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Curve that touches three points: Difference between revisions
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=={{header|zkl}}==
{{trans|Go}}
<lang zkl></lang>▼
Uses Image Magick and
the PPM class from http://rosettacode.org/wiki/Bitmap/Bresenham%27s_line_algorithm#zkl
<lang zkl>const X=0, Y=1; // p.X == p[X]
var p=L(L(10.0, 10.0), L(100.0, 200.0), L(200.0, 10.0)); // (x,y)
fcn lagrange(x){ // float-->float
(x - p[1][X])*(x - p[2][X])/(p[0][X] - p[1][X])/(p[0][X] - p[2][X])*p[0][Y] +
(x - p[0][X])*(x - p[2][X])/(p[1][X] - p[0][X])/(p[1][X] - p[2][X])*p[1][Y] +
(x - p[0][X])*(x - p[1][X])/(p[2][X] - p[0][X])/(p[2][X] - p[1][X])*p[2][Y]
}
fcn getPoints(n){ // int-->( (x,y) ..)
pts:=List.createLong(2*n+1);
dx,pt,cnt := (p[1][X] - p[0][X])/n.toFloat(), p[0][X], n;
do(2){
foreach i in (cnt){
x:=pt + dx*i;
pts.append(L(x,lagrange(x)));
}
dx,pt,cnt = (p[2][X] - p[1][X])/n, p[1][X], n+1;
}
pts
}
fcn main{
var [const] n=50; // more than enough for this
img,color := PPM(210,210,0xffffff), 0; // white background, black curve
foreach x,y in (p){ img.cross(x.toInt(),y.toInt(), 0xff0000) } // mark 3 pts
a,b := p[0][X].toInt(), p[0][Y].toInt(); // curve starting point
foreach x,y in (getPoints(n)){
x,y = x.toInt(),y.toInt();
img.line(a,b, x,y, color); // can only deal with ints
a,b = x,y;
}
img.writeJPGFile("quadraticCurve.zkl.jpg");
{{out}}
Image at [http://www.zenkinetic.com/Images/RosettaCode/quadraticCurve.zkl.jpg sunflower quadratic curve]
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