# d3/d3-shape

Switch branches/tags
Nothing to show
Fetching contributors…
Cannot retrieve contributors at this time
105 lines (91 sloc) 3.13 KB
 function sign(x) { return x < 0 ? -1 : 1; } // Calculate the slopes of the tangents (Hermite-type interpolation) based on // the following paper: Steffen, M. 1990. A Simple Method for Monotonic // Interpolation in One Dimension. Astronomy and Astrophysics, Vol. 239, NO. // NOV(II), P. 443, 1990. function slope3(that, x2, y2) { var h0 = that._x1 - that._x0, h1 = x2 - that._x1, s0 = (that._y1 - that._y0) / (h0 || h1 < 0 && -0), s1 = (y2 - that._y1) / (h1 || h0 < 0 && -0), p = (s0 * h1 + s1 * h0) / (h0 + h1); return (sign(s0) + sign(s1)) * Math.min(Math.abs(s0), Math.abs(s1), 0.5 * Math.abs(p)) || 0; } // Calculate a one-sided slope. function slope2(that, t) { var h = that._x1 - that._x0; return h ? (3 * (that._y1 - that._y0) / h - t) / 2 : t; } // According to https://en.wikipedia.org/wiki/Cubic_Hermite_spline#Representations // "you can express cubic Hermite interpolation in terms of cubic Bézier curves // with respect to the four values p0, p0 + m0 / 3, p1 - m1 / 3, p1". function point(that, t0, t1) { var x0 = that._x0, y0 = that._y0, x1 = that._x1, y1 = that._y1, dx = (x1 - x0) / 3; that._context.bezierCurveTo(x0 + dx, y0 + dx * t0, x1 - dx, y1 - dx * t1, x1, y1); } function MonotoneX(context) { this._context = context; } MonotoneX.prototype = { areaStart: function() { this._line = 0; }, areaEnd: function() { this._line = NaN; }, lineStart: function() { this._x0 = this._x1 = this._y0 = this._y1 = this._t0 = NaN; this._point = 0; }, lineEnd: function() { switch (this._point) { case 2: this._context.lineTo(this._x1, this._y1); break; case 3: point(this, this._t0, slope2(this, this._t0)); break; } if (this._line || (this._line !== 0 && this._point === 1)) this._context.closePath(); this._line = 1 - this._line; }, point: function(x, y) { var t1 = NaN; x = +x, y = +y; if (x === this._x1 && y === this._y1) return; // Ignore coincident points. switch (this._point) { case 0: this._point = 1; this._line ? this._context.lineTo(x, y) : this._context.moveTo(x, y); break; case 1: this._point = 2; break; case 2: this._point = 3; point(this, slope2(this, t1 = slope3(this, x, y)), t1); break; default: point(this, this._t0, t1 = slope3(this, x, y)); break; } this._x0 = this._x1, this._x1 = x; this._y0 = this._y1, this._y1 = y; this._t0 = t1; } } function MonotoneY(context) { this._context = new ReflectContext(context); } (MonotoneY.prototype = Object.create(MonotoneX.prototype)).point = function(x, y) { MonotoneX.prototype.point.call(this, y, x); }; function ReflectContext(context) { this._context = context; } ReflectContext.prototype = { moveTo: function(x, y) { this._context.moveTo(y, x); }, closePath: function() { this._context.closePath(); }, lineTo: function(x, y) { this._context.lineTo(y, x); }, bezierCurveTo: function(x1, y1, x2, y2, x, y) { this._context.bezierCurveTo(y1, x1, y2, x2, y, x); } }; export function monotoneX(context) { return new MonotoneX(context); } export function monotoneY(context) { return new MonotoneY(context); }