Create a new scene in Maya. Switch to the nDynamics menu set.

Choose nParticles

Choose Create nParticles

Press the Enter key on the numeric keypad to create the particles.

You'll see several circles on the grid. The ball-type nParticle style automatically creates blobby surface particles. Blobby surfaces are spheres rendered using Maya Software or mental ray. Blobby surfaces use standard Maya shaders when rendered and can be blended together to form a gooey surface.

Figure 13.1. Use the nParticle menu to specify the nParticle style.

Set the length of the timeline to 600. Rewind and play the animation. The particles will fall in space.

Open the Attribute Editor for the nParticle1 object, and switch to the nucleus1 tab. The settings on this tab control the Nucleus solver, which sets the overall dynamic attributes of the connected nDynamic systems (see Figure 13.2).

By default a Nucleus solver has Gravity enabled. Enable Use Plane in the Ground Plane settings (Figure 13.3). This creates an invisible floor that the nParticles can rest on. Set the Plane Origin's Translate Y to −1.

Figure 13.2. The settings on the nucleus1 tab define the behavior of the environment for all connected nDynamic nodes.

Figure 13.3. The ground plane creates an invisible floor that keeps the nParticles from falling.

The Nucleus solver also has wind settings. Set Wind Speed to 3 and Wind Noise to 4. By default Wind Direction is set to 1, 0, 0 (Figure 13.4). The fields correspond to the X, Y, and Z axes, so this means that the nParticles will be blown along the positive X axis. Rewind and play the animation. Now the nParticles are moving along with the wind, and a small amount of turbulence is applied.

Figure 13.4. The settings for Air Density, Wind Speed, Wind Direction, and Wind Noise are found under the Nucleus solver's attributes.

Continue with the scene from the previous section. Add an emitter to the scene by choosing nParticles

Open the Attribute Editor for the emitter1 object, and set Rate to 10. Set Emitter Type to Omni.

Rewind and play the scene. The omni emitter spawns particles from a point at the center of the grid. Note that after the particles are born, they collide with the ground plane and are pushed by the nucleus wind in the same direction as the other particles (see Figure 13.5).

The new nParticles are connected to the same Nucleus solver. If you open the Attribute Editor for the nParticle2 object, you'll see the tabs for nucleus1 and nParticle2, as well as the tab for nParticle1. If you change the settings on the nucleus1 tab, both nParticle1 and nParticle2 are affected.

Figure 13.5. A second nParticle system is spawned from an emitter. These nParticles also collide with the ground plane and are pushed by the wind.

Select nParticle2 and choose nSolver

Open the Outliner and, in the Outliner's Display menu, turn off DAG Objects Only. This allows you to see all the nodes in the scene. If you scroll down, you'll see nucleus1 and nucleus2 nodes (see Figure 13.6).

Select nParticle2 and choose nSolver

Figure 13.6. The nucleus nodes are visible in the Outliner.

Select emitter1 and set Emitter Type to Volume. In the emitter's Attribute Editor, set Volume Shape in the Volume Emitter Attributes section to Sphere. Use the Move tool to position the emitter above the ground plane. The emitter is now a volume, which you can scale up in size using the Scale tool (hot key = r). nParticles are born from random locations within the sphere (see Figure 13.7).

The directional emitter type is similar to the omni and volume emitters in that it shoots nParticles into a scene. The directional emitter emits the nParticles in a straight line. The range of the directional emitter can be altered using the Spread slider, causing it to behave more like a sprinkler or fountain.

Figure 13.7. Volume emitters spawn nParticles from random locations within the volume.

Open the Attribute Editor to the nParticleShape1 tab. This is where you'll find the attributes that control particle behavior, and there are a lot of them. As an experiment, expand the Force Field Generation rollout and set Point Force Field to Worldspace.

Rewind and play the animation. As the emitter spawns particles in the scene, a few nParticles from nParticle2 are attracted to nParticle1. NParticle1 is emitting a force field that attracts individual nParticles from nParticle2 like a magnet. You can also make the nParticles attract themselves by increasing the Self Attract slider (see Figure 13.8).

Create a new Maya scene. Create a polygon plane (Create

Scale the plane 25 units in X and Z.

Switch to the nDynamics menu set. Set the nParticle style to Balls (nParticles

Choose nParticles

Figure 13.9. The options for creating a surface emitter

Set the timeline to 600.

Open the Attribute Editor to the nucleus1 tab, and set Gravity to 0.

Rewind and play the animation. Particles appear randomly on the surface.

Open the Attribute Editor to the nParticle Shape tab. Expand the Particle Size rollout. Set Radius to 1.

Click on the right side of the Radius Scale ramp to add a point. Adjust the position of the point on the left side of the ramp edit curve for Radius Scale so that it's at 0 on the left side and moves up to 1 on the right side (see Figure 13.10).

Figure 13.10. The Radius Scale ramp curve adjusts the radius of the nParticles.

Rewind and play the animation. The particles now scale up as they are born (by default Radius Scale Input is set to Age). Notice that adjacent particles push each other as they grow. The ball-style particle has Self Collision on by default, so the particles will bump into each other (see Figure 13.11).

Set Radius Scale Randomize to 0.5. The balls each have a random size. By increasing this slider, you increase the random range for the maximum radius size of each nParticle.

Set Input Max to 3. This sets the maximum range along the X axis of the Radius Scale ramp. Since Radius Scale Input is set to Time, this means each nParticle takes 3 seconds to achieve its maximum radius, so they slowly grow in size.

Figure 13.11. The balls scale up as they are born and push each other as they grow.

Open the forge_v01.ma scene from the chapter13scenes folder on the DVD. You'll see a very simple scene consisting of a tub on a stand. A bucket is in front of the tub. The tub will be used to pour molten metal into the bucket.

