Develop Reference

bug with collisions, is there a better way or workaround for this? javafx

so lately i've been learning about abstract classes and interfaces, and i saw a neat yt video about falling sand games (think Noita) so i wanted to take a crack at it as some particles share a characteristic that can be abstracted, and behavior that's not specific to only particles that can be interfaced. only going to be implementing 2, maybe 3 types of "particle" but it seems im having trouble with gravity.
i've spent a few hours trying to figure out a good way of doing it and this is what i got so far out of my attempts (which include: gravity somehow working backwards, collision being ignored, and working, but sunk a few pixels into the object)
// the drop method is called every second, and force == 1
// drop is a method from the Gravity interface, Sand implements gravity and overrides drop.
#Override
public void drop(Particle self) {
for (Particle p : Controller.particle) {
if (p.equals(self)) {
continue;
}
if (self.rectangle.getBoundsInParent().intersects(p.rectangle.getBoundsInParent())) {
Behavior.repulseUpward(self, force);
}
}
Behavior.gravityDrop(self, force);
}
public class Behavior {
static void gravityDrop(Particle p, double force) {
// in the future ill replace bottomLine with what's inside it but for now its more
// readable to me.
double bottomLine = (Controller.height - p.rectangle.getHeight());
if (p.rectangle.getLayoutY() < bottomLine) {
p.setPosition(p.rectangle.getLayoutX(), p.rectangle.getLayoutY() + force);
}
}
static void repulseUpward(Particle p, double force) {
p.setPosition(p.rectangle.getLayoutX(), p.rectangle.getLayoutY() - force);
}
}
(if i've forgotton any code that you think would be relevant ill add it)
this gives me the behavior i was hoping for! exceeeeeept if say two shapes are 20 pix wide, and are spaced 20 pix apart, it will still detect a collision and cause themselves to suspend in air. Is there any fix to get around this situation or do i have to scrap the drop method again?
Picture of the problem here

(Kind of solved but still appreciate better answers) Android Studio: How to identify certain special pages in a PDF file?

I am writing an app that generates Maths worksheets for school students. It will, for example, generate 2 to 5 pages of simple Maths questions and 1 to 2 pages of answers. The PDF can be saved to file and loaded again later. Then it has a print function that can print all the pages. I want to make it skip printing the answer pages.
Is it possible to automatically identify which pages are the answer pages? I can only think of a workaround by making those answer pages have special height or width but not even sure if this works. Are there any better ways to do this?

Ok, I continued the project and used the following method: when constructing the PDF, I put the word "Answer on the top left corner with a gray rectangle surrounding it drawn with drawRect(). Then before the actual printing, I used the following code inside the PrintDocumentAdapter() class to check whether the color of the pixel 0,0 is gray or not.
#Override
public void onStart() {
if (parcelFileDescriptor != null) {
try {
pdfRenderer = new PdfRenderer(parcelFileDescriptor);
} catch (IOException e) {
e.printStackTrace();
}
}
int tempTotal = pdfRenderer.getPageCount();
Bitmap[] tempBitmap = new Bitmap[tempTotal];
finalTotal = tempTotal;
for (int pageNum = 0; pageNum < tempTotal; pageNum++) {
PdfRenderer.Page tempPage = pdfRenderer.openPage(pageNum);
tempBitmap[pageNum] = Bitmap.createBitmap(WS_WIDTH, WS_HEIGHT, Bitmap.Config.ARGB_8888);
tempPage.render(tempBitmap[pageNum], null, null, PdfRenderer.Page.RENDER_MODE_FOR_PRINT);
if (tempBitmap[pageNum].getPixel(0, 0) == Color.GRAY) {
finalTotal--;
}
tempPage.close();
}
}
It works fine. At least should cause no problem if the users only attempt to print PDF files constructed with my app. :P
Please tell me if you know a better way to do this. Thanks!

Java application - swing - pop up on right click changes background colour

I am having issues with my java application and I can't find a suitable reply.
In summary a right click triggered default pop up menu changes my chart's background color behind the pop up.
You can find images below. I am happy to keep the default popup without the "buggy" behaviour or develop my own if required.
A click of a button starts a stream of data and adds a chart to a JInternalFrame component:
If I right click on the image a default pop up comes up:
If I then click away the rectangle area covered by the popup will overlay the chart like this:
TimeseriesMonitorModel model = new DefaultTweetMonitorModel();
jif.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
try {
jif.setContentPane(new TweetSeriesChartPane(model, TweetMonitor.keywords, tkc));
jif.setSize(jif.getWidth(), jif.getHeight());
} catch (InterruptedException ex) {
Logger.getLogger(TweetMonitor.class.getName()).log(Level.SEVERE, null, ex);
}
jif.setVisible(true);
where jif is the Jinternalframe and
public TweetSeriesChartPane(TimeseriesMonitorModel model, String[] seriesNames, TweetKeywordCount tkc) throws InterruptedException {
this.seriesNames = seriesNames;
this.tkc = tkc;
this.model = model;
XYChartTimeseries myRealTimeChart = new XYChartTimeseries();
chart = myRealTimeChart.getChartWithTitle();
List[] tweetData = model.getFrequencyCount(new AtomicIntegerArray(seriesNames.length)); // we are starting from 0
int i = 0;
for (String keyword : seriesNames) {
List<Integer> yData = (List<Integer>) tweetData[1].get(i);
chart.addSeries(keyword, tweetData[0], yData); // adding first value
i++;
}
setLayout(new BorderLayout());
XChartPanel<XYChart> chartPane = new XChartPanel<>(chart);
add(chartPane);
UpdateWorker worker = new UpdateWorker(this, seriesNames, this.tkc);
worker.execute();
}

