Remove clients of getTotalMatrix (#4487)

Instead of using getTotalMatrix and setMatrix, we can just use
save/restore, which is more idiomatic.

The getTotalMatrix/setMatrix pattern was introduced to improve
performance, but the original code was calling getTotalMatrix/setMatrix
at every node in the sprite tree, which is much slower than the normal
save/transform/restore pattern.

Related to #4254

packages/flutter/test/engine/canvas_test_flakey_see_1854.dart

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-import 'dart:ui' as ui show PictureRecorder;
-import 'dart:ui' show Rect, Color, Paint, Canvas;
-
-import 'package:test/test.dart';
-import 'package:vector_math/vector_math_64.dart';
-
-void main() {
-
-  ui.PictureRecorder recorder = new ui.PictureRecorder();
-  Canvas canvas = new Canvas(recorder, new Rect.fromLTRB(0.0, 0.0, 100.0, 100.0));
-
-  test("matrix access should work", () {
-    // Matrix equality doesn't work!
-    // https://github.com/google/vector_math.dart/issues/147
-    expect(canvas.getTotalMatrix(), equals(new Matrix4.identity().storage));
-    Matrix4 matrix = new Matrix4.identity();
-    // Round-tripping through getTotalMatrix will lose the z value
-    // So only scale to 1x in the z direction.
-    matrix.scale(2.0, 2.0, 1.0);
-    canvas.setMatrix(matrix.storage);
-    canvas.drawPaint(new Paint()..color = const Color(0xFF00FF00));
-    expect(canvas.getTotalMatrix(), equals(matrix.storage));
-  });
-
-}

packages/flutter_sprites/lib/flutter_sprites.dart

@@ -17,6 +17,7 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
+import 'package:meta/meta.dart';
 import 'package:mojo/core.dart';
 import 'package:sky_services/media/media.mojom.dart';
 import 'package:vector_math/vector_math_64.dart';

packages/flutter_sprites/lib/src/layer.dart

@@ -30,16 +30,16 @@ class Layer extends Node with SpritePaint {
     ..isAntiAlias = false;
 
   @override
-  void _prePaint(Canvas canvas, Matrix4 matrix) {
-    super._prePaint(canvas, matrix);
+  void _prePaint(Canvas canvas) {
+    super._prePaint(canvas);
 
     _updatePaint(_cachedPaint);
     canvas.saveLayer(layerRect, _cachedPaint);
   }
 
   @override
-  void _postPaint(Canvas canvas, Matrix4 totalMatrix) {
+  void _postPaint(Canvas canvas) {
     canvas.restore();
-    super._postPaint(canvas, totalMatrix);
+    super._postPaint(canvas);
   }
 }

packages/flutter_sprites/lib/src/node.dart

@@ -55,7 +55,6 @@ class Node {
   int _addedOrder;
   int _childrenLastAddedOrder = 0;
   bool _childrenNeedSorting = false;
-  Matrix4 _savedTotalMatrix;
 
   /// Decides if the node and its children is currently paused.
   ///
@@ -508,20 +507,20 @@ class Node {
 
   // Rendering
 
-  void _visit(Canvas canvas, Matrix4 totalMatrix) {
+  void _visit(Canvas canvas) {
     assert(canvas != null);
     if (!visible) return;
 
-    _prePaint(canvas, totalMatrix);
-    _visitChildren(canvas, totalMatrix);
-    _postPaint(canvas, totalMatrix);
+    _prePaint(canvas);
+    _visitChildren(canvas);
+    _postPaint(canvas);
   }
 
-  void _prePaint(Canvas canvas, Matrix4 matrix) {
-    _savedTotalMatrix = new Matrix4.copy(matrix);
-
-    // Get the transformation matrix and apply transform
-    matrix.multiply(transformMatrix);
+  @mustCallSuper
+  void _prePaint(Canvas canvas) {
+    canvas
+      ..save()
+      ..transform(transformMatrix.storage);
   }
 
   /// Paints this node to the canvas.
@@ -543,7 +542,7 @@ class Node {
   void paint(Canvas canvas) {
   }
 
-  void _visitChildren(Canvas canvas, Matrix4 totalMatrix) {
+  void _visitChildren(Canvas canvas) {
     // Sort children if needed
     _sortChildren();
 
@@ -553,24 +552,24 @@ class Node {
     while (i < _children.length) {
       Node child = _children[i];
       if (child.zPosition >= 0.0) break;
-      child._visit(canvas, totalMatrix);
+      child._visit(canvas);
       i++;
     }
 
     // Paint this node
-    canvas.setMatrix(totalMatrix.storage);
     paint(canvas);
 
     // Visit children in front of this node
     while (i < _children.length) {
       Node child = _children[i];
-      child._visit(canvas, totalMatrix);
+      child._visit(canvas);
       i++;
     }
   }
 
-  void _postPaint(Canvas canvas, Matrix4 totalMatrix) {
-    totalMatrix.setFrom(_savedTotalMatrix);
+  @mustCallSuper
+  void _postPaint(Canvas canvas) {
+    canvas.restore();
   }
 
   // Receiving update calls

packages/flutter_sprites/lib/src/sprite_box.dart

@@ -353,15 +353,14 @@ class SpriteBox extends RenderBox {
   @override
   void paint(PaintingContext context, Offset offset) {
     final Canvas canvas = context.canvas;
-    canvas.save();
-
     // Move to correct coordinate space before drawing
-    canvas.translate(offset.dx, offset.dy);
-    canvas.transform(transformMatrix.storage);
+    canvas
+      ..save()
+      ..translate(offset.dx, offset.dy)
+      ..transform(transformMatrix.storage);
 
     // Draw the sprite tree
-    Matrix4 totalMatrix = new Matrix4.fromFloat64List(canvas.getTotalMatrix());
-    _rootNode._visit(canvas, totalMatrix);
+    _rootNode._visit(canvas);
 
     canvas.restore();
   }