lots of changes, added smoothing, added many parameters, fixed grid

SVGChartBuilder.php

@@ -2,34 +2,72 @@
 
 class SVGChartBuilder {
 
-  public static function renderStockChart($chartData, $width = 700) {
-    $absoluteDeltas = [];
-    $previousValue = null;
-    $yMin = $xMin = INF;
-    $yMax = $xMax = -INF;
-
-    foreach ($chartData as $thisX => $thisY) {
-      if (!is_null($previousValue)) {
-        $absoluteDeltas[] = abs($thisY - $previousValue);
-      }
-      if ($thisY < $yMin) {
-        $yMin = $thisY;
-        $yMinX = $thisX;
-      }
-      if ($thisY > $yMax) {
-        $yMax = $thisY;
-        $yMaxX = $thisX;
-      }
-      $previousValue = $thisY;
-    }
-    $yRange = $yMax - $yMin;
+  public static function renderStockChart($chartData, $width = 700, $lineColor = "#FF2F00", $gridLabelColor = "#999", $smoothed = false) {
+    // we assume $chartData is sorted by key and keys and values are all numeric
+    $previousY = $previousY = null;
     end($chartData);
     $xMax = key($chartData);
     reset($chartData);
     $xMin = key($chartData);
     $xRange = $xMax - $xMin;
     $count = count($chartData);
-    $averageDelta = abs(array_sum($absoluteDeltas)/$count);
+    $deltaX = $xRange / $count;
+    $yMin = INF; // so the first comparison sets this to an actual value
+    $yMax = -INF;
+    $averageAbsSlope = 0; // we will add all of them then divide to get an average
+    $secants = []; // slope between this point and the previous one
+    $tangents = []; // slope across the point
+
+    foreach ($chartData as $x => $y) {
+      if ($y < $yMin) {
+        $yMin = $y;
+        $yMinX = $x;
+      }
+      if ($y > $yMax) {
+        $yMax = $y;
+        $yMaxX = $x;
+      }
+      if (!is_null($previousY)) {
+        $averageAbsSlope += abs($y - $previousY); // just add up all the Y differences
+        $secants[$previousX] = ($y - $previousY) / $deltaX;
+      }
+      if ($x == $xMax) {
+        $secants[$x] = ($y - $previousY) / $deltaX;
+      }
+      $previousY = $y;
+      $previousX = $x;
+    }
+    $yRange = $yMax - $yMin;
+    $averageAbsSlope /= $yRange * $deltaX; // turn this absolute-deltas total into a slope
+
+    // take all these slopes and average them with their neighbors
+    // unless they change direction, then make them zero
+    // also restrict them a bit when they are very different
+    $previousSecant = $previousX = null;
+    foreach ($secants as $x => $secant) {
+      if (!is_null($previousSecant)) {
+        $tangents[$x] = ($secant + $previousSecant) / 2;
+        if ($secant == 0 || $previousSecant == 0 || $secant * $previousSecant <= 0)
+        {
+          $tangents[$x] = 0;
+        } else {
+          if ($tangents[$x] / $previousSecant > 3) {
+            $tangents[$x] = 3 * $previousSecant;
+          } else if ($tangents[$x] / $secant > 3) {
+            $tangents[$x] = 3 * $secant;
+          }
+        }
+      }
+      if ($x == $xMax) {
+        $tangents[$x] = $secant;
+      }
+      if ($x == $xMin) {
+        $tangents[$x] = $secant;
+      }
+
+      $previousX = $x;
+      $previousSecant = $secant;
+    }
 
     /*
     We want the height of the median y-delta to be the same as
@@ -37,11 +75,13 @@ class SVGChartBuilder {
     45 degrees. This improves comprehension.
     http://vis4.net/blog/posts/doing-the-line-charts-right/
     */
-    $aspectRatio = max(0.25, $yRange / $averageDelta / $count);
+    $aspectRatio = max(0.25, min(0.75, 1 / $averageAbsSlope));
     $height = floor($aspectRatio * $width);
 
