changes the seed of the burst shape for this group of particles.  In practice, this is very useful for making the source feel for chaotic at each frame.