Add RackWidget::setSelectedModulesPosNearest() so dragging selected modules uses nearest position to the drag start.

include/app/RackWidget.hpp

@@ -86,6 +86,7 @@ struct RackWidget : widget::OpaqueWidget {
 	bool areSelectedModulesBypassed();
 	void deleteSelectedModulesAction();
 	bool requestSelectedModulePos(math::Vec delta);
+	void setSelectedModulesPosNearest(math::Vec delta);
 	void appendSelectionContextMenu(ui::Menu* menu);
 
 	// Cable methods

src/app/ModuleWidget.cpp

@@ -463,7 +463,7 @@ void ModuleWidget::onDragMove(const DragMoveEvent& e) {
 				if (internal->selected) {
 					pos = (pos / RACK_GRID_SIZE).round() * RACK_GRID_SIZE;
 					math::Vec delta = pos.minus(box.pos);
-					APP->scene->rack->requestSelectedModulePos(delta);
+					APP->scene->rack->setSelectedModulesPosNearest(delta);
 				}
 				else {
 					if ((APP->window->getMods() & RACK_MOD_MASK) == RACK_MOD_CTRL)

src/app/RackWidget.cpp

@@ -1,6 +1,7 @@
 #include <map>
 #include <algorithm>
 #include <queue>
+#include <functional>
 
 #include <osdialog.h>
 
@@ -496,7 +497,7 @@ bool RackWidget::requestModulePos(ModuleWidget* mw, math::Vec pos) {
 	return true;
 }
 
-void RackWidget::setModulePosNearest(ModuleWidget* mw, math::Vec pos) {
+static void eachNearestGridPos(math::Vec pos, std::function<bool(math::Vec pos)> f) {
 	// Dijkstra's algorithm to generate a sorted list of Vecs closest to `pos`.
 
 	// Comparison of distance of Vecs to `pos`
@@ -520,7 +521,7 @@ void RackWidget::setModulePosNearest(ModuleWidget* mw, math::Vec pos) {
 	while (!queue.empty()) {
 		math::Vec testPos = queue.top();
 		// Check testPos
-		if (requestModulePos(mw, testPos))
+		if (f(testPos))
 			return;
 		// Move testPos to visited set
 		queue.pop();
@@ -545,6 +546,12 @@ void RackWidget::setModulePosNearest(ModuleWidget* mw, math::Vec pos) {
 	assert(false);
 }
 
+void RackWidget::setModulePosNearest(ModuleWidget* mw, math::Vec pos) {
+	eachNearestGridPos(pos, [&](math::Vec pos) -> bool {
+		return requestModulePos(mw, pos);
+	});
+}
+
 void RackWidget::setModulePosForce(ModuleWidget* mw, math::Vec pos) {
 	mw->setPosition(pos.div(RACK_GRID_SIZE).round().mult(RACK_GRID_SIZE));
 
@@ -835,6 +842,12 @@ bool RackWidget::requestSelectedModulePos(math::Vec delta) {
 	return true;
 }
 
+void RackWidget::setSelectedModulesPosNearest(math::Vec delta) {
+	eachNearestGridPos(delta, [&](math::Vec delta) -> bool {
+		return requestSelectedModulePos(delta);
+	});
+}
+
 void RackWidget::appendSelectionContextMenu(ui::Menu* menu) {
 	int n = getNumSelectedModules();
 	menu->addChild(createMenuLabel(string::f("%d selected %s", n, n == 1 ? "module" : "modules")));