[PD] Drawing lines in gem with alpha fade

[Andrew Faraday]

Cyrille 
Thanks for mentioning the motion blur features in gem. I've been messing about with these for a while and I thought I'd show off some pretty patching that's resulted. 
As always, constructive criticism is appreciated 

> Date: Sat, 23 Jan 2010 01:15:09 +0000
> From: claudiusmaximus at goto10.org
> To: james at 4thharmonic.com
> CC: pd-list at iem.at
> Subject: Re: [PD] Drawing lines in gem with alpha fade
> 
> James Dunn wrote:
> > Thanks - it's interesting but doesn't seem to do quite what I need. Even 
> > with a maximum alpha value, I still want the lines to stay on full 
> > brightness for longer. Also, I'm drawing some fine lines and there are 
> > some weird artefacts like blocks appearing in the trail. Is there 
> > something else I could try?
> 
> This is probably caused by the texture being 8-bit per channel, so decay 
> coefficients are quantized in 1/256 increments, which makes long decay 
> times hard to achieve (the slowest decay's coefficient is 255/256, which 
> isn't as close to 1.0 as you want, I guess).
> 
> You could keep some data about the history of each line segment 
> (position, time created, colour, etc), and draw them all fresh each 
> frame - this will be much less efficient than texture feedback but you 
> would have more control over the fade, with  the possibility to do 
> things like change colour (not just alpha) over time with 
> other-than-exponential decay curves, etc.
> 
> Probably pd/doc/Gem/02.advanced/20.double-gemhead_vs_repeat.pd helps.
> 
> If that gets too slow you could combine the drawing of the line segments 
> into one glBegin/End block at the price of some flexibility.  And if 
> that gets too slow, there's probably something that can be done with 
> vertex arrays/buffers or whatever they're called (if it's even possible 
> in Gem - I'm not sure, but I'd like to find out!).
> 
> 
> Claude
> 
> > 
> > Quoth cyrille henry, on 22/01/10 21:45:
> >> have a look at example 07.texture/08.MotionBlur.pd
> >> all you have to do is remplace the teapot with a line that you can 
> >> draw or not (to make it fade out)
> >>
> >> Cyrille
> >>
> >>
> >> James Dunn a écrit :
> >>> I've been sending x/y values to [curve] to draw some lines in gem and 
> >>> the only way I've been able to get them to stay rendered is to use 
> >>> single buffer mode using [buffer 1( messaged to [gemwin].
> >>>
> >>> Can someone suggest a better method using double buffer perhaps? I 
> >>> would like the lines to fade out after some seconds. I looked at 
> >>> pix_snap2tex and gemframebuffer but could only get one line rendered. 
> >>> Is this possible with the particle objects?
> >>>
> >>> thanks
> >>>
> >>> James
> 
> -- 
> http://claudiusmaximus.goto10.org
> 
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