In my Flutter app I use a CustomPainter to allow a user to draw their signature on the screen. I need to find a way to save this as an image.
PictureRecorder works nicely when you are able to pass the PictureRecorder object to the canvas as per previous StackOverflow answers:
final recorder = new PictureRecorder();
Canvas(recorder).drawSomething;
final picture = recorder.endRecording();
However when using CustomPainter the canvas is an argument of the Paint() function.
class myPainter extends CustomPainter {
#override
void paint(Canvas canvas, Size size) {
drawToCanvas(canvas);
#override
bool shouldRepaint(CustomPainter old) {
return false;
}
So in summary:
How can I produce an image from a CustomPainter?
If the answer is to use a PictureRecorder, how can I pass the recorder to the canvas?
You don't need to pass the PictureRecorder to the canvas in the CustomPainter paint method. Instead you can call paint directly with a different canvas that has a picture recorder. For Example:
Future<Image> getImage() async {
final PictureRecorder recorder = PictureRecorder();
myPainter.paint(Canvas(recorder), mySize);
final Picture picture = recorder.endRecording();
return await picture.toImage(width, height);
}
Related
I read almost all the posts but still can't find a proper way if any to load a local image as ui.image so that it can be used in canvas.drawImage in Flutter. I have come out with the following code block to get an ui.image from an Asset image. However, it took a few seconds event for a 32x32 size of image and I can't figure it out when it is fully loaded and ready to be drawn in canvas.
static Future<ui.Image> askImage(String path) async {
Completer<ImageInfo> completer = Completer();
final img = Image(image: AssetImage(path));
img.image
.resolve(ImageConfiguration())
.addListener(ImageStreamListener((ImageInfo info, bool _) {
completer.complete(info);
}));
ImageInfo imageInfo = await completer.future;
return imageInfo.image;
}
static ui.Image load2(String xxxx) {
ui.Image info;
askImage(xxxx).then((info) {
if (info != null) {
print(info.width);
print(info.height);
}
return (info);
});
}
I'm also looking at the Image package 'https://pub.dev/packages/image' but I'm not sure how to convert Image from that package to ui.image which is needed for canvas.drawImage function in Flutter. I also saw an old post here (https://flutter2015.firefirestyle.net/rendering/doc-5) but I'm not sure where does the ImageResource comes from.
I have these two images
What I want to do is to xor them to get this image:
I have tried to do it using CustomPaint and setting BlendMode to XOR But it gives me a black screen
Here's the code I used:
class XorPainter extends CustomPainter {
#override
void paint(Canvas canvas, Size size) async {
if (imageA != null && imageB != null) {
canvas.drawImage(imageA, Offset.zero, Paint());
canvas.save();
canvas.drawImage(
imageB, Offset.zero, Paint()..blendMode = BlendMode.xor);
canvas.restore();
}
}
#override
bool shouldRepaint(CustomPainter oldDelegate) {
return true;
}
For more information: see this
I believe its more of a a misconception of the BlendMode.xor, what they do is just like a regular xor truth table where every pixel is either 0 (transparent) if both of them are some color or unaffected where both overlap if one of them is transparent in that same area, because of that you will always get a transparent black square (unless for example you make the apple image with a transparent background, in which case the second image will have an empty space with the shape of the apple in the middle). I think what you really wanted was difference or exlusion to have that negated effect
class XorPainter extends CustomPainter {
final ui.Image imageA;
final ui.Image imageB;
XorPainter(this.imageA, this.imageB);
#override
void paint(Canvas canvas, Size size) async {
canvas.drawImage(imageA, Offset.zero, Paint());
canvas.saveLayer(null, Paint()..blendMode = BlendMode.difference); // or BlendMode.exclusion
canvas.drawImage(imageB, Offset.zero, Paint());
canvas.restore();
}
#override
bool shouldRepaint(CustomPainter oldDelegate) {
return true;
}
}
I am trying to collect a signature from the user and save it to an image. I have made it far enough that I can draw on the screen, but now I'd like to click a button to save to an image and store in my database.
