Determine the max value in LinearUnit dynamically

The range between min and max should always be divisable by the amount of
ticks, to ensure that the vertical lines are always at a full discrete value.

fixes #6769

library/Icinga/Chart/Unit/LinearUnit.php

@@ -90,17 +90,52 @@ class LinearUnit implements AxisUnit
         }
         sort($datapoints);
         if (!$this->staticMax) {
-            $this->max = max($this->max, $datapoints[count($datapoints)-1]);
+            $this->max = max($this->max, $datapoints[count($datapoints) - 1]);
         }
         if (!$this->staticMin) {
             $this->min = min($this->min, $datapoints[0]);
         }
-
+        if (!$this->staticMin || !$this->staticMax) {
+            $this->updateMaxValue();
+        }
         $this->currentTick = 0;
         $this->currentValue = $this->min;
         return $this;
     }
 
+    /**
+     * Refresh the range depending on the current values of min, max and nrOfTicks
+     */
+    private function updateMaxValue()
+    {
+        $this->max = $this->calculateTickRange($this->max - $this->min, $this->nrOfTicks) *
+             $this->nrOfTicks + $this->min;
+    }
+
+    /**
+     * Determine the minimum tick range that is necessary to display the given value range
+     * correctly
+     *
+     * @param   int range   The range to display
+     * @param   int ticks   The amount of ticks to use
+     *
+     * @return  int         The value for each tick
+     */
+    private function calculateTickRange($range, $ticks)
+    {
+        $factor = 1;
+        $steps = array(1, 2, 5);
+        $step = 0;
+        while ($range / ($factor * $steps[$step]) > $ticks) {
+            $step++;
+            if ($step === count($steps)) {
+                $step = 0;
+                $factor *= 10;
+            }
+        }
+        return $steps[$step] * $factor;
+    }
+
     /**
      * Transform the absolute value to an axis relative value
      *
@@ -114,7 +149,7 @@ class LinearUnit implements AxisUnit
         } elseif ($value > $this->max) {
             return 100;
         } else {
-            return 100 * ($value - $this->min) / ($this->max - $this->min);
+            return 100 * ($value - $this->min) / $this->max - $this->min;
         }
     }
 
@@ -176,6 +211,7 @@ class LinearUnit implements AxisUnit
         if ($max !== null) {
             $this->max = $max;
             $this->staticMax = true;
+            $this->updateMaxValue();
         }
     }
 
@@ -189,6 +225,7 @@ class LinearUnit implements AxisUnit
         if ($min !== null) {
             $this->min = $min;
             $this->staticMin = true;
+            $this->updateMaxValue();
         }
     }
 

modules/monitoring/application/controllers/ChartController.php

@@ -140,7 +140,8 @@ class Monitoring_ChartController extends Controller
         }
         $this->view->chart = new GridChart();
         $this->view->chart->setAxisLabel('', t('Services'))
-            ->setXAxis(new \Icinga\Chart\Unit\StaticAxis());
+            ->setXAxis(new \Icinga\Chart\Unit\StaticAxis())
+            ->setAxisMin(null, 0);
 
         $this->view->chart->drawBars(
             array(
@@ -190,7 +191,9 @@ class Monitoring_ChartController extends Controller
             );
         }
         $this->view->chart = new GridChart();
-        $this->view->chart->setAxisLabel('', t('Hosts'))->setXAxis(new StaticAxis());
+        $this->view->chart->setAxisLabel('', t('Hosts'))
+            ->setXAxis(new StaticAxis())
+            ->setAxisMin(null, 0);
         $this->view->chart->drawBars(
             array(
                 'label' => t('Up'),