-    function labelFormat($float, $sigFigs, $minPlaces = 0) {
-      return number_format($float, max($minPlaces, $sigFigs));
+    function labelFormat($float, $places, $minPlaces = 0) {
+      $value = number_format($float, max($minPlaces, $places));
+      // add a trailing space if there's no decimal
+      return (strpos($value, ".") === false ? $value . "." : $value);
     }
 
     /* Transform data coords to chart coords */
@@ -66,58 +106,72 @@ class SVGChartBuilder {
     }
 
     $chartPoints = "M";
+    $chartSplines = "M".
+      transformX($xMin, $xMin, $xRange, $width).",".
+      transformY($chartData[$xMin], $yMax, $yRange, $height);
     foreach ($chartData as $x => $y) {
-      $chartPoints .= transformX($x, $xMin, $xRange, $width) . ',' . transformY($y, $yMax, $yRange, $height) . '
-      ';
+      $chartPoints .=
+        transformX($x, $xMin, $xRange, $width).",".
+        transformY($y, $yMax, $yRange, $height) . "\n";
+
+      $controlX = $deltaX / 3 / sqrt(1 + $tangents[$x]**2);
+      $controlY = $tangents[$x] * $controlX;
+      if ($x != $xMin) {
+        $chartSplines .= " S".
+          transformX($x - $controlX, $xMin, $xRange, $width).",".
+          transformY($y - $controlY, $yMax, $yRange, $height)." ".
+          transformX($x, $xMin, $xRange, $width).",".
+          transformY($y, $yMax, $yRange, $height);
+      }
     }
 
-    $numLabels = min(4, ceil($height / 40));
+    $numLabels = 1 + ceil($height / 60);
     $labelInterval = $yRange / $numLabels;
     $labelModulation = 10 ** (1 + floor(-log($yRange / $numLabels, 10)));
-//    if (fmod($labelInterval, $labelModulation / 5) < $labelInterval * 0.5) {
+
+    // 0.1 here is a fudge factor so we get multiples of 2.5 a little more often
+    if (fmod($labelInterval * $labelModulation, 2.5) < fmod($labelInterval * $labelModulation, 2) + 0.1) {
       $labelModulation /= 2.5;
-//    } else if (fmod($labelInterval, $labelModulation / 2) < $labelInterval * 0.25) {
-//      $labelModulation /= 2;
-//    }
-//    var_dump($labelInterval, $labelModulation, $labelInterval * $labelModulation, ceil($labelInterval * $labelModulation) / $labelModulation);
+    } else {
+      $labelModulation /= 2;
+    }
     $labelInterval = ceil($labelInterval * $labelModulation) / $labelModulation;
-    $labelPlaces = getPrecision($labelInterval);
+    $labelPrecision = getPrecision($labelInterval);
 
     // Top and bottom grid lines
     $gridLines =
-    "M10,0 ".$width.",0
-    M10,".$height.",".$width.",".$height."
-    ";
+      "M10,0 ".$width.",0\n".
+      "M10,".$height.",".$width.",".$height."\n";
 
     // Top and bottom grid labels
     $gridText =
-      '<text x="6" y="4">'.labelFormat($yMax, $labelPlaces + 1).'</text>' .
-      '<text x="6" y="'.($height + 4).'">'.labelFormat($yMin, $labelPlaces + 1).'</text>';
+      '<text x="6" y="4">'.labelFormat($yMax, $labelPrecision + 1).'</text>' .
+      '<text x="6" y="'.($height + 4).'">'.labelFormat($yMin, $labelPrecision + 1).'</text>';
 
