GaugePanel: Setting the neutral-point of a gauge

packages/grafana-ui/src/components/Gauge/Gauge.test.tsx

@@ -19,6 +19,9 @@ const field: FieldConfig = {
     mode: ThresholdsMode.Absolute,
     steps: [{ value: -Infinity, color: '#7EB26D' }],
   },
+  custom: {
+    neeutral: 0,
+  },
 };
 
 const props: Props = {

packages/grafana-ui/src/components/Gauge/Gauge.tsx

@@ -98,6 +98,7 @@ export class Gauge extends PureComponent<Props> {
           gauge: {
             min,
             max,
+            neutralValue: field.custom?.neutral,
             background: { color: backgroundColor },
             border: { color: null },
             shadow: { show: false },

public/app/plugins/panel/gauge/module.tsx

@@ -9,11 +9,22 @@ import { PanelOptions, defaultPanelOptions } from './models.gen';
 import { GaugeSuggestionsSupplier } from './suggestions';
 
 export const plugin = new PanelPlugin<PanelOptions>(GaugePanel)
-  .useFieldConfig()
+  .useFieldConfig({
+    useCustomConfig: (builder) => {
+      builder.addNumberInput({
+        path: 'neutral',
+        name: 'Neutral',
+        description: 'Leave empty to use Min as neutral point',
+        category: ['Gauge'],
+        settings: {
+          placeholder: 'auto',
+        },
+      });
+    },
+  })
   .setPanelOptions((builder) => {
     addStandardDataReduceOptions(builder);
     addOrientationOption(builder);
-
     builder
       .addBooleanSwitch({
         path: 'showThresholdLabels',

public/vendor/flot/jquery.flot.gauge.js

@@ -325,9 +325,9 @@
          */
         Gauge.prototype.drawGauge = function(gaugeOptionsi, layout, cellLayout, label, data) {
 
-
             var blur = gaugeOptionsi.gauge.shadow.show ? gaugeOptionsi.gauge.shadow.blur : 0;
-
+            var color = getColor(gaugeOptionsi, data);
+            var angles = calculateAnglesForGauge(gaugeOptionsi, layout, data);
 
             // draw gauge frame
             drawArcWithShadow(
@@ -343,19 +343,74 @@
                 blur);
 
             // draw gauge
-            var c1 = getColor(gaugeOptionsi, data);
-            var a2 = calculateAngle(gaugeOptionsi, layout, data);
             drawArcWithShadow(
                 cellLayout.cx, // center x
                 cellLayout.cy, // center y
                 layout.radius - 1,
                 layout.width - 2,
-                toRad(gaugeOptionsi.gauge.startAngle),
-                toRad(a2),
-                c1,           // line color
+                toRad(angles.a1),
+                toRad(angles.a2),
+                color,
                 1,            // line width
-                c1,           // fill color
+                color,           // fill color
                 blur);
+
+            if(gaugeOptionsi.gauge.neutralValue != null)  {
+                drawZeroMarker(gaugeOptionsi, layout, cellLayout, color);
+            }
+        }
+
+        /**
+         * Calcualte the angles for the gauge, depending on if there are
+         * negative numbers or not.
+         * 
+         * @method calculateAnglesForGauge
+         * @param {Object} gaugeOptionsi the options of the gauge
+         * @param  {Number} data the value of the gauge
+         * @returns {Object}
+         */
+        function calculateAnglesForGauge(gaugeOptionsi, layout, data) {
+            let angles = {};
+            var neutral = gaugeOptionsi.gauge.neutralValue;
+
+            if (neutral != null) {
+                if (data < neutral) {
+                    angles.a1 = calculateAngle(gaugeOptionsi, layout, data);
+                    angles.a2 = calculateAngle(gaugeOptionsi, layout, neutral);
+                } else {
+                    angles.a1 = calculateAngle(gaugeOptionsi, layout, neutral);
+                    angles.a2 = calculateAngle(gaugeOptionsi, layout, data);
+                }
+            } else {
+                angles.a1 = gaugeOptionsi.gauge.startAngle;
+                angles.a2 = calculateAngle(gaugeOptionsi, layout, data);
+            }
+
+            return angles;
+        }
+
+        /**
+         * Draw zero marker for Gauge with negative values
+         * 
+         * @method drawZeroMarker
+         * @param  {Object} gaugeOptionsi the options of the gauge
+         * @param  {Object} layout the layout properties
+         * @param  {Object} cellLayout the cell layout properties
+         * @param  {String} color line color
+         */
+        function drawZeroMarker(gaugeOptionsi, layout, cellLayout, color) {
+            var diff = (gaugeOptionsi.gauge.max - gaugeOptionsi.gauge.min) / 600;
+
+            drawArc(context,
+                cellLayout.cx,
+                cellLayout.cy,
+                layout.radius - 2,
+                layout.width - 4,
+                toRad(calculateAngle(gaugeOptionsi, layout, gaugeOptionsi.gauge.neutralValue-diff)),
+                toRad(calculateAngle(gaugeOptionsi, layout, gaugeOptionsi.gauge.neutralValue+diff)),
+                color,
+                2,
+                gaugeOptionsi.gauge.background.color);
         }
 
         /**
@@ -529,6 +584,13 @@
                     drawThresholdValue(gaugeOptionsi, layout, cellLayout, i + "_" + j, threshold.value, a);
                 }
             }
+
+            var neutral = gaugeOptionsi.gauge.neutralValue;
+            if (neutral != null && 
+                neutral>gaugeOptionsi.gauge.min && 
+                neutral<gaugeOptionsi.gauge.max) {
+                drawThresholdValue(gaugeOptionsi, layout, cellLayout, "Neutral" + i, neutral, calculateAngle(gaugeOptionsi, layout, neutral));
+            }
         }
 
         /**