B-Spline

components/sections/bsplines/interpolation-graph.js

@@ -0,0 +1,72 @@
+module.exports = {
+  degree: 3,
+  activeDistance: 9,
+
+  setup() {
+    this.size(600, 300);
+    this.draw();
+  },
+
+  draw() {
+    this.clear();
+    var pad = 25;
+    this.grid(pad);
+    this.stroke(0);
+    this.line(pad,0,pad,this.height);
+    var y = this.height - pad;
+    this.line(0,y,this.width,y);
+    this.N(3, 3, pad);
+  },
+
+  // based on http://www.ibiblio.org/e-notes/Splines/Bspline.java
+  N(n, k, pad) {
+    var n1 = n+1;
+    var nt = n+k+1;
+    var w2 = this.width/2;
+    var h1 = this.height;
+    var ti = [0,1,2,3,4,5,6];
+    var step = 0.1, t = ti[0];
+    var N = [[],[],[],[],[],[],[],[]];
+
+    var i1 = 0;
+    for (var l = 0; l < w2; l++) {
+      while (t >= ti[i1] ) {
+        i1++;
+      }
+      var i = i1-1;
+      for (var s = 0; s < nt; s++) {
+        N[s][l] = 0;
+      }
+      N[i][l] = 1;
+      //  basis functions calculation
+      for (var m = 2; m <= k; m++) { 
+        var jb = i-m+1;
+        if (jb < 0) {
+          jb = 0;
+        }
+        for (var j = jb; j <= i; j++) {
+          N[j][l] = N[j][l]*(t - ti[j])/(ti[j+m-1] - ti[j]) +
+                    N[j+1][l]*(ti[j+m] - t)/(ti[j+m] - ti[j+1]);
+        }
+      }
+      t += step;
+    }
+
+    var stw = this.width/6;
+    for (let j = 0; j < n1; j++) {
+      t = ti[0];
+      let to = t;
+      for (let l = 1; l < w2; l++) {
+        t += step;
+        let t1 = t;
+        this.line(
+          pad + stw * to,
+          h1 - (h1 * N[j][l-1]) - pad,
+          pad + stw * t1,
+          h1 - (h1 * N[j][l]) - pad
+        );
+        to = t1;
+      }
+    }
+  }
+};