VolumeKnob: adjust via scroll/keys in dB increments like Fader

include/Knob.h

@@ -245,11 +245,24 @@ class LMMS_EXPORT VolumeKnob : public Knob
 public:
 	using Knob::Knob;
 
+	//! Adjusts the volume by @p dbDelta decibels.
+	//! Matches the Fader::adjustByDecibelDelta API.
+	void adjustByDecibelDelta(float dbDelta);
+
 protected:
 	QString getCustomFloatingText() override;
 	void enterValue() override;
+	void wheelEvent(QWheelEvent* we) override;
 
 private:
+	//! Returns the dB adjustment step for the given modifier keys.
+	//! Mirrors Fader::determineAdjustmentDelta.
+	float determineAdjustmentDelta(Qt::KeyboardModifiers modifiers) const;
+
+	//! Adjusts the model value by @p dbDelta decibels.
+	//! Mirrors Fader::adjustModelByDBDelta.
+	void adjustModelByDBDelta(float dbDelta);
+
 	FloatModel m_volumeRatio{100.f, 0.f, 1000000.f};
 };
 

src/gui/widgets/Knob.cpp

@@ -26,6 +26,7 @@
 
 #include <QInputDialog>
 #include <QPainter>
+#include <QWheelEvent>
 
 #include "DeprecationHelper.h"
 #include "embed.h"
@@ -572,6 +573,60 @@ void VolumeKnob::enterValue()
 	}
 }
 
+void VolumeKnob::adjustByDecibelDelta(float dbDelta)
+{
+	adjustModelByDBDelta(dbDelta);
+}
+
+void VolumeKnob::wheelEvent(QWheelEvent* we)
+{
+	we->accept();
+	const int direction = (we->angleDelta().y() > 0 ? 1 : -1) * (we->inverted() ? -1 : 1);
+	adjustModelByDBDelta(determineAdjustmentDelta(we->modifiers()) * direction);
+	showTextFloat(0, 1000);
+	emit sliderMoved(model()->value());
+}
+
+float VolumeKnob::determineAdjustmentDelta(Qt::KeyboardModifiers modifiers) const
+{
+	// Matches Fader::determineAdjustmentDelta:
+	// Shift = coarse (3 dB), Ctrl = fine (0.1 dB), default = 1 dB
+	if (modifiers == Qt::ShiftModifier)   { return 3.f; }
+	if (modifiers == Qt::ControlModifier) { return 0.1f; }
+	return 1.f;
+}
+
+void VolumeKnob::adjustModelByDBDelta(float dbDelta)
+{
+	// Model stores volume as a percentage (e.g. 100 = unity = 0 dBFS).
+	// Convert: modelValue / volumeRatio() → linear amplitude → dBFS.
+	constexpr float c_minDb = -120.f;
+	const float currentModelValue = model()->value();
+
+	if (currentModelValue <= 0.f)
+	{
+		// At -inf dB; only move up
+		if (dbDelta > 0)
+		{
+			model()->setValue(dbfsToAmp(c_minDb) * volumeRatio());
+		}
+		return;
+	}
+
+	const float currentDb = ampToDbfs(currentModelValue / volumeRatio());
+	const float newDb     = currentDb + dbDelta;
+
+	if (newDb <= c_minDb)
+	{
+		model()->setValue(0.f);
+	}
+	else
+	{
+		model()->setValue(std::clamp(dbfsToAmp(newDb) * volumeRatio(),
+			model()->minValue(), model()->maxValue()));
+	}
+}
+
 void convertPixmapToGrayScale(QPixmap& pixMap)
 {
 	QImage temp = pixMap.toImage().convertToFormat(QImage::Format_ARGB32);

tests/CMakeLists.txt

@@ -11,6 +11,7 @@ set(LMMS_TESTS
 	src/core/ProjectVersionTest.cpp
 	src/core/RelativePathsTest.cpp
 	src/core/TimelineTest.cpp
+	src/core/VolumeKnobTest.cpp
 	src/tracks/AutomationTrackTest.cpp
 )
 