Set the nParticle style to Water by choosing nParticles

Select the tub object and choose Create nParticles

Figure 13.12. Select the tub object is selected, and it will be filled with nParticles.

Set the display to Wireframe. You'll see a few particles stuck in the rim of the tub. If you play the scene, the particles fall through space.

There are two problems. The first problem is that the object has been built with a thick wall, so Maya is trying to fill the inside of the surface with particles rather than the well in the tub. The second problem is that the tub is not set as a collision surface (see Figure 13.13).

Select the nParticle1 object in the Outliner and delete it. Note that this does not delete the nucleus1 solver created with the particle, and that's okay; the next nParticle object you create will be automatically connected to this same solver.

There are a couple solutions to this problem. When you create the nParticle object, you can choose Double Walled in the Fill Object options, which in many cases solves the problem for objects that have a simple shape, such as a glass. For more convoluted shapes the nParticles may try to fill different parts of the object. For instance, in the case of the tub, as long as the Resolution setting in the options is at 10 or below, the tub will fill with nParticles just fine (increasing Resolution increases the number of nParticles that will fill the volume). However, if you create a higher-resolution nParticle, you'll find that nParticles are placed in the well of the tub and on the handles where the tub is held by the frame.

Figure 13.13. The nParticles lodge within the thick walls of the tub.

Another solution is to split the polygons that make up the object so that only the parts of the tub that actually collide with the nParticles are used to calculate how the nParticles fill the object.

Switch to shaded view. Select the tub object, and move the view so you can see the bottom of its interior.

Chose the Paint Selection tool, right-click on the tub, and choose Face to switch to face selection. Use the Paint Selection tool to select the faces at the very bottom of the tub (see Figure 13.14).

Figure 13.14. Select the faces at the bottom of the tub with the Paint Selection tool.

Figure 13.15. Expand the selection to include all the faces up to the rim of the tub.

Hold the Shift key and press the > key on the keyboard to expand the selection. Keep pressing the > key until all the interior polygons are selected up to the edge of the tub's rim (see Figure 13.5).

Switch to wireframe mode, and make sure none of the polygons on the outside of the tub have been selected by accident. Hold the Ctrl key and select any unwanted polygons to deselect them.

Switch to the Polygon menu set and choose Mesh

Select the polysurface1 and polysurface2 nodes, and choose Edit

Name the interior mesh insideTub and the exterior mesh outsideTub.

Switch to the nDynamics menu set. Select the insideTub mesh, and choose nParticles

In the options, set Solver to nucleus1, and set Resolution to 15.

The Fill Bounds settings determine the minimum and maximum boundaries within the volume that will be filled. In other words, if you want to fill a glass from the middle of the glass to the top, leaving the bottom half of the glass empty, set the minimum in Y to 0.5 and the maximum to 1 (the nParticles would still drop to the bottom of the glass if Gravity were enabled, but for a split second you would confuse both optimists and pessimists).

Figure 13.16. Split the tub into two separate mesh objects using the Extract command.

Leave all the Fill Bounds settings at the default. Turn off Double Walled and Close Packing. Click Particle Fill to apply it. After a couple seconds you'll see the tub filled with little blue spheres (see Figure 13.17).

Rewind and play the animation. The spheres drop through the bottom of the tub. To make them stay within the tub, you'll need to create a collision surface.

Figure 13.17. The inside of the tub is filled with nParticles.

Rewind the animation and select the insideTub mesh. Choose nMesh

Play the animation. You'll see the nParticles drop down and collide with the bottom of the tub. They'll slosh around for awhile and eventually settle.

When creating a collision between an nParticle and a passive collision surface, there are two sets of controls you can tune to adjust the way the collision happens. Collision settings on the nParticle shape control how the nParticle reacts when colliding with surfaces, and collision settings on the passive object control how objects react when they collide with it.

For example, if you dumped a bunch of basketballs and Ping-Pong balls on a granite table and a sofa, you would see that the table and the sofa have their own collision behavior based on their physical properties, and the Ping-Pong balls and basketballs also have their own collision behavior based on their physical properties. When a collision event occurs between a Ping-Pong ball and the sofa, the physical properties of both objects are factored together to determine the behavior of the Ping-Pong ball at the moment of collision. Likewise a basketball has its own physical properties that are factored in with the same sofa properties when a collision occurs between the sofa and a basketball.

The nDynamics systems have a variety of ways to calculate collisions as well as ways to visualize and control the collisions between elements in the system.

Select the nRigid node in the Outliner, and switch to the nRigidShape1 tab in the Attribute Editor. Expand the Collisions rollout.

The Collide option turns collisions on or off for the surface. It's sometimes useful to temporarily disable collisions when working on animating objects in a scene using nDynamics. Likewise the Enable option above the Collisions rollout disables all nDynamics for the surface when it is unchecked.

Set the Solver Display option to Collision Thickness. Turning this option on creates an interactive display so you can see how the collisions for this surface are calculated (see Figure 13.18).

Switch to wireframe view (hot key = 4). Move the Thickness slider back and forth, and the envelope grows and shrinks, indicating how thick the surface will seem when the dynamics are calculated.

Figure 13.18. You can display the collision surface thickness using the controls in the nRigid body shape node.

The thickness will not change its appearance when rendered, only how the nParticles will collide with the object. A very high Thickness value makes it seem as though there is an invisible force field around the object.

Switch back to smooth shaded view (hot key = 5). Collision Flag is set to Face by default, meaning that collisions are calculated based on the faces of the collision object. This is the most accurate but slowest way to calculate collisions.

Set Collision Flag to Vertex. Rewind and play the animation. You'll see the thickness envelope drawn around each vertex of the collision surface.

The nParticles fall through the bottom of the surface, and some may collide with the envelopes around the vertices on their way through the bottom. The calculation of the dynamics is faster, though. This setting may work well for dense meshes, and it will calculate much faster than the Face method.