I've managed to temporary solve the above.
I've checked specifically this line of code
XChartPanel<XYChart> chartPane = new XChartPanel<>(chart);
which extends Chart and Jpanel. The code is from the knowm-chart dependency https://github.com/knowm/XChart/blob/develop/xchart/src/main/java/org/knowm/xchart/XChartPanel.java)
Apparently it adds a listener and the customized PopUpMenu. After reviewing it, it looks like it didn't do any repainting when the mouse was clicked outside the PopUpMenu area.
So I created a new class and tried to customise it. However, the repaint was flickering the screen and I couldn't get it to work only in the PopUpMenu area.
I ended up disabling the .addMouseListener call so now I don't get any popUpMenu. I sad compromise, but oh well.
BTW:
Thanks to both, regardless of the last unneeded comment which didn't add any value.
I did read the link and I though I provided enough information.
In any case, posting to code helped me troubleshoot it

Making listener wait javafx

I checked some questions here but I couldn't find a proper answer. Maybe I am using wrong keywords to search. But what I found didn't help. So here is my question. I have some circles and line that are sliding in a certain way.
What I want is to update balance variable after the animations perform.
DoubleProperty balance = new SimpleDoubleProperty();
And I update the balance as follows:
if (shapeADone == false) {
intersecting = arc.centerXProperty().lessThan(boldLine.getEndX() - 13);
intersecting.addListener((obs, wasIntersecting, isNowIntersecting) -> {
System.out.println("Collision!");
animation1.stop();
animation2.stop();
animation3.stop();
});
again = true;
balance.setValue(-1);
} else {
fadeB();
balance.setValue(1);
}
But in main method I want to do something like this
level1.balance.addListener(ov -> {
System.out.println("The new value is " +
level1.balance.doubleValue());
if (level1.balance.getValue()==1) {
//delay setting scene
primaryStage.setScene(scene2);
}
});
I have some animations to perform before setting scene2 but since balance instantly updating, my animations can't be performed.
I want to know if there is a way to delay listening balance or setting scene.
I tried Thread.sleep and balance.wait but it gives runtime errors.
Edit: This question clearly shows that I was lack of knowlodge about javafx. What I want to do is simple and solution is even more simple. When animation perform to the end I update the value of balance. All I wanted was make sure that animation is showed to the end.

Here is the answer :
else{
animation3.setOnFinished(event -> balance.setValue(1));
fadeB();
}
As Sedrick's comment I change the code like this.
Adding setOnFinish to animations which need to be performed solve the problem. It's working.

How to start a number of moving Sprite objects on different time?

I created a live wallpaper service using AndEngine library. On screen there are a number of bird Sprite objects that flying repeatedly from the left to right started in random y-coordinate (I'm using LoopEntityModifier and PathModifier for this, see my previous question if you're curious). The birds shouldn't start flying in same time, but there is a gap/interval about 3 seconds before another bird showed up from left most screen.
The question is what technique that I have to use to achieve that?
I had created array of Sprites to hold the bird sprites. The code is like this...
public class MyLiveWallpaperService extends BaseLiveWallpaperService {
private BirdSprite[] birdSprites; // BirdSprite is actually an extension class from AnimatedSprite
...
#Override
public Scene onLoadScene() {
...
birdSprites= new BirdSprite[4];
for (int i=0; i<4; ++i) {
birdSprites[i] = new BirdSprite(0, 0, birdTextureRegion);
scene.getChild(LAYER_FRONT).attachChild(birdSprites[i]);
}
}
}
The above code produces four birds that show-up on left screen in same time. I tried by adding Thread.sleep(3000) before calling attachChild, but it affects whole application. The live wallpapaper application become hanged for several seconds when started.

This is the solution I found by using TimerHandler:
scene.registerUpdateHandler(new TimerHandler(3, true, new ITimerCallback() {
#Override
public void onTimePassed(TimerHandler pTimerHandler) {
// your code here will be executed every 3 seconds (see 1st argument of TimerHandler)
...
scene.getChild(LAYER_FRONT).attachChild(birdSprites[i]);
}
}));
Please let me know if you have better solution.