improved checkered background performance

lib/widgets/collection/thumbnail/vector.dart

@@ -31,8 +31,8 @@ class VectorImageThumbnail extends StatelessWidget {
               final availableSize = constraints.biggest;
               final fitSize = applyBoxFit(fit, entry.displaySize, availableSize).destination;
               final offset = fitSize / 2 - availableSize / 2;
-              final child = DecoratedBox(
-                decoration: CheckeredDecoration(checkSize: extent / 8, offset: offset),
+              final child = CustomPaint(
+                painter: CheckeredPainter(checkSize: extent / 8, offset: offset),
                 child: SvgPicture(
                   UriPicture(
                     uri: entry.uri,

lib/widgets/common/fx/checkered_decoration.dart

@@ -1,57 +1,40 @@
 import 'package:flutter/material.dart';
 
-class CheckeredDecoration extends Decoration {
-  final Color light, dark;
+class CheckeredPainter extends CustomPainter {
+  final Paint lightPaint, darkPaint;
   final double checkSize;
   final Offset offset;
 
-  const CheckeredDecoration({
-    this.light = const Color(0xFF999999),
-    this.dark = const Color(0xFF666666),
+  CheckeredPainter({
+    Color light = const Color(0xFF999999),
+    Color dark = const Color(0xFF666666),
     this.checkSize = 20,
     this.offset = Offset.zero,
-  });
+  })  : lightPaint = Paint()..color = light,
+        darkPaint = Paint()..color = dark;
 
   @override
-  _CheckeredDecorationPainter createBoxPainter([VoidCallback onChanged]) {
-    return _CheckeredDecorationPainter(this, onChanged);
-  }
-}
+  void paint(Canvas canvas, Size size) {
+    final background = Rect.fromLTWH(0, 0, size.width, size.height);
+    canvas.drawRect(background, lightPaint);
 
-class _CheckeredDecorationPainter extends BoxPainter {
-  final CheckeredDecoration decoration;
-
-  const _CheckeredDecorationPainter(this.decoration, VoidCallback onChanged) : super(onChanged);
-
-  @override
-  void paint(Canvas canvas, Offset offset, ImageConfiguration configuration) {
-    final size = configuration.size;
-    var dx = offset.dx;
-    var dy = offset.dy;
-
-    final lightPaint = Paint()..color = decoration.light;
-    final darkPaint = Paint()..color = decoration.dark;
-    final checkSize = decoration.checkSize;
-
-    // save/restore because of the clip
-    canvas.save();
-    canvas.clipRect(Rect.fromLTWH(dx, dy, size.width, size.height));
-
-    canvas.drawPaint(lightPaint);
-
-    dx += decoration.offset.dx % (decoration.checkSize * 2);
-    dy += decoration.offset.dy % (decoration.checkSize * 2);
+    final dx = offset.dx % (checkSize * 2);
+    final dy = offset.dy % (checkSize * 2);
 
     final xMax = size.width / checkSize;
     final yMax = size.height / checkSize;
     for (var x = -2; x < xMax; x++) {
       for (var y = -2; y < yMax; y++) {
         if ((x + y) % 2 == 0) {
-          final rect = Rect.fromLTWH(dx + x * checkSize, dy + y * checkSize, checkSize, checkSize);
-          canvas.drawRect(rect, darkPaint);
+          final check = Rect.fromLTWH(dx + x * checkSize, dy + y * checkSize, checkSize, checkSize);
+          if (check.overlaps(background)) {
+            canvas.drawRect(check.intersect(background), darkPaint);
+          }
         }
       }
     }
-    canvas.restore();
   }
+
+  @override
+  bool shouldRepaint(CustomPainter oldDelegate) => false;
 }

lib/widgets/settings/entry_background.dart

@@ -50,8 +50,8 @@ class _EntryBackgroundSelectorState extends State<EntryBackgroundSelector> {
           break;
         case EntryBackground.checkered:
           child = ClipOval(
-            child: DecoratedBox(
-              decoration: CheckeredDecoration(
+            child: CustomPaint(
+              painter: CheckeredPainter(
                 checkSize: radius,
               ),
             ),

lib/widgets/viewer/visual/raster.dart

@@ -1,8 +1,8 @@
 import 'dart:math';
 
 import 'package:aves/image_providers/region_provider.dart';
-import 'package:aves/model/entry_images.dart';
 import 'package:aves/model/entry.dart';
+import 'package:aves/model/entry_images.dart';
 import 'package:aves/model/settings/entry_background.dart';
 import 'package:aves/model/settings/settings.dart';
 import 'package:aves/utils/math_utils.dart';
@@ -199,8 +199,8 @@ class _RasterImageViewState extends State<RasterImageView> {
         builder: (context, fullImageLoaded, child) {
           if (!fullImageLoaded) return SizedBox.shrink();
 
-          return DecoratedBox(
-            decoration: CheckeredDecoration(
+          return CustomPaint(
+            painter: CheckeredPainter(
               checkSize: checkSize,
               offset: offset,
             ),

lib/widgets/viewer/visual/vector.dart

@@ -36,8 +36,8 @@ class VectorViewCheckeredBackground extends StatelessWidget {
             Positioned(
               width: decorationSize.width,
               height: decorationSize.height,
-              child: DecoratedBox(
-                decoration: CheckeredDecoration(
+              child: CustomPaint(
+                painter: CheckeredPainter(
                   checkSize: checkSize,
                   offset: offset,
                 ),