Add line snapping

lib/models/snap.dart

@@ -0,0 +1 @@
+// TODO snap candidates

lib/widgets/editor/editor_config.dart

@@ -23,6 +23,7 @@ class EditorConfig {
   // Painter Configuration
 
   static const crossMarkerSize = 25.0;
+  static const crossXMarkerSize = 15.0;
 
   static const minorGridSize = 20.0;
   static const majorGridDensity = 5; // 100.0 is the majorGridSize

lib/widgets/editor/editor_logic.dart

@@ -0,0 +1,39 @@
+import 'dart:ui';
+
+import 'package:vector_math/vector_math_64.dart';
+
+class EditorLogic {
+  static bool interceptsSquare(Offset parent, Offset child, double size) {
+    Rect rect = Rect.fromCenter(center: parent, width: size, height: size);
+    return rect.contains(child);
+  }
+
+  static bool interceptsCircle(Offset parent, Offset child, double radius) {
+    double distance = (parent - child).distanceSquared;
+    return distance < radius * radius;
+  }
+
+  static Offset nearestPointOnLine(Offset start, Offset end, Offset offset) {
+    final Vector2 startVector = Vector2(start.dx, start.dy);
+    final Vector2 endVector = Vector2(end.dx, end.dy);
+    final Vector2 pointVector = Vector2(offset.dx, offset.dy);
+
+    final Vector2 lineVector = endVector - startVector;
+
+    final Vector2 startToPointVector = pointVector - startVector;
+
+    final double lineLengthSquared = lineVector.length2;
+    final double t = (lineVector.dot(startToPointVector)) / lineLengthSquared;
+
+    Vector2 nearestPoint;
+    if (t < 0) {
+      nearestPoint = startVector;
+    } else if (t > 1) {
+      nearestPoint = endVector;
+    } else {
+      nearestPoint = startVector + lineVector * t;
+    }
+
+    return Offset(nearestPoint.x, nearestPoint.y);
+  }
+}

lib/widgets/editor/editor_painter.dart

@@ -187,6 +187,20 @@ class EditorPainter extends CustomPainter {
     canvas.drawRect(rect, snapPaint);
   }
 
+  void drawCrossXMarker(Canvas canvas, Offset offset) {
+    final Paint crossPaint = Paint()
+      ..color = Colors.blue
+      ..strokeWidth = 1.5 * scaleInverse
+      ..style = PaintingStyle.stroke;
+
+    double halfSize = EditorConfig.crossXMarkerSize * scaleInverse / 2;
+
+    canvas.drawLine(offset.translate(-halfSize, -halfSize),
+        offset.translate(halfSize, halfSize), crossPaint);
+    canvas.drawLine(offset.translate(-halfSize, halfSize),
+        offset.translate(halfSize, -halfSize), crossPaint);
+  }
+
   void establishGridSnap(Canvas canvas) {
     if (activeShouldSnapToGrid!) {
       drawSnapMarker(canvas, activePointerGridSnap!);
@@ -203,6 +217,12 @@ class EditorPainter extends CustomPainter {
       return;
     }
 
+    Offset? nearestLineSnap = editorData.nearestLineSnap(activePointer!);
+    if (nearestLineSnap != null) {
+      drawCrossXMarker(canvas, nearestLineSnap);
+      return;
+    }
+
     establishGridSnap(canvas);
   }
 

lib/widgets/editor/editor_painter_data.dart

@@ -4,7 +4,9 @@ import 'package:flutter/material.dart';
 import 'package:logging/logging.dart';
 import 'package:toolfoam/models/tools/tf_tool_data.dart';
 import 'package:toolfoam/widgets/editor/editor_config.dart';
-import 'package:toolfoam/widgets/editor/editor_util.dart';
+
+import '../../models/line.dart';
+import 'editor_logic.dart';
 
 class EditorData extends ChangeNotifier {
   EditorData({
@@ -72,9 +74,35 @@ class EditorData extends ChangeNotifier {
     return shouldSnapToGrid(activePointer!);
   }
 
+  Offset? nearestLineSnap(Offset offset, {String? ignoreUuid}) {
+    Offset? nearestLineSnap;
+    double nearestDistance = double.infinity;
+    for (Line line in toolData.lines) {
+      if (line.point1 == ignoreUuid || line.point2 == ignoreUuid) continue;
+
+      Offset start = toolData.points[line.point1]!;
+      Offset end = toolData.points[line.point2]!;
+
+      Offset nearestPoint = EditorLogic.nearestPointOnLine(start, end, offset);
+      Offset delta = nearestPoint - offset;
+      double distance = delta.distanceSquared;
+
+      bool isNearest = distance < nearestDistance;
+      double threshold = EditorConfig.defaultSnapTolerance / 2 * scaleInverse;
+      bool isSnap = distance < threshold * threshold;
+
+      if (isNearest && isSnap) {
+        nearestLineSnap = nearestPoint;
+        nearestDistance = distance;
+      }
+    }
+
+    return nearestLineSnap;
+  }
+
   MapEntry<String, Offset>? nearestPointSnap(
       Offset offset, String? ignoreUuid) {
-    MapEntry<String, Offset>? nearestPointSnap = null;
+    MapEntry<String, Offset>? nearestPointSnap;
     double nearestDistance = double.infinity;
     for (MapEntry<String, Offset> entry in toolData.points.entries) {
       if (entry.key == ignoreUuid) continue;
@@ -99,6 +127,10 @@ class EditorData extends ChangeNotifier {
   Offset effectivePointerCoordinates(Offset offset, {String? ignoreUuid}) {
     MapEntry<String, Offset>? pointSnap = nearestPointSnap(offset, ignoreUuid);
     if (pointSnap != null) return pointSnap.value;
+
+    Offset? lineSnap = nearestLineSnap(offset);
+    if (lineSnap != null) return lineSnap;
+
     if (shouldSnapToGrid(offset)) return gridSnap(offset);
 
     return offset;