Develop Reference

Box2d creates specific body and fixture seemingly at random

I have created an android application similar to Not Tetris 2 using Libgdx with Box2d.
It can successfully remove a slice from the world, which obviously involves duplicating several bodies and destroying/creating fixtures. However, seemingly at random, a body with a 2x2 fixture will appear. The body and fixture are displayed using information related to the objects around it when it is created, so I narrowed its creation down to the following function:
Body duplicateBody(Body original){
BodyDef d = new BodyDef();
d.position.set(original.getPosition());
d.angle = original.getAngle();
d.linearVelocity.set(original.getLinearVelocity());
d.angularVelocity = original.getAngularVelocity();
Body dup = world.createBody(d);
dup.setType(BodyDef.BodyType.DynamicBody);
return dup;
}
I use this function in 2 different contexts:
Making a copy of the body if a "slice" cuts one in two -- I then transfer the fixtures which are below to it.
When a fixture is below the line then it is added to a body created for ones below
Making a copy of the body when groups of fixtures are separated
I commented out the code responsible for the third instance and still had the 2x2 boxes spawning, so here are the functions relevant to the others:
...
if (below && !above) {
//copy fixture, add copy to lower body and remove original
Body top = fixture.getBody();
FixtureDef n = new FixtureDef();
PolygonShape s = new PolygonShape();
s.set(getLocalVerticesOfFixture(fixture));
n.shape = s;
n.density = fixture.getDensity();
//create lower body if a lower one doesn't already exist
if (!topBottomPairs.containsKey(top)) {
Body dup = duplicateBody(top);
topBottomPairs.put(top, dup);
}
//delete fixture
remove.add(fixture);
Fixture f = topBottomPairs.get(top).createFixture(n);
s.dispose();
}
...
if (below && above) {
//copy fixture, add copy to lower body, but keep original on upper as it needs to split
FixtureDef n = new FixtureDef();
PolygonShape s = new PolygonShape();
s.set(getLocalVerticesOfFixture(fixture));
n.shape = s;
n.density = fixture.getDensity();
Body top = fixture.getBody();
//create lower body if a lower one doesn't already exist
if (!topBottomPairs.containsKey(top)) {
Body dup = duplicateBody(top);
topBottomPairs.put(top, dup);
}
Fixture second = topBottomPairs.get(top).createFixture(n);
s.dispose();
}
....
private Vector2[] getLocalVerticesOfFixture(Fixture fixture) {
PolygonShape shape = ((PolygonShape) fixture.getShape());
Vector2[] localVertices = new Vector2[shape.getVertexCount()];
for (int i = 0; i < shape.getVertexCount(); i++) {
localVertices[i] = new Vector2();
shape.getVertex(i, localVertices[i]);
}
return localVertices;
}
I also have this remove fixture function which runs on all fixtures I want to remove:
private void smartDeleteFixture(Fixture f){
f.getBody().destroyFixture(f);
if(f.getBody().getFixtureList().size == 0){
world.destroyBody(f.getBody());
}
}
Nowhere do I create vertices, let alone a fixture of a 2x2 shape. I was wondering if this duplication function has any flaws, or if I stumbled upon some "default shape" that box2d uses.
Edit: I have removed anything not related to the manipulation of box2d bodies. Hope that helps

Deleted this question as I decided to perform a major recode and hoped that would fix my problem. It did not, but I figured out the cause.
I looked through box2d and found a couple instances of code similar to this in the polygon shape class:
if (n < 3)
{
// Polygon is degenerate.
b2Assert(false);
SetAsBox(1.0f, 1.0f);
return;
}
These instances check the number of vertices after various operations and turn the shape into a 2x2 box if there are fewer than 3. One of these operations makes the shape convex. Another checks if vertices are close together (closer than 0.0025f), deleting one if so.
In my case, the problem was simple. Some of my vertices were less than 0.0025f from each other, resulting in them being deleted, the vert count dropping below 3, an assertion being ignored, and then my shape being turned into a 2x2 box. I hope this helps someone out.

MPAndroidChart Linechart unconnected data points

I am investigating MPAndroidChart for usage in my company's Android and iOS application and I have found a problem that I need a solution to in order to be able to use this framework.
The application will mostly use the Line Chart functionality and the supplied data can contain NULL entries. I have seen other posts that discusses this matter and apparently there is no solution to showing NULL values yet. MPAndroidChart with null values
The author suggests simply not adding the data point to the set, but in my case it's very important that there is a "hole" in the graph were there is more than two consecutive NULL values (or however to represent it) i.e that the graph is not continous between two points with NULL values in between. Is there any way I can accomplish this with this framework?
I have been looking into the possibility of separating the data points into different data sets, but it seems like kind of a hack.
Thank you!
Dataset example:
[1 2 10 NULL NULL NULL 20 25 30]
The Line must NOT connect the numbers 10 and 20.

