1 CENTROIDS EMITTING PARTICLES

Transcription

1 1 CENTROIDS EMITTING PARTICLES 1. Launch Houdini. 2. From the desktop selector button located at the top of the interface, select the Training desktop. 3. Select the sky, logo and ground objects and delete them. Houdini Training Side Effects Software

2 4. From the list of generator object located at the top of the network editor, place a new Geometry object into the Network editor. 5. Rename it to be particles. 6. Press the R key to enter into its SOP editor. 7. You may need to change the main viewer to be viewing the particles SOP editor also. 8. Delete the default file SOP. 9. From the list of generator objects, place an add SOP into the network editor. Toggle on the Point 0 button to create a single point located at the origin. 10. From the list of generator SOPs place a sphere SOP to the left of the add SOP. Ensure that there are no connections at this point. Toggle the sphere SOPs template flag on. Change its Primitive type to be Polygon Leave everything else at its defaults That s it for the sphere. It is going to be used as a template to copy a single point per primitive. OPTIONAL STEP 11. Append a facet SOP to the sphere SOP. Toggle on the Unique Points option. This makes each primitiv object unique. 12. \ on the output of the add SOP, and from the Filters menu, append a copy SOP. In the # of copies field enter the following exporession: nprims(../sphere1 ) The nprims expression will return the total number primitives in the sphere1 SOP to the # of copies field. If you [ click on the #of copies field, the value field will toggle between the expression which you entered, and the number of primitives in sphere1 (which incidently is 80) 13. Append a point SOP to the copy SOP. Toggle on the Display flag of the point SOP. In the Position X field, delete the default $TX, and enter the following expression: prim(../sphere1,$pt, P,0) The prim expression will take each point, and position it to each corresponding primitive in sphere1. The P in the exporession instructs it to calculate the position, and the 0 at the end of the expression is for what Axis is to be considered. In this case it is the X axis. 2 Side Effects Software 1997 Houdini Training

3 Ac to copy this expression. T to tab over to the next field (notice how the $TY is already highlighted) Av to paste the copied expression into the $TY field. Modify the expression to read: prim(../sphere1,$pt, P,1) T to the $TZ field, and Av to paste in the expression in the last field, once again, modify it to read: prim(../sphere1,$pt, P,2) Toggle on the display of points in the viewing window. 14. Append a second point SOP to the first. Working with its parameters: Toggle on its Display flag. Change the Keep Normal field to Add Normal. In the $NX field enter the following expression: ($BBX-0.5)*2 In the $NY field enter the expression, but change it for the Y Axis: ($BBY-0.5)*2 Once more for the Z axis. ($BBZ-0.5)*2 Houdini Training Side Effects Software

4 In the viewport, toggle on the Display of point normals. Now you have defined 80 points to birth particles from, and by aiming the normals outward, it will give the particles an initial velocity going away from the sphere. 15. Append a particle SOP to the point SOP. Toggle on its Display flag. Press play. Open the Forces folder. In the External Force Y field, enter -1. Now the particle will fall down after bursting outward form the sphere. If you would like them to burst outward with a higher velocity, all you have to do is to increase the multiplier from 2 to whatever you like. 4 Side Effects Software 1997 Houdini Training

5 copying to the Centroid 2 COPYING TO THE CENTROID 1. Delete the particle SOP. 2. Place a tube SOP to the left of the existing SOP networks. Change its Radius to Decrease its height to be Append a transform SOP to the tube SOP. Translate it.27 units in Z. Rotate it 90 degrees on X. 4. Append a copy SOP to the transform SOP. 5. Pipe the output of the point2 SOP into the right (Template) input of the copy SOP. Refer to the illustration below. 6. Press the T key, and from the Filters menu, place a merge SOP into the Network Editor. Pipe the output of the copy2 SOP into the merge SOP. Pipe the output of the sphere1 (or facet1) SOP into the merge SOP, Houdini Training Side Effects Software

6 copying to the Centroid Toggle on the Display and Render flags of the merge SOP. That s it...although this lesson did cover two separate aspects of the use of the polygonal sphere, you could then move on, and have the cones emit particles etc. etc. etc. 6 Side Effects Software 1997 Houdini Training