Particles
Objective: To become familiar with a simple particle example.
Time: 10-15 minutes
Experience: Beginner
New Tools: Particles, parenting
To add flames to the rocket thruster, you will use the particle
SOP. For both Houdini and Houdini Select, you can use Particle Systems
that are useful for effects such as: Fire, Smoke, Gases, and Flocking
simulations. With Houdini, you can use Particle Operations (POPs)
for even more complex results.
Particle Thruster
Type T in the Viewport, and select: Generators > Geometry. Click
with your \ to accept it. You see a generic 3D cube appear in the
Viewport. Find the new geo1 object tile, and rename it to: ‘Flames.’
In the network pane, connect the Rocket to the Flames. This parents
the flames to the rocket. Playback the animation to preview the
new relationship. Go back to frame 1 when you are finished.
Particle Surface Emitter
Click on the moonscape tile with your \ and select Toggle Display
to hide it.
Click with \ on the flames tile, and select Edit SOPS to enter the
Flames object. Once inside, delete file1, and the generic box disappears.
Change your view to a wireframe view then click on the See one/all
objects button to see the rocket and flame at the same time.
You need some geometry to act as a source for particles. Press the
T key and select Generators > Sphere. Set the sphere parameters
to:
Primitive Type to NURBS
Radius to 0.25, 0.25, 0.25 (use ] on the Radius parameter to do
three at a time)
Home the view (W h) then make it an ortho view (W o). Zoom in closely
(W ]) to the exhaust area of the rocket in order to more precisely
position the sphere.
To make things easier, enable Snapping from the Snap Menu.
Press the T key and select Filters > Transform, then press \
to accept the selection, Press t to call up the Translate Handle.,
and then drag the pivot so that it snaps to the centre of the bottom
cap.
You don’t need the whole sphere, and you don’t want
our particle source to intersect the blast shield either. Press
T and select Filters > Carve then press the \ to accept the selection.
Set the Parameters to:
First U to Off;
First V to On.
By dragging on the First V ring itself, or using the slider in parameters,
tweak the First V Ring down so it no longer intersects the bottom
cap (about 0.6).
Now that you have a satisfactory emitter surface, you will also
need a surface for which the particles will Collide (i.e. the ‘moonscape’).
You will bring it in from the moonscape Object.
Press T and select Generators > Object Merge. In the parameter
pane for object_merge1, the Source 1 parameter should be set to
the moonscape object. Also, set the Transform Object parameter at
the bottom to: This Object. You should see the ground plane light
up yellow to indicate that it is selected, and in place.
Adding the Particles
Press T and select Filters > Particle. The blue help text at
the top of the Houdini window says, ‘Select the points to
animate, and right-click to complete’, but right now, you
have the ground plane selected instead of the sphere. Click with
[ on the wireframe of the emitter sphere to select it; and then
click with \ accept these as the points to animate.
Then the blue text says, ‘select the full collision geometry,
and right-click to complete’ – so click with [ on the
ground plane (it turns white), click it again with [ so it becomes
yellow, and finally – click with \ to finish. The emitter
disappears, and you get a small number of particles.
Click the Play button in the Playbar – you see a couple particles
appear, but they do not break away from the emitting surface.
You need to specify the strength and direction of the force which
moves the particles. While the animation is still playing, go into
the Forces page of the particle1’s parameters, and use ] in
the External Force - Y field to give us some thrust – a value
of about -3.0 works well.
Turn off Ortho (o), Home the View (W h), and Zoom the View (W ])
as necessary. Playback the results to see the particles in motion.
Conclusion
You have now explored Houdini’s workspace and worked with
some of its tools and operators. This workflow gives you an understanding
of how the interface lets you build up procedural models interactively
and then animate them at both the object and operator levels. These
basic concepts will play a role in all of your work with Houdini
as you explore all the tools available for animating in 3D.
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