Eliminate unnecessary widget renders from control changes.

Instead of re-rendering on every control change (via
WWidget::onConnectedControlChanged), check for changes in what we would render
first.

Updated: WDisplay, WKnob, WKnobComposed, WSliderComposed, WStatusLight
Left unchanged: WWaveformViewer, WPushButton, WOverview, WVuMeter

1 files changed, 17 insertions, 3 deletions

diff --git a/src/widget/wdisplay.cpp b/src/widget/wdisplay.cpp
index 81177b3d62..3942efa2e2 100644
--- a/src/widget/wdisplay.cpp
+++ b/src/widget/wdisplay.cpp
@@ -27,6 +27,7 @@
 
 WDisplay::WDisplay(QWidget * parent)
         : WWidget(parent),
+          m_iCurrentPixmap(0),
           m_pPixmapBack(NULL),
           m_bDisabledLoaded(false) {
     setPositions(0);
@@ -112,7 +113,7 @@ void WDisplay::setPixmap(QVector<PaintablePointer>* pPixmaps, int iPos,
     }
 }
 
-int WDisplay::getActivePixmapIndex() const {
+int WDisplay::getPixmapForParameter(double dParameter) const {
     // When there are an even number of pixmaps by convention we want a value of
     // 0.5 to align to the lower of the two middle pixmaps. In Mixxx < 1.12.0 we
     // accomplished this by the below formula:
@@ -149,7 +150,16 @@ int WDisplay::getActivePixmapIndex() const {
     // Subtracting an epsilon prevents out of bound values at the end of the
     // range and biases the middle value towards the lower of the 2 center
     // pixmaps when there are an even number of pixmaps.
-    return static_cast<int>(getControlParameterDisplay() * numPixmaps() - 0.00001);
+    return static_cast<int>(dParameter * numPixmaps() - 0.00001);
+}
+
+void WDisplay::onConnectedControlChanged(double dParameter, double dValue) {
+    Q_UNUSED(dValue);
+    int pixmap = getPixmapForParameter(dParameter);
+    if (pixmap != m_iCurrentPixmap) {
+        // paintEvent updates m_iCurrentPixmap.
+        update();
+    }
 }
 
 void WDisplay::paintEvent(QPaintEvent* ) {
@@ -171,7 +181,11 @@ void WDisplay::paintEvent(QPaintEvent* ) {
         return;
     }
 
-    int idx = getActivePixmapIndex();
+    int idx = getPixmapForParameter(getControlParameterDisplay());
+
+    // onConnectedControlChanged uses this to detect no-ops but it does not
+    // clamp so don't clamp.
+    m_iCurrentPixmap = idx;
 
     // Clamp active pixmap index to valid ranges.
     if (idx < 0) {