[PD] emulating early video synths - sync

[Paris Treantafeles]

Hello List,

I've created a few patches with PD/GEM to emulate early video synths  
such as the Sandin, etc. which I'm quite happy with.
At the heart of these patches is pix_sig2pix~
One thing I can't figure out though has to do with preventing the  
image from "rolling" - i.e. to stand still.
The early video synths did this by having a "sync" input to oscillators.
So if you fed one oscillator a vertical sync (~60 Hz) you would get  
stationary vertical bars whose width would depend on the main  
frequency of the oscillator. Doing this with another oscillator  
receiving a horizontal sync (~1500 Hz) results in horizontal bars.
By mixing these and perhaps another (and adjusting the attenuation of  
these), various shapes appear.
I can get all of this and more (e.g. add some filters for subtractive  
synthesis) but what I'm missing is how to do the sync correctly.
Trying various values as reset inputs to say "phasor~" doesn't do it.
I'm wondering if this is in fact related to blocksize~ instead.
e.g. should the reset values of the oscillators be related in someway  
to the value set in blocksize~

Does anyone have any ideas about this?

Thanks for any suggestions!

Best,
p