couple view and controller + offset working

lib/core/render.dart

@@ -1,5 +1,6 @@
 import 'package:flutter/material.dart';
 import 'package:flutter/rendering.dart';
+import 'package:infinite_lazy_2d_grid/core/controller.dart';
 
 import 'background.dart';
 
@@ -10,19 +11,30 @@ import 'background.dart';
 
 /// An infinite canvas that places all the children at the specified positions.
 class CanvasView extends StatelessWidget {
-  final List<Offset> ssPositions; // screen space positions;
-  final List<Widget> children; // children, in the same order as positions
   final CanvasBackground canvasBackground;
+  final CanvasController controller;
 
-  const CanvasView({required this.ssPositions, required this.children, required this.canvasBackground, super.key})
-    : assert(children.length == ssPositions.length, 'Children and positions must have the same length');
+  const CanvasView({required this.controller, required this.canvasBackground, super.key});
 
   @override
   Widget build(BuildContext context) {
     return Container(
       color: canvasBackground.bgColor,
       child: GestureDetector(
-        child: _CanvasRenderObject(canvasBackground: canvasBackground, ssPositions: ssPositions, children: children),
+        onScaleUpdate: controller.handleGesture,
+        child: ListenableBuilder(
+          listenable: controller,
+          builder: (_, _) {
+            final childrenWithPositions = controller.widgetsWithScreenPositions();
+            final ssPositions = childrenWithPositions.map((e) => e.$1).toList();
+            final children = childrenWithPositions.map((e) => e.$2).toList();
+            return _CanvasRenderObject(
+              canvasBackground: canvasBackground,
+              ssPositions: ssPositions,
+              children: children,
+            );
+          },
+        ),
       ),
     );
   }
@@ -46,7 +58,9 @@ class _CanvasRenderObject extends MultiChildRenderObjectWidget {
 
   @override
   void updateRenderObject(BuildContext context, _CanvasRenderBox renderObject) {
-    // static for now
+    renderObject
+      ..ssPositions = ssPositions
+      ..canvasBackground = canvasBackground;
   }
 }
 
@@ -57,10 +71,12 @@ class _CanvasRenderBox extends RenderBox
     with
         ContainerRenderObjectMixin<RenderBox, _WidgetParentData>,
         RenderBoxContainerDefaultsMixin<RenderBox, _WidgetParentData> {
-  final CanvasBackground canvasBackground;
-  final List<Offset> ssPositions;
+  CanvasBackground _canvasBackground;
+  List<Offset> _ssPositions;
 
-  _CanvasRenderBox({required this.ssPositions, required this.canvasBackground});
+  _CanvasRenderBox({required ssPositions, required canvasBackground})
+    : _ssPositions = ssPositions,
+      _canvasBackground = canvasBackground;
 
   @override
   void setupParentData(RenderBox child) {
@@ -69,6 +85,20 @@ class _CanvasRenderBox extends RenderBox
     }
   }
 
+  set ssPositions(List<Offset> ssPositions) {
+    if (_ssPositions != ssPositions) {
+      _ssPositions = ssPositions;
+      markNeedsPaint();
+    }
+  }
+
+  set canvasBackground(CanvasBackground canvasBackground) {
+    if (_canvasBackground != canvasBackground) {
+      _canvasBackground = canvasBackground;
+      markNeedsPaint();
+    }
+  }
+
   @override
   void performLayout() {
     size = constraints.biggest; // expand as much as possible for the parent
@@ -89,12 +119,12 @@ class _CanvasRenderBox extends RenderBox
     final canvas = context.canvas;
 
     // use the canvas background painter, pass it the canvas and that should handle drawing the background
-    canvasBackground.paint(canvas, size);
+    _canvasBackground.paint(canvas, size);
 
     RenderBox? child = firstChild;
     for (int idx = 0; child != null; idx++) {
       final _WidgetParentData parentData = child.parentData! as _WidgetParentData;
-      context.paintChild(child, ssPositions[idx]);
+      context.paintChild(child, _ssPositions[idx]);
       child = parentData.nextSibling;
     }
   }
@@ -109,11 +139,11 @@ class _CanvasRenderBox extends RenderBox
 
     // Check children in reverse order (last painted = first hit)
     RenderBox? child = lastChild;
-    for (int idx = ssPositions.length - 1; child != null; idx--) {
+    for (int idx = _ssPositions.length - 1; child != null; idx--) {
       final _WidgetParentData parentData = child.parentData! as _WidgetParentData;
 
       // Transform the hit position relative to the child's position
-      final childPosition = ssHitPosition - ssPositions[idx];
+      final childPosition = ssHitPosition - _ssPositions[idx];
 
       if (child.hitTest(BoxHitTestResult.wrap(result), position: childPosition)) {
         return true;