Updated scopehal with interpolation improvements to peak search and FFT position fix

Author: azonenberg

lib

@@ -6,14 +6,11 @@ This is a running list of significant bug fixes and new features since the last
 
 * Core: Changed rate limiting sleep in InstrumentThread loop from 10ms to 1ms to avoid bogging down high performance instruments like the ThunderScope
 * Drivers: ThunderScope now overlaps socket IO and GPU processing of waveforms giving a significant increase in WFM/s rate
-* Filters: CDR PLL is now GPU accelerated for the common case (no gating, deep waveform) and runs about 7.5x faster (https://github.com/ngscopeclient/scopehal/issues/977)
+* Filters: Added GPU acceleration for several filters including CDR PLL (7.5x speedup), 100baseTX (2.5x speedup), eye pattern (25x speedup), histogram (12x speedup), TIE (5.3x speedup) and more (https://github.com/ngscopeclient/scopehal/issues/977).
 * Filters: CDR PLL now outputs the input signal sampled by the recovered clock in a second data stream.
-* Filters: 100baseTX Ethernet is now GPU accelerated for a subset of processing and runs about 2.5x faster than before
-* Filters: Eye pattern is now GPU accelerated for the common case (DDR clock on uniformly sampled input) and runs about 25x faster
-* Filters: Histogram filter is now GPU accelerated and runs about 12x faster
+* Filters: Peak detector for FFT etc now does quadratic interpolation for sub-sample peak fitting
 * Filters: Horizontal bathtub curve now works properly with MLT-3 / PAM-3 eyes as well as NRZ. No PAM-4 or higher support yet.
 * Filters: PcapNG export now has an additional mode selector for use with named pipes, allowing live streaming of PcapNG formatted data to WireShark
-* Filters: TIE measurement is now GPU accelerated and runs about 5.3x faster than before
 * GUI: enabled mouseover BER measurements on MLT-3 / PAM-3 eyes as well as NRZ. No PAM-4 or higher support yet.
 
 ## Breaking changes since v0.1.1
@@ -25,6 +22,7 @@ We try to maintain compatibility with older versions of ngscopeclient but occasi
 ## Bugs fixed since v0.1.1
 
 * Filters: PcapNG export did not handle named pipes correctly (no github ticket)
+* Filters: FFT waveforms were shifted one bin to the right of the correct position
 * Filters: Frequency and period measurement had a rounding error during integer-to-floating-point conversion causing half a cycle of the waveform to be dropped under some circumstances leading to an incorrect result, with worse error at low frequencies and short memory depths. This only affected the "summary" output not the trend plot.
 * GUI: Pressing middle mouse on the Y axis to autoscale would fail, setting the full scale range to zero volts, if the waveform was resident in GPU memory and the CPU-side copy of the buffer was stale
 

release-notes/CHANGELOG.md

@@ -1378,9 +1378,8 @@ void WaveformArea::RenderSpectrumPeaks(ImDrawList* list, shared_ptr<DisplayedCha
 	for(auto p : peaks)
 	{
 		//Draw the circle for the peak
-		auto x = (p.m_x * data->m_timescale) + data->m_triggerPhase;
 		list->AddCircle(
-			ImVec2(m_group->XAxisUnitsToXPosition(x), YAxisUnitsToYPosition(p.m_y)),
+			ImVec2(m_group->XAxisUnitsToXPosition(p.m_x), YAxisUnitsToYPosition(p.m_y)),
 			radius,
 			circleColor,
 			0,
@@ -1390,11 +1389,11 @@ void WaveformArea::RenderSpectrumPeaks(ImDrawList* list, shared_ptr<DisplayedCha
 		bool hit = false;
 		for(size_t i=0; i<channel->m_peakLabels.size(); i++)
 		{
-			if( llabs(channel->m_peakLabels[i].m_peakXpos - x) < neighborThresholdXUnits )
+			if( llabs(channel->m_peakLabels[i].m_peakXpos - p.m_x) < neighborThresholdXUnits )
 			{
 				//This peak is close enough we'll call it the same. Update the position.
 				hit = true;
-				channel->m_peakLabels[i].m_peakXpos = x;
+				channel->m_peakLabels[i].m_peakXpos = p.m_x;
 				channel->m_peakLabels[i].m_peakYpos = p.m_y;
 				channel->m_peakLabels[i].m_peakAlpha = 255;
 				channel->m_peakLabels[i].m_fwhm = p.m_fwhm;
@@ -1408,8 +1407,8 @@ void WaveformArea::RenderSpectrumPeaks(ImDrawList* list, shared_ptr<DisplayedCha
 			PeakLabel npeak;
 
 			//Initial X position is just left of the peak
-			npeak.m_labelXpos = x - m_group->PixelsToXAxisUnits(5 * ImGui::GetFontSize());
-			npeak.m_peakXpos = x;
+			npeak.m_labelXpos = p.m_x - m_group->PixelsToXAxisUnits(5 * ImGui::GetFontSize());
+			npeak.m_peakXpos = p.m_x;
 			npeak.m_peakYpos = p.m_y;
 			npeak.m_fwhm = p.m_fwhm;
 

src/ngscopeclient/WaveformArea.cpp

@@ -2,7 +2,7 @@
 *                                                                                                                      *
 * ngscopeclient                                                                                                        *
 *                                                                                                                      *
-* Copyright (c) 2012-2025 Andrew D. Zonenberg and contributors                                                         *
+* Copyright (c) 2012-2026 Andrew D. Zonenberg and contributors                                                         *
 * All rights reserved.                                                                                                 *
 *                                                                                                                      *
 * Redistribution and use in source and binary forms, with or without modification, are permitted provided that the     *
@@ -149,6 +149,8 @@ struct ConfigPushConstants
 	@brief State for a single peak label
 
 	All positions/sizes are in waveform units, not screen units, so that they scale/move correctly with the waveform
+
+	X axis positions are in base units, not scaled by timebase
  */
 struct PeakLabel
 {