Develop Reference

Attaching a sprite to a Box2d body for movement

Im new on Box2d got a problem and couldnt solve it.
I want to move my player left and right when the user touch my left and right buttons.
I created a fixture I can move body and fixture but not the player sprite
How can I attach my player sprite to my body ?
and How should I control body because I cant stop it.
I want to find a proper way of controlling player in box2d. I couldnt use setLinerVelocity etc.
this is my codes
public World world;
public Body bplayer;
public Box2DDebugRenderer b2dr;
public Matrix4 cameraBox2D;
PlayScreen
buttonimage.addListener(new ClickListener() {
public boolean touchDown(InputEvent event, float x, float y, int pointer, int button)
{
bplayer.setLinearVelocity(-5*PPM , 0);
return true;
}
});
world = new World(new Vector2(player.getPosition().x , player.getPosition().y) , false);
b2dr = new Box2DDebugRenderer();
bplayer = createPlayer(player.getPosition().x , player.getPosition().y);
show method
buttonimage.setPosition(160,0);
rightbuttonimage.setPosition(320,0);
pauseimage.setPosition(220,-20);
cameraBox2D = camera.combined.cpy();
Render method
Gdx.gl.glClearColor(0, 0, 2f, 1);
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);
sb.setProjectionMatrix(camera.combined);
player.position.y += 500 * Gdx.graphics.getDeltaTime();
sb.begin();
sb.draw(bg, 0, camera.position.y - (camera.viewportHeight/2));
sb.draw(player.sprite, player.getPosition().x , player.getPosition().y);
for (Tube tube : tubes) {
sb.draw(tube.getlefttube(), tube.getposlefttube().x, tube.getposlefttube().y);
sb.draw(tube.getrighttube(), tube.getposrighttube().x, tube.getposrighttube().y);
sb.draw(tube.getLight() , tube.getPoslight().x , tube.getPoslight().y);
}
delta*=speed;
sb.end();
update(delta);
b2dr.render(world , cameraBox2D);
stage.draw();
app.batch.begin();
app.font23.draw(app.batch,"Lights collected :" + dropsGathered , 0, 720);
app.batch.end();
cameraUpdate method
Vector3 position = camera.position;
position.x = player.position.x;
position.y = player.position.y;
camera.position.set(position);
createPlayer method
Body pBody;
BodyDef def = new BodyDef();
def.type = BodyDef.BodyType.DynamicBody;
def.position.set(x * PPM, y * PPM );
def.fixedRotation = true;
pBody = world.createBody(def);
return pBody;
update method
world.step(1 / 60f , 6 , 2);
for(int i = 0; i < tubes.size; i++) {
Tube tube = tubes.get(i);
if (camera.position.y - (camera.viewportWidth/2) > tube.getposlefttube().y + tube.getlefttube().getWidth()) {
tube.reposition(tube.getposlefttube().y + ( TUBE_COUNT) );
}
if (tube.collides(player.getBounds())){
app.setScreen(new GameOver(app));
}
if (tube.gathered(player.getBounds())){
dropsGathered++;
}
if (dropsGathered >= 50){
//app.setScreen(new Stage2(app));
}
}
camera.update();
handleInput();
camera.position.y = player.getPosition().y + 300;
player.update(delta);
camera.update();
cameraUpdate(delta);
stage.act(delta);

Do not use the Sprite class. Use the TextureRegion class instead. Sprite is confusingly subclassed from TextureRegion, so when you call batch.draw(sprite, ...) its position and rotation parameters are ignored because it is being treated as a TextureRegion.
You could use a Sprite by calling sprite.draw(batch) but a Sprite is redundant because your Body already has position and rotation parameters.
Use a TextureRegion directly with the SpriteBatch. You can orient it with rotation parameters passed into the draw method.

