Essential Blender- P24 doc

Switch to the "Particle Motion" panel. Figure PT.4: The Particle Motion panel. This panel tells particles how to move. Set the "Normal:" and "Random:" spinners both to "0.030" and press Alt-A to see the results. This time, the particles fly off the sphere, which is what you wanted. The reason you entered a value into the "Normal" control was that you wanted each particle to shoot off along the "normal" of the emitter object. The short description is simply that giving a velocity in the "Normal" control will cause particles to emit away from the surface of the object. A better description of normals is available in Chapter 4. Figure PT.5: Particles flying off in the direction of the surface Normals. Particle Patterns You may have noticed in the animated playback that the particles seem to be flying off the sphere in a certain pattern. This is because Blender emits the particles from the object based on the order of faces and vertices within the object. When a primitive object like a sphere is created, the faces are ordered very neatly. In order to truly randomize the way that particles emit from a mesh, you must enter Edit Mode on the mesh (Tab-key), select all vertices (A-key), thenand then click the "Hash" button on the Mesh Tools panel of the Editing buttons (F9). The Hash function scrambles the order of vertices, meaning that particles will now seem to emit in a much more random fashion. What you would really like, though, is for your particles to fall down through the other obstacles in the scene. This is where the "Force" controls come in. The upper bank of X/Y/Z force controls exerts a constant force on particles along the global axis of your choice. So, to make your particles "fall" as though they are affected by gravity, you need to assign a velocity along the global Z (vertical) axis. Set the "Z" force control to "-0.50," and preview with Alt-A. Figure PT.6: [no text] Note: If you find that your computer shows the animation slowly or sloppily, reduce the "Disp" on the Particles panel in order to show fewer particles. If things are running fine, and you have a fast enough machine, try setting the "Disp" value to 100, to show 100% of the particles. Barriers and Deflection RMB to select the rotated plane immediately below the emitter, then click the "Deflection" button on the "Fields and Deflection" panel to the left of the particle panels. Figure PT.7: The Fields and Deflection panel. In this tutorial, you're only concerned about the upper section, labeled "Particles." By turning on Deflection, you tell the particle system to treat the object as a barrier. Pressing Alt-A now shows this, which is clearly wrong: Figure PT.8: These particles are going crazy! The problem is that by default, particle paths are calculated at a fairly low resolution. You can adjust this with the "Keys" control of the particle motion panel. RMB to reselect the particle-emitting sphere, then set Keys to "50." What this value actually means is that along the total life of the particle (75 frames in your example), it will have its location calculated 50 different times. Before you changed the value, it had been set to 8, which meant that Blender was only calculating the particle position about once every ten frames. Obviously, 50 will be much more accurate. Alt-A again, and this time you will see that the particles bounce off the plane. Figure PT.8.1: Particles properly deflecting from the top plane. Let's do one more thing with the deflection settings of the plane. RMB select the plane, then change the Deflection "Damping" setting to "0.8." Damping takes motion energy away from particles, slowing them down when they collide with the deflection object. Pressing Alt-A doesn't seem to show any difference. Annoying. Certain changes to the scene will not be detected or automatically taken into account by particle systems. When this happens, you have to tell the particles to recalculate manually. Fortunately, this is easy to do. To force a particle system to recalculate, RMB select the particle emitter, then click the "RecalcAll" button in the main Particles panel. Alt-A now shows the particles sliding off the end of the plane, as opposed to rebounding like they did before you changed the "Damping" value. There's one more thing to learn about Deflection. The deflection calculations are sensitive to which way mesh faces are pointing. Select one of the deflection planes and use the Tab key to go into Edit mode. In the "Mesh Tools 1" panel of the Editing buttons, enable the "Draw Normals" button and set the NSize value immediately above it to 1.0. You will see a light blue line extending upward and away from the plane. This line indicates the Normal, or facing direction, of the plane's quad face. The deflection tools consider the Normal direction to be the "hard" side of the plane. If you were to rotate the plane 180 degrees and recalculate the particle system, you would see the particles no longer bouncing and sliding off the plane, but passing through it and slightly changing direction afterward. Be sure to keep surface Normals in mind if your objects are not deflecting correctly. Figure PT.9: The particles sliding off the damped plane. One at a time, select both the other plane and the open-topped cube, enable Deflection for them, and set their damping values to "0.8." When you're done doing that, don't forget to reselect the emitting sphere and manually recalculate the particle system. Preview the particle animation with Alt-A, and you will see your particles fall from the ball, deflect off each plane, then end up in the bottom of the cube. Figure PT.10, 10.1: The particle system cruising along. Particles seem to be escaping from the bottom of the cube, and occasionally a particle may pass through one of the planes. The particle physics system is not a full, actual physics simulation and will be subject to little annoyances like this. Applying Other Environmental Forces Create an Empty and position it between the sphere and the first deflection plane. Use Alt-R to clear any rotations that might be on the Empty. With the new Empty selected, choose "Vortex" from the "Fields" drop down menu in the Fields and Deflection panel. Figure PT.11: The Fields drop down with Vortex selected. Set the "Strength" field to "50," and play the animation. If you are in a front or side view, the effect might not be obvious, so use the MMB to rotate the 3D view a bit. Now, you can see that the particles, as they fall, are swirling in a cyclonic fashion. You can also see that the empty now has ghosted "vortex" lines. Figure PT.12 Now that you've seen what Vortex can do, reduce its strength to 15 or so. That will cause the particles to follow the vortex force a bit, but to still stay pretty much within the confines of the rest of the scene. You can save this file for later reference if you like. After that, start a new Blender session with Ctrl-X for the next part of the tutorial. Strand Particles Blender's particle generator is not only capable of making standard particles as seen in the previous section, but also creates "Strands" that can be used to simulate hair, fur or even feathers. Let's start by adding a sphere from the Spacebar toolbox: Add -> Mesh -> UVsphere. You can accept the default creation values of 32. Put the sphere into Object mode with the Tab key.