Magic Cauldron effect

Jeff Haas

Make Magazine always has interesting things in their email newsletter. The other day, there was a link to this Magic Cauldron project:
https://community.makezine.com/share/ianmckay/magic-cauldron-6da6b1

I thought the idea was interesting, and the way he put it in a cauldron with glass beads to diffuse the glow was good, but after I saw the second video, I figured the lighting effect could be a lot better. It looks too much like someone flipped a switch to pick the selected color, instead of a magical, mystical glow. So I spent some time on it:
- Wrote my version for the Propeller instead of the Arduino
- When activated, swirling colors fade in, then fade down
- The selected color turns on and then fades out

I'm not quite happy with the transition from the swirling rainbow to the selected color, but I figure I'd share it here, someone may find a use for it. You'll need an Adafruit NeoPixel ring to see the effect.

JonnyMac

A couple notes that may be helpful.

You don't need RealRandom to seed Heater's PRNG object -- there's enough jitter in the start-up of the cnt register that I now do it like this:

prng.seed(-cnt, -cnt ~> 2, $EA7_BEEF, cnt <- 2, cnt)

I needed a color morph effect for a WS2812 project and did it like this:

pub morph(rgb1, rgb2, phase) | idx

  phase &= $FF

  if (phase == 0)
    return rgb1

  if (phase == $FF)
    return rgb2

  repeat idx from 0 to 2
    result.byte[idx] := rgb2.byte[idx] * phase / $FF
    result.byte[idx] += rgb1.byte[idx] * ($FF-phase) / $FF

This can be useful for smooth color-to-color transitions.

Jeff Haas

Jon, thanks!

I should have some time this weekend to try these out.

Jeff Haas

Hi Jon,

The revised seed method for PRNG is great, thanks.

It took a bit for me to figure out a good way to use the morph method. Here's an abbreviated version of what I've got so far:

pub main | fade

       repeat fade from 0 to 255
           strip.fill(0,15,(morph($00_00_FF, $00_00_00, fade)))     ' fade Blue to Black
           time.pause(5)

This is a really nice fade effect. I think I see how to apply this to the wheel effects, it seems there's an additional level of nesting required, but that's as far as I've got right now.

Jeff

JonnyMac

The morph method is meant to provide a transition from one color to another. In my case with the meditation ring, I had to go from red, to orange, to yellow, to green, etc... and then pink was in the mix. Anyway, it worked well.

When you're fading a pure color up or down, you can simplify. To go from blue to black, you could also do this:

  t := cnt
  repeat fade from 255 to 0
    strip.fill(0, 15, (fade << 0))
    waitcnt(t += (5 * MS_001))

If you change << 0 to << 1 you'll fade the green channel, << 2 for the red channel. My acting teacher used to say that as there are many roads that lead to Rome, there are many ways to approach a problem. Here's another road for your programming travels!

It like to use waitcnt in these cases as it takes care of the loop overhead and ensures the fade timing is constant.

Jeff Haas

Jon, thanks again. I set up multiple morphs to see how the colors changed, it's really nice. You'll have to tell us a bit more about the meditation ring.

For the fade code, there's something I'm missing. Maybe it's too late Sunday night, but...

This works for me:

         strip.fill(0, 15, $00_00_FF)     ' Blink Blue on

         time.pause(4000)                 ' Hold color for a moment
          
         t := cnt
         repeat fade from 255 to 0
            strip.fill(0, 15, (fade << 0))  ' Results in Blue fading out
            waitcnt(t += (5 * MS_001))

This does not:

         strip.fill(0, 15, $00_FF_00)   ' Blink Green on

         time.pause(4000)                ' Hold color for a moment
          
         t := cnt
         repeat fade from 255 to 0
            strip.fill(0, 15, (fade << 1))   ' Results in Blue flashing twice
            waitcnt(t += (5 * MS_001))

Setting strip.fill(0, 15, (fade << 2)) results in Blue flashing three times.

JonnyMac

That's what I get for making a suggestion without testing! The color shift needs to be multipled by 8 for bits. This is running on my desk:

pub main | ch                                              
                                                                 
  setup

  repeat
    repeat ch from 2 to 0
      fade_down(0, PIXELS-1, ch, 2000)


pub fade_down(first, last, ch, ms) | level

'' Fade one channel from 100% to 0%
'' -- channel is 2..0 (RED, GRN, BLU)
'' -- ms is total duration of fade

  ch <<= 3                                                      ' convert ch byte to bits
  ms := ((ms * 1000) >> 8) #> 50                                  ' convert to us, divide by 256

  repeat level from 255 to 0                                    ' 100% to 0%
    strip.fill(first, last, level << ch)                        ' set color
    time.pause_us(ms)                                           ' hold

Jeff Haas

I just got a chance to try this. Works great!

Thanks again.