From c8fb681b6fca571d27ae787ee3d03cc94d833dad Mon Sep 17 00:00:00 2001
From: Roland Conybeare <rconybeare@gmail.com>
Date: Sun, 1 May 2016 12:43:03 -0400
Subject: [PATCH] change file mode.

---
 d3/drag6/fx.js | 109 ++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 108 insertions(+), 1 deletion(-)
 mode change 120000 => 100644 d3/drag6/fx.js

diff --git a/d3/drag6/fx.js b/d3/drag6/fx.js
deleted file mode 120000
index e5391b1..0000000
--- a/d3/drag6/fx.js
+++ /dev/null
@@ -1 +0,0 @@
-../drag5/fx.js
\ No newline at end of file
diff --git a/d3/drag6/fx.js b/d3/drag6/fx.js
new file mode 100644
index 0000000..d5b4736
--- /dev/null
+++ b/d3/drag6/fx.js
@@ -0,0 +1,108 @@
+!function() {
+    /* module for working with a particular one-parameter function -- call it f(x) */
+
+    var fx
+	= { /*procedure to evaluate f(x)*/
+	    target_fn: null,
+	    /* like target_fn(),  but returns a point */
+	    eval_fn: null
+	};
+
+    /* the (linear) function of (x) that is
+     * tangent to fx.target_fn at x0
+     */
+    fx.make_tangent_fn = function(x0, fn, fn_deriv) {
+	var fx0 = fn(x0);
+	var dfx0 = fn_deriv(x0);
+
+	return function(x) { return fx0 + (x - x0) * dfx0; }
+    } /*make_tangent_fn*/
+
+    /* f :: num -> num
+     * returns pf :: num -> Point,  pf(x) = {x: x, y: f(x)}
+     */
+    fx.make_pt_fn = function(f) {
+	return function(x) { return {x: x, y: f(x)}; };
+    } /*make_pt_fn*/
+
+    /* x0 :: num
+     * fn :: num -> num
+     * fn_deriv :: num -> num
+     * returns :: (num -> Point)
+     */
+    fx.make_tangent_pt_fn = function(x0, fn, fn_deriv) {
+	return fx.make_pt_fn(fx.make_tangent_fn(x0, fn, fn_deriv));
+    } /*make_tangent_pt_fn*/
+
+    /* transform points using d3 scales
+     *   f({x,y}) = {xscale(x),yscale(y)}
+     *
+     * xscale :: D3scale
+     * yscale :: D3scale
+     */
+    fx.scale_fn = function(xscale, yscale)
+    {
+	return function(p) {
+	    return {x: xscale(p.x), y: yscale(p.y)};
+	}
+    } /*scale_fn*/
+
+    /* transform points using d3 scales, inverted
+     *   f({x,y}) = {xscale.invert(x),yscale.invert(y)}
+     *
+     * xscale :: D3scale
+     * yscale :: D3scale
+     */
+    fx.invert_scale_fn = function(xscale, yscale)
+    {
+	return function(p) {
+	    return {x: xscale.invert(p.x), y: yscale.invert(p.y)};
+	}
+    } /*invert_scale_fn*/
+
+    /* make an array of points, representing
+     * fx evaluated at regularly-spaced intervals;
+     * clip so that all points returned fall within the rectangle
+     * defined by (0,0) and box_pt
+     *
+     * fx :: number -> Point
+     * lo_x, hi_x :: number
+     * n_pt :: number
+     * xyscale :: Xyscale
+     * box_pt :: Point
+     */
+    fx.make_target_pt_v = function(fx, lo_x, hi_x, n_pt, xyscale, box_pt)
+    {
+	var target_pt_v = [];
+	var target_pt_i = 0;
+	var p = null;
+	var pm1 = null;
+
+	/* evaluate f(x) at regularly spaced x-coordinates on interval [lo_x, hi_x] 
+	 * keep only points with screen coords that fall inside the rectangle
+	 * with corners {(0,0), box_pt}, plus:
+	 * one point just before and one point just after
+	 */
+	for(var i=0; i<n_pt; ++i) {
+	    tmp = lo_x + (i * (hi_x - lo_x) / n_pt);
+	    pm1 = p;
+	    p = xyscale.scale_pt(fx(tmp));
+
+	    if(pt.box_contains(box_pt, p)) {
+		if((pm1 !== null) && !pt.box_contains(box_pt, pm1)) {
+		    /* pm1 outside box,  substitute clipped version */
+		    target_pt_v[target_pt_i++] = pt.clip_line(pm1, p, box_pt);
+		}
+		target_pt_v[target_pt_i++] = p;
+	    } else if((pm1 !== null) && pt.box_contains(box_pt, pm1)) {
+		/* if pm1 was inside the box,  then include p 
+		   after all */
+		target_pt_v[target_pt_i++] = pt.clip_line(p, pm1, box_pt);
+	    }
+	}
+
+	return target_pt_v;
+    } /*make_target_pt_v*/
+
+    this.fx = fx;
+}();