How to avoid ghost drawing after clearing SurfaceView canvas

Hi I am working on plotting a real time graph of incoming signals using SurfaceView.
The sampling rate is 128Hz and the target graph refresh rate is 50Zh.
Things run pretty smoothly, the points are drawn real-time properly.
I plot the data in segments of a few points using Path()
for each segment I call path.computeBounds() to get a rect that I will use to call holder.lockCanvas(rect) and draw the path. Using a rect prevents flickering and reduces cpu usage
when the graph reaches the end I lock the entire canvas and clear the background, draw the graph frame and then continue on plotting.
the problem is that at the beginning of each new "page" I get a ghost image from the last page:
I believe this is caused by double buffering / use of a dirty area when plotting.
I have looked for solutions to this problem but none seem adequate for this type of application. Any help is most welcome.
Thanks
Jean-Pierre
Code follows:
private void draw() {
Point point = null;
Canvas canvas = null;
Path path = new Path();
ArrayList<Point> pointArray;
float oldX = -1;
boolean setToClear = false;
boolean isNewSegment = false;
if (samplesInQueue == 0) {
return;
}
pointArray = new ArrayList<Point>((int) samplesInQueue);
for (int i = 0; i < samplesInQueue; i++) {
// take a peek at the point without retrieving it from the point
// queue
point = Points.peek();
// check if first point of segment is the start of a page
if (i == 0) {
if (lastSegmentEndPoint != null) {
if (point.x < lastSegmentEndPoint.x) {
// yes then we will need to clear the screen now
isNewSegment = true;
}
} else {
// yes then we will need to clear the screen now
isNewSegment = true;
}
}
if (point != null) {
if (point.x > oldX) {
// put consecutive points in the path point array
point = Points.poll();
samplesInQueue--;
pointArray.add(point);
oldX = point.x;
} else {
// we have a wrap around, stop and indicate we need to clear
// the screen on the next pass
if (!isNewSegment) {
setToClear = true;
}
break;
}
}
}
// no points, return
if (pointArray.size() == 0) {
return;
}
// fill the path
for (int i = 0; i < pointArray.size(); i++) {
Point p = pointArray.get(i);
if (i == 0) {
if (lastSegmentEndPoint != null) {
if (p.x >= lastSegmentEndPoint.x) {
// if we have the end of the last segment, move to it
// and line to the new point
path.moveTo(lastSegmentEndPoint.x, lastSegmentEndPoint.y);
path.lineTo(p.x, p.y);
} else {
// otherwise just line to the new point
path.moveTo(p.x, p.y);
}
} else {
path.moveTo(p.x, p.y);
}
} else {
path.lineTo(p.x, p.y);
}
}
if (clear || isNewSegment) {
if (clear) {
clear = false;
}
// we need to clear, lock the whole canvas
canvas = holder.lockCanvas();
// draw the graph frame / scales
drawGraphFrame = true;
drawGraphFrame(canvas);
} else {
// just draw the path
RectF bounds = new RectF();
Rect dirty = new Rect();
// calculate path bounds
path.computeBounds(bounds, true);
int extra = 0;
dirty.left = (int) java.lang.Math.floor(bounds.left - extra);
dirty.top = (int) java.lang.Math.floor(bounds.top - extra);
dirty.right = (int) java.lang.Math.round(bounds.right + 0.5);
dirty.bottom = (int) java.lang.Math.round(bounds.bottom + 0.5);
// just lock what is needed to plot the path
canvas = holder.lockCanvas(dirty);
}
// draw the path
canvas.drawPath(path, linePaint);
// unlock the canvas
holder.unlockCanvasAndPost(canvas);
// remember last segment end point
lastSegmentEndPoint = pointArray.get(pointArray.size() - 1);
// set clear flag for next pass
if (setToClear) {
clear = true;
}
}
Draw frame / clear graph code
private void drawGraphFrame(Canvas canvas) {
if (!drawGraphFrame) {
return;
}
if (canvas == null) {
Log.e(TAG, "trying to draw on a null canvas");
return;
}
drawGraphFrame = false;
// clear the graph
canvas.drawColor(Color.BLACK, Mode.CLEAR);
// draw the graph frame
canvas.drawLine(leftMargin, topMargin, leftMargin, mCanvasHeight - bottomMargin, framePaint);
canvas.drawLine(leftMargin, mCanvasHeight - bottomMargin, mCanvasWidth - rightMargin, mCanvasHeight
- bottomMargin, framePaint);
// more drawing
}

Your problem is quite straight forward.. your only locking the new portion of the canvas that the new path covers. So the best thing to do is to make your path and dirty rect's private members of your class. Then at the start of your draw method get the path's current bounds (the old bounds) in your dirty rect. Now call path.rewind(); and start modifying your path. After do a union on the dirty rect with the new bounds. Now your dirty rect covers the old and new rect's. So your clear will remove the old path. This also reduces overhead because you don't want to be allocating 100+ objects per second for rect's and path's. Now since your drawing an oscilloscope then you probably want to adjust the old bounds to only be a portion of the width of the view. The same amount your new portion covers.
Hope that's cleared things up.