This is what I ended up coming up with to solve this - for anyone in the future. It iterates through and creates new entries in a data set until it hits a null value, and then it creates data sets with "fake" entries that use a boolean in the entry constructor. Boolean can be found from
"entry.getData()"
and you can then you can use this to set that Dataset to not be visible
"mLineDataSet.setVisible(false);"
Note: Do not try to set Dataset Color to transparent - the library has a bug where if certain entries are null the graph doesn't even appear.
private void createDataSets() {
for (int index = 0; index < mGraph.getGraphDataSets().size(); index++) {
lastIndexCreated = 0;
final GraphDataSet mDataSet = mGraph.getGraphDataSets().get(index);
final ArrayList<Entry> mEntries = getEntries(mDataSet.getYValues(), lastIndexCreated);
final LineDataSet mLineDataSet = getDataSet(mEntries, mDataSet, color);
mGraphLineData.addDataSet(mLineDataSet);
lastIndexCreated = mEntries.size() - 1;
while (lastIndexCreated < mDataSet.getYValues().size() - 1) {
final LineDataSet set = getDataSet(mEntriesSet, mDataSet, colorSecondary);
if (mEntriesSet.size() != 0)
mGraphLineData.addDataSet(set);
lastIndexCreated = (int) mEntriesSet.get(mEntriesSet.size() - 1).getX();
}
}
}
private ArrayList<Entry> getEntries(final List<Float> yValues, final int firstValueIndex) {
final ArrayList<Entry> mEntries = new ArrayList<>();
for (int i = firstValueIndex; i < yValues.size(); i++) {
if (yValues.get(i) != null)
//boolean here is false means that dataset is not fake and should be shown
mEntries.add(new Entry(i, yValues.get(i), false));
else if (firstValueIndex == i) {
//add a "Fake" data entry, and use mEntry.getData to set line to not be visible.
mEntries.add(new Entry(i, 0, true));
break;
} else {
break;
}
}
return mEntries;
}

Starling Feathers - Available features 101

New to Starling-Feathers, before I start to develop my mobile app, I would like to know what are the best practice to develop the following features using Feathers:
Partial view slide - A part of the next view is shown and the user can drag to see it all. Could this be done with Feathers ScreenNavigator?
Sliding menu from the top
Dragging text elements with title pushing the last items
Since it is hard to describe I've added an animated gif to describe my goals. Thanks for all your advices
I would like to maximize the use of Feathers built in widgets and will appreciate code examples :)

I think these are not that much hard to do in core flash or you can also do it in Starling feathers too. YOu can use list item to do the third point (Dragging text elements with title pushing the last items) .
First and second you can use it with tweening effect i think.
For the third one using feathers list.
(re formated post)
private function addFeatherList():void{
Flist = new List();
Flist.width = 250;
Flist.height = 300;
Flist.x = GAME_W/2 - Flist.width/2;
Flist.y = sampText.height + 5;
this.addChild( Flist );
fontArr = Font.enumerateFonts(true);
for (var i:int=0; i<fontArr.length; i++){
ListArr[i] = { text:Font(fontArr[i]).fontName }
}
var groceryList:ListCollection = new ListCollection( ListArr );
Flist.dataProvider = groceryList;
Flist.itemRendererProperties.labelField = "text";
FeathersControl.defaultTextRendererFactory=function():ITextRenderer{
var render:TextFieldTextRenderer=new TextFieldTextRenderer();
render.textFormat = new TextFormat("Verdana",8,0xFFFFFF,false);
return render;
}
Flist.itemRendererFactory = function():IListItemRenderer //list.itemRendererProperties.accessorySourceField list.itemRendererFactory
{
var renderer:DefaultListItemRenderer = new DefaultListItemRenderer();
renderer.addEventListener(Event.TRIGGERED, onListTriggered);
return renderer;
}
}

Distance Travelled

I am creating a Phonegap App (using jQuery and Google Maps API V3) related to travelling and would like to show the user the distance he/she has travelled since starting the app.
Is there any Google function for this? Or can anyone recommend what I can do to get the total distance travelled?