Set Collision Flag to Edge; rewind and play the animation. The envelope is now drawn around each edge of the collision surface, creating a wireframe network (see Figure 13.19).

The calculation is much faster than when Collision Flag is set to Face, but the nParticles stay within the tub. You may notice some bumping as the nParticles collide with the wireframe. Many times this may not be noticeable at all, which makes the Edge method useful for calculating collisions.

Figure 13.19. When Collision Flag is set to Vertex, the nParticles collide with each vertex of the collision surface, allowing some to fall through the bottom. When the flag is set to Edge, the nParticles collide with the edges and the calculation speed improves.

The other settings in the Collisions section include:

Make sure that Collision Flag is set to Edge and that Bounce, Friction, and Stickiness are set to 0. Set Collision Thickness to 0.05.

Select the nParticle1 object, and open the Attribute Editor to the nParticleShape1 tab. Expand the Collisions rollout for the nParticle1 object. These control how the nParticles collide with collision objects in the scene.

Click on the Display Color swatch to open the Color Chooser, and pick a red color. Set Solver Display to Collision Thickness. Now the nParticles each have a red envelope around them. Changing the color of the display makes it easier to distinguish from the nRigid collision surface display.

Set Collide Width Scale to 0.25. The envelope becomes a dot inside each nParticle. The nParticles have not changed size, but if you play the animation, you'll see that they fall through the space between the edges of the collision surface (see Figure 13.20).

Figure 13.20. Reducing the Collide Width Scale value of the nParticles causes them to fall through the spaces between the edges of the nRigid object.

Scroll down to the Liquid Simulation tab and uncheck Enable Liquid Simulation. This makes it easier to see how the nParticles behave when self-collision is on. The Liquid Simulation settings alter the behavior of nParticles; this is covered later in the chapter.

Turn on Self Collide and set Solver Display to Self Collision Thickness.

Set Collide Width Scale to 1 and Self Collide Width Scale to 0.1. Turn on wireframe view (hot key = 4) and play the animation; watch it from a side view.

The nParticles have separate Collision Thickness settings for collision surfaces and self-collisions. Self Collide Width Scale is relative to Collide Width Scale. Increasing Collide Width Scale also increases Self Collide Width Scale (see Figure 13.21).

Figure 13.21. Reducing the Self Collide Width Scale value causes the nParticles to overlap as they collide.

Scroll up to the Particle Size settings and adjust the Radius; set it to 0.8. Both Collide Width Scale and Self Collide Width Scale are relative to the radius of the nParticles. Increasing the radius can cause the nParticles to pop out of the top of the tub.

Set Radius to 0.4 and Collide Width Scale to 1, and turn off Self Collide. Turn Enable Liquid Simulation back on.

The nParticles also have their own Bounce, Friction, and Stickiness settings. The Max Self Collide Iterations slider sets a limit on the number of calculated self-collisions per substep when Self Collide is on. This keeps the nParticles from locking up or the system from slowing down too much. If you have a lot of self-colliding nParticles in a simulation, lowering this value can increase performance.

The Collision Layer setting sets a priority for collision events. If two nDynamic objects using the same Nucleus solver are set to the same Collision Layer value, they will collide normally. If they have different layer settings, those with lower values will receive higher priority. In other words, they will be calculated first in a chain of collision events. Both nCloth and passive objects will collide with nParticles in the same or higher collision layers. So if the passive collision object has a Collision Layer setting of 10, an nParticle with a Collision Layer setting of 3 will pass right through it, but an nParticle with a Collision Layer value of 12 won't.

Save the scene as forge_v02.ma. To see a version of the scene so far, open forge_v02.ma from the chapter13scenes folder on the DVD.

Continue with the scene from the last section or open the forge_v02.ma scene from the chapter13scenes folder on the DVD. In this scene the tub has already been filled with particles, and collisions have been enabled.

Select nParticle1 in the Outliner and name it moltenMetal. Open its Attribute Editor to the moltenMetalShape tab. Expand the Liquid Simulation rollout (Figure 13.22).

Figure 13.22. Turning on Enable Liquid Simulation causes the nParticles to behave like water.

Liquid simulation has already been enabled because the nParticle style was set to Water when the nParticles were created. If you need to remove the liquid behavior from the nParticle, you can uncheck the Enable Liquid Simulation checkbox; for the moment, leave the box checked.

Switch to a side view and turn on wireframe mode. Play the animation and observe the behavior of the nParticles.

If you look at the Collisions settings for moltenMetal, you'll see that the Self Collide attribute is off, but the nParticles are clearly colliding with each other. This type of collision is part of the liquid behavior defined by the Incompressibility attribute (this is discussed a little later in the chapter).

Play the animation back several times; notice the behavior when:

Turn Liquid Behavior back on and turn Self Collide off. Open the Particle Size rollout, and set Radius to 0.25; play the animation. There seems to be much less fluid for the same number of particles when the radius size is lowered.

Play the animation for about 140 frames until all the nParticles settle. With the moltenMetal shape selected, choose nSolvers

Select moltenMetal. At the top of the Attribute Editor, uncheck Enable to temporarily disable the nParticle simulation so you can easily animate the tub.

Select tub1 in the Outliner and switch to the side view. Select the Move tool (hot key = w). Hold the d key on the keyboard, and move the pivot for tub1 so it's aligned with the center of the handles that hold it in the frame (see Figure 13.24).

Figure 13.23. Setting Initial State makes the nParticles start out from their settled position.

Figure 13.24. Align the pivot point for the tub group with the handles from the side view.

Set the timeline to frame 20. In the Channel Box, select the Rotate X channel for the tub1 group node, right-click, and set a keyframe.

Set the timeline to frame 100. Set the value of tub1's Rotate X channel to 85, and set another key. Move the timeline to frame 180, and set another keyframe.

Set the timeline to 250, set Rotate X to 0, and set a fourth key.

