Added axis transformation support

git-svn-id: https://flot.googlecode.com/svn/trunk@202 1e0a6537-2640-0410-bfb7-f154510ff394

API.txt

@@ -166,8 +166,6 @@ If you want the legend to appear somewhere else in the DOM, you can
 specify "container" as a jQuery object/expression to put the legend
 table into. The "position" and "margin" etc. options will then be
 ignored. Note that Flot will overwrite the contents of the container.
-Most of the above settings do not apply
-
 
 
 Customizing the axes
@@ -178,9 +176,13 @@ Customizing the axes
     min: null or number
     max: null or number
     autoscaleMargin: null or number
+    
     labelWidth: null or number
     labelHeight: null or number
 
+    transform: null or fn: number -> number
+    inverseTransform: null or fn: number -> number
+    
     ticks: null or number or ticks array or (fn: range -> ticks array)
     tickSize: number or array
     minTickSize: number or array
@@ -208,6 +210,29 @@ nearest whole tick. The default value is "null" for the x axis and
 labels in pixels. They're useful in case you need to align several
 plots.
 
+"transform" and "inverseTransform" are callbacks you can put in to
+change the way the data is drawn. You can design a function to
+compress or expand certain parts of the axis non-linearly, e.g.
+suppress weekends or compress far away points with a logarithm or some
+other means. When Flot draws the plot, each value is first put through
+the transform function. Here's an example, the x axis can be turned
+into a natural logarithm axis with the following code:
+
+  xaxis: {
+    transform: function (v) { return Math.log(v); },
+    inverseTransform: function (v) { return Math.exp(v); }
+  }
+
+Note that for finding extrema, Flot assumes that the transform
+function does not reorder values (monotonicity is assumed).
+
+The inverseTransform is simply the inverse of the transform function
+(so v == inverseTransform(transform(v)) for all relevant v). It is
+required for converting from canvas coordinates to data coordinates,
+e.g. for a mouse interaction where a certain pixel is clicked. If you
+don't use any interactive features of Flot, you may not need it.
+
+
 The rest of the options deal with the ticks.
 
 If you don't specify any ticks, a tick generator algorithm will make

NEWS.txt

@@ -111,6 +111,8 @@ Changes:
 
 - More configurable grid.
 
+- Axis transformation support, useful for non-linear plots, e.g. log
+  axes and compressed time axes (like omitting weekends).
   
 Bug fixes:
 

jquery.flot.js

@@ -28,6 +28,8 @@
                 },
                 xaxis: {
                     mode: null, // null or "time"
+                    transform: null, // null or f: number -> number to transform axis
+                    inverseTransform: null, // if transform is set, this should be the inverse function
                     min: null, // min. value to show, null means set automatically
                     max: null, // max. value to show, null means set automatically
                     autoscaleMargin: null, // margin in % to add if auto-setting min/max
@@ -561,27 +563,42 @@
         }
 
         function setupGrid() {
-            function setTransformationHelpers(axis) {
-                var s, m;
+            function setTransformationHelpers(axis, o) {
+                function identity(x) { return x; }
+                
+                var s, m, t = o.transform || identity,
+                    it = o.inverseTransform;
                     
                 // add transformation helpers
                 if (axis == axes.xaxis || axis == axes.x2axis) {
                     // precompute how much the axis is scaling a point
                     // in canvas space
-                    s = axis.scale = plotWidth / (axis.max - axis.min);
-                    m = axis.min;
-                    
+                    s = axis.scale = plotWidth / (t(axis.max) - t(axis.min));
+                    m = t(axis.min);
+
                     // data point to canvas coordinate
-                    axis.p2c = function (p) { return (p - m) * s; };
-                    // canvas coordinate to data point 
-                    axis.c2p = function (c) { return m + c / s; };
+                    if (t === identity) // slight optimization
+                        axis.p2c = function (p) { return (p - m) * s; };
+                    else
+                        axis.p2c = function (p) { return (t(p) - m) * s; };
+                    // canvas coordinate to data point
+                    if (!it)
+                        axis.c2p = function (c) { return m + c / s; };
+                    else
+                        axis.c2p = function (c) { return it(m + c / s); };
                 }
                 else {
-                    s = axis.scale = plotHeight / (axis.max - axis.min)
-                    m = axis.max;
+                    s = axis.scale = plotHeight / (t(axis.max) - t(axis.min));
+                    m = t(axis.max);
                     
-                    axis.p2c = function (p) { return (m - p) * s; };
-                    axis.c2p = function (p) { return m - p / s; };
+                    if (t === identity)
+                        axis.p2c = function (p) { return (m - p) * s; };
+                    else
+                        axis.p2c = function (p) { return (m - t(p)) * s; };
+                    if (!it)
+                        axis.c2p = function (c) { return m - c / s; };
+                    else
+                        axis.c2p = function (c) { return it(m - c / s); };
                 }
             }
 
@@ -686,7 +703,7 @@
             }
             
             for (axis in axes)
-                setTransformationHelpers(axes[axis]);
+                setTransformationHelpers(axes[axis], options[axis]);
 
             if (options.grid.show)
                 insertLabels();