Add color picker gradient color stop duplication by holding Alt (#4291)

* Add color picker gradient color stop duplication by holding Alt

* Fix bugs

* Bug fix

editor/src/messages/color_picker/color_picker_message_handler.rs

@@ -339,6 +339,31 @@ impl ColorPickerMessageHandler {
 					self.snapshot_old();
 				}
 			}
+			SpectrumInputUpdate::InsertDuplicate { index, position } => {
+				let source = index as usize;
+				let Some(insert_index) = gradient.duplicate_stop(source, position) else { return };
+				// The dragged stop (the duplication source) stays active. Its index shifts up if the frozen copy landed at or before it.
+				let dragged_index = if insert_index <= source { source + 1 } else { source };
+				self.active_marker_index = Some(dragged_index as u32);
+				self.active_marker_is_midpoint = false;
+			}
+			SpectrumInputUpdate::RemoveDuplicate { index } => {
+				let anchor = index as usize;
+				if anchor >= gradient.position.len() || gradient.position.len() <= 2 {
+					return;
+				}
+				// Never remove the active (dragged) stop itself, this should only ever target the frozen copy.
+				if self.active_marker_index == Some(anchor as u32) {
+					return;
+				}
+				gradient.remove(anchor);
+				// Keep the dragged stop active. Its index shifts down if the removed copy came before it.
+				if let Some(active) = self.active_marker_index
+					&& (anchor as u32) < active
+				{
+					self.active_marker_index = Some(active - 1);
+				}
+			}
 			SpectrumInputUpdate::DeleteMarker { index } => {
 				// Enforce minimum stop count. The gradient editor needs at least 2 stops to remain meaningful.
 				if gradient.position.len() <= 2 || (index as usize) >= gradient.position.len() {

editor/src/messages/layout/utility_types/widgets/input_widgets.rs

@@ -612,6 +612,16 @@ pub enum SpectrumInputUpdate {
 	DeleteMarker {
 		index: u32,
 	},
+	/// Insert a copy (same color and midpoint) of the marker at `index` at `position`, keeping the marker at `index` active.
+	InsertDuplicate {
+		index: u32,
+		position: f64,
+	},
+	/// Remove the marker at `index` while keeping the currently active marker active (renumbered to account for the removal).
+	/// Used to un-duplicate when Alt is released mid-drag, deleting the frozen copy left by [`InsertDuplicate`](Self::InsertDuplicate).
+	RemoveDuplicate {
+		index: u32,
+	},
 	/// Emitted when the user double-clicks a marker. The consumer decides what (if anything) to reset the marker to.
 	ResetMarker {
 		index: u32,

editor/src/messages/portfolio/document/node_graph/node_graph_message_handler.rs

@@ -1785,6 +1785,7 @@ impl<'a> MessageHandler<NodeGraphMessage, NodeGraphMessageContext<'a>> for NodeG
 					responses.add(OverlaysMessage::Draw);
 				}
 				if is_stroke_node || is_fill_node || is_shape_generator_node || is_text_node {
+					responses.add(SelectToolMessage::SelectionChanged);
 					responses.add(PenToolMessage::SelectionChanged);
 					responses.add(FreehandToolMessage::SelectionChanged);
 					responses.add(SplineToolMessage::SelectionChanged);