perf: reduce repainting in animations

By profiling qTox using perf I discovered, that
NotificationIcon::updateGradient takes significant amount of CPU time
even though qTox is idle and no one is typing.

This commit fixes:

1) correctly determine visibility of NotificationIcon
2) only invalidate boundingRect in fixed intervals
3) apply the same fixes to Spinner since it has the same problem

src/chatlog/content/broken.cpp

@@ -50,11 +50,6 @@ void Broken::setWidth(qreal width)
     Q_UNUSED(width)
 }
 
-void Broken::visibilityChanged(bool visible)
-{
-    Q_UNUSED(visible)
-}
-
 qreal Broken::getAscent() const
 {
     return 0.0;

src/chatlog/content/broken.h

@@ -33,7 +33,6 @@ public:
     void paint(QPainter* painter, const QStyleOptionGraphicsItem* option,
                        QWidget* widget) override;
     void setWidth(qreal width) override;
-    void visibilityChanged(bool visible) override;
     qreal getAscent() const override;
 
 private:

src/chatlog/content/notificationicon.cpp

@@ -30,13 +30,12 @@ NotificationIcon::NotificationIcon(QSize Size)
 {
     pmap = PixmapCache::getInstance().get(Style::getImagePath("chatArea/typing.svg"), size);
 
-    updateTimer = new QTimer(this);
+    // Timer for the animation, if the Widget is not redrawn, no paint events will
-    updateTimer->setInterval(1000 / 30);
+    // arrive and the timer will not be restarted, so this stops automatically
-    updateTimer->setSingleShot(false);
+    updateTimer.setInterval(1000 / framerate);
+    updateTimer.setSingleShot(true);
 
-    updateTimer->start();
+    connect(&updateTimer, &QTimer::timeout, this, &NotificationIcon::updateGradient);
-
-    connect(updateTimer, &QTimer::timeout, this, &NotificationIcon::updateGradient);
 }
 
 QRectF NotificationIcon::boundingRect() const
@@ -54,6 +53,10 @@ void NotificationIcon::paint(QPainter* painter, const QStyleOptionGraphicsItem*
     painter->fillRect(QRect(0, 0, size.width(), size.height()), grad);
     painter->drawPixmap(0, 0, size.width(), size.height(), pmap);
 
+    if (!updateTimer.isActive()) {
+        updateTimer.start();
+    }
+
     Q_UNUSED(option)
     Q_UNUSED(widget)
 }
@@ -70,10 +73,12 @@ qreal NotificationIcon::getAscent() const
 
 void NotificationIcon::updateGradient()
 {
+    // Update for next frame
     alpha += 0.01;
 
-    if (alpha + dotWidth >= 1.0)
+    if (alpha + dotWidth >= 1.0) {
         alpha = 0.0;
+    }
 
     grad = QLinearGradient(QPointF(-0.5 * size.width(), 0), QPointF(3.0 / 2.0 * size.width(), 0));
     grad.setColorAt(0, Qt::lightGray);
@@ -82,6 +87,7 @@ void NotificationIcon::updateGradient()
     grad.setColorAt(qMin(1.0, alpha + dotWidth), Qt::lightGray);
     grad.setColorAt(1, Qt::lightGray);
 
-    if (scene() && isVisible())
+    if (scene() && isVisible()) {
         scene()->invalidate(sceneBoundingRect());
+    }
 }

src/chatlog/content/notificationicon.h

@@ -23,8 +23,7 @@
 
 #include <QLinearGradient>
 #include <QPixmap>
-
+#include <QTimer>
-class QTimer;
 
 class NotificationIcon : public ChatLineContent
 {
@@ -42,10 +41,12 @@ private slots:
     void updateGradient();
 
 private:
+    static constexpr int framerate = 30; // 30Hz
+
     QSize size;
     QPixmap pmap;
     QLinearGradient grad;
-    QTimer* updateTimer = nullptr;
+    QTimer updateTimer;
 
     qreal dotWidth = 0.2;
     qreal alpha = 0.0;

src/chatlog/content/spinner.cpp

@@ -26,14 +26,18 @@
 #include <QTime>
 #include <QVariantAnimation>
 
+#include <math.h>
+
 Spinner::Spinner(const QString& img, QSize Size, qreal speed)
     : size(Size)
     , rotSpeed(speed)
 {
     pmap = PixmapCache::getInstance().get(img, size);
 
-    timer.setInterval(1000 / 30); // 30Hz
+    // Timer for the animation, if the Widget is not redrawn, no paint events will
-    timer.setSingleShot(false);
+    // arrive and the timer will not be restarted, so this stops automatically
+    timer.setInterval(1000 / framerate);
+    timer.setSingleShot(true);
 
     blendAnimation = new QVariantAnimation(this);
     blendAnimation->setStartValue(0.0);
@@ -56,14 +60,17 @@ void Spinner::paint(QPainter* painter, const QStyleOptionGraphicsItem* option, Q
 {
     painter->setClipRect(boundingRect());
 
-    QTransform trans = QTransform()
+    QTransform trans = QTransform().rotate(curRot)
-                           .rotate(QTime::currentTime().msecsSinceStartOfDay() / 1000.0 * rotSpeed)
                            .translate(-size.width() / 2.0, -size.height() / 2.0);
     painter->setOpacity(alpha);
     painter->setTransform(trans, true);
     painter->setRenderHint(QPainter::SmoothPixmapTransform);
     painter->drawPixmap(0, 0, pmap);
 
+    if (!timer.isActive()) {
+        timer.start(); // update bounding rectangle for next frame
+    }
+
     Q_UNUSED(option)
     Q_UNUSED(widget)
 }
@@ -73,14 +80,6 @@ void Spinner::setWidth(qreal width)
     Q_UNUSED(width)
 }
 
-void Spinner::visibilityChanged(bool visible)
-{
-    if (visible)
-        timer.start();
-    else
-        timer.stop();
-}
-
 qreal Spinner::getAscent() const
 {
     return 0.0;
@@ -88,6 +87,12 @@ qreal Spinner::getAscent() const
 
 void Spinner::timeout()
 {
-    if (scene())
+    // Use global time, so the animations are synced
+    float angle = QTime::currentTime().msecsSinceStartOfDay() / 1000.0f * rotSpeed;
+    // limit to the range [0.0 - 360.0]
+    curRot = remainderf(angle, 360.0f);
+
+    if (scene()) {
         scene()->invalidate(sceneBoundingRect());
+    }
 }

src/chatlog/content/spinner.h

@@ -37,16 +37,17 @@ public:
     void paint(QPainter* painter, const QStyleOptionGraphicsItem* option,
                        QWidget* widget) override;
     void setWidth(qreal width) override;
-    void visibilityChanged(bool visible) override;
     qreal getAscent() const override;
 
 private slots:
     void timeout();
 
 private:
+    static constexpr int framerate = 30; // 30Hz
     QSize size;
     QPixmap pmap;
     qreal rotSpeed;
+    qreal curRot;
     QTimer timer;
     qreal alpha = 0.0;
     QVariantAnimation* blendAnimation;