Improve spectrum analyzer performance by caching most used computatio…

…ns (#6003)

plugins/SpectrumAnalyzer/SaProcessor.cpp

@@ -225,12 +225,9 @@ void SaProcessor::analyze(LocklessRingBuffer<sampleFrame> &ring_buffer)
 							if (band_end - band_start > 1.0)
 							{
 								// band spans multiple pixels: draw all pixels it covers
-								for (target = (int)band_start; target < (int)band_end; target++)
+								for (target = std::max((int)band_start, 0); target < band_end && target < waterfallWidth(); target++)
 								{
-									if (target >= 0 && target < waterfallWidth())
-									{
-										pixel[target] = makePixel(m_normSpectrumL[i], m_normSpectrumR[i]);
-									}
+									pixel[target] = makePixel(m_normSpectrumL[i], m_normSpectrumR[i]);
 								}
 								// save remaining portion of the band for the following band / pixel
 								// (in case the next band uses sub-pixel drawing)
@@ -265,12 +262,9 @@ void SaProcessor::analyze(LocklessRingBuffer<sampleFrame> &ring_buffer)
 						else
 						{
 							// Linear: always draws one or more pixels per band
-							for (target = (int)band_start; target < band_end; target++)
+							for (target = std::max((int)band_start, 0); target < band_end && target < waterfallWidth(); target++)
 							{
-								if (target >= 0 && target < waterfallWidth())
-								{
-									pixel[target] = makePixel(m_normSpectrumL[i], m_normSpectrumR[i]);
-								}
+								pixel[target] = makePixel(m_normSpectrumL[i], m_normSpectrumR[i]);
 							}
 						}
 					}
@@ -573,6 +567,9 @@ float SaProcessor::getFreqRangeMax() const
 
 
 // Map frequency to pixel x position on a display of given width.
+// NOTE: Results of this function may be cached by SaSpectrumView. If you use
+// a new function call or variable that can affect results of this function,
+// make sure to also add it as a trigger for cache update in SaSpectrumView.
 float SaProcessor::freqToXPixel(float freq, unsigned int width) const
 {
 	if (m_controls->m_logXModel.value())

plugins/SpectrumAnalyzer/SaSpectrumView.cpp

@@ -47,7 +47,13 @@ SaSpectrumView::SaSpectrumView(SaControls *controls, SaProcessor *processor, QWi
 	m_controls(controls),
 	m_processor(processor),
 	m_freezeRequest(false),
-	m_frozen(false)
+	m_frozen(false),
+	m_cachedRangeMin(-1),
+	m_cachedRangeMax(-1),
+	m_cachedLogX(true),
+	m_cachedDisplayWidth(0),
+	m_cachedBinCount(0),
+	m_cachedSampleRate(0)
 {
 	setMinimumSize(360, 170);
 	setSizePolicy(QSizePolicy::Minimum, QSizePolicy::Minimum);
@@ -69,6 +75,9 @@ SaSpectrumView::SaSpectrumView(SaControls *controls, SaProcessor *processor, QWi
 
 	m_cursor = QPointF(0, 0);
 
+	// Initialize the size of bin → pixel X position LUT to the maximum allowed number of bins + 1.
+	m_cachedBinToX.resize(FFT_BLOCK_SIZES.back() / 2 + 2);
+
 	#ifdef SA_DEBUG
 		m_execution_avg = m_path_avg = m_draw_avg = 0;
 	#endif
@@ -348,10 +357,31 @@ QPainterPath SaSpectrumView::makePath(std::vector<float> &displayBuffer, float r
 	// Bins falling to interval [x_start, x_next) contribute to a single point.
 	float max = m_displayBottom;
 	float x_start = -1;		// lower bound of currently constructed point
+
+	// Speed up bin → x position translation by building a LUT cache.
+	// Update the cache only when range or display width are changed.
+	float rangeMin = m_processor->getFreqRangeMin(m_controls->m_logXModel.value());
+	float rangeMax = m_processor->getFreqRangeMax();
+	if (rangeMin != m_cachedRangeMin || rangeMax != m_cachedRangeMax || m_displayWidth != m_cachedDisplayWidth ||
+		m_controls->m_logXModel.value() != m_cachedLogX || m_processor->binCount() + 1 != m_cachedBinCount ||
+		m_processor->getSampleRate() != m_cachedSampleRate)
+	{
+		m_cachedRangeMin = rangeMin;
+		m_cachedRangeMax = rangeMax;
+		m_cachedDisplayWidth = m_displayWidth;
+		m_cachedLogX = m_controls->m_logXModel.value();
+		m_cachedBinCount = m_processor->binCount() + 1;
+		m_cachedSampleRate = m_processor->getSampleRate();
+		for (unsigned int n = 0; n < m_cachedBinCount; n++)
+		{
+			m_cachedBinToX[n] = freqToXPixel(binToFreq(n), m_displayWidth);
+		}
+	}
+
 	for (unsigned int n = 0; n < m_processor->binCount(); n++)
 	{
-		float x = freqToXPixel(binToFreq(n), m_displayWidth);
-		float x_next = freqToXPixel(binToFreq(n + 1), m_displayWidth);
+		float x = m_cachedBinToX[n];
+		float x_next = m_cachedBinToX[n + 1];
 		float y = ampToYPixel(displayBuffer[n], m_displayBottom);
 
 		// consider making a point only if x falls within display bounds

plugins/SpectrumAnalyzer/SaSpectrumView.h

@@ -31,6 +31,7 @@
 
 #include <string>
 #include <utility>
+#include <vector>
 #include <QPainterPath>
 #include <QWidget>
 
@@ -120,6 +121,15 @@ private slots:
 	unsigned int m_displayRight;
 	unsigned int m_displayWidth;
 
+	// cached frequency bin → x position conversion for better performance
+	std::vector<float> m_cachedBinToX;
+	float m_cachedRangeMin;
+	float m_cachedRangeMax;
+	bool m_cachedLogX;
+	unsigned int m_cachedDisplayWidth;
+	unsigned int m_cachedBinCount;
+	unsigned int m_cachedSampleRate;
+
 	#ifdef SA_DEBUG
 		float m_execution_avg;
 		float m_refresh_avg;