Canvas does not draw smooth lines
I am not able to get anitialiazed lines when doing freehand drawing in javafx canvas. Following is the code .
import javafx.application.*; import javafx.event.*; import javafx.scene.*; import javafx.scene.canvas.*; import javafx.scene.control.*; import javafx.scene.input.*; import javafx.scene.shape.*; import javafx.stage.*; public class Test2 extends Application < GraphicsContext gc; public static void main(String[] args) < launch(args); >private class MouseDragged implements EventHandler < public void handle( MouseEvent e ) < gc.lineTo( e.getX(), e.getY() ); gc.stroke(); >> private class MousePressed implements EventHandler < public void handle( MouseEvent e ) < gc.moveTo( e.getX(), e.getY() ); >> @Override public void start(Stage stage) < Canvas canvas = new Canvas(500, 500); canvas.setOnMouseDragged( new MouseDragged() ); canvas.setOnMousePressed( new MousePressed() ); gc = canvas.getGraphicsContext2D(); gc.setLineCap( StrokeLineCap.ROUND ); gc.setLineJoin( StrokeLineJoin.ROUND ); gc.setLineWidth( 0.1 ); Group root = new Group(canvas); Scene scene = new Scene(root); stage.setTitle("Test2"); stage.setScene(scene); stage.show(); >> g2.setRenderingHint( RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON ); The old JavaFX issue tracker link is dead. Feature requests can be logged against bugreport.java.com (I think), though you would probably have better luck getting the feature request implemented if you discussed in on the openjfx-dev mailing list first before logging it.
Note that the actual issue here might be drawing over the same points multiple times, which makes the antialiased lines appear aliased. See related question: How to apply antialiasing to javafx methods like GraphicsContext.fillArc()?
Canvas to image drawing not successful
First code snippet is my main render method. I am creating buffer strategy, then getState().render(g) is passing Graphics object and it calls a bunch of g.drawImage() methods, after all that, saveImage() gets called and it produces completely black image (games screenshot expected). Second snippet is saving canvas to image.
private void render() < bs = display.getCanvas().getBufferStrategy(); if (bs == null) < display.getCanvas().createBufferStrategy(3); return; >g = bs.getDrawGraphics(); g.clearRect(0, 0, width, height); if (State.getState() != null) State.getState().render(g); // this just calls g.drawImage many times saveImage(g); bs.show(); g.dispose(); > private void saveImage(Graphics g) < BufferedImage image = new BufferedImage(getCanvas().getWidth(), getCanvas().getHeight(), BufferedImage.TYPE_INT_RGB); Graphics2D graphics = image.createGraphics(); display.getCanvas().paint(graphics); graphics.dispose(); try < FileOutputStream out = new FileOutputStream("snapshot.png"); ImageIO.write(image, "png", out); out.close(); >catch (FileNotFoundException e) < e.printStackTrace(); >catch (IOException e) < e.printStackTrace(); >> There are two entirely different Graphics objects involved, one acquired from a BufferedImage and one acquired from BufferStrategy . That doesn’t work well together. It’s also not clear why you are doing it that way. Apparently, your actual rendering routine is State.getState().render(g) , so you may call it with either Graphics object, depending on whether you want to render to a buffer for on-screen rendering or into the BufferedImage for saving. Don’t call paint on a Canvas …
@Holger This is a video game so it’s rendering on screen, but I wanted to learn how to take a screenshot. I tried geting Graphics object from Canvas with no luck. What should I call on Canvas than? Thanks.
You should never mix up screen rendering routines and file I/O operations. Besides that, the structure should be simple, there has to be code in your application drawing into a Graphics . That code can be called either with a Graphics of a screen buffer or with a Graphics from a BufferedImage to produce the same graphic for different purposes. If done right, i.e. when not letting rendering routines modify shared state, you could even execute the code concurrently with the different Graphics , without slowing down the game.
Or you take a true screenshot, which is not even related to Graphics . Or in other words, the standard graphic operations as exposed though Graphics are not capable of reading the screen buffers back.
1 Answer 1
You can not take a screenshots using ordinary operations on a Graphics object¹.
If your system supports it, you can use the AWT Robot class, i.e. its method createScreenCapture to create a screenshot.
For systems not supporting reading back screen data, the best option is to design the application so that the same rendering routines (operating on a Graphics ) can be used in both contexts, when rendering in a screen buffer and when rendering in an off-screen image to be saved. This might not always reproduce the exact image, but is the best you can get on such systems.
¹ it would be possible through some tricks, e.g. implementing a custom Composite , recording the incoming data, but it would be much more complicated to implement than using Robot and undergo the same restrictions, i.e. it still wouldn’t work on all platforms.