Select moltenMetal, and in the Attribute Editor, check the Enable checkbox. Rewind the animation and play it. The nParticles pour out of the tub like water (see Figure 13.25).

Figure 13.25. When you animate the tub, the nParticles pour out of it like water.

Switch to the perspective view. When you play the animation, the water goes through the bucket and the floor. Select the bucket and Choose nMesh

By default the liquid simulation settings approximate the behavior of water. To create a more molten metal–like quality, increase Viscosity to 10. Viscosity sets the liquid's resistance to flow. Sticky, gooey, or oily substances have a higher viscosity.

Set Liquid Radius Scale to 0.5. This sets the amount of overlap between nParticles when Liquid Simulation is enabled. Lower values create more overlap. By lowering this setting, the fluid looks more like a cohesive surface.

The other settings in the Liquid Simulation rollout can be used to alter the behavior of the liquid:

To complete the behavior of molten metal, set Rest Density back to 2, and set Incompressibility to 0.5. In the Collisions rollout, set Friction to 0.5 and Stickiness to 0.25. Expand the Dynamic Properties rollout and increase Mass to 6. Note that you may want to reset the initial state after changing the settings because the nParticles will now collapse into a smaller area (see Figure 13.26).

Save the scene as forge_v03.ma. To see a version of the scene to this point, open forge_v03.ma from the chapter13scenes folder.

Figure 13.26. Adjusting the settings under Liquid Simulation, Collisions, and Dynamic Properties makes the nParticles behave like a heavy, slowmoving liquid.

Continue with the scene from the previous section or open the forge_v03.ma scene from the chapter13scenes folder on the DVD.

Play the animation to about frame 160.

Select the moltenMetal object in the Outliner, and choose Modify

If you look at the particles, you'll see they are still there but a polygon mesh has been added to the scene. You can adjust the quality of this mesh in the Attribute Editor of the nParticle object used to generate the mesh.

Select the moltenMetal object in the Outliner, and open the Attribute Editor to the moltenMetalShape tab. Expand the Shading rollout and set Opacity to 0.

Figure 13.27. Converting an nParticle into a polygon creates a polygon mesh around the nParticle object.

Lowering the opacity of the nParticles makes it easier to see the mesh. If you hide the nParticles or disable nParticles in the View menu of the viewport, the polygon mesh will not animate with the nParticles. The simulation has to be visible, so the easiest workaround is to make the nParticles completely transparent.

In the Render Stats section of the Attribute Editor, turn off all the checkboxes. This ensures that the nParticles are not seen in the render.

Expand the Output Mesh section. Set Threshold to 0.8 and Blobby Radius Scale to 1.8.

These settings smooth the converted mesh. Higher Threshold settings create a smoother but thinner mesh; increasing Blobby Radius Scale does not affect the radius of the original nParticles. Rather it uses this value as a multiple to determine the size of the enveloping mesh around each nParticle. Using the Threshold and Blobby Radius Scale settings together you can fine-tune the look of the converted mesh.

Set Motion Streak to 0.5. This stretches the mesh in areas where there is motion in the direction of the motion to create a more fluid-like behavior.

Mesh Triangle Size determines the resolution of the mesh. Lowering this value increases the smoothness of the mesh but also slows down the simulation. Set this value to 0.3 for now, as shown in Figure 13.28. Once you're happy with the overall look of the animation, you can set it to a lower value. This way the animation continues to update at a reasonable pace.

Select the polySurface1 node in the Outliner. Rename it metalMesh.

Right-click on the metalMesh object in the viewport. Use the pop-up menu to assign a ramp material. Choose Assign New Material

Figure 13.29. Assign a Ramp shader to the metalMesh object.

In the Common Materials Attributes section, set the Color Input to Facing Angle.

Click on the color swatch, and use the Color Chooser to pick a bright orange color.

Click on the right side of the ramp to add a second color. Make it a reddish orange.

Create a similar but darker ramp for the Incandescence channel.

Set Specularity to 0.24 and the specular color to a bright yellow. Raise the Glow intensity in the Special Effects rollout to 0.15.

Back in the moltenMetal particle Attribute Editor, decrease the Mesh Triangle Size to 0.1 (it will take a couple minutes to update), and render a test frame using mental ray. Set the Quality preset in the Quality tab to Production.

Save the scene as forge_v04.ma. To see a version of the finished scene, open forge_v04.ma from the chapter13scenes folder on the DVD (see Figure 13.30).

Figure 13.30. Render the molten metal in mental ray.

Open the capsule_v01.ma scene from the chapter13scenes directory on the DVD. You'll see a simple polygon capsule model. The capsule is contained in a group named spaceCapsule. In the group there is another surface named capsule emitter. This will serve as the surface emitter for the flames (see Figure 13.31).

Figure 13.31. The capsule group consists of two polygon meshes. The base of the capsule has been duplicated to serve as an emitter surface.

Creating an Emitter Surface from a Model

The capsule emitter geometry was created by selecting the faces on the base of the capsule and duplicating them (Edit Mesh

Play the animation. The capsule has expressions that randomize the movement of the capsule to make it vibrate. The expressions are applied to the Translate channels of the group node. To see the Expressions, open the Expression Editor (Window

Figure 13.32. Create the vibration of the capsule using random function expressions applied to each of the translation channels of the capsule.

In the viewport, choose to look through the renderCam. The camera has been set up so the capsule looks as though it's entering the atmosphere at an angle.

In the Outliner, expand the spaceCapsule and choose the capsuleEmitter object. Switch to the nDynamics menu set and choose nParticles

Select the capsuleEmitter and choose nParticles

Rewind and play the animation. The nParticles are born on the emitter and then start falling through the air. This is because the Nucleus solver has Gravity activated by default. For now this is fine; leave the settings on the Nucleus solver where they are.

