Appendix: DMX
This page provides information and definitions about DMX for users who want to use it for VRSL but are unfamiliar.
Note that this will only cover knowledge required for VRSL use, is not comprehensive, and at some times may be inaccurate for clarity or simplicity.
DMX512, often shortened to just DMX, "is a standard for digital communication networks that are commonly used to control lighting and effects." (Wikipedia)
DMX is built on the idea of Channels.
A channel is basically a slot for an 8-bit value (0 to 255) which lights can treat as data.
The 512 in DMX512 refers to how a single DMX cable can carry a maximum of 512 channels. This isn't expressly relevant to us, as we don't run any cables in VRSL, but knowing the nomenclature is, and this unit of 512 channels is referred to as 1 Universe.
DMX Light Fixtures occupy a certain amount of channels based on their complexity.
A very simple light can be just one channel. In fact, this is exactly the case for the Disco Ball.
This chart is called a Fixture Definition and describes how many channels a fixture requires to function, and what value each channel corresponds to.
Here, Dimmer basically means brightness, as it refers to the dimmer circuit within lights that's responsible for controlling the brightness.
We can find fixtures with more channels when we add capability for color. Strobes are cool too so lets add that.
Here, we have separate control values for the Red, Green, and Blue light. We also have Strobe which basically toggles the light between off and its other current settings. Put another way, a light fixture with Strobe enabled, but Dimmer disabled, will not be on.
Moving from 5 channels to 13 channels is a big step up, and rightfully so! A Moving Head, a light fixture with the capability to change where its pointed, has much more capabilities than the simpler lights we've seen.
There's a lot to unpack!
Firstly, Pan and Tilt are rather intuitively what's used to provide a light with the desired rotation, but what's Pan Fine and Tilt Fine?
Well, as said before, the value range of a DMX channel is 0 to 255.
If we use that value as an angle by treating 0 as 0° and 255 as 360°, 1 would be ~1.4°. In other words 1.4° is the smallest movement we can tell a light about. That's a little limiting, and especially problematic if we'd like to do a slow movement over a long amount of time.
As such, the Fine channels are provided to add extra precision. You can think of it as 0 as 0° and 255 now as 1.4°. This second value is then added to the first for the final angle. With both channels, the smallest movement possible is now 0.005°. Much more precision indeed.
As shown here, with only one channel we can't actually get a value representing 90°: the closest is either 89.6° or 91°. But with the addition of the Fine channel, we are indeed able to specify exactly 90°.
Next, is Zoom. The Zoom value dictates the size of the cone a light shines in. A high value is a wide light, and a low value creates a sharp beam.
Another thing moving heads have are GOBOs. GOBOs are discs that block parts of the light source so it shines as a pattern instead of a solid beam.
GOBOs can be static, but they can also be made to spin using the GOBO Spin Speed parameter.
The final feature is the Mover Speed channel, also called Smoothing Strength. This is a parameter only found in VRSL Fixtures which serves to provide smoothing between Pan and Tilt values in the event of inconsistent refresh rate or other signal degradation.
Then there's also lasers but idk about those yet.
Once all the light fixtures have been placed at a venue, the final step before they can be used is that the fixtures must be patched. Patching is the processes of defining a fixture in address space, but more sense can be made with an analogy to a queue line.
The makeup of a DMX signal is the values of all 512 channels being broadcast sequentially. For a light to respond to a DMX signal, it must be instructed as to which of these values correspond to it, otherwise known as its address.
Pictured here is a 5-Channel fixture and its address: Ch54.
What we define as its address refers to the first channel that it will read. As this is a 5-Channel fixture, the four channels after Channel 54 are also used by the light.
Note the word choice "used", and not "reserved". Any fixture on a DMX network can read any address. It is possible due to human error or other reasons that the addresses of two light fixtures overlap.
This is called a patch conflict, and as you can see, both lights are now no longer able to be controlled meaningfully.
There is a situation, though, in which we can use an overlap in a purposeful way: if there are two light fixtures which we know will always use the same values, and are the same channel count.
This should be done whenever possible because channels in our address space are not an unlimited resource, and efficient addressing means we can have more fixtures out of the same size address space.
Once addresses are assigned to fixtures, the same addresses and fixture definitions for your fixtures must be defined within your DMX software. Doing so will not be covered as it varies between software, and any software worth your time should make doing so an easy process.