Adding a Nebula Effect

In this post, we’ll walk through how to use Artemis Bridge Tools to add a cool random-looking nebula effect invented by Badgeguy .   Here’s a video clip of what it looks like (watch the top row of lights):

Understanding the effect

In his post here, Badgeguy explains:

My WITHIN_NEBULA effect is even crazier, with 3 different continuous effects that only affect specific channels each (one effects the red IDs, then next the green IDs, and the last the blue IDs).  This allows me to move the colors along the strip with the same trigger, but at different rates for each color and each time block, allowing for some cool mixing of colors that has a random feel to it, unless you watch it long enough and can determine the start point again

Each color has a single light that is on 100%, but with 3 lights on either side in decreasing brightness to give what we might call a “corona” effect around the central light.  Thus the value on the relevant channel of successive lights looks like this:

Each color then moves such that the 100%-on (value 255) location moves back and forth between the 2^nd light from the left end of the light strip and the 2^nd light from the right end of the strip.  You might choose to have it traverse all the way from end to end, but in this walkthrough we’ll use Badgeguy’s exact effect.

So to make the colors move we need to know, for each color, the starting location, the initial direction of movement (left or right), and the speed.  Badgeguy’s nebula effect uses the following:

In Badgeguy’s setup, there are 12 lights in a row.   That means we can think of the initial state of the colors as looking something like this:

We can see that the two colors that start closest to each other (red and blue) begin by moving farther apart, and the two colors with the biggest gap in between (blue and green) begin by moving closer together.

In a setup with a different number of lights (I have 13 lights there in my own setup), we can still use the same table for starting location, direction, and speed, it just means that blue and green will start a different distance apart.

Finally, let’s note some things about the speeds for the math geeks out there.   To ensure that the light effects for two colors don’t overlap for very long, we want their speeds to be sufficiently different.   And to ensure that the full sequence will not repeat for a long time, we want the three speed values to all be what math geeks would call “relatively prime”, which means that they have no factors in common.  101 and 173 are prime and 142 = 2 x 71, so while they’re not all prime, there are no factors in common (we could have also replaced 142 with 137, which is prime).   This means that the sequence won’t be exactly repeated for 101 x 142 x 173 milliseconds = over 41 minutes.  Tiny differences in color aren't very distinguishable though, so in practice it may appear to repeat after a minute or so.  Still, it's long enough to look pretty random and mesmerize spectators for some time!

Creating the actual commands

Ok, now that we understand how we want the effect to work and why, let’s see how to create it.

First, we open our DMXcommands file using Artemis DMX Editor.   We will need to add three commands, one for each color, with two sequences of timeblocks (forward and backward movement across the light strip) in each command.   Let’s start with red.

We add a new command using the Command Add button, set the cue to WITHIN_NEBULA, check the Continuous box, set the msec to 101 per our table earlier, and optionally fill in some comment such as “red nebula effect”.  Our screen now looks something like this:

We now click Chase Effect… to add a move sequence.  We select the full light strip (T1 to T13 in my setup) because we want the corona to span all 13 lights, even though we only want the center to move between 11 of them but we’ll take care of that part later.

The time will be filled in automatically since we already entered 101 before.  We set the moving color to red, and make green and blue be transparent by clicking their “Trans.” checkboxes.   We then say we want a single light with corona of size 3 that will transition gradually at each step, and click OK.  At this point, we have a command that causes a red light with corona to move from the left end of the strip all the way to the right end of the strip, and repeats.   However, since we want it to move back and forth, we need to add the other direction too.  

To do so, first we’ll need to add an empty timeblock where we want the sequence to go.   Select any timeblock cell in the last timeblock, i.e., any cell in the region circled in the following diagram, and click the Time Block Add button to add a timeblock immediately after it:

Now we can again click on Chase Effect… and add an effect exactly as before except with the devices reversed (i.e., T13 as the first device, and T1 as the last device).

We now have an effect that moves from end to end, but we still have two problems.  First, we don't want the effect to move to the light on either end, and second, we want to start at the 3^rd light from the left.  Let’s fix those one at a time.

Trimming off the two ends turns out to be easy since all the right timeblocks are already there, we just have extras.   We use the Time Block Delete button (after clicking a cell in the timeblock to delete) to delete the first two timeblocks, so that the first timeblock left starts with the 2^nd light (T2 in the example) all on.  Similarly we delete the last timeblock in the first sequence, which transitioned the last light to all on, as well as the first two timeblocks and last timeblock of the second sequence.   This leaves us with 20 timeblocks for 13 lights (ten moving from T2 to T11, and ten more moving from T12 to T3).

Now we just have to fix where in the order the sequence starts.  We want the red sequence to start with the third light from the left (T3) rather than T2.  So we just take one timeblock from the top and move it to the end of the sequence.  That is, we click on the top timeblock and use the Time Block Down button until it moves all the way to the end.   If we wanted to start later in the sequence, we’d repeat until the right time block is left at the top, but for red we’re now done!

We just have to repeat the same process to add a command for green, and then one for blue.  The steps are exactly the same as above.  Just remember to use the right values from the table earlier.   When adding the blue command, you will probably find it faster to add the reverse chase effect before adding the forward chase effect, since we want blue to start by moving right-to-left instead of left-to-right.  That’s it!