json based animation toy

experimental/docs/interpolatorFunctions.js

+function interp(A, B, t) {
+    return A + (B - A) * t;
+}
+
+function interp_cubic_coords(x1, x2, x3, x4, t)
+{
+    var ab = interp(x1, x2, t);
+    var bc = interp(x2, x3, t);
+    var cd = interp(x3, x4, t);
+    var abc = interp(ab, bc, t);
+    var bcd = interp(bc, cd, t);
+    var abcd = interp(abc, bcd, t);
+    return abcd;
+}
+
+// FIXME : only works for path with single cubic
+function path_partial(value, path) {
+    assert(isArray(path));
+    var out = [];
+    for (var cIndex = 0; cIndex < path.length; ++cIndex) {
+        out[cIndex] = {};
+        var curveKey = Object.keys(path[cIndex])[0];
+        var curve = path[cIndex][curveKey];
+        var outArray;
+        switch (curveKey) {
+            case "cubic":
+                var x1 = curve[0], y1 = curve[1], x2 = curve[2], y2 = curve[3];
+                var x3 = curve[4], y3 = curve[5], x4 = curve[6], y4 = curve[7];
+                var t1 = 0, t2 = value;
+                var ax = interp_cubic_coords(x1, x2, x3, x4, t1);
+                var ay = interp_cubic_coords(y1, y2, y3, y4, t1);
+                var ex = interp_cubic_coords(x1, x2, x3, x4, (t1*2+t2)/3);
+                var ey = interp_cubic_coords(y1, y2, y3, y4, (t1*2+t2)/3);
+                var fx = interp_cubic_coords(x1, x2, x3, x4, (t1+t2*2)/3);
+                var fy = interp_cubic_coords(y1, y2, y3, y4, (t1+t2*2)/3);
+                var dx = interp_cubic_coords(x1, x2, x3, x4, t2);
+                var dy = interp_cubic_coords(y1, y2, y3, y4, t2);
+                var mx = ex * 27 - ax * 8 - dx;
+                var my = ey * 27 - ay * 8 - dy;
+                var nx = fx * 27 - ax - dx * 8;
+                var ny = fy * 27 - ay - dy * 8;
+                var bx = (mx * 2 - nx) / 18;
+                var by = (my * 2 - ny) / 18;
+                var cx = (nx * 2 - mx) / 18;
+                var cy = (ny * 2 - my) / 18;
+                outArray = [
+                    ax, ay, bx, by, cx, cy, dx, dy
+                ];
+                break;
+            default:
+                assert(0);  // unimplemented
+        }
+        out[cIndex][curveKey] = outArray;
+    }
+    return out;
+}
+
+function interp_paths(value, paths) {
+    assert(isArray(paths));
+    assert(paths.length == 2);
+    var curves0 = paths[0];
+    assert(isArray(curves0));
+    var curves1 = paths[1];
+    assert(isArray(curves1));
+    assert(curves0.length == curves1.length);
+    var out = [];
+    for (var cIndex = 0; cIndex < curves0.length; ++cIndex) {
+        out[cIndex] = {};
+        var curve0Key = Object.keys(curves0[cIndex])[0];
+        var curve1Key = Object.keys(curves1[cIndex])[0];
+        assert(curve0Key == curve1Key);
+        var curve0 = curves0[cIndex][curve0Key];
+        var curve1 = curves1[cIndex][curve1Key];
+        assert(isArray(curve0));
+        assert(isArray(curve1));
+        assert(curve0.length == curve1.length);
+        var outArray = [];
+        for (var i = 0; i < curve1.length; ++i) {
+            outArray[i] = curve0[i] + (curve1[i] - curve0[i]) * value;
+        }
+        out[cIndex][curve0Key] = outArray;
+    }
+    return out;
+}