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Index › Programming Questions & Help › Syntax Questions › Interpolate Value Function using Splines
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Interpolate Value Function using Splines (Read 1562 times)
rs3d
Interpolate Value Function using Splines
Aug 30th, 2005, 12:00pm  
Hello, I would like to have a simple function
that allows to get interpolated values out
of 3 given parameters. Interpolated should
happen with some spline/curve function and
no simple linear one:

v = interpolate (a,b,c, step);

a,b,c   floats

step    ranges from 0 (equals a) to 1 (equals c) and
       allows outputting interpolated values in the
       range ... 0.5 would logically output b

I know this isn't that hard, but since my math
is faded, for many of you, it would be a snap ...

Thanks for helping, Rob
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fry
Re: Interpolate Value Function using Splines
Reply #1 - Aug 30th, 2005, 4:17pm  
sure, the functions are even called curve() and bezier():
http://processing.org/reference/curve_.html
http://processing.org/reference/bezier_.html
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rgovostes
Re: Interpolate Value Function using Splines
Reply #2 - Aug 31st, 2005, 2:23am  
Right, but I think rs3d is asking for a way to do this with numbers, not drawing. I've not tested this, but I'd imagine it would do the trick:

Code:
float interpolate(float a, float b, float c, float step) {
   if(step <= 0.5) {
	step *= 2;
	return (b * step) + (a * (1 - step));
   } else { 
	step = (step - 0.5) * 2;
	return (c * step) + (b * (1 - step));
   }
}
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rs3d
Re: Interpolate Value Function using Splines
Reply #3 - Aug 31st, 2005, 12:11pm  
Thanks rgovostes, you are right ... but the
thing is, it doesn't interpolate smoothly
with a bspline or cubic function. This just
creates a linear interpolation ...

Thanks, RS
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Quasimondo
Re: Interpolate Value Function using Splines
Reply #4 - Aug 31st, 2005, 1:46pm  
You might have a look at Robert Penner's easing functions: http://www.robertpenner.com/easing/ - it's pretty easy to convert them from ActionScript to Java and I'm pretty sure that they'll do exactly what you need.
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Mario Klingemann | Quasimondo | Incubator | côdeazur
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fry
Re: Interpolate Value Function using Splines
Reply #5 - Aug 31st, 2005, 3:15pm  
sorry, linked to the wrong functions, it's curvePoint and bezierPoint:
http://processing.org/reference/curvePoint_.html
http://processing.org/reference/bezierPoint_.html
(they used to be just called curve and bezier in earlier alphas.. i can't keep my own api straight)

they evaluate a bezier (a cubic spline) or catmull-rom curve at a point, and can be used for easing functions like was being asked for. don't be fooled by the fact that the reference describes it in terms of evaluating curves at x and y points and drawin them.. you'll notice that the x and y dimensions have to be evaluated separately, because this is just a 1D curve function.
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rs3d
Re: Interpolate Value Function using Splines
Reply #6 - Aug 31st, 2005, 9:22pm  
Thanks, the Robert Penner ones are great inspirations, too!
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