From 705600ef50b453b2aa2950da169933bcc413f008 Mon Sep 17 00:00:00 2001
From: Kevin Mehall <km@kevinmehall.net>
Date: Sat, 4 Feb 2017 09:56:07 -0800
Subject: [PATCH 1/2] Make ctrl+scroll zoom in and out of cursor point, rather
 than center

---
 plotview.cpp | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/plotview.cpp b/plotview.cpp
index e71e76a..ac4d106 100644
--- a/plotview.cpp
+++ b/plotview.cpp
@@ -170,9 +170,14 @@ bool PlotView::viewportEvent(QEvent *event) {
     if (event->type() == QEvent::Wheel) {
         QWheelEvent *wheelEvent = (QWheelEvent*)event;
         if (QApplication::keyboardModifiers() & Qt::ControlModifier) {
-            if (wheelEvent->angleDelta().y() > 0) {
+            // `updateViewRange()` keeps the center sample in the same place after zoom. Apply
+            // a scroll adjustment to keep the sample under the mouse cursor in the same place instead.
+            int fromCenter = wheelEvent->pos().x() - width()/2;
+            if (wheelEvent->angleDelta().y() > 0 && zoomLevel < fftSize) {
                 emit zoomIn();
-            } else if (wheelEvent->angleDelta().y() < 0) {
+                horizontalScrollBar()->setValue(horizontalScrollBar()->value() + fromCenter * samplesPerLine());
+            } else if (wheelEvent->angleDelta().y() < 0 && zoomLevel > 1) {
+                horizontalScrollBar()->setValue(horizontalScrollBar()->value() - fromCenter * samplesPerLine());
                 emit zoomOut();
             }
             return true;

From 90d798a93b64e1c8add62ab218ff870163b08fbf Mon Sep 17 00:00:00 2001
From: Kevin Mehall <km@kevinmehall.net>
Date: Sat, 4 Feb 2017 10:21:26 -0800
Subject: [PATCH 2/2] Make scroll wheel zoom less jumpy on fractional-scroll
 devices like touchpads

---
 plotview.cpp | 27 ++++++++++++++++++---------
 plotview.h   |  1 +
 2 files changed, 19 insertions(+), 9 deletions(-)

diff --git a/plotview.cpp b/plotview.cpp
index ac4d106..c8aa80c 100644
--- a/plotview.cpp
+++ b/plotview.cpp
@@ -170,15 +170,24 @@ bool PlotView::viewportEvent(QEvent *event) {
     if (event->type() == QEvent::Wheel) {
         QWheelEvent *wheelEvent = (QWheelEvent*)event;
         if (QApplication::keyboardModifiers() & Qt::ControlModifier) {
-            // `updateViewRange()` keeps the center sample in the same place after zoom. Apply
-            // a scroll adjustment to keep the sample under the mouse cursor in the same place instead.
-            int fromCenter = wheelEvent->pos().x() - width()/2;
-            if (wheelEvent->angleDelta().y() > 0 && zoomLevel < fftSize) {
-                emit zoomIn();
-                horizontalScrollBar()->setValue(horizontalScrollBar()->value() + fromCenter * samplesPerLine());
-            } else if (wheelEvent->angleDelta().y() < 0 && zoomLevel > 1) {
-                horizontalScrollBar()->setValue(horizontalScrollBar()->value() - fromCenter * samplesPerLine());
-                emit zoomOut();
+            bool canZoomIn = zoomLevel < fftSize;
+            bool canZoomOut = zoomLevel > 1;
+            int delta = wheelEvent->angleDelta().y();
+            if ((delta > 0 && canZoomIn) || (delta < 0 && canZoomOut)) {
+                scrollZoomStepsAccumulated += delta;
+
+                // `updateViewRange()` keeps the center sample in the same place after zoom. Apply
+                // a scroll adjustment to keep the sample under the mouse cursor in the same place instead.
+                int fromCenter = wheelEvent->pos().x() - width()/2;
+                if (scrollZoomStepsAccumulated >= 120) {
+                    scrollZoomStepsAccumulated -= 120;
+                    emit zoomIn();
+                    horizontalScrollBar()->setValue(horizontalScrollBar()->value() + fromCenter * samplesPerLine());
+                } else if (scrollZoomStepsAccumulated <= -120) {
+                    scrollZoomStepsAccumulated += 120;
+                    horizontalScrollBar()->setValue(horizontalScrollBar()->value() - fromCenter * samplesPerLine());
+                    emit zoomOut();
+                }
             }
             return true;
         }
diff --git a/plotview.h b/plotview.h
index 231939a..5cce114 100644
--- a/plotview.h
+++ b/plotview.h
@@ -75,6 +75,7 @@ private:
     bool cursorsEnabled;
     off_t sampleRate = 0;
     bool timeScaleEnabled;
+    int scrollZoomStepsAccumulated = 0;
 
     void addPlot(Plot *plot);
     void emitTimeSelection();