To randomize the generation of the nParticles, you can use a texture. To help visualize how the texture creates the particles, you can apply it to the surface emitter.

Select the capsuleEmitter and open the UV Texture Editor. The base already has UVs projected on the surface.

Select the capsuleEmitter, right-click on the surface in the viewport, and use the pop-up menu to create a new Lambert texture (Assign New Material

Open the Attribute Editor for flameGenShader, and click on the checkered box to the right of the Color channel to create a new render node for color. In the Create Render Node window, click Ramp to create a ramp texture.

Open the Attribute Editor for the ramp (it should open automatically when you create the ramp). Name the ramp flameRamp. Make sure texture view is on in the viewport so you can see the ramp on the capsuleEmitter surface (hot key = 6).

Set the ramp's Type to Circular Ramp, and set Interpolation to None. Remove the blue color from the top of the ramp by clicking on the blue box at the right side at the top of the ramp. Click on the color swatch and use the Color Chooser to change the green color to white and then the red color to black.

Set Noise to 0.5 and Noise Freq to 0.3 to add some variation to the pattern (see Figure 13.33).

In the Outliner, select the nParticle node and hide it (hot key = Ctrl+h) so you can animate the ramp without having the nParticle simulation slow down the playback. Set the renderer to High Quality display.

Figure 13.33. Apply the ramp to the shader on the base capsuleEmitter object.

Select the flameRamp node and open it in the Attribute Editor (select the node by choosing it from the Textures area of the Hypershade). Rewind the animation and drag the white color marker on the ramp down toward the bottom. Its Selected Position should be at .05.

Right-click Selected Position and choose Set Key (see Figure 13.34).

Figure 13.34. Position the white color marker at the bottom of the ramp and keyframe it.

Set the timeline to frame 100, move the white color marker to the top of the ramp, and set another key.

Play the animation; you'll see the dark areas on the ramp grow over the course of 100 frames.

Open the Graph Editor (Window

Figure 13.35. Add keyframes to the ramp's animation on the Graph Editor to make a more erratic motion.

Animate U Wave and V Wave with Expressions

To add some variation to the ramp's animation, you can animate the U and V Wave values or create an expression. In the U Wave field, type =0.5+(0.5*noise(time));. The noise(time) part of the expression creates a random set of values between −1 and 1 over time. Noise creates a smooth curve of randomness values as opposed to the rand function, which creates a discontinuous string of random values (as seen in the vibration of the capsule). By dividing the result in half and then adding 0.5, the range of values is kept between 0 and 1. To speed up the rate of the noise, multiply time by 5 so the expression is =0.5+(0.5*noise(time*5));. You can use an expression to make the V Wave the same as the U Wave; just type =flameRamp.uWave; in the field for the V Wave attribute. When you play the animation, you'll see a more varied growth of the color over the course of the animation.

In the Outliner, select the capsuleEmitter node and expand it. Select the flameGenerator emitter node and open its Attribute Editor. Scroll to the bottom of the editor and expand Texture Emission Attributes.

Open the Hypershade to the Textures tab. MMB-drag flameRamp from the Textures area onto the color swatch for Texture Rate to connect the ramp to the emitter (see Figure 13.36). Select Enable Texture Rate and Emit From Dark.

Increase Rate to 2400, unhide the nParticle1 node, and play the animation. You'll see that the nParticles are now emitted from the dark part of the ramp.

Figure 13.36. Drag the ramp texture with the middle mouse button from the Hypershade onto the Texture Rate color swatch to make a connection.

Select the capsuleEmitter shape and hide it. Save the scene as capsule_v02.ma. To see a version of the scene to this point, open capsule_v02.ma from the chapter13scenes folder on the DVD.

Disable High Quality Renderer in the viewport to improve playback speed—make sure nParticles is enabled in the viewport's Show menu.

Continue with the scene from the previous section or open the capsule_v02.ma file from the chapter13scenes directory. Make sure High-Quality Rendering is disabled in the viewport in order to improve playback speed (nParticles should be enabled in the viewport's Show menu as well). Select the capsule emitter and hide it; this also improves performance.

Select the nParticle1 object. Rename it flames. Open the Attribute Editor and choose the nucleus1 tab.

Set Gravity to 0 and play the animation. The particles emerge from the base of the capsule and stop after a short distance. This is because by default the nParticles have a Drag value of 0.01 set in their Dynamic Properties settings.

Switch to the flamesShape tab, expand the Dynamic Properties rollout, and set Drag to 0. Play the animation, and the nParticles emerge and continue to travel at a steady rate.

Switch back to the nucleus1 tab. Set the Wind Direction fields to 0, 1, 0 so the wind is blowing straight up along the Y axis. Set Wind Speed to 5 (see Figure 13.37). Play the animation—there's no change; the nParticles don't seem affected by the wind.

Figure 13.37. The settings for the wind on the nucleus tab

For the Wind settings in the Nucleus solver to work, the nParticle needs to have a Drag value, even a small one. This is why all the nParticle styles except Water have drag applied by default. If you create a Water-style particle and add a Wind setting, it won't affect the water until you set the Drag field above 0. Think of drag as a friction setting for the wind. In fact, the higher the Drag setting, the more the wind can grab the particle and push it along, so it actually has a stronger pull on the nParticle.

Set the Drag value to 0.01 and play the animation. The particles now emerge and then move upward through the capsule.

Switch to the nucleus1 tab; set Air Density to 5 and Wind Speed to 25. The Air Density setting also controls, among other things, how much influence the wind has on the particles.

A very high air density acts like a liquid, and a high wind speed acts like a current in the water. It depends on what you're trying to achieve in your particular effect, but you can use drag or air density or a combination to set how much influence the Wind settings have on the nParticle. And of course another attribute to take into consideration is the particle's mass. Since these are flames, presumably the mass will be very low.