This is what I have so far:
import 'package:flutter/material.dart';
class SignaturePadPage extends StatefulWidget {
SignaturePadPage({Key key}) : super(key: key);
#override
_SignaturePadPage createState() => new _SignaturePadPage();
}
class _SignaturePadPage extends State<SignaturePadPage> {
List<Offset> _points = <Offset>[];
#override
Widget build(BuildContext context) {
return Container(
color: Colors.white,
child: GestureDetector(
onPanUpdate: (DragUpdateDetails details) {
setState(() {
RenderBox referenceBox = context.findRenderObject();
Offset localPosition =
referenceBox.globalToLocal(details.globalPosition);
_points = new List.from(_points)..add(localPosition);
});
},
onPanEnd: (DragEndDetails details) => _points.add(null),
child: new CustomPaint(painter: new SignaturePainter(_points)),
),
);
}
}
class SignaturePainter extends CustomPainter {
SignaturePainter(this.points);
final List<Offset> points;
void paint(Canvas canvas, Size size) {
Paint paint = new Paint()
..color = Colors.black
..strokeCap = StrokeCap.round
..strokeWidth = 5.0;
for (int i = 0; i < points.length - 1; i++) {
if (points[i] != null && points[i + 1] != null)
canvas.drawLine(points[i], points[i + 1], paint);
}
}
bool shouldRepaint(SignaturePainter other) => other.points != points;
}
Not sure where to go from there...
You can capture the output of a CustomPainter with PictureRecorder. Pass your PictureRecorder instance to the constructor for your Canvas. The Picture returned by PictureRecorder.endRecording can then be converted to an Image with Picture.toImage. Finally, extract the image bytes using Image.toByteData.
Here's an example: https://github.com/rxlabz/flutter_canvas_to_image
Add the rendered method in your widget
ui.Image get rendered {
// [CustomPainter] has its own #canvas to pass our
// [ui.PictureRecorder] object must be passed to [Canvas]#contructor
// to capture the Image. This way we can pass #recorder to [Canvas]#contructor
// using #painter[SignaturePainter] we can call [SignaturePainter]#paint
// with the our newly created #canvas
ui.PictureRecorder recorder = ui.PictureRecorder();
Canvas canvas = Canvas(recorder);
SignaturePainter painter = SignaturePainter(points: _points);
var size = context.size;
painter.paint(canvas, size);
return recorder.endRecording()
.toImage(size.width.floor(), size.height.floor());
}
Then using state fetch the rendered image
var image = signatureKey.currentState.rendered
Now, you can produce png Image using toByteData(format: ui.ImageByteFormat.png) and store using asInt8List()
var pngBytes = await image.toByteData(format: ui.ImageByteFormat.png);
File('your-path/filename.png')
.writeAsBytesSync(pngBytes.buffer.asInt8List());
For complete example, on how to export canvas as png check out this example
https://github.com/vemarav/signature
The existing solutions worked for me, but the images I captured with PictureRecorder were always blurry vs. what was rendering on-screen. I eventually realized I could use some elementary Canvas tricks to pull this off. Basically, after you create the PictureRecorder's Canvas, set its size to multiple times your desired scale (here I have it set to 4x). Then just canvas.scale it. Boom - your generated images are no longer blurry vs. what appears on screens with modern resolutions!
You may want to crank the _overSampleScale value higher for printed or images that may be blown up/expanded, or lower if you're using this a ton and want to improve image preview loading performance. Using it on-screen, you'll need to constrain your Image.memory Widget with a Container of the actual width and height, as with the other solutions. Ideally this number would be the ratio between Flutter's DPI in its fake "pixels" (i.e. what PictureRecorder captures) and the actual DPI of the screen.
