Nuts and Volts - November 2011

byte
byte
byte
byte
byte

$00, $FF, $08, $01, $00, $00, $00,
 $00
$FF, $08, $01, $00, $00, $00, $00,
 $00
$08, $FF, $00, $00, $00, $00, $00,
 $00
$01, $08, $FF, $00, $00, $00, $00,
 $00
$00, $01, $08, $FF, $00, $00, $00,
 $00

If you look very closely, you'll see that one element of each line is full bright ($FF), and the position in the table creates the scanning effect. Now look again. Here's where we can make things cool by using a dimmer instead of straight shifts of a single LED. If you look, you will see the values $08 and $01 adjacent to the lit LED. Once you see it in action, the values will make sense. What's happening here is that we're creating a motion trail on the downstream side of the moving element. This gives a richer look to our version of the Larson Scanner, and is one of those subtle details that people appreciate — even if they don't know exactly why.

Let's have a look at the demo program. In keeping with the new version of BSG, when the program starts the center element will fade on. This is easily handled with a loop:

repeat level from 0 to 255
  bright := leds.ezlog(level)
  leds.set(3, bright)
  pause(7)

This is simple. We're looping through the brightness of the LED to create a fade on effect. Note, though, that we're using a method called ezlog() to modify the value. A friend showed me this trick for "bending" a linear set of LED values into a quasi-log curve. What this does is provide a more natural fade effect when looking at the LED. The set() method moves a value to a dimmer channel. After a short hold, we drop into the program main scanner loop.

repeat
  repeat row from 0 to 13
 bytemove(leds.address, @cylon[row*8], 8)
 pause(100)

The outer repeat causes this loop to run forever; the inner repeat loops through the DAT table. The only tricky aspect is moving the table to the modulation object. One of the methods in that object is called address() which provides the hub address of the duty cycle array. By knowing this address, we can use bytemove to copy eight bytes from the table directly into the duty cycle array. A short pause is used to control the speed of the animation. That's it; a cooler version of the ubiquitous Larson Scanner.

GAME ON!

Now, if you still don't think LEDs are cool, let me tell

SPIN ZONE

you about another aspect of my busy summer. In August, I traveled to Seattle for the PAX Prime gaming convention. Honestly, I'm not very much of a gamer, but I love the technology and programming used in online and console games. In fact, a lot of the disciplines used in the gaming industry were born in the visual effects world of the movie industry.

So, why did I go? Well, I had the incredible good fortune to be asked by Hollywood FX master, Steve Wang, to do lighting in characters that he was building for a display. Steve and his massively talented team took two characters from the new game, Firefall (from Red 5 Studios), and made them full sized and unbelievably lifelike. They are so realistic, you expect them to walk off the platform. Figure 2 is a photo of Steve (lower left with big brown dog) and most of the build crew. Can you find me? With us real humans in the photo you get a sense of the scale of this display; and it was built in just six weeks!

The characters are phenomenal but can't move, so Steve asked me to provide lighting control that let us easily animate the lights on the character for extra pizazz. This is where the Propeller really shines — no pun intended. When Steve has a lighting change request, it doesn't take long to implement using Spin.

To give you an idea, each character controller's master cog launches the dimmer cog (PASM) and up to four animation cogs which are all written in Spin. The state of each of these Spin cogs is stored in a global hub variable so that the master cog, "listens" for a start signal from the project master controller. On receiving the start signal, the master cog runs the show by changing the various states of the other lighting control cogs. The neat part is that the lighting cogs are written in Spin (easy) and as they are, they can access the methods of the dimmer object that was started by the master cog. That's right, the dimmer object is being accessed by up to five cogs.

Figure 3 shows the male character, Typhon, all lit up. Most of the front lighting pulsates up and down in a smooth pattern, though the white headlights have an occasional "twitch" as if there was a loose wire while moving. Figure 4 is a close-up of Typhon's back. In the image, you'll see that there are two cylindrical protrusions