Nasty hack to get a useful Y-axis label @ bw chart

res/qml/UsagePanel.qml

@@ -1,7 +1,7 @@
 import QtQuick 2.0
 import QtQuick.Layouts 1.3
 import QtQuick.Controls 2.0
-import QtCharts 2.0
+import QtCharts 2.1
 
 import QClipboard 1.0
 import BandwidthChartData 1.0
@@ -11,6 +11,8 @@ Container {
     property var down: 0
     property var up: 0
 
+    property var lastCategoryLabel: null
+
     BandwidthChartData {
         id: chartData
     }
@@ -25,6 +27,7 @@ Container {
         // console.log("new 'down' value: "+ down);
         chartData.addDownloadSample(down);
         chartData.updateDownloadSeries(rxData.upperSeries);
+        recalculateGraphScale(chartData.getHighestSample());
     }
 
     Layout.preferredHeight: 249
@@ -34,6 +37,24 @@ Container {
         color: Style.panelBackgroundColor
     }
 
+    function recalculateGraphScale(highestSample) {
+        yAxis.max = highestSample;
+        const label = makeRate(highestSample);
+
+        // if we need a new label, remove and re-add. ughly hack.
+        // essentially, we use a single CategoryAxis category because this lets us position
+        // a tick interval at a specific location with a specific label.
+        // ValueAxis has no way of doing this.
+        if (! lastCategoryLabel) {
+            yAxis.append(label, highestSample);
+            lastCategoryLabel = label;
+        } else if (lastCategoryLabel != label) {
+            yAxis.remove(lastCategoryLabel);
+            yAxis.append(label, highestSample);
+            lastCategoryLabel = label;
+        }
+    }
+
     function makeRate(value)
     {
       var unit_idx = 0;
@@ -113,7 +134,7 @@ Container {
 
         ValueAxis {
             id: xAxis
-            labelFormat: "%d"
+            labelFormat: "%e"
             min: 0
             max: 128
             labelsVisible: false
@@ -121,13 +142,11 @@ Container {
             titleVisible: false
         }
 
-        ValueAxis {
+        CategoryAxis {
             id: yAxis
             min: 0
             max: 10000
-            gridVisible: false
-            labelFormat: "%d"
-            titleVisible: false
+            labelsPosition: CategoryAxis.AxisLabelsPositionOnValue
         }
 
         AreaSeries {

src/BandwidthChartData.cpp

@@ -24,27 +24,32 @@ BandwidthChartData::BandwidthChartData(QObject *parent)
     }
 }
 
-static void appendSample(QVector<QPointF>& samples, uint64_t maxSamples, qreal sample) {
+static void appendSample(QVector<QPointF>& samples, uint64_t maxSamples, int64_t& highest, qreal sample) {
+    highest = 0;
     if ((uint64_t)samples.size() >= maxSamples) {
         // shift entire dataset, discarding first (oldest), and append new sample
         for (uint64_t i=0; i<maxSamples-1; ++i) {
             // TODO: use timestamps instead of indices
             auto next = samples[i+1];
             samples[i].setY(next.y());
+
+            highest = std::max(highest, (int64_t)next.y());
         }
         samples[maxSamples-1].setY(sample);
     } else {
         QPointF point(samples.size(), sample);
         samples.append(point);
     }
+
+    highest = std::max(highest, (int64_t)sample);
 }
 
 void BandwidthChartData::addUploadSample(qreal sample) {
-    appendSample(m_uploadSamples, m_numSamples, sample);
+    appendSample(m_uploadSamples, m_numSamples, m_highestUploadSample, sample);
 }
 
 void BandwidthChartData::addDownloadSample(qreal sample) {
-    appendSample(m_downloadSamples, m_numSamples, sample);
+    appendSample(m_downloadSamples, m_numSamples, m_highestDownloadSample, sample);
 }
 
 void BandwidthChartData::updateUploadSeries(QtCharts::QAbstractSeries *series) {
@@ -59,3 +64,15 @@ void BandwidthChartData::updateDownloadSeries(QtCharts::QAbstractSeries *series)
     xySeries->replace(m_downloadSamples);
 }
 
+int BandwidthChartData::getHighestUploadSample() {
+    return m_highestUploadSample;
+}
+
+int BandwidthChartData::getHighestDownloadSample() {
+    return m_highestDownloadSample;
+}
+
+int BandwidthChartData::getHighestSample() {
+    return std::max(m_highestUploadSample, m_highestDownloadSample);
+}
+

src/BandwidthChartData.hpp

@@ -31,12 +31,26 @@ public:
     Q_INVOKABLE void updateUploadSeries(QtCharts::QAbstractSeries *series);
     Q_INVOKABLE void updateDownloadSeries(QtCharts::QAbstractSeries *series);
 
+    /**
+     * Get the highest samples currently being tracked
+     */
+    Q_INVOKABLE int getHighestUploadSample();
+    Q_INVOKABLE int getHighestDownloadSample();
+
+    /**
+     * Get the greater of the highest upload or highest download samples
+     */
+    Q_INVOKABLE int getHighestSample();
+
 private:
 
     uint64_t m_numSamples;
     QVector<QPointF> m_uploadSamples;
     QVector<QPointF> m_downloadSamples;
 
+    int64_t m_highestUploadSample = 0;
+    int64_t m_highestDownloadSample = 0;
+
 };
 
 #endif // BANDWIDTH_CHART_DATA_H