Plotter and waterfall performance enhancements (#1383)

* cache meter font

* cache peak circles

* sliding window waterfall implementation

* use polygons for fills

* prevent rounding errors

* avoid duplicate fills on mac

* stop using alpha composition

* use precomputed solid colors

* static allocation

* opaque drawing without background fills

* prevent extra redraws on meter

* add to authors list

* fix fills

* fix centering on peak pixmap

* use two draws for waterfall

* fix no plotter case

* fix peak alignment

README.md

@@ -211,6 +211,7 @@ The following people and organisations have contributed to gqrx:
 * Grigory Shipunov
 * Gwenhael Goavec-Merou
 * Herman Semenov
+* James Yuzawa
 * Jaroslav Škarvada
 * Jeff Long
 * Jiawei Chen

src/applications/gqrx/mainwindow.ui

@@ -21,7 +21,7 @@
    <set>QMainWindow::AllowNestedDocks|QMainWindow::AllowTabbedDocks|QMainWindow::AnimatedDocks</set>
   </property>
   <property name="unifiedTitleAndToolBarOnMac">
-   <bool>true</bool>
+   <bool>false</bool>
   </property>
   <widget class="QWidget" name="centralWidget">
    <layout class="QVBoxLayout" name="verticalLayout_2">
@@ -349,9 +349,6 @@
         <verstretch>0</verstretch>
        </sizepolicy>
       </property>
-      <property name="autoFillBackground">
-       <bool>true</bool>
-      </property>
       <property name="frameShape">
        <enum>QFrame::StyledPanel</enum>
       </property>

src/qtgui/meter.cpp

@@ -53,6 +53,7 @@ CMeter::CMeter(QWidget *parent) : QFrame(parent)
 
     m_dBFS = MIN_DB;
     m_Sql = -150.0;
+    m_font = QFont("Arial");
 }
 
 CMeter::~CMeter()
@@ -71,9 +72,14 @@ QSize CMeter::sizeHint() const
 
 void CMeter::setLevel(float dbfs)
 {
+    const float old = m_dBFS;
     float alpha = dbfs < m_dBFS ? ALPHA_DECAY : ALPHA_RISE;
     m_dBFS -= alpha * (m_dBFS - dbfs);
-    update();
+    // only redraw when the label needs to change
+    if (qRound(m_dBFS * 10) != qRound(old * 10))
+    {
+        update();
+    }
 }
 
 void CMeter::setSqlLevel(float dbfs)
@@ -116,9 +122,8 @@ void CMeter::draw(QPainter &painter)
         painter.drawLine(QLineF(x, hline, x, hline + 8));
     }
 
-    QFont font("Arial");
-    font.setPixelSize(height() / 4);
-    painter.setFont(font);
+    m_font.setPixelSize(height() / 4);
+    painter.setFont(m_font);
 
     painter.setPen(QColor(0xDA, 0xDA, 0xDA, 0xFF));
     painter.drawText(marg, height() - 2, QString::number((double)m_dBFS, 'f', 1) + " dBFS" );
@@ -148,9 +153,8 @@ void CMeter::drawOverlay(QPainter &painter)
     }
 
     // draw scale text
-    QFont font("Arial");
-    font.setPixelSize(height() / 4);
-    painter.setFont(font);
+    m_font.setPixelSize(height() / 4);
+    painter.setFont(m_font);
     qreal rwidth = (hstop - marg) / 5.0;
     QRectF rect(marg - rwidth / 2, 0, rwidth, majstart);
 

src/qtgui/meter.h

@@ -58,4 +58,5 @@ public slots:
 
     float   m_dBFS;
     float   m_Sql;
+    QFont   m_font;
 };