My simple answer is just using this function clear_holder() wherever you want to clear the canvas. I copy and paste 3 line for 3 times because it need 3 times clear to leave holder blank.
After clearing holder, you should draw any new thing you want!
This link give me this source code!
private void clear_holder(SurfaceHolder holder){
Canvas c = holder.lockCanvas();
c.drawColor( 0, PorterDuff.Mode.CLEAR );
holder.unlockCanvasAndPost(c);
c = holder.lockCanvas();
c.drawColor( 0, PorterDuff.Mode.CLEAR );
holder.unlockCanvasAndPost(c);
c = holder.lockCanvas();
c.drawColor( 0, PorterDuff.Mode.CLEAR );
holder.unlockCanvasAndPost(c);
}

It looks like you are clearing the canvas so, it's not double buffering problem. I think it's related to your path been reused.
Try adding adding the next line when starting new page.
path.reset();

Collision ImageViews not working

I'm trying to generate random ImageViews on a Layout without the ImageViews intersecting each other. I'm generating a random point within the screen dimensions like this:
private Point generateRandomLocation(Point dimensions) {
Random random = new Random();
// generate random x
int x = random.nextInt((dimensions.x - 0) + 1);
// generate random y
int y = random.nextInt((dimensions.y - 0) + 1);
Point location = new Point(x, y);
if(!collision(location)) {
return new Point(x, y);
} else {
return generateRandomLocation(dimensions);
}
}
The collision method contains the following method to determine wether the ImageViews collide or not. BubbleImage is a simple extension of ImageView.
private boolean collision(Point location) {
// takes 100 as inital width & height
int x_1 = location.x;
int y_1 = location.y;
int x_2;
int y_2;
boolean collided = false;
// get all bubbleimages
for (int i = 0; i < mainLayout.getChildCount(); i++) {
View childView = mainLayout.getChildAt(i);
if (childView instanceof BubbleImage) {
x_2 = (int) childView.getX();
y_2 = (int) childView.getY();
// create rectangles
Rect rect1 = new Rect(x_1, y_1, x_1 + 100, y_1 - 100);
Rect rect2 = new Rect(x_2, y_2, x_2 + 100, y_2 - 100);
collided = Rect.intersects(rect1, rect2);
}
}
return collided;
}
Anyone spotting the faulty logic here?
Edit: Rect.intersects() seems to be returning false, even when the imageviews are intersecting.

When creating new Rects rect1 & rect2, the constructor is Rect(left, top, right, bottom). E.g. Rect(10, 10, 20, 20), because android screen origin is in the top left corner.
You have created the Rects in a wrong way, as Rect(left, bottom, right, top). Try switching the 2nd and 4th parameters in the constructor calls, or increase the 4th parameter to be bigger than 2nd.
Like this:
Rect rect1 = new Rect(x_1, y_1, x_1 + 100, y_1 + 100);

LibGDX PhysicsBox2D, if i set linear velocity, physics does not work correctly

my world is world = new World(new Vector2(0, 0), true); //there is no gravity
and i have walls in the left, right, top bottom of the screen, so elements do not fly off the display.
I have the following code in my render class:
Gdx.gl.glClearColor(0, 0, 0.2f, 1);
Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT);
camera.update();
Box2DDebugRenderer debugRenderer = new Box2DDebugRenderer();
batch.setProjectionMatrix(camera.combined);
batch.begin();
batch.draw(texture, 0, 0);
for (Element element : elements) {
element.body.setUserData(element);
element.rect.x = element.body.getPosition().x-16;//16 = half the width of element
element.rect.y = element.body.getPosition().y-16;
if (element.goodOrEvil == 0) {
batch.draw(happyImage, element.rect.x, element.rect.y);
} else if (element.goodOrEvil == 1) {
batch.draw(sadImage, element.rect.x, element.rect.y);
}
} //i draw the elements that i have to fix the bodies to
batch.end();
debugRenderer.render(world, camera.combined);
Iterator<Element> iter = elements.iterator();
//next i set the accelerometer to move the elements, so that i could control them, i need to move all the elements in the same direction, in the same time
while (iter.hasNext()) {
Element element = iter.next();
element.body.setLinearVelocity(Gdx.input.getAccelerometerY() * 50, -Gdx.input.getAccelerometerX() * 50);
}
if (TimeUtils.nanoTime() - lastDropTime > 1000000000)
spawnElement(); // this creates a new element
world.step(1 / 45f, 6, 2);
Here is my spawnElement() class:
private void spawnElement() {
Rectangle elementRect = new Rectangle();
elementRect.x = MathUtils.random(0, 800 - 32);
elementRect.y = 400;
elementRect.width = 32;
elementRect.height = 32;
Element element = new Element(elementRect, (int) elementRect.x % 2);
elements.add(element);
// First we create a body definition
BodyDef bodyDef = new BodyDef();
// We set our body to dynamic, for something like ground which doesnt
// move we would set it to StaticBody
bodyDef.type = BodyType.DynamicBody;
// Set our body's starting position in the world
bodyDef.position.set(elementRect.x, elementRect.y);
// Create our body in the world using our body definition
body = world.createBody(bodyDef);
// Create a circle shape and set its radius to 6
CircleShape circle = new CircleShape();
circle.setRadius(6f);
// Create a fixture definition to apply our shape to
FixtureDef fixtureDef = new FixtureDef();
fixtureDef.shape = circle;
fixtureDef.density = 0.5f;
fixtureDef.friction = 0.4f;
fixtureDef.restitution = 0.6f; // Make it bounce a little bit
// Create our fixture and attach it to the body
Fixture fixture = body.createFixture(fixtureDef);
element.body = body;
lastDropTime = TimeUtils.nanoTime();
}
Now if i set gravity to exist world = new World(new Vector2(-2, -20), true); and comment out this line: element.body.setLinearVelocity(Gdx.input.getAccelerometerY() * 50, -Gdx.input.getAccelerometerX() * 50); the physics works great, but i cannot control my objects. If i leave the code as it is (no gravity and that line in), i can control my objects, but when an element hits the wall, and another element comes, they overlap, and only then start to divide. I need them to hit one another, and remain close, but not overlap at all. Any ideea on how this could be made?