-    // Start at the first "nice" Y value > min + 50% of the interval
-    // Keep going until max - 50% of the interval
-    // Add Interval each iteration
+    // Main labels and grid lines
     for (
-      $labelY = $yMin - fmod($yMin, $labelInterval) + $labelInterval;
-      $labelY < $yMax;
-      $labelY += $labelInterval
+      $labelY = $yMin - fmod($yMin, $labelInterval) + $labelInterval; // Start at the first "nice" Y value > min
+      $labelY < $yMax; // Keep going until max
+      $labelY += $labelInterval // Add Interval each iteration
     ) {
       $labelHeight = transformY($labelY, $yMax, $yRange, $height);
-      if (
-        $labelY < $yMax - 0.1 * $labelInterval &&
-        $labelY > $yMin + 0.1 * $labelInterval
+      if ( // label is not too close to the min or max
+        $labelHeight < $height - 25 &&
+        $labelHeight > 25
       ) {
+        $gridText .= '<text	x="-4" y="'.($labelHeight + 4).'">'.labelFormat($labelY, $labelPrecision).'</text>';
         $gridLines .= " M0,".$labelHeight." ".$width.",".$labelHeight;
-      }
-      if (
-        $labelY < $yMax - 0.3 * $labelInterval &&
-        $labelY > $yMin + 0.3 * $labelInterval
+      } else if ( // label is too close
+          $labelHeight < $height - 4 &&
+          $labelHeight > 4
         ) {
-        $gridText .= '<text	x="-4" y="'.($labelHeight + 4).'">'.labelFormat($labelY, $labelPlaces).'</text>';
+          $gridLines .= " M".( // move grid line over when it's very close to the min or max label
+            $labelHeight < $height - 10 && $labelHeight > 10 ? 0 : 10
+          ).",".$labelHeight." ".$width.",".$labelHeight;
         }
     }
 
-    return '<?xml version="1.0" standalone="no"?>
+    print '<?xml version="1.0" standalone="no"?>
 <svg
   viewBox="-90 -10 '.( $width + 100 ).' '.( $height + 20 ).'"
   width="'.( $width + 100 ).'"
@@ -130,15 +184,15 @@ class SVGChartBuilder {
       <circle cx="1" cy="1" r="1" style="stroke: none; fill:#000000;"/>
     </marker>
     <linearGradient id="fadeFromNothing" x1="0%" y1="0%" x2="100%" y2="0%">
-      <stop offset="0.5%" stop-color="#1C75BC" stop-opacity="0"></stop>
-      <stop offset="5%" stop-color="#1C75BC" stop-opacity="1"></stop>
-      <stop offset="100%" stop-color="#1C75BC" stop-opacity="1"></stop>
+      <stop offset="0.5%" stop-color="'.( $lineColor ).'" stop-opacity="0"></stop>
+      <stop offset="5%" stop-color="'.( $lineColor ).'" stop-opacity="1"></stop>
+      <stop offset="100%" stop-color="'.( $lineColor ).'" stop-opacity="1"></stop>
     </linearGradient>
       <style type="text/css"><![CDATA[
         .chart__gridLines {
           font-family: sans-serif;
           font-size: 10;
-          fill: #7f7f7f;
+          fill: '.( $gridLabelColor ).';
           text-anchor: end;
           shape-rendering: crispEdges;
         }
@@ -163,7 +217,9 @@ class SVGChartBuilder {
       <path class="chart__gridLinePaths" d="'.( $gridLines ).'" />
       '.( $gridText ).'
   </g>
-  <path class="chart__plotLine" d="'.( $chartPoints ).'" />
+  <g class="chart__plotLine">
+    <path d="'.( $smoothed ? $chartSplines : $chartPoints ).'" />
+  </g>
 </svg>';
   }
 }

buffer.php

@@ -1,4 +1,4 @@
-<?PHP
+<?php
   // Adapted for The Art of Web: www.the-art-of-web.com
   // Based on PHP code by Dennis Pallett: www.phpit.net
   // Please acknowledge use of this code by including this header.

index.php

@@ -25,4 +25,4 @@ foreach ($last24h as $item) {
   $chartData[$item->date] = $item->weightedAverage;
 }
 
-print SVGChartBuilder::renderStockChart($chartData);
+print SVGChartBuilder::renderStockChart($chartData, 700, "#1C75BC");