Canvas 颤振-画布绘制Z顺序
使用Flatter的Canvas 颤振-画布绘制Z顺序,canvas,dart,flutter,Canvas,Dart,Flutter,使用Flatter的CustomPainter在画布中绘制各种图像s,然后在屏幕上渲染。我期望任何绘制的重叠图像的深度顺序与在画布上绘制的相同(例如,Canvas.drawImage(图像1,…);Canvas.drawImage(图像2,…);Canvas.drawImage(图像3,…)将在屏幕上呈现三个图像,其中image1分别出现在image2和image3下方。然而,我发现在某些情况下,渲染图像的顺序并没有完全保留 请参见下面的示例代码: import 'dart:async'; im
CustomPainter
在画布中绘制各种图像
s,然后在屏幕上渲染。我期望任何绘制的重叠图像的深度顺序与在画布上绘制的相同(例如,Canvas.drawImage(图像1,…);Canvas.drawImage(图像2,…);Canvas.drawImage(图像3,…)
将在屏幕上呈现三个图像,其中image1
分别出现在image2
和image3
下方。然而,我发现在某些情况下,渲染图像的顺序并没有完全保留
请参见下面的示例代码:
import 'dart:async';
import 'dart:ui' as ui;
import 'package:flutter/material.dart';
import 'package:flutter/services.dart';
import 'package:flutter/services.dart' show rootBundle;
void main() => runApp(new ExampleApp());
class ExampleApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return new MaterialApp(
title: 'Ground Example',
theme: new ThemeData(
primarySwatch: Colors.blue,
),
home: ExampleScreen(),
);
}
}
class ExampleScreen extends StatefulWidget {
final Offset initPos = Offset(0.0, 0.0);
@override
_ExampleScreenState createState() => _ExampleScreenState();
}
class _ExampleScreenState extends State<ExampleScreen> {
ui.Image _image1;
ui.Image _image2;
ui.Image _image3;
bool _prepDone;
@override
void initState() {
_prepDone = false;
super.initState();
//_draggedToOffset = widget.initPos;
}
_ExampleScreenState() {
_prepare();
}
_prepare() {
loadImage('assets/wfw_1.png').then((image1) {
_image1 = image1;
}).whenComplete(() {
loadImage('assets/wnfw_2.png').then((image2) {
_image2 = image2;
}).whenComplete(() {
loadImage('assets/wfw_1.png').then((image3) {
_image3 = image3;
}).whenComplete(() {
_prepDone = true;
_handle();
});
});
});
}
_handle() {
setState(() {});
}
@override
Widget build(BuildContext context) {
return new Container(
constraints: BoxConstraints.expand(),
color: Colors.grey,
child: new Stack(children: <Widget>[
_prepDone ? Container(child: buildPainter()) : Container()
]));
}
buildPainter() {
return Container(
child: CustomPaint(
painter: ExamplePainter(_image1, _image2, _image3),
));
}
}
class ExamplePainter extends CustomPainter {
ui.Image _image1;
ui.Image _image2;
ui.Image _image3;
Paint _paint = Paint();
ExamplePainter(this._image1, this._image2, this._image3);
@override
void paint(Canvas canvas, Size size) {
canvas.drawImage(_image1, Offset(100.0, 35.0), _paint);
canvas.drawImage(_image2, Offset(70.0, 50.0), _paint);
canvas.drawImage(_image3, Offset(40.0, 65.0), _paint);
}
@override
bool shouldRepaint(ExamplePainter oldDelegate) {
return true;
}
}
Future<ui.Image> loadImage(String assetPath) async {
ImageStream stream = new AssetImage(assetPath, bundle: rootBundle)
.resolve(ImageConfiguration.empty);
Completer<ui.Image> completer = new Completer<ui.Image>();
void listener(ImageInfo frame, bool synchronousCall) {
final ui.Image image = frame.image;
completer.complete(image);
stream.removeListener(listener);
}
stream.addListener(listener);
return completer.future;
}
导入'dart:async';
将“dart:ui”导入为ui;
进口“包装:颤振/材料.省道”;
导入“包:flifter/services.dart”;
导入“包:flatter/services.dart”显示根包;
void main()=>runApp(新示例app());
类ExampleApp扩展了无状态小部件{
@凌驾
小部件构建(构建上下文){
返回新材料PP(
标题:“基本示例”,
主题:新主题数据(
主样本:颜色。蓝色,
),
主页:ExampleScreen(),
);
}
}
类ExampleScreen扩展StatefulWidget{
最终偏移量initPos=偏移量(0.0,0.0);
@凌驾
_示例ScreenState createState()=>_示例ScreenState();
}
类\u示例ScreenState扩展状态{
ui.Image\u image1;
ui.Image\u image2;
ui.Image\u image3;
预习;
@凌驾
void initState(){
_预处理=假;
super.initState();
//_draggedToOffset=widget.initPos;
}
_示例ScreenState(){
_准备();
}
_准备(){
loadImage('assets/wfw_1.png')。然后((image1){
_image1=image1;
}).完成时(){
loadImage('assets/wnfw_2.png')。然后((image2){
_image2=image2;
}).完成时(){
loadImage('assets/wfw_1.png')。然后((image3){
_image3=image3;
}).完成时(){
_prepDone=true;
_句柄();
});
});
});
}
_句柄(){
setState((){});
}
@凌驾
小部件构建(构建上下文){
退回新货柜(
约束:BoxConstraints.expand(),
颜色:颜色。灰色,
子级:新堆栈(子级:[
_预处理?容器(子:buildPainter()):容器()
]));
}
建筑油漆工(){
返回容器(
孩子:定制油漆(
画家:例如画家(_image1,_image2,_image3),
));
}
}
类ExamplePainter扩展了CustomPainter{
ui.Image\u image1;
ui.Image\u image2;
ui.Image\u image3;
油漆_油漆=油漆();
例如画家(这个。_图像1,这个。_图像2,这个。_图像3);
@凌驾
空心油漆(帆布,尺寸){
画布.drawImage(_image1,偏移量(100.0,35.0),_paint);
画布.drawImage(_image2,偏移量(70.0,50.0),_paint);
画布.drawImage(_image3,偏移量(40.0,65.0),_paint);
}
@凌驾
bool应重新绘制(例如Painter oldDelegate){
返回true;
}
}
未来加载映像(字符串assetPath)异步{
ImageStream=新的AssetImage(assetPath,bundle:rootBundle)
.resolve(ImageConfiguration.empty);
Completer Completer=新的Completer();
无效侦听器(ImageInfo帧,bool synchronousCall){
最终ui.Image=frame.Image;
完成(图像);
stream.RemovelListener(监听器);
}
addListener(监听器);
返回completer.future;
}
其中:
image1
和image3
是:。
image2
是:
Renderer输出在我的笔记本电脑的Android Emulator设备上如下所示:
可以看出,image2
是在最后绘制的图像(image3
)之上渲染的,当时我希望它在image2
(即介于image1
和image3
之间)之下渲染
我能够解决该问题的唯一方法是:
在drawImage(..)
调用之间添加一个虚拟drawRect(..)
调用,或者通过将image2
的Offset.dy
设置为Offset.dy+0.001
我对Dart和Flatter基本上是新手,所以我不确定是a)我的代码错了,b)我对Flatter渲染引擎的理解错了,还是c)Dart:ui中某个地方有个bug?我想是c)因为在更新到Flatter版本0.10.2
后,顺序现在保持不变