instead of using element.body.setLinearVelocity(Gdx.input.getAccelerometerY() * 50, -Gdx.input.getAccelerometerX() * 50);
i have used this:
Vector2 gravity = new Vector2(Gdx.input.getAccelerometerY() * 50, -Gdx.input.getAccelerometerX() * 50);
world.setGravity(gravity);
And then it answers just like when i set a static gravity, but i change the gravity at every render, with values from my accelerometer

Adding Endless parallax background in cocos2d android

I am working on CoCos2d with android.I want to add an endless scrolling background to my Screen by using CCParallaxNode.
I am able to add background and move it but after the completion of that move action the screen goes black.
Can someone help me out?
My code is
CCParallaxNode parallaxNode;
CCSprite spacedust1;
CCSprite spacedust2;
CCSprite planetsunrise;
CCSprite galaxy;
CCSprite spacialanomaly;
CCSprite spacialanomaly2;
parallaxNode = CCParallaxNode.node();
spacedust1 = CCSprite.sprite("bg_front_spacedust.png");
spacedust2 = CCSprite.sprite("bg_front_spacedust.png");
planetsunrise = CCSprite.sprite("bg_planetsunrise.png");
galaxy = CCSprite.sprite("bg_galaxy.png");
spacialanomaly = CCSprite.sprite("bg_spacialanomaly.png");
spacialanomaly2 = CCSprite.sprite("bg_spacialanomaly2.png");
// 3) Determine relative movement speeds for space dust and background
// CGPoint cgPoint = CGPoint.ccp(0.1, 0.1);
CGPoint dustSpeed = CGPoint.ccp(10, 10);
CGPoint bgSpeed = CGPoint.ccp(5, 5);
// CGPoint bgSpeed = ccp(0.05, 0.05);
parallaxNode.addChild(spacedust1, 0, dustSpeed.x, dustSpeed.y, 0,
winSize.height / 2);
parallaxNode.addChild(spacedust2, 0, dustSpeed.x, dustSpeed.y,
spacedust1.getContentSize().width, winSize.height / 2);
parallaxNode.addChild(galaxy, -1, bgSpeed.x, bgSpeed.y, 0, 10);
parallaxNode.addChild(planetsunrise, -1, bgSpeed.x, bgSpeed.y, 600, 5);
parallaxNode
.addChild(spacialanomaly, -1, bgSpeed.x, bgSpeed.y, 900, 20);
parallaxNode.addChild(spacialanomaly2, -1, bgSpeed.x, bgSpeed.y, 1500,
30);
CCIntervalAction go = CCMoveBy.action(4, CGPoint.ccp(winSize.width, 0));
CCIntervalAction goBack = go.reverse();
CCIntervalAction seq = CCSequence.actions(go, goBack);
CCRepeatForever action = CCRepeatForever.action(goBack);
parallaxNode.runAction(action);

