YopSolo.fr

[Flash 9+]

september 2015

Smooth step for AS3

Smoothstep is a scalar interpolation function commonly used in computer graphics and video game engines.
The function interpolates smoothly between two input values based on a third one that should be between the first two. The returned value is clamped between 0 and 1.
The slope of the smoothstep function tends toward zero at both edges. This makes it easy to create a sequence of transitions using smoothstep to interpolate each segment rather than using a more sophisticated or expensive interpolation technique.

source : https://en.wikipedia.org/wiki/Smoothstep

package
{
import flash.display.Sprite;

/**
* ...
* @author YopSolo
*/
public class Main extends Sprite
{

public function Main()
{
var step:Number = .01;

graphics.lineStyle(0, 0x0000ff); // blue
for (var x:Number = 0.0; x < 1; x += step)
{
var y:Number = 1 - smoothstep(0, 1, x);
if (x == 0.0)
{
graphics.moveTo(x * 400, y * 400);
}
else
{
graphics.lineTo(x * 400, y * 400);
}
}

// smoothstep2
graphics.lineStyle(0, 0x00ff00); // green
for (x = 0.0; x < 1; x += step)
{
y = 1 - smoothstep2(0, 1, x);
if (x == 0.0)
{
graphics.moveTo(x * 400, y * 400);
}
else
{
graphics.lineTo(x * 400, y * 400);
}
}

// Cos
graphics.lineStyle(0, 0xff0000); // red
for (x = 0; x < 1; x += step)
{
y = Math.cos(Math.PI * x) * .5 + .5;
if (x == 0)
{
graphics.moveTo(x * 400, y * 400);
}
else
{
graphics.lineTo(x * 400, y * 400);
}
}
}

//http://en.wikipedia.org/wiki/Smoothstep
private function smoothstep(e0:Number, e1:Number, x:Number):Number
{
x = Math.min(Math.max((x - e0) / (e1 - e0), 0.0), 1.0);
return x * x * (3 - 2 * x);
}

private function smoothstep2(edge0:Number, edge1:Number, x:Number):Number
{
// Scale, bias and saturate x to 0..1 range
x = Math.min(Math.max((x - edge0) / (edge1 - edge0), 0.0), 1.0);
// Evaluate polynomial
return x * x * x * (x * (x * 6 - 15) + 10);
}

}

}