plugins/grid.js

   1 /**
   2  * @license
   3  * Copyright 2012 Dan Vanderkam (danvdk@gmail.com)
   4  * MIT-licensed (http://opensource.org/licenses/MIT)
   5  */
   6 /*global Dygraph:false */
   7
   8 Dygraph.Plugins.Grid = (function() {
   9
  10 /*
  11
  12 Current bits of jankiness:
  13 - Direct layout access
  14 - Direct area access
  15
  16 */
  17
  18 "use strict";
  19
  20
  21 /**
  22  * Draws the gridlines, i.e. the gray horizontal & vertical lines running the
  23  * length of the chart.
  24  *
  25  * @constructor
  26  */
  27 var grid = function() {
  28 };
  29
  30 grid.prototype.toString = function() {
  31   return "Gridline Plugin";
  32 };
  33
  34 grid.prototype.activate = function(g) {
  35   return {
  36     willDrawChart: this.willDrawChart
  37   };
  38 };
  39
  40 grid.prototype.willDrawChart = function(e) {
  41   // Draw the new X/Y grid. Lines appear crisper when pixels are rounded to
  42   // half-integers. This prevents them from drawing in two rows/cols.
  43   var g = e.dygraph;
  44   var ctx = e.drawingContext;
  45   var layout = g.layout_;
  46   var area = e.dygraph.plotter_.area;
  47
  48   function halfUp(x)  { return Math.round(x) + 0.5; }
  49   function halfDown(y){ return Math.round(y) - 0.5; }
  50
  51   var x, y, i, ticks;
  52   if (g.getOption('drawYGrid')) {
  53     ticks = layout.yticks;
  54     ctx.save();
  55     ctx.strokeStyle = g.getOption('gridLineColor');
  56     ctx.lineWidth = g.getOption('gridLineWidth');
  57     for (i = 0; i < ticks.length; i++) {
  58       // TODO(danvk): allow secondary axes to draw a grid, too.
  59       if (ticks[i][0] !== 0) continue;
  60       x = halfUp(area.x);
  61       y = halfDown(area.y + ticks[i][1] * area.h);
  62       ctx.beginPath();
  63       ctx.moveTo(x, y);
  64       ctx.lineTo(x + area.w, y);
  65       ctx.closePath();
  66       ctx.stroke();
  67     }
  68     ctx.restore();
  69   }
  70
  71   if (g.getOption('drawXGrid')) {
  72     ticks = layout.xticks;
  73     ctx.save();
  74     ctx.strokeStyle = g.getOption('gridLineColor');
  75     ctx.lineWidth = g.getOption('gridLineWidth');
  76     for (i = 0; i < ticks.length; i++) {
  77       x = halfUp(area.x + ticks[i][0] * area.w);
  78       y = halfDown(area.y + area.h);
  79       ctx.beginPath();
  80       ctx.moveTo(x, y);
  81       ctx.lineTo(x, area.y);
  82       ctx.closePath();
  83       ctx.stroke();
  84     }
  85     ctx.restore();
  86   }
  87 };
  88
  89 grid.prototype.destroy = function() {
  90 };
  91
  92 return grid;
  93
  94 })();