WIP: interval improvements

Author: oesmith

lib/morris.grid.coffee

@@ -160,11 +160,32 @@ class Morris.Grid extends Morris.EventEmitter
       @ymin -= 1 if ymin
       @ymax += 1
 
-    @yInterval = (@ymax - @ymin) / (@options.numLines - 1)
-    if @yInterval > 0 and @yInterval < 1
-        @precision =  -Math.floor(Math.log(@yInterval) / Math.log(10))
-    else
-        @precision = 0
+    if @options.axes is true or @options.grid is true
+      # calculate grid placement
+      span = @ymax - @ymin
+      ymag = Math.floor(Math.log(span) / Math.log(10))
+      unit = Math.pow(10, ymag)
+
+      # calculate initial grid min and max values
+      gmin = Math.round(@ymin / unit) * unit
+      gmax = Math.round(@ymax / unit) * unit
+      step = (gmax - gmin) / (@options.numLines - 1)
+
+      # ensure zero is plotted where the range includes zero
+      if gmin < 0 and gmax > 0
+        gmin = Math.round(@ymin / step) * step
+        gmax = Math.round(@ymax / step) * step
+
+      # special case for decimal numbers
+      if step < 1
+        smag = Math.floor(Math.log(step) / Math.log(10))
+        @grid = for y in [gmin..gmax] by step
+          parseFloat(y.toFixed(1 - smag))
+      else
+        @grid = (y for y in [gmin..gmax] by step)
+
+      @ymin = gmin
+      @ymax = gmax
 
     @dirty = true
     @redraw() if redraw
@@ -259,13 +280,10 @@ class Morris.Grid extends Morris.EventEmitter
   #
   drawGrid: ->
     return if @options.grid is false and @options.axes is false
-    firstY = @ymin
-    lastY = @ymax
-    for lineY in [firstY..lastY] by @yInterval
-      v = parseFloat(lineY.toFixed(@precision))
-      y = @transY(v)
+    for lineY in @grid
+      y = @transY(lineY)
       if @options.axes
-        @drawYAxisLabel(@left - @options.padding / 2, y, @yAxisFormat(v))
+        @drawYAxisLabel(@left - @options.padding / 2, y, @yAxisFormat(lineY))
       if @options.grid
         @drawGridLine("M#{@left},#{y}H#{@left + @width}")
 

morris.js

@@ -0,0 +1,42 @@
+gridLines = (ymin, ymax, nlines = 5) ->
+  interval = ymax - ymin
+  omag = Math.floor(Math.log(interval) / Math.log(10))
+  unit = Math.pow(10, omag)
+
+  ymin1 = Math.round(ymin / unit) * unit
+  ymax1 = Math.round(ymax / unit) * unit
+  step = (ymax1 - ymin1) / (nlines - 1)
+
+  # ensure zero is plotted where the range includes zero
+  if ymin1 < 0 and ymax1 > 0
+    ymin1 = Math.round(ymin / step) * step
+    ymax1 = Math.round(ymax / step) * step
+
+  # small numbers
+  if step < 1
+    smag = Math.floor(Math.log(step) / Math.log(10))
+    (parseFloat(y.toFixed(1 - smag)) for y in [ymin1..ymax1] by step)
+  else
+    (y for y in [ymin1..ymax1] by step)
+
+describe 'Morris.Grid#gridLines', ->
+
+  it 'should draw at fixed intervals', ->
+    gridLines(0, 4).should.deep.equal [0, 1, 2, 3, 4]
+    gridLines(0, 400).should.deep.equal [0, 100, 200, 300, 400]
+
+  it 'should pick intervals that show significant numbers', ->
+    gridLines(98, 502).should.deep.equal [100, 200, 300, 400, 500]
+    gridLines(98, 302).should.deep.equal [100, 150, 200, 250, 300]
+    gridLines(98, 202).should.deep.equal [100, 125, 150, 175, 200]
+
+  it 'should draw zero when it falls within [ymin..ymax]', ->
+    gridLines(-100, 300).should.deep.equal [-100, 0, 100, 200, 300]
+    gridLines(-50, 350).should.deep.equal [0, 100, 200, 300, 400]
+    gridLines(-500, 300).should.deep.equal [-400, -200, 0, 200, 400]
+    gridLines(100, 500).should.deep.equal [100, 200, 300, 400, 500]
+    gridLines(-500, -100).should.deep.equal [-500, -400, -300, -200, -100]
+
+  it 'should generate decimal labels to 2 signigicant figures', ->
+    gridLines(0, 1).should.deep.equal [0, 0.25, 0.5, 0.75, 1]
+    gridLines(0.1, 0.5).should.deep.equal [0.1, 0.2, 0.3, 0.4, 0.5]

morris.min.js

@@ -13,7 +13,7 @@ describe 'Morris.Grid#setData', ->
 
   describe 'ymin/ymax', ->
     beforeEach ->
-      @defaults = 
+      @defaults =
         element: 'graph'
         xkey: 'x'
         ykeys: ['y', 'z']