Set Air Density back to 1. Play the animation. The particles start out slowly but gain speed as the wind pushes them along. Set the Mass attribute in the Dynamic Properties section to 0.01. The particles are again moving quickly through the capsule (see Figure 13.38).

Switch to the nucleus1 tab and set Wind Noise to 10. Because the particles are moving fast, Wind Noise needs to be set to a high value before there's any noticeable difference in the movement. Wind noise adds turbulence to the movement of the particles as they are pushed by the wind.

Figure 13.38. Set the Mass and Drag attributes to a low value, enabling the nParticle flames to be pushed by the wind on the Nucleus solver.

To make the nParticles collide with the capsule, select the capsule node and choose nMesh

Select the nRigid1 node in the Outliner, and name it flameCollide.

Expand the Wind Field Generation settings in the flameCollideShape node. Set Air Push Distance to 0.5 and Air Push Vorticity to 1.5 (see Figure 13.39).

A passive object can generate wind as it moves through particles or nCloth objects to create the effect of air displacement. In this case, the capsule is just bouncing around, so the Air Push Distance setting helps jostle the particles once they have been created. If you were creating the look of a submarine moving through murky waters with particulate matter, the Air Push Distance setting could help create the look of the particles being pushed away by the submarine, and the Air Push Vorticity setting could create a swirling motion in the particles that have been pushed aside. In the case of the capsule animation, it adds more turbulence to the nParticle flames.

Figure 13.39. The Wind Field Generation settings on the flame-CollideShape node

The Wind Shadow Distance and Diffusion settings block the effect of the Nucleus solver's Wind setting on nParticles or nCloth objects on the side of the passive object opposite the direction of the wind. The Wind Shadow Diffusion attribute sets the amount at which the wind curls around the passive object.

Air Push Distance is more processor intensive than Wind Shadow Distance, and the Maya documentation recommends that you do not combine Air Push Distance and Wind Shadow Distance.

nParticles have these settings as well. You can make an nParticle system influence an nCloth object using the Air Push Distance setting.

Save the scene as capsule_v03.ma. To see a version of the scene to this point, open capsule_v03.ma from the chapter13scenes folder on the DVD.

Continue with the scene from the previous section or open the capsule_v04.ma file from the chapter13scenes folder on the DVD.

Set the timeline to 200 frames.

In the Outliner, expand the capsuleEmitter section, and select the flameGenerator emitter. Increase Rate (Particle/Sec) to 25,000. This will create a much more believable flame effect.

Select the flames node in the Outliner. Switch to the nDynamics menu set, and choose nCache

Figure 13.42. The options for creating an nCache

The scene will play through, and the cache file will be written to disk. It will take a fair amount of time to create the cache, anywhere from 5 to 10 minutes depending on the speed of your machine.

You can use the options in the nCache menu to attach an existing cache file to an nParticle or to delete, append, merge, or replace caches.

To render using the Hardware Render Buffer choose Window

To set the render attributes in the Buffer, choose Render

The render buffer renders each frame of the sequence and then takes a screengrab of the screen. It's important to deactivate screen savers and keep other interface or application windows from overlapping the render buffer.

Set Filename to capsuleFlameRender and Extension to name.0001.ext. Set Start Frame to 1 and End Frame to 200. Keep By Frame set to 1.

Keep Image Format set to Maya IFF. This file format is compatible with compositing programs like Adobe After Effects.

To change the resolution, you can manually replace the numbers in the Resolution field or click the Select button to choose a preset. Click this button and choose the 640 × 480 preset.

In the viewport window, you may want to turn off the display of the resolution or film gate. The view in the Hardware Render Buffer updates automatically.

Under Render Modes, turn on Full Image Resolution and Geometry Mask. Geometry Mask renders all the geometry as a solid black mask so only the nParticles will render. You can composite the rendered particles over a separate pass of the software-rendered version of the geometry.

To create the soft look of the frames, expand the Multi-Pass Render Options rollout. Enable Multi-Pass Rendering and set Render Passes to 36. This means the buffer will take 36 snapshots of the frame and slightly jitter the position of the nParticles in each pass. The passes will then be blended together to create the look of the flame. For flame effects, this actually works better than the buffer's Motion Blur option. Leave Motion Blur at 0 (see Figure 13.43).

Figure 13.43. The settings for the Hardware Render Buffer

Play the animation to about frame 45. In the Hardware Render Buffer, click the clapboard icon to see a preview of how the render will look (see Figure 13.44). If you're happy with the look, choose Render

When the sequence is finished, choose Flipbooks

Save the scene as capsule_v05.ma. To see a version of the scene to this point, open the capsule_v05.ma scene from the chapter13scenes directory on the DVD.

Figure 13.44. When Geometry Mask is enabled, the Hardware Render Buffer renders only the nParticles.

Open the generator_v01.ma scene in the chapter13scenes folder on the DVD. You'll see a device built out of polygons. This will act as your experimental lab as you learn how to control nParticles with fields.

Switch to the nDynamics menu set, and choose nParticles

Choose nParticles

Figure 13.45. The settings for the volume emitter

In the Volume Emitter Attributes rollout, set Volume Shape to Sphere. You can leave the rest of the settings at the default. Click Create to make the emitter.

Select the energyGenerator1 emitter in the Outliner. Use the Move tool (hot key = w) to position the emitter around one of the balls at the end of the generators in the glass chamber. You may want to scale it up to about 1.25 (Figure 13.46).

Figure 13.46. Place the volume emitter over one of the balls inside the generator device.

Set the timeline to 800, and play the animation. The nParticles are born and fly out of the emitter.

Notice that the nParticles do not fall even though Gravity is enabled in the Nucleus solver and the nParticle has a mass of 1. This is because in the Dynamic properties for the Cloud style of nParticle, the Ignore Solver Gravity checkbox is enabled.