static const double _overSampleScale = 4;
Future<ui.Image> get renderedScoreImage async {
final recorder = ui.PictureRecorder();
Canvas canvas = Canvas(recorder);
final size = Size(widget.width * _overSampleScale, widget.height * _overSampleScale);
final painter = SignaturePainter(points: _points);
canvas.save();
canvas.scale(_overSampleScale);
painter.paint(canvas, size);
canvas.restore();
final data = recorder.endRecording()
.toImage(size.width.floor(), size.height.floor());
return data;
}
Given all the data that you need to paint your custom painter, this is all you need to do (in this example, "points" were needed for my customer painter,of course this will change based on your usecase):
Future<void> _handleSavePressed() async {
PictureRecorder recorder = PictureRecorder();
Canvas canvas = Canvas(recorder);
var painter = MyCustomPainter(points: points);
var size = _containerKey.currentContext.size;
painter.paint(canvas, size);
ui.Image renderedImage = await recorder
.endRecording()
.toImage(size.width.floor(), size.height.floor());
var pngBytes =
await renderedImage.toByteData(format: ui.ImageByteFormat.png);
Directory saveDir = await getApplicationDocumentsDirectory();
String path = '${saveDir.path}/custom_image.jpg';
File saveFile = File(path);
if (!saveFile.existsSync()) {
saveFile.createSync(recursive: true);
}
saveFile.writeAsBytesSync(pngBytes.buffer.asUint8List(), flush: true);
await GallerySaver.saveImage(path, albumName: 'iDream');
print('Image was saved!');
}
Answer based on https://gist.github.com/OPY-bbt/a5418127d8444393a2ef25ad2d966dc0
Follow the complete class to draw a PNG image using Flutter > 3.0.0
import 'dart:typed_data';
import 'dart:ui';
import 'dart:ui' as ui;
import 'package:flutter/material.dart';
class BitmapUtils {
Future<Uint8List> generateImagePngAsBytes(String text) async {
ByteData? image = await generateSquareWithText(text);
return image!.buffer.asUint8List();
}
Future<ByteData?> generateSquareWithText(String text) async {
final recorder = PictureRecorder();
final canvas = Canvas(
recorder, Rect.fromPoints(Offset(0.0, 0.0), Offset(200.0, 200.0)));
final stroke = Paint()
..color = Colors.grey
..style = PaintingStyle.stroke;
canvas.drawRect(Rect.fromLTWH(0.0, 0.0, 200.0, 200.0), stroke);
final textPainter = TextPainter(
text: TextSpan(
text: text,
style: TextStyle(
color: Colors.black,
fontSize: 30,
),
),
textDirection: TextDirection.ltr,
textAlign: TextAlign.center);
textPainter.layout();
// Draw the text centered around the point (50, 100) for instance
final offset =
Offset(50 - (textPainter.width / 2), 100 - (textPainter.height / 2));
textPainter.paint(canvas, offset);
final picture = recorder.endRecording();
ui.Image img = await picture.toImage(200, 200);
final ByteData? pngBytes =
await img.toByteData(format: ImageByteFormat.png);
return pngBytes;
}
}
I looked into this thread but the methods are deprecated and for me doesn't even work. I tried to do something similiar but failed. My sample code:
public interface Resources extends ClientBundle{
#Source("images/castle.png")
ImageResource castleIcon();
And the class that draws the image:
private void drawImage() {
Resources res = GWT.create(Resources.class);
final Image icon = new Image(res.castleIcon().getSafeUri());
icon.addLoadHandler(new LoadHandler() {
#Override
public void onLoad(LoadEvent event) {
icon.setPixelSize(100, 80);
}
});
context.drawImage(createImageElement(icon), x - 65, y - 20);
}
private ImageElement createImageElement(Image image) {
return ImageElement.as(image.getElement());
}
I've tried this approach but it fails to render transparent background
Transparency should work fine with PNG on a canvas. Are you sure your image is really transparent? Maybe your PNG is somehow incompatibly with the canvas implementation. Try a proper 24-bit PNG with alpha transparency...
I am using a loop to invoke double buffering painting. This, together with overriding my only Panel's repaint method, is designed to pass complete control of repaint to my loop and only render when it necessary (i.e. some change was made in the GUI).