It can be done easily. You have to understand, by using a Google Maps API for jQuery you have all needed tools to do it by yourself.
First, you need to define a time period (lets say 1 minute). We will need it to create a reference point of our movements. Next step is to use phonegap/cordova geolocation API to calculate our position (latitude and longitude):
http://docs.phonegap.com/en/1.0.0/phonegap_geolocation_geolocation.md.html
At this point choose do you want to:
Store a position (latitude and longitude) every 1 minute in some js array
Or do the same thing like in point 1 and also show it on the map with gmap addMarker ability.
At the end you need to calculate a distance. Loop through the position array and use latitude and longitude to calculate a distance between every available point. Here you will find function used for a such calculation (with a js example):
http://www.movable-type.co.uk/scripts/latlong.html
Or you can use Google Maps APi function:
google.maps.geometry.spherical.computeDistanceBetween (latLngA, latLngB);
EDIT:
Here's a working example for you: http://jsfiddle.net/Gajotres/6YpAG/
Code:
$(document).ready(function(){
// Chicago
var coordinateObject= new Object();
coordinateObject.lat = '41.83682786072714';
coordinateObject.lng = '-87.626953125';
geoLocationHandler.addLocation(coordinateObject);
// New York
var coordinateObject= new Object();
coordinateObject.lat = '40.58058466412761';
coordinateObject.lng = '-74.00390625';
geoLocationHandler.addLocation(coordinateObject);
// Toronto
var coordinateObject= new Object();
coordinateObject.lat = '43.70759350405294';
coordinateObject.lng = '-79.365234375';
geoLocationHandler.addLocation(coordinateObject);
var len = geoLocationHandler.arrLocations.length;
for (var i = 0; i < len; i++) {
if(i == 1){
geoLocationHandler.distance += geoLocationHandler.calcDistance(geoLocationHandler.arrLocations[i-1].lat,geoLocationHandler.arrLocations[i-1].lng,geoLocationHandler.arrLocations[i].lat,geoLocationHandler.arrLocations[i].lng);
}
}
alert(geoLocationHandler.distance);
});
var geoLocationHandler = {
arrLocations : [],
distance : 0,
addLocation:function(obj){
geoLocationHandler.arrLocations.push(obj);
},
calcDistance:function(fromLat, fromLng, toLat, toLng) {
return google.maps.geometry.spherical.computeDistanceBetween(new google.maps.LatLng(fromLat, fromLng), new google.maps.LatLng(toLat, toLng));
}
};
Final result is a distance expressed in meters.
Every time you have a new coordination use this to create a new object and add it to the array:
var coordinateObject= new Object();
coordinateObject.lat = '41.83682786072714'; // Change with your latitude
coordinateObject.lng = '-87.626953125'; // Change with your longitude
geoLocationHandler.addLocation(coordinateObject);

Plot graph using multiple database values in Android app

I am currently using afreechart to plot a graph in my Android app. I am using the TimeSeries graph, that they've exemplified in their sample app. For me, data to be extracted from two databases.Two questions :
1. How to plot this TimeSeries graph using values from my two databases?
2. The whole graph is not as smooth as one would want to. Especially when scrolling or flicking. And hence, it's inconsistent with the app design. Any way I could make it smoother?
If the questions above seems unnecessary or in some way wrong, please point me to a way where I can plot a graph using multiple database values, even if it's not using afreechart. Thanks.
I tried using simple 'for' loops in createDataset(), like :
private static XYDataset createDataset() {
mfirstDbHelper.open();
msecondDbHelper.open();
int firstdb_count = (int) DatabaseUtils.queryNumEntries(mfirstDbHelper.mDb,firstDbAdapter.DATABASE_TABLE);
int seconddb_count = (int) DatabaseUtils.queryNumEntries(msecondDbHelper.mDb,secondDbAdapter.DATABASE_TABLE);
TimeSeriesCollection dataset = new TimeSeriesCollection();
for(int i=1;i<=seconddb_count;i++){
Cursor seconddb = msecondDbHelper.fetchItem(i);
TimeSeries s1 = new TimeSeries(seconddb.getString(
seconddb.getColumnIndexOrThrow(secondDbAdapter.KEY_ITEMNAME)));
for(int j=1;j<=firstdb_count;j++){
Cursor firstdb = mfirstDbHelper.fetchItem(j);
int first_sp_id = Integer.parseInt(firstdb.getString(
firstdb.getColumnIndexOrThrow(firstDbAdapter.KEY_ID)));
if(first_sp_id == i){
int value = Integer.parseInt(firstdb.getString(
firstdb.getColumnIndexOrThrow(firstDbAdapter.KEY_VALUE)));
String date = firstdb.getString(
firstdb.getColumnIndexOrThrow(firstDbAdapter.KEY_DATE));
String dateParts[] = date.split("-");
String day = dateParts[0];
String month = dateParts[1];
String year = dateParts[2];
int d = Integer.parseInt(day);
int m = Integer.parseInt(month);
int y = Integer.parseInt(year);
s1.add(new Day(d,m,y), value);
dataset.addSeries(s1);
}
firstdb.close();
}
seconddb.close();
}
mfirstDbHelper.close();
msecondDbHelper.close();
return dataset;
}
}
I have changed the Month() in sample to Day(), and have made sure there's no error in that area.
Am getting the error:
ERROR/AndroidRuntime(706): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.kev/com.kev.MyProject}: java.lang.NullPointerException
Also, obviously, this code redraws the graph "s1" over and over again. I do not know how to overcome this problem, and the error. Am still fairly new to programming, especially Android app development, so any blunders above, feel free to smack me in the head and correct my code.
Oh, one more thing, I can't use startManagingCursor() since it's a DemoView and not Activity. So, don't know if its causing any problems either.
Afreechart TimeSeries sample:
http://code.google.com/p/afreechart/source/browse/#svn%2Ftrunk%2Fafreechart_sample%2Fsrc%2Forg%2Fafree%2Fchart%2Fdemo
Afreechart TimeSeries sample - View:
http://code.google.com/p/afreechart/source/browse/trunk/afreechart_sample/src/org/afree/chart/demo/view/TimeSeriesChartDemo01View.java
Thanks again, for your time. :)