Java Canvas is not visible
in my JavaApplication I have a JLayeredPane in my JFrame. The JLayeredPane contains a Canvas as a lower panel where I display a Video with a videoplayer framework. On an upper level the JLayeredPane contains an JFXPanel where I display a JavaFX.WebView. The Webview is complete transparent. The problem is that the Canvas is only visible where the WebView is not diplayed and I see the background from the JFrame where the WebView is placed. If I disable the JFXPanel I can see the whole Canvas with the video. I also tried to add a JPanel as the lower Level. The result was like I want to be the Canvas. I can see the complete JPanel and on top of it, it displays the WebView. So, what can I do to make the Canvas be strong enough to display all-over the Frame. I think canvas.setOpaque would fix the problem but this Method is not available. UPDATE:
//BROWSER this.jfxPanel = new JFXPanel(); this.jfxPanel.setOpaque(false); this.jfxPanel.setBounds(0,0,MainFrame.VIDEO_SIZE_X,MainFrame.VIDEO_SIZE_Y); PlatformImpl.startup(new Runnable() < public void run() < webView = new WebView(); webView.setPrefSize(MainFrame.VIDEO_SIZE_X-100,MainFrame.VIDEO_SIZE_Y-100); webEngine = webView.getEngine(); webView.setStyle("-fx-background-color: rgba(0,0,0,0)"); Scene scene = new Scene(webView,MainFrame.VIDEO_SIZE_X-100,MainFrame.VIDEO_SIZE_Y-100); scene.setFill(javafx.scene.paint.Color.TRANSPARENT); webEngine.documentProperty().addListener(new DocListener()); webEngine.loadContent("Test Transparent"); jfxPanel.setScene(scene); > >); //add browser in upper level to JLayeredPane this.videoPanel.add(jfxPanel, new Integer(100)); //CANVAS this.videoCanvas = new Canvas(); this.videoCanvas.setVisible(true); this.videoCanvas.setBounds(0,0, MainFrame.VIDEO_SIZE_X,MainFrame.VIDEO_SIZE_Y); //add canvas at lower level to JLayeredPane this.videoPanel.add(this.videoCanvas, new Integer(0)); The videoPanel is the JLayeredPane. It is setVisible(true) and has the same size like canvas and the browser. Thanks in advance!
I have added some Code about! @GilbertLeBlanc I have to use Awt for the Player. JavaFX for the browser and the other elements are for the GUI..
Android Canvas always drawing a blackscreen
i’ve a problem canvas always draw a black screen no matter what i want to draw. no matter when i want that the contentview is the View class or i take a layout and add the class or i let the canvas draw a background and so on
public class GameSurface extends SurfaceView < private SurfaceHolder holder; GameThread gameThread; Bitmap background; public GameSurface(Context context) < super(context); holder = getHolder(); gameThread = new GameThread(this); background = BitmapFactory.decodeResource(getResources(), R.drawable.background1); holder.addCallback(new SurfaceHolder.Callback() < @Override public void surfaceCreated(SurfaceHolder holder) < gameThread.setRunning(true); gameThread.start(); >@Override public void surfaceChanged(SurfaceHolder holder, int format, int width, int height) < >@Override public void surfaceDestroyed(SurfaceHolder holder) < boolean retry = true; gameThread.setRunning(false); while (retry)< try < gameThread.join(); retry = false; >catch (InterruptedException e) < e.printStackTrace(); >> > >); > @Override protected void onDraw(Canvas canvas) < canvas.drawBitmap(background,0,0,new Paint()); >> As per my knowledge by default background of any View is transparent. As you are drawing image , check the transparency level of image background. This type of issues comes when images are not having transparency. Please check
i don’t know what you are trying to tell me. it’s a normal background what matter what it shows but alwas its all black more not and only when i call canvas drawing. maybe it’s a bug? i’m using android studio
Javafx Canvas rect does not draw
i do something very basical and i just can’t figure out what went wrong. i try to draw a grid on a canvas, which seems straight forward, but i have problems with the outline of my rectangles. They simply are not drawn!!
canvas.getGraphicsContext2D().setFill(Color.YELLOW); canvas.getGraphicsContext2D().setStroke(Color.BLACK); canvas.getGraphicsContext2D().setLineWidth(2d); for (int dy = 0; dy < height; dy ++)< for (int dx = 0; dx < width; dx ++)< canvas.getGraphicsContext2D().setFill(new Color( random.nextDouble(), random.nextDouble(), random.nextDouble() ,1)); canvas.getGraphicsContext2D().fillRect(dx*32,dy*32,32,32); canvas.getGraphicsContext2D().rect(dx*32,dy*32,32,32); >> 
the result is quite funny since it DOES draw, but not the outline. can’t be that hard, can it? what am i missing?
1 Answer 1
You just append elements to the path, but you never do anything with it. You need to invoke some method using the path. In your case you need to call stroke :
@Override public void start(Stage stage) throws IOException < Canvas canvas = new Canvas(512, 512); Scene scene = new Scene(new Pane(canvas)); Random random = new Random(); final int height = 16; final int width = 16; GraphicsContext gc = canvas.getGraphicsContext2D(); gc.setStroke(Color.BLACK); gc.setLineWidth(2d); for (int dy = 0; dy < height; dy++) < for (int dx = 0; dx < width; dx++) < gc.setFill(new Color(random.nextDouble(), random.nextDouble(), random.nextDouble(), 1)); gc.fillRect(dx * 32, dy * 32, 32, 32); gc.rect(dx * 32, dy * 32, 32, 32); >> // draw the path we've constructed during the loop gc.stroke(); stage.setScene(scene); stage.show(); > I’m out of office, I’ll try it out tomorrow morning (timezone Europe) +1 for the very convincing explanation!
that’s it — just ONE LINE CODE ( canvas.getGraphicsContext2D().stroke(); ) was missing — i am standing deeply in your debt!! thank you very very much