Add Knob::horizontal

include/app/Knob.hpp

@@ -16,6 +16,8 @@ struct Knob : ParamWidget {
 	/** Enable snapping at integer values */
 	bool snap = false;
 	float snapValue = NAN;
+	/** Drag horizontally instead of vertically */
+	bool horizontal = false;
 
 	void onHover(const event::Hover &e) override;
 	void onButton(const event::Button &e) override;

include/app/SliderKnob.hpp

@@ -7,6 +7,7 @@ namespace rack {
 
 
 struct SliderKnob : Knob {
+	// Bypass Knob's circular hitbox detection
 	void onHover(const event::Hover &e) override {
 		ParamWidget::onHover(e);
 	}

src/app/Knob.cpp

@@ -64,7 +64,10 @@ void Knob::onDragMove(const event::DragMove &e) {
 			// Continuous encoders scale as if their limits are +/-1
 			range = 2.f;
 		}
-		float delta = KNOB_SENSITIVITY * -e.mouseDelta.y * speed * range;
+		float delta = (horizontal ? e.mouseDelta.x : -e.mouseDelta.y);
+		delta *= KNOB_SENSITIVITY;
+		delta *= speed;
+		delta *= range;
 
 		// Drag slower if mod is held
 		int mods = app()->window->getMods();