adding push function with shift key

include/app.hpp

@@ -185,6 +185,8 @@ struct RackWidget : OpaqueWidget {
 	bool requestModuleBox(ModuleWidget *m, Rect box);
 	/** Moves a module to the closest non-colliding position */
 	bool requestModuleBoxNearest(ModuleWidget *m, Rect box);
+	/** Moves a module by one grid unit, pushing other modules recursively. If pushLeft is true, the push direction is left, otherwise right */
+	bool pushModule(ModuleWidget *m, bool pushLeft);
 
 	void step() override;
 	void draw(NVGcontext *vg) override;

src/app/ModuleWidget.cpp

@@ -424,7 +424,22 @@ void ModuleWidget::onDragMove(EventDragMove &e) {
 	if (!gRackWidget->lockModules) {
 		Rect newBox = box;
 		newBox.pos = gRackWidget->lastMousePos.minus(dragPos);
-		gRackWidget->requestModuleBoxNearest(this, newBox);
+		if (windowIsShiftPressed()) {
+			// push left or right in grid steps
+			float dx = newBox.pos.x - box.pos.x;
+			int steps = int(dx / RACK_GRID_WIDTH);
+			while (steps) {
+				if (steps < 0) {
+					gRackWidget->pushModule(this, true);
+					steps++;
+				} else {
+					gRackWidget->pushModule(this, false);
+					steps--;
+				}
+			}
+		} else {
+			gRackWidget->requestModuleBoxNearest(this, newBox);
+		}
 	}
 }
 
@@ -559,4 +574,4 @@ Menu *ModuleWidget::createContextMenu() {
 }
 
 
-} // namespace rack
+} // namespace rack

src/app/RackWidget.cpp

@@ -470,6 +470,50 @@ bool RackWidget::requestModuleBoxNearest(ModuleWidget *m, Rect box) {
 	return false;
 }
 
+bool RackWidget::pushModule(ModuleWidget *m, bool pushLeft) {
+	// calculate desired position
+	Rect newBox = m->box;
+	if (pushLeft) {
+		newBox.pos.x -= RACK_GRID_WIDTH;
+	} else {
+		newBox.pos.x += RACK_GRID_WIDTH;
+	}
+	
+	// can't be pushed over the left border
+	if (newBox.pos.x < 0.0f) return false;
+	
+	// get intersection widget after moving
+	Widget *iw = NULL;
+	int count = 0;
+	for (Widget *child2 : moduleContainer->children) {
+		if (m == child2) continue;
+		if (newBox.intersects(child2->box)) {
+			iw = child2;
+			count++;
+		}
+	}
+	
+	// if a module is higher than one grid unit, it can push only one module, otherwise we would need a rollback,
+	// if e.g. one of two modules can't be pushed
+	if (count > 1) return false;
+	
+	// if there is any intersected widget, try to push it recursively
+	if (iw) {
+		ModuleWidget *w2 = dynamic_cast<ModuleWidget*>(iw);
+		if (pushModule(w2, pushLeft)) {
+			// if successful, set new position for this widget
+			m->box = newBox;
+			return true;
+		} else {
+			return false;
+		}
+	} else {
+		// no intersection, just set the new position
+		m->box = newBox;
+		return true;
+	}
+}
+
 void RackWidget::step() {
 	// Expand size to fit modules
 	Vec moduleSize = moduleContainer->getChildrenBoundingBox().getBottomRight();