From d59b6f341a39df8b051e0777ec7885f93fab25f5 Mon Sep 17 00:00:00 2001
From: Robert Konigsberg <konigsberg@google.com>
Date: Tue, 4 Jan 2011 11:00:50 -0500
Subject: [PATCH] Converted log scaled graphs from log(e) to log(10)

---
 dygraph.js          | 32 ++++++++++++++++++++++----------
 tests/logscale.html | 21 ++++++++++-----------
 2 files changed, 32 insertions(+), 21 deletions(-)

diff --git a/dygraph.js b/dygraph.js
index 8a5d870..d738e54 100644
--- a/dygraph.js
+++ b/dygraph.js
@@ -79,6 +79,11 @@ Dygraph.DEFAULT_WIDTH = 480;
 Dygraph.DEFAULT_HEIGHT = 320;
 Dygraph.AXIS_LINE_WIDTH = 0.3;
 
+Dygraph.LOG_SCALE = 10;
+Dygraph.LOG_BASE_E_OF_TEN = Math.log(Dygraph.LOG_SCALE);
+Dygraph.log10 = function(x) {
+  return Math.log(x) / Dygraph.LOG_BASE_E_OF_TEN;
+}
 
 // Default attribute values.
 Dygraph.DEFAULT_ATTRS = {
@@ -447,22 +452,22 @@ Dygraph.prototype.toDataYCoord = function(y, axis) {
     // the following steps:
     //
     // Original calcuation:
-    // pct = (logr1 - Math.log(y)) / (logr1 - Math.log(yRange[0]));
+    // pct = (logr1 - Dygraph.log10(y)) / (logr1 - Dygraph.log10(yRange[0]));
     //
     // Move denominator to both sides:
-    // pct * (logr1 - Math.log(yRange[0])) = logr1 - Math.log(y);
+    // pct * (logr1 - Dygraph.log10(yRange[0])) = logr1 - Dygraph.log10(y);
     //
     // subtract logr1, and take the negative value.
-    // logr1 - (pct * (logr1 - Math.log(yRange[0]))) = Math.log(y);
+    // logr1 - (pct * (logr1 - Dygraph.log10(yRange[0]))) = Dygraph.log10(y);
     //
     // Swap both sides of the equation, and we can compute the log of the
     // return value. Which means we just need to use that as the exponent in
     // e^exponent.
-    // Math.log(y) = logr1 - (pct * (logr1 - Math.log(yRange[0])));
+    // Dygraph.log10(y) = logr1 - (pct * (logr1 - Dygraph.log10(yRange[0])));
 
-    var logr1 = Math.log(yRange[1]);
-    var exponent = logr1 - (pct * (logr1 - Math.log(yRange[0])));
-    var value = Math.pow(Math.E, exponent);
+    var logr1 = Dygraph.log10(yRange[1]);
+    var exponent = logr1 - (pct * (logr1 - Dygraph.log10(yRange[0])));
+    var value = Math.pow(Dygraph.LOG_SCALE, exponent);
     return value;
   }
 };
@@ -494,8 +499,8 @@ Dygraph.prototype.toPercentYCoord = function(y, axis) {
     // (yRange[1] - y) / (yRange[1] - yRange[0]) is the % from the bottom.
     pct = (yRange[1] - y) / (yRange[1] - yRange[0]);
   } else {
-    var logr1 = Math.log(yRange[1]);
-    pct = (logr1 - Math.log(y)) / (logr1 - Math.log(yRange[0]));
+    var logr1 = Dygraph.log10(yRange[1]);
+    pct = (logr1 - Dygraph.log10(y)) / (logr1 - Dygraph.log10(yRange[0]));
   }
   return pct;
 }
@@ -948,11 +953,18 @@ Dygraph.movePan = function(event, g, context) {
   // y-axis scaling is automatic unless this is a full 2D pan.
   if (context.is2DPan) {
     // Adjust each axis appropriately.
+    // NOTE(konigsberg): I don't think this computation for y_frac is correct.
+    // I think it doesn't take into account the display of the x axis.
+    // See, when I tested this with console.log(y_frac), and move the mouse
+    // cursor to the botom, the largest y_frac was 0.94, and not 1.0. That
+    // could also explain why panning tends to start with a small jumpy shift.
     var y_frac = context.dragEndY / g.height_;
+
     for (var i = 0; i < g.axes_.length; i++) {
       var axis = g.axes_[i];
       var maxValue = axis.draggingValue + y_frac * axis.dragValueRange;
       var minValue = maxValue - axis.dragValueRange;
+      console.log(axis.draggingValue, axis.dragValueRange, minValue, maxValue, y_frac);
       axis.valueWindow = [ minValue, maxValue ];
     }
   }
@@ -1939,7 +1951,7 @@ Dygraph.numericTicks = function(minV, maxV, self, axis_props, vals) {
       // Construct the set of ticks.
       for (var i = 0; i < nTicks; i++) {
         ticks.push( {v: vv} );
-        vv = vv * Math.E;
+        vv = vv * Dygraph.LOG_SCALE;
       }
     } else {
       // Basic idea:
diff --git a/tests/logscale.html b/tests/logscale.html
index b190617..9c17ead 100644
--- a/tests/logscale.html
+++ b/tests/logscale.html
@@ -19,21 +19,20 @@
     <script type="text/javascript">
       function Data() {
         return "Date,A\n" +
-        "20101201,1\n"+
-        "20101202,5\n"+
-        "20101203,10\n"+
-        "20101204,100\n"+
-        "20101205,250\n"+
-        "20101206,1000\n"+
-        "20101207,30\n"+
-        "20101208,80\n"+
-        "20101209,100\n"+
-        "20101210,250\n"+
+        "20101201,5\n"+
+        "20101202,10\n"+
+        "20101203,100\n"+
+        "20101204,250\n"+
+        "20101205,1000\n"+
+        "20101206,30\n"+
+        "20101207,80\n"+
+        "20101208,100\n"+
+        "20101209,250\n"+
         "";
       }
       var g = new Dygraph(document.getElementById("div_g"),
                       Data, { logscale : true });
-      Dygraph.addEvent(g.canvas_, 'mousemove', function(e) {
+      Dygraph.addEvent(g.canvas_, '_mousemove', function(e) {
         var y = Dygraph.pageY(e) - Dygraph.findPosY(g.canvas_);
         console.log(y, g.toDataYCoord(y));
       });
-- 
2.7.4