Requirements: Digital Fusion 3.1 or greater, DFX+ 3.1 with Module 7
Flow:  Flow (4 Kb)
Images:  TGA (1 Mb)
Archive:  Printable Microsoft Word Document (522 Kb)

This week we'll explore one of the more common uses for our particle systems, smoke. For billows of smoke, setting your particle type to point cluster can help to generate large volumes quickly and efficiently. In this tip we will add some smoke to a smoke stack.

Be sure to download the above footage/still for this example.

In a new flow;

1. Add a loader and point it to the frame provided.
2. To build the basics for any particle system, add a particle emitter and a particle renderer.
3. Merge the particle renderer over the clip by dragging a connection from the Pender output (little red box) to the output of the loader. This shortcut will automatically create a merge for you, and composite the first selected tool over the second selected tool.

4. Open the controls for the merge, and set the subtractive/additive slider to 1.

5. To ensure conformation of the two layers, open the settings for the particle renderer, and select the image tab if it isn't already. Check to make sure it is the same size and aspect as the background, in this case, 720x486x1.1111.

Let's start by adjusting a few of the parameters of our particle emitter to get the basic motion down for our smoke stack. One of the best ways to do this is to use the interactive playback button located next to the start render button. This function will continuously loop the currently displayed tool for the duration of the render range as fast as your processor will allow.

6. First set your render range to 0 to 89.
7. Next drag the Prender tool to the large view. Now press the interactive play button.

You should now see particles being generated within the sphere emitter region, but they aren't doing a whole lot right now. Lets play with a few sliders under the Pemitter tool, and watch what happens.

8. Open the controls for the Pemitter tool, and find the velocity section. Open it.
9. Try dragging the slider for the velocity. You should begin to see the particles move from the emitter towards the right hand side of the screen. We want a very slow motion, so set an initial velocity of 0.007.
10. To add some variation to the particles, set a velocity variance to 0.005. Variations make the animation seem less mechanical, and more organic.
11. Now drag the angle slider to a value around 100. As you do this you will see the particles change direction from straight to the right, now up and a bit to the left.
12. Again, lets add some variation; change the angle variation to 15.

Ok, we now have the basic motion for our smoke system, but it doesn't look much like smoke right now. Let's adjust the visual qualities of our particle system by entering the style tab of our particle emitter tool.

13. Change the style drop down from point to point cluster. This creates a number of points per particle, so increases the visual volume of the smoke.
14. Set the Number of points slider to 10.
15. Change the apply mode from add to merge. This will take the alpha of each particle into account as it produces the smoke. Leaving it on add, would just continually add up particles until we were left with blown out white smoke.
16. Open the color section, and find the color over life gradient. This works much like the gradient in the new background tool; however in this case the far left side of the gradient represents the particles birth, and the far right represents the particles death, which is tied to the lifespan controls. Lets modify the first color entry (Currently white) and drag it to about half way along the gradient.
17. Add a second color entry by clicking just below the gradient area, near the beginning of the gradient. Change this color to a light gray.
18. Lets add some variation to the color, so find the color variance settings and open them. Here you can see 4 clip sliders. These work by adding or subtracting to the currently defined color. In this case, lets add some darker areas by dragging the left side of each the R,G, and B. Move them to a value of about -0.4 (seen in the left box next to each clip).
19. For the alpha adjust it to about -0.25. We want less variation in the alpha than in the color. Also be sure the "lock color variance" is checked. This varies each of the channels equally. If you uncheck this, it will add independent variation, and look multicolored.

Currently we have entered the desired values for our motion and color, but let's add a few more finessing touches. Next we'll add a fade in and fade out for the particles, as well as a scale over life.

20. Open the controls for size.
21. Set your size to 2, and size variance to .5.
22. You will also see a size over life graph. This works similar to the gradient, in that the left hand side is a particles birth, and the right hand side is a particles death. The top line is 2X the current size, middle line is current size setting, and at the bottom is 0X the current size setting. Adjust your graph to look like this. This will cause the particle to start at approximately a size of 1, and scale to 4.
23. Open the fade controls. To save screen space you may wish to close the color and size controls by clicking on the arrows again.
24. This is another clip slider. This slider is based on percentages of the overall particle life. To set a fade in of 10%, adjust the first value to 0.1. In this case our particle life is 160 frames, so our particles will fade in over 16 frames. Lets also add a fade out, so set your fade out range to 0.6. This will fade the particles out over the last 40% of their lives.

The final stage of this little project is to adjust the particle emitter center so it is positioned correctly, and set up a pre-roll and post process blur on the particle render tool. I'd like to take a second and explain what it is that the pre-roll frames do. With out a pre-roll, the particles don't begin to emit from the smoke stack until frame 0. This is fine if you want it to look like the smoke is just starting, however if you wish to just cut to the action, you need to tell fusion to start calculating earlier.

25. If you are still interactively playing, stop the playback now. We have no need to check the motion any longer.
26. Select the region tab of the particle emitter, and modify the settings to match the following:
    1. X center = .407, Y center = 0.29, size = 0.013
    Alternatively, select either the particle emitter or particle renderer, and adjust the interactive controls to match the below image. This just makes the smoke come out just above the stack.

27. Open the controls for the particle renderer, and check the automatic pre-roll check box.
28. Open the controls and set the pre-generate frames to 160. If you drag the slider this value will only go to 100, but as with most of the controls in Digital Fusion, it will accept a larger value if typed in.
29. Lastly adjust the blur to 2. This will post process the image generated by the particle renderer with a blur.

There you have it, a basic particle system to emulate a smoke stack. If you're interested in learning more about particles, try my tutorial on bitmap particles.