I see that since not a single answer worked for you. I will provide a simple code which will help you for your parralax scrolling background.
Add this code in your game layers constructor
background1 = CCSprite.sprite("bg2.png");
background2 = CCSprite.sprite("bg2.png");
background1.setPosition(CGPoint.ccp(winSize.width*0.5f,winSize.height*0.5f));
addChild(background1);
background2.setPosition(CGPoint.ccp(winSize.width+winSize.width*0.5f,winSize.height*0.5f));
addChild(background2);
and a scroll method which is scheduled every millisecond.
add this in constructor
this.schedule("scroll");
and now the scroll method.
public void scroll(float dt) {
CGPoint pos1 = background1.getPosition();
CGPoint pos2 = background2.getPosition();
pos1.x -= 5.0f;
pos2.x -= 5.0f;
if(pos1.x <=-(winSize.width*0.5f) )
{
pos1.x = pos2.x + winSize.width;
}
if(pos2.x <=-(winSize.width*0.5f) )
{
pos2.x = pos1.x + winSize.width;
}
background1.setPosition(pos1);
background2.setPosition(pos2);
}
mark my answer if it worked.

Call this method from the class Constructor. I found this trick from Example : "shotingblock-master" available on github...
private void endlessBackground() {
// Create the two background sprites which will alternate
_oddBackground = CCSprite.sprite("blue_background.png");
_evenBackground = CCSprite.sprite("blue_background.png");
// One starts dead centre and one starts exactly one screen height above
oddBackground.setPosition(_winSize.width / 2, _winSize.height / 2);
evenBackground.setPosition(_winSize.width / 2, _winSize.height
+ (_winSize.height / 2));
// Schedule the scrolling action
schedule("scroll");
// Add sprites to the layer
addChild(_oddBackground).addChild(_evenBackground);
}
public void scroll(float dt) {
// move them 100*dt pixels down
_oddBackground.setPosition(_oddBackground.getPosition().x,
_oddBackground.getPosition().y - 150 * dt);
_evenBackground.setPosition(_evenBackground.getPosition().x,
_evenBackground.getPosition().y - 150 * dt);
// reset position when they are off from view.
if (_oddBackground.getPosition().y < -_winSize.height / 2) {
_oddBackground.setPosition(_winSize.width / 2, _winSize.height / 2);
_evenBackground.setPosition(_winSize.width / 2, _winSize.height
+ (_winSize.height / 2));
}
}
}
IT works excellent in my case. May be it'll help full for you.

try using this:
CCTexture2D *texture = CCTextureCache::sharedTextureCache()->addImage("pic.png");
ccTexParams params = {GL_LINEAR, GL_LINEAR, GL_REPEAT, GL_REPEAT};
texture->setTexParameters(&params);
CCSprite *sprite = CCSprite::spriteWithTexture(texture, CCRectMake(0, 0, 90, 90));
and make sure that The image's height and width must be power of 2.

It looks like the CCRepeatForever action is only running it goBack, which means that it's not reversing. Try the following:
CCIntervalAction go = CCMoveBy.action(4, CGPoint.ccp(winSize.width, 0));
CCIntervalAction goBack = go.reverse();
CCIntervalAction seq = CCSequence.actions(go, goBack);
CCRepeatForever action = CCRepeatForever.action(seq); // change to seq instead of goBack
parallaxNode.runAction(action);

This is trick for make it happen. You can Use the large png and working on it or check the sample test code which is available in coocs2d-android library
CCSprite background = CCSprite.sprite("background.png");
// create a void node, a parent node
CCParallaxNode voidNode = CCParallaxNode.node();
// background image is moved at a ratio of 0.4x, 0.5y
voidNode.addChild(background, -1, 0.4f, 0.5f, 0, 0);
// write your own code for the parallax node
CCIntervalAction goUp = CCMoveBy.action(4, CGPoint.make(0,-200));
CCIntervalAction goDown = goUp.reverse();
CCIntervalAction go = CCMoveBy.action(8, CGPoint.make(-1000, 0));
CCIntervalAction goBack = go.reverse();
CCIntervalAction seq = CCSequence.actions(goUp, go, goDown, goBack);
voidNode.runAction(CCRepeatForever.action(seq));
addChild(voidNode);

Please check out below link for Parallax vertical endless background:
http://kalpeshsantoki.blogspot.in/2014/07/create-vertical-endless-parallax.html
CGSize winSize = CCDirector.sharedDirector().displaySize();
//I made graphics for screen 720*1200....so I made this dynamic scale to support multiple screens
float sX = winSize.width / 720.0f;
float sY = winSize.height / 1200.0f;
background = CCVerticalParallaxNode.node(sX, sY, true);
background.addEntity(1f, "background.png", 0);
background.addEntity(3, "road_simple.png", winSize.width / 2);
background.addEntity(1.7f, "road_side.png", 0);
addChild(background);