Select the energyGenerator1 emitter and duplicate it (hot key = Ctrl+d). Use the Move tool to position this second emitter over the ball on the opposite generator.

If you play the animation, the second emitter creates no nParticles. This is because duplicating the emitter did not create a second nParticle object, but that's okay; you're going to connect the same nParticle object to both emitters.

Select nParticle1 and rename it energy. Select energy and choose Window

Figure 13.47. Use the Dynamic Relationships Editor to connect the energy nParticle to both emitters.

Close the Dynamic Relationships Editor, and rewind and play the animation. You'll see both emitters now generate nParticles—the same nParticle object actually.

Select the energy object and open the Attribute Editor. Switch to the nucleus tab and set Gravity to 1.

In the energyShape tab, expand the Dynamic Properties rollout and turn off Ignore Solver Gravity, so the energy nParticles slowly fall after they are emitted from the two generator poles (see Figure 13.48).

Figure 13.48. The energy nParticles are emitted from both emitters. Gravity is set to a low value, causing the nParticles to slowly fall.

Select the energy nParticle node in the Outliner. In the Attribute Editor, open the Lifespan rollout, and set the Lifespan mode to Random Range. Set Lifespan to 6 and Lifespan Random to 4. The nParticles will now live between 4 and 8 seconds each.

With the energy nParticle selected, choose Fields

Select curve1 in the Outliner, and use the Move tool to position it between the generators. The field consists of a curve surrounded by a tubular field.

Use the Show menu to disable the display of polygons so the glass case is not in the way. Select curve1 in the Outliner and right-click on the curve; choose CVs to edit the curve's control vertices. Use the Move tool to position the CVs at the end of the curve inside each generator ball. Use the Move tool to add some bends to the curve (see Figure 13.49).

Rewind and play the animation. A few of the nParticles will be pushed along the curve. So far, it's not very exciting.

Figure 13.49. Position the CVs of the Volume Axis curve to add bends to the curve. The field surrounds the curve, forming a tube.

Select the volumeAxisField1 node in the Outliner, and open its Attribute Editor. Use the following settings:

Play the animation. You'll see the nParticles move around within the field. Faster-moving particles fly out of the field.

Figure 13.50. The settings for the Volume Axis Curve field

This is interesting, but it can be improved to create a more dynamic look.

In the Attribute Editor for the Volume Axis Curve field, remove the edit points from the Curve Radius ramp. Edit the curve so it has three points. The points at either end should have a value of 1; the point at the center should have a value of 0.1.

Select the edit point at the center, and in the Selected Position field type =0.5+(0.5*(noise(time*4)));. This is similar to the expression that was applied to the ramp in the "Surface Emission" section of this chapter. In this case, it moves the center point back and forth along the curve, creating a moving shape for the field (see Figure 13.51).

Save the scene as generator_v02.ma. To see a version of the scene to this point, open the generator_v02.ma scene from the chapter13scenes folder on the DVD.

Continue with the scene from the previous section or open the generator_v02.ma scene from the chapter13scenes folder on the DVD.

Expand the Housing group in the Outliner. Select the dome object and choose nMesh

To keep the particles from escaping the chamber, you'll also need to convert the seal and base objects to passive collision objects. Select the seal object and choose nMesh

Figure 13.52. Parts of the generator device are converted to collision objects, trapping the nParticles inside.

Play the animation. As some of the nParticles are thrown from the Volume Axis field, they are now contained within the glass chamber (see Figure 13.52).

Open the settings for the energyShape node in the Attribute Editor. Set Radius Scale Input to Age. Edit the Radius Scale ramp so it slopes up from 0 on the left to 1 in the middle and back down to 0 on the left. Set Input Max to 3 and Radius Scale Randomize to 0.5 (see Figure 13.53).

Select the domeCollide node, and open the Attribute Editor to the domeCollideShape tab. Expand the Force Field Generation settings, and set Force Field to Single Sided. This generates a force field based on the positive normal direction of the collision surface.

Figure 13.53. Edit the Radius Scale settings to create a more randomized radius for the nParticles.

Along Normal generates the field along the surface normals of the collision object. In this case the difference between Along Normal and Single Sided is not noticeable. Double Sided generates the field based on both sides of the collision surface.

The normals for the dome shape are actually pointing outward. You can see this if you choose Display

Set Field Magnitude to 100 and Field Distance to 4, and play the animation. The particles are repelled from the sides of the dome when they are within four field units of the collision surface. A lower field magnitude will repel the particles with a weaker force, allowing them to collide with the dome before being pushed back to the center. If you set Magnitude to 1000, the nParticles never reach the collision surface.

Set Field Magnitude to −100. The nParticles are now pulled to the sides of the dome when they are within four field units of the collision surface, much like a magnet. Setting a negative value of −1000 causes them to stick to the sides.

The Field Scale Edit ramp controls the strength of the field within the distance set by the Field Distance value. The right side of the ramp is the leading edge of the field—in this case four field units in from the surface of the dome. The left side represents the scale of the force field on the actual collision surface.

Figure 13.54. Reverse the normals for the dome surface so they point inward.

You can create some interesting effects by editing this curve. If Field Magnitude is at a value of −100 and you reverse the curve, the nParticles are sucked to the dome quickly when they are within four units of the surface. However, they do not stick very strongly to the side, so they bounce around a little within the four-unit area. Experiment creating different shapes for the curve, and see how it affects the behavior of the nParticles. By adding variation to the center of the curve, you get more of a wobble as the nParticle is attracted to the surface.

Save the scene as generator_v03.ma. To see a version of the scene to this point, open the generator_v03.ma scene from the chapter13scenes folder on the DVD.

Continue with the scene from the previous section or open the generator_v03.ma scene from the chapter13scenes folder on the DVD.

In the Attribute Editor for domeCollide, set the Field Scale ramp so it's a straight line across the top of the curve editor. Set Field Magnitude to 1.

