Clamp easing functions to [0,1].

Rather than have a treshold in transitions, we now clamp the easing functions.
This guarantees that when the transition ends, the tweens will be called with
t=1, and produce clean output values. Previously, that was not the case for
certain easing functions, such as exp-out and elastic.

d3.js

@@ -591,9 +591,15 @@ d3.ease = function(name) {
   var i = name.indexOf("-"),
       t = i >= 0 ? name.substring(0, i) : name,
       m = i >= 0 ? name.substring(i + 1) : "in";
-  return d3_ease_mode[m](d3_ease[t].apply(null, Array.prototype.slice.call(arguments, 1)));
+  return d3_ease_clamp(d3_ease_mode[m](d3_ease[t].apply(null, Array.prototype.slice.call(arguments, 1))));
 };
 
+function d3_ease_clamp(f) {
+  return function(t) {
+    return t <= 0 ? 0 : t >= 1 ? 1 : f(t);
+  };
+}
+
 function d3_ease_reverse(f) {
   return function(t) {
     return 1 - f(1 - t);
@@ -1802,15 +1808,15 @@ function d3_transition(groups, id) {
       function tick(elapsed) {
         if (lock.active !== id) return stop();
 
-        var t = Math.min(1, (elapsed - delay) / duration),
+        var t = (elapsed - delay) / duration,
             e = ease(t),
             n = tweened.length;
 
         while (n > 0) {
           tweened[--n].call(node, e);
         }
 
-        if (t === 1) {
+        if (t >= 1) {
           stop();
           d3_transitionInheritId = id;
           event.end.dispatch.call(node, d, i);

src/core/ease.js

@@ -60,9 +60,15 @@ d3.ease = function(name) {
   var i = name.indexOf("-"),
       t = i >= 0 ? name.substring(0, i) : name,
       m = i >= 0 ? name.substring(i + 1) : "in";
-  return d3_ease_mode[m](d3_ease[t].apply(null, Array.prototype.slice.call(arguments, 1)));
+  return d3_ease_clamp(d3_ease_mode[m](d3_ease[t].apply(null, Array.prototype.slice.call(arguments, 1))));
 };
 
+function d3_ease_clamp(f) {
+  return function(t) {
+    return t <= 0 ? 0 : t >= 1 ? 1 : f(t);
+  };
+}
+
 function d3_ease_reverse(f) {
   return function(t) {
     return 1 - f(1 - t);

src/core/transition.js

@@ -57,15 +57,15 @@ function d3_transition(groups, id) {
       function tick(elapsed) {
         if (lock.active !== id) return stop();
 
-        var t = Math.min(1, (elapsed - delay) / duration),
+        var t = (elapsed - delay) / duration,
             e = ease(t),
             n = tweened.length;
 
         while (n > 0) {
           tweened[--n].call(node, e);
         }
 
-        if (t === 1) {
+        if (t >= 1) {
           stop();
           d3_transitionInheritId = id;
           event.end.dispatch.call(node, d, i);

test/core/ease-test.js

@@ -51,33 +51,33 @@ suite.addBatch({
       var e = ease("bounce");
       assert.inDelta(e(.5), 0.765625, 1e-6);
     },
-    "all easing functions return approximately 0 for t = 0": function(ease) {
-      assert.inDelta(ease("linear")(0), 0, 1e-9);
-      assert.inDelta(ease("poly", 2)(0), 0, 1e-9);
-      assert.inDelta(ease("quad")(0), 0, 1e-9);
-      assert.inDelta(ease("cubic")(0), 0, 1e-9);
-      assert.inDelta(ease("sin")(0), 0, 1e-9);
-      assert.inDelta(ease("exp")(0), 0, 1e-3); // XXX
-      assert.inDelta(ease("circle")(0), 0, 1e-9);
-      assert.inDelta(ease("elastic")(0), 0, 1e-9);
-      assert.inDelta(ease("back")(0), 0, 1e-9);
-      assert.inDelta(ease("bounce")(0), 0, 1e-9);
-    },
-    "all easing functions return approximately 1 for t = 1": function(ease) {
-      assert.inDelta(ease("linear")(1), 1, 1e-9);
-      assert.inDelta(ease("poly", 2)(1), 1, 1e-9);
-      assert.inDelta(ease("quad")(1), 1, 1e-9);
-      assert.inDelta(ease("cubic")(1), 1, 1e-9);
-      assert.inDelta(ease("sin")(1), 1, 1e-9);
-      assert.inDelta(ease("exp")(1), 1, 1e-9);
-      assert.inDelta(ease("circle")(1), 1, 1e-9);
-      assert.inDelta(ease("elastic")(1), 1, 1e-3); // XXX
-      assert.inDelta(ease("back")(1), 1, 1e-9);
-      assert.inDelta(ease("bounce")(1), 1, 1e-9);
+    "all easing functions return exactly 0 for t = 0": function(ease) {
+      assert.equal(ease("linear")(0), 0);
+      assert.equal(ease("poly", 2)(0), 0);
+      assert.equal(ease("quad")(0), 0);
+      assert.equal(ease("cubic")(0), 0);
+      assert.equal(ease("sin")(0), 0);
+      assert.equal(ease("exp")(0), 0);
+      assert.equal(ease("circle")(0), 0);
+      assert.equal(ease("elastic")(0), 0);
+      assert.equal(ease("back")(0), 0);
+      assert.equal(ease("bounce")(0), 0);
+    },
+    "all easing functions return exactly 1 for t = 1": function(ease) {
+      assert.equal(ease("linear")(1), 1);
+      assert.equal(ease("poly", 2)(1), 1);
+      assert.equal(ease("quad")(1), 1);
+      assert.equal(ease("cubic")(1), 1);
+      assert.equal(ease("sin")(1), 1);
+      assert.equal(ease("exp")(1), 1);
+      assert.equal(ease("circle")(1), 1);
+      assert.equal(ease("elastic")(1), 1);
+      assert.equal(ease("back")(1), 1);
+      assert.equal(ease("bounce")(1), 1);
     },
     "the -in suffix returns the identity": function(ease) {
-      assert.equal(ease("linear-in"), ease("linear"));
-      assert.equal(ease("quad-in"), ease("quad"));
+      assert.inDelta(ease("linear-in")(.25), ease("linear")(.25), 1e-6);
+      assert.inDelta(ease("quad-in")(.75), ease("quad")(.75), 1e-6);
     },
     "the -out suffix returns the reverse": function(ease) {
       assert.inDelta(ease("sin-out")(.25), 1 - ease("sin-in")(.75), 1e-6);
@@ -94,10 +94,10 @@ suite.addBatch({
       assert.inDelta(ease("bounce-out-in")(.25), .5 * ease("bounce-out")(.5), 1e-6);
       assert.inDelta(ease("elastic-out-in")(.25), .5 * ease("elastic-out")(.5), 1e-6);
     },
-    "does not clamp input time": function(ease) {
+    "clamps input time": function(ease) {
       var e = ease("linear");
-      assert.inDelta(e(-1), -1, 1e-6);
-      assert.inDelta(e(2), 2, 1e-6);
+      assert.inDelta(e(-1), 0, 1e-6);
+      assert.inDelta(e(2), 1, 1e-6);
     },
     "poly": {
       "supports an optional polynomial": function(ease) {