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Subject: Re: Add layers in LCX
From: Matthijs van Duin
Date: Sun, 29 Jun 2003 13:14:53 +0200

On Sun, Jun 29, 2003 at 11:04:57AM +0100, David Raison wrote:
For channels defined in both layers the value in the lower layer is added to the value in the upper layer fine. However, I get strange behaviour on channels that are only defined in the upper layer - It seems I can set them only to 0 or 255.

Yes, you should never use an add-layer by itself (actually you can build some fun tricks with it, like extremely slow fades, but it's usually not what you want :)


For a test I set up a RoboScan508. This has 5 channels mapped as 43 Lamp control, 44 Colour, 45 Gobo, 46 Pan, 47 Tilt.

:d02    46[128]   47[128]
:d03    46[128]   47[030]
:d04    46[030]   47[030]
:d05    46[030]   47[128]

Now in the next layer (flagged as ADD) I define channel 43 as 11, 44 as 0, 45 as 0, 46 as 129 and 47 as 128. In the DMX monitor I now see 46 and 47 'looping' in time to the 'BA' layer.

I should note that you should probably center your patterns around 128/128, since an add-layer can do adjustment in range -128..127.

Channel 43 shows as 0. In fact for all values between 0 and 127 channel 43 shows 0, values 129 to 255 cause the channel to show 255.

Yes, because we wanted add-layer to be able to subtraction as well as addition, there is an offset of 128. This means that 128 = add 0, while 0 = subtract 128.

There seems to be a fade involved, as you can see the channel to fade from 0 to 255 and vica versa as you cross the boundary. NB A value of 128 will stop the 'fade'.

What you're seeing is the add-layer being applied every frame. Because the channel is never *set* to any value (using a layer in copy mode), it just keeps adding on top of the current value. So if the add-layer is set to 127 it will subtract one every frame, causing a fade down to 0 of 20 steps per second. Setting it to 128 will add 0 every frame, hence stopping the 'fade'. Setting it to 129 will add one every frame, causing a fade up.

This is why a channel that is in use should always be in at least one layer in copy mode, unless the cumulative behavior is something you want for some effect.

Now the question is how to make some channels ADD from below, while defining others as required?

Hmm.. how about swapping the two layers? Set the shutter, color, gobo and pan/til origin in the copy layer, and run the pattern in the add-layer. That should fix the problem.

--
Matthijs van Duin  --  May the Forth be with you!
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