Select the dome object and choose nMesh

Open the tools options for the Artisan Brush. The color should be set to black, and Paint Operation should be set to Paint. Use the brush to paint a pattern on the surface of the dome. Make large, solid lines on the surface; avoid blurring the edges so the end result is clear (see Figure 13.55).

Figure 13.55. Use the Artisan Brush tool to paint a pattern for the field magnitude on the collision surface.

When you've finished, click the Select tool in the toolbox to close the Artisan Brush options. Open the Hypershade. In the Textures tab, you'll see the texture map you just created. You can also use file textures or even animated sequences for the map source.

Select the dome in the scene. In the Work Area of the Hypershade, right-click and choose Graph

Figure 13.56. Connect the newly painted texture to the color of the dome shader.

If you play the animation, you won't see much of a result. The reason is that the values of the map are too weak and the movement of the nParticles is too fast to be affected by the field.

In the Hypershade, select the file1 texture and open its Attribute Editor. The outAlpha of the texture is connected to the field magnitude of the collision surface. You can see this when you graph the network in the Hypershade. To increase the strength of the map, expand the Color Balance section. Set Alpha Gain to 1000 and Alpha Offset to −500. Chapter 2 has a detailed explanation of how the Alpha Gain and Alpha Offset attributes work. Essentially this means that the light areas of the texture cause the force field magnitude to be at a value of 500, and the dark areas cause it to be at −500.

Play the animation. You'll see that most of the nParticles stay in the center of the dome, but occasionally one or two nParticles will fly out and stick to the side. They stick to the areas where the texture is dark (see Figure 13.57).

Figure 13.57. The painted force field texture causes most of the nParticles to remain hovering around the center, but a few manage to stick to the dark areas.

Vertex maps assign values to the vertices of the surface using the colors painted by the brush; texture maps use a file texture. One may work better than the other depending on the situation. You can paint vertex maps by choosing nMesh

When using a texture or vertex map for the force field, the Force Field Magnitude setting acts as a multiplier for the strength of the map.

Back in the domeCollide node, set Field Magnitude to 10 and play the animation. You'll see more nParticles stick to the surface where the texture has been painted.

To smooth their motion, you can adjust the Field Scale ramp.

Save the scene as generator_v04.ma. To see a version of the scene to this point, open generator_v04.ma from the chapter13scenes folder on the DVD.

Open the generator_v04 scene from the chapter13scenes folder on the DVD.

Select the energy nParticle object and choose Fields

In the Attribute Editor for the Turbulence field, set Magnitude to 100, Attenuation to 0, and Frequency to 0.5.

Attach a Vortex field to the energy nParticle. By default the vortex travels around the Y axis, which works well for this scene. Set the Magnitude of the vortex to 25 and the Attenuation to 0.5.

To see the particles behave properly, you'll probably want to create a playblast. Set the timeline to 300, and choose Window

Save the scene as generator_v05.ma. To see a version of the scene to this point, open generator_v05.ma from the chapter13scenes folder on the DVD.

Open the generator_v05.ma scene from the chapter13scenes folder on the DVD.

Select the energy nParticle node in the Outliner, and open its Attribute Editor to the energyShape1 tab.

Expand the Shading attributes in the bottom of the editor. Set Opacity to 0.8.

Set Color Input to Age. Make the left side of the ramp bright green and the right side a slightly dimmer green.

Set Incandescence Input to Age. Edit the ramp so the far-left side is white followed closely by bright green. Make the center a dimmer green and the right side completely black (see Figure 13.58).

Select each of the emitter nodes, and raise the Rate value to 1000.

Select the domeShader node in the Hypershade, and break the connection between the color and the file texture (don't delete the file texture—it still controls the force field magnitude). Set the color of the domeShader to a dark gray.

Play the animation for about 80 frames. Open the render settings, and set the renderer to mental ray. In the Quality tab, set the Quality preset to Production.

Figure 13.58. The shading attributes for the energy nParticle

Select the energy nParticle, and in the Render Stats section of the energyShape tab, check the boxes for Visible in Reflections and Refractions.

Create a test render of the scene. You can see in the glass of the chamber and the metal base that the nParticles are reflected. Open the Hypershade and select the metal shader. Increase Reflectivity in the Attribute Editor to 0.8. The nParticles are more visible in the reflection on the base (see Figure 13.59).

Select the dome shader, and in its Attribute Editor under Raytrace Options, activate Refractions and set the Refractive Index to 1.2. Under the Specular Shading rollout, increase Reflectivity to 0.8. Create another test render. You can see the effect refraction has on the nParticles.

You can render the point, multipoint, streak, and multiStreak render types using mental ray. They will appear in reflections and refractions as well; however, you'll notice that in the Render Stats section for these nParticle types, the options for Reflections and Refractions are unavailable.

In the Hypershade select the npCloudVolume shader. This shader is created with the nParticle. Graph the network in the Hypershade Work Area (see Figure 13.60).

Figure 13.59. The nParticles are visible in reflections on the surfaces.

Figure 13.60. Shaders are automatically created for the nParticles. The particleSamplerInfo node connects the attributes of the nParticle to the shader.

You can see that a particleSampler node is automatically connected to the volume shader. This node transfers the settings you create in the nParticle's Attribute Editor for color, opacity, and transparency to the shader. An npCloudBlinn shader is also created. This shader is applied when you switch the Particle Type to Points. You can further refine the look of the nParticles by adjusting the settings in the npCloudVolume shaders Attribute Editor.

You can add a shader glow to the particles by increasing Glow Intensity in the npCloudVolume shader; however, the glow does not appear behind refractive surfaces with standard Maya shaders.

When you are happy with the look of the render, you can create an nCache for the energy nParticle and render the sequence using mental ray.

Save the scene as generator_v06.ma. To see a finished version of the scene, open the generator_v06.ma file from the chapter13scenes directory.