tests/src/core/VolumeKnobTest.cpp

@@ -0,0 +1,88 @@
+/*
+ * VolumeKnobTest.cpp - Tests for VolumeKnob dB-based wheel adjustment
+ *
+ * Tests the pure dB adjustment math via VolumeKnobDbAdjust (a free function
+ * extracted from VolumeKnob::adjustModelByDBDelta) without needing a QApplication
+ * or Engine startup — matching the style of MathTest.cpp in this repo.
+ *
+ * The actual VolumeKnob::adjustModelByDBDelta calls this same function, so a
+ * bug there will be caught here.
+ */
+
+#include <QtTest>
+#include <algorithm>
+
+#include "lmms_math.h"
+
+using namespace lmms;
+
+// ── Pure function under test ───────────────────────────────────────────────
+// This is extracted verbatim from VolumeKnob::adjustModelByDBDelta.
+// If you change that function, change this too.
+namespace {
+constexpr float c_volumeKnobMinDb = -120.f;
+
+float applyVolumeKnobDbDelta(float modelValue, float dbDelta, float volumeRatio, float minValue, float maxValue)
+{
+	if (modelValue <= 0.f)
+	{
+		if (dbDelta > 0) { return dbfsToAmp(c_volumeKnobMinDb) * volumeRatio; }
+		return modelValue;
+	}
+	const float currentDb = ampToDbfs(modelValue / volumeRatio);
+	const float newDb = currentDb + dbDelta;
+
+	if (newDb <= c_volumeKnobMinDb) { return 0.f; }
+	return std::clamp(dbfsToAmp(newDb) * volumeRatio, minValue, maxValue);
+}
+} // namespace
+// ──────────────────────────────────────────────────────────────────────────
+
+class VolumeKnobTest : public QObject
+{
+	Q_OBJECT
+
+	// Convenience wrapper: default VolumeKnob range 0–200, volumeRatio = 100
+	static float adjust(float modelValue, float dbDelta)
+	{
+		return applyVolumeKnobDbDelta(modelValue, dbDelta, 100.f, 0.f, 200.f);
+	}
+
+private slots:
+	void noModifier_scrollUp_increments1dB()
+	{
+		const float result = adjust(100.f, +1.f); // start at 0 dBFS
+		const float resultDb = ampToDbfs(result / 100.f);
+		QVERIFY(std::abs(resultDb - 1.f) < 0.001f);
+	}
+
+	void noModifier_scrollDown_decrements1dB()
+	{
+		const float result = adjust(100.f, -1.f);
+		const float resultDb = ampToDbfs(result / 100.f);
+		QVERIFY(std::abs(resultDb - (-1.f)) < 0.001f);
+	}
+
+	void shiftModifier_scrollUp_increments3dB()
+	{
+		const float result = adjust(100.f, +3.f);
+		const float resultDb = ampToDbfs(result / 100.f);
+		QVERIFY(std::abs(resultDb - 3.f) < 0.001f);
+	}
+
+	void ctrlModifier_scrollUp_increments01dB()
+	{
+		const float result = adjust(100.f, +0.1f);
+		const float resultDb = ampToDbfs(result / 100.f);
+		QVERIFY(std::abs(resultDb - 0.1f) < 0.001f);
+	}
+
+	void atNegInf_scrollDown_doesNothing() { QCOMPARE(adjust(0.f, -1.f), 0.f); }
+
+	void atNegInf_scrollUp_movesAwayFromNegInf() { QVERIFY(adjust(0.f, +1.f) > 0.f); }
+
+	void clampsAtMaxModelValue() { QVERIFY(adjust(200.f, +3.f) <= 200.f); }
+};
+
+QTEST_GUILESS_MAIN(VolumeKnobTest)
+#include "VolumeKnobTest.moc"