This is my rendering routine:
Log.write("renderer painting");
setNeedsRendering(false);
Graphics g = frame.getBufferStrategy().getDrawGraphics();
g.setFont(font);
g.setColor(Color.BLACK);
g.fillRect(0, 0, window.getWidth(),window.getHeight());
if(frame != null)
window.paint(g);
g.dispose();
frame.getBufferStrategy().show();
As you can see, it is pretty standard. I get the grpahics object from the buffer strategy (initialized to 2), make it all black and pass it to the paint method of my "window" object.
After window is done using the graphics object, I dispose of it and invoke show on the buffer strategy to display the contents of the virtual buffer.
It is important to note that window passes the graphics object to many other children components the populate the window and each one, in turn, uses the same instance of the graphics object to draw something onto the screen: text, shapes, or images.
My problem begins to show when the system is running and a large image is rendered. The image appears to be cut into seveeal pieces and drawn again and again (3-4 times) with different offsets inside of where the image is supposed to be rendered. See my attached images:
This is the original image:
alt text http://img109.imageshack.us/img109/8308/controller.png
This is what I get:
alt text http://img258.imageshack.us/img258/3248/probv.png
Note that in the second picture, I am rendering shapes over the picture - these are always at the correct position.
Any idea why this is happening?
If I save the image to file, as it is in memory, right before the call to g.drawImage(...) it is identical to the original.
Uh, you are using Swing ?
Normally Swing automatically renders the image, you can't switch it off. The repaint()
method is out of bounds because Swing has a very complicated rendering routine due to
method compatibility for AWT widgets and several optimizations, inclusive drawing only
when necessary !
If you want to use the High-Speed Drawing API, you use a component with a BufferStrategy
like JFrame and Window, use
setIgnoreRepaint(false);
to switch off Swing rendering, set up a drawing loop and paint the content itself.
Or you can use JOGL for OpenGL rendering. The method you are using seems completely
at odds with correct Java2D usage.
Here the correct use:
public final class FastDraw extends JFrame {
private static final transient double NANO = 1.0e-9;
private BufferStrategy bs;
private BufferedImage frontImg;
private BufferedImage backImg;
private int PIC_WIDTH,
PIC_HEIGHT;
private Timer timer;
public FastDraw() {
timer = new Timer(true);
JMenu menu = new JMenu("Dummy");
menu.add(new JMenuItem("Display me !"));
menu.add(new JMenuItem("Display me, too !"));
JMenuBar menuBar = new JMenuBar();
menuBar.add(menu);
setJMenuBar(menuBar);
setIgnoreRepaint(true);
setVisible(true);
addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent evt) {
super.windowClosing(evt);
timer.cancel();
dispose();
System.exit(0);
}
});
try {
backImg = javax.imageio.ImageIO.read(new File("MyView"));
frontImg = javax.imageio.ImageIO.read(new File("MyView"));
}
catch (IOException e) {
System.out.println(e.getMessage());
}
PIC_WIDTH = backImg.getWidth();
PIC_HEIGHT = backImg.getHeight();
setSize(PIC_WIDTH, PIC_HEIGHT);
createBufferStrategy(1); // Double buffering
bs = getBufferStrategy();
timer.schedule(new Drawer(),0,20);
}
public static void main(String[] args) {
new FastDraw();
}
private class Drawer extends TimerTask {
private VolatileImage img;
private int count = 0;
private double time = 0;
public void run() {
long begin = System.nanoTime();
Graphics2D g = (Graphics2D) bs.getDrawGraphics();
GraphicsConfiguration gc = g.getDeviceConfiguration();
if (img == null)
img = gc.createCompatibleVolatileImage(PIC_WIDTH, PIC_HEIGHT);
Graphics2D g2 = img.createGraphics();
// Zeichenschleife
do {
int valStatus = img.validate(gc);
if (valStatus == VolatileImage.IMAGE_OK)
g2.drawImage(backImg,0,0,null);
else {
g.drawImage(frontImg, 0, 0, null);
}
// volatile image is ready
g.drawImage(img,0,50,null);
bs.show();
} while (img.contentsLost());
time = NANO*(System.nanoTime()-begin);
count++;
if (count % 100 == 0)
System.out.println(1.0/time);
}
}