[PD] freehand drawing on video in GEM

marius schebella marius.schebella at gmail.com
Mon Jul 21 23:17:02 CEST 2008

I think what you need to do is create some kind of b/w mask. basically 
you start with a black texture and add white to wherever the point of 
light goes. you can either take the video material and filter it, so 
that only the light is visible and then create a feedbackloop that 
always adds to the last image, but you could also use blob and draw a 
curve, like you suggested. creating a long render chain of 
openglcommands on the fly could work, but becomes slower with every 
frame, so this will only work for a certain amount of time. but you can 
still use gemframebuffer and a feedback loop to draw white 
rectangles/circles/curves into a black texture and use it a the mask.
at some point you probably want to reset your window?
I will try to come up with a test-patch for that problem. would 
perfectly fit into a gem tutorial anyway.

Spencer Russell wrote:
> I need to blob track a point of light in a video and use it to draw
> freehand in the GEM window, possibly mixed with previously-recorded
> video clips. I'd also like to connect the adjacent points with lines
> so that the drawing is continuous.
> I'm still pretty new to GEM, but I'm working on getting my head around
> all the render order and buffering ideas, I'm just not sure what the
> best approach is. I've tried using gemframebuffer going to a pix_snap,
> but it takes up 100% CPU, so I figure there's got to be a better way.
> Is there some sort of way I can just keep appending vertices to a list
> and use something like [curve]?
> Thanks,
> spencer
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