Develop Reference

Xamarin ARcore change position of 3D object

I am trying to implement ARcore with Xamarin and want to set a 3D object in a specific geolocation (like in pokemongo). I tried to go through this sample that I found in this forum: https://blog.xamarin.com/augmented-reality-xamarin-android-arcore/ but it seems that I can't change the position of the 3d object and it is set according to the tap gesture only on a plane.
Is there a way to place an object and track it? I did manage to do that with ARkit, but until now no success for the ARcore Android.
Any ideas would be helpful.

It looks like the Xamarin wrapper for ARCore simply wraps OpenGL. As a result, drawing the object requires setting multiple matrices (Model, View and Projection) matrices:
objectRenderer.UpdateModelMatrix(anchorMatrix, scaleFactor);
objectRenderer.Draw(viewMatrix, projectionMatrix, lightIntensity);
If you simply remove this from within the foreach (var planeAttachment in planeAttachments) {
loop, then you can set the anchorMatrix (a.k.a. the modelMatrix) to a fixed/hardcoded translation then it'll fix itself relative to the camera.
Here's a decent article on View matrices: https://www.3dgep.com/understanding-the-view-matrix/#The_View_Matrix
-- Begin Shameless Plug --
However, if you are open to trying new platforms, my team has built a cross-platform React-Native library for AR/VR development (Viro React): https://viromedia.com/viroreact/
If you're more familiar with SceneKit on iOS, we have built an analogous solution on Android w/ AR/VR support (ViroCore): https://viromedia.com/virocore/
Either solution would allow you to skip over the intricacies of OpenGL and simply position your objects/models with relative ease.
ie.
Placing your model 1 meter in front of you would be as simple as (in Viro React):
<Viro3dObject source={require("./res/model.obj")} position={[0,0,-1]} type="OBJ" />

Unity 2D Android ball jumping script AddForce

I am new to Unity and I am trying to learn the basics, I learn physics at school(ten grade).
What I have done so far - added a ball to my project and used gravity on it with RigidBody.
I want to make the ball jump suddenly on air when there is some touch input, for example - flappy bird.
My script is basic:
void Update()
{
if (Input.touchCount == 1)
{
GetComponent<Rigidbody>().AddForce(new Vector2(0, 10), ForceMode.Impulse);
}
}
With this script, the ball is falling(gravity) and when I touch the script, is Y coordinate changes but it happens by sudden (no animation) and it changes by like ~1 and continue falling(I can't keep the ball on screen) , also I can make it jump only once, if I press multiple times it will jump only once, as you can see here:
https://vid.me/aRfk
Thank you for helping.

I have created same scene in Unity3D Editor and played a little with same setup you have. And yes I had similar problems adding force on Update and also (but less) on FixedUpdate. But adding force on LateUpdate seems to work okay.
Here is my code:
public Rigidbody2D rb2dBall;
void LateUpdate()
{
if(Input.GetKeyUp(KeyCode.Space))
{
rb2dBall.AddForce (Vector2.up * 10f, ForceMode2D.Impulse);
}
}
And also I turned on interpolation:
I cant say why the physics bahaves like this, could be some bug in Unity3D 5.X since on FixedUpdate it should work fine.

Firstly, when working with physics in Unity, it's highly recomended to use the FixedUpdate method, instead of the Update. You can check in this link http://docs.unity3d.com/ScriptReference/MonoBehaviour.FixedUpdate.html
The second thing is that maybe you are not applying so much force at the ball, the force needed to give a quite impulse will depends of the mass of your ball's rigidbody. So try to do something like that:
GetComponent<Rigidbody>().AddForce(Vector2.up * 100, ForceMode.Impulse);
Change the fixed value 100 to adjust your needs.

Drawing smoother pixel trails with as3

I am trying to make a slice effect when user moves his fingers on the screen on Android Device like in Fruit Ninja
I have a movieClip named Particle which has a circle
I tried following
stage.addEventListener(MouseEvent.MOUSE_DOWN , stratSlice);
stage.addEventListener(MouseEvent.MOUSE_UP , endSlice);
function startSlice(e:MouseEvent):void
{
stage.addEventListener(MouseEvent.MOUSE_MOVE , drawSlice);
}
function endSlice(e:MouseEvent):void
{
stage.addEventListener(MouseEvent.MOUSE_MOVE , drawSlice);
}
function drawSlice(e:MouseEvent):void
{
var p:Particle = new Particle();
addChild(p);
p.x = mouseX;
p.y = mouseY;
}
but when I run it The slice is broken I want it to be seamless.

Adding e.updateafterevent() in the mouse move handler might improve performance a bit.
In general your code will probably not work as well as other particle effects you see in games such as fruits ninja. For good results you will need to use a particle engine such as
StarDust: https://code.google.com/p/stardust-particle-engine/
Flint: http://flintparticles.org/
Partigen: http://www.desuade.com/partigen/engine
Starling Particle: https://github.com/PrimaryFeather/Starling-Extension-Particle-System
I know starling works great on android, not sure about the others

How to collide objects with high speed in Unity

I try to create game for Android and I have problem with high speed objects, they don't wanna to collide.
I have Sphere with Sphere Collider and Bouncy material, and RigidBody with this param (Gravity=false, Interpolate=Interpolate, Collision Detection = Continuous Dynamic)
Also I have 3 walls with Box Collider and Bouncy material.
This is my code for Sphere
function IncreaseBallVelocity() {
rigidbody.velocity *= 1.05;
}
function Awake () {
rigidbody.AddForce(4, 4, 0, ForceMode.Impulse);
InvokeRepeating("IncreaseBallVelocity", 2, 2);
}
In project Settings I set: "Min Penetration For Penalty Force"=0.001, "Solver Interation Count"=50
When I play on the start it work fine (it bounces) but when speed go to high, Sphere just passes the wall.
Can anyone help me?
Thanks.
Edited
var hit : RaycastHit;
var mainGameScript : MainGame;
var particles_splash : GameObject;
function Awake () {
rigidbody.AddForce(4, 4, 0, ForceMode.Impulse);
InvokeRepeating("IncreaseBallVelocity", 2, 2);
}
function Update() {
if (rigidbody.SweepTest(transform.forward, hit, 0.5))
Debug.Log(hit.distance + "mts distance to obstacle");
if(transform.position.y < -3) {
mainGameScript.GameOver();
//Application.LoadLevel("Menu");
}
}
function IncreaseBallVelocity() {
rigidbody.velocity *= 1.05;
}
function OnCollisionEnter(collision : Collision) {
Instantiate(particles_splash, transform.position, transform.rotation);
}
EDITED added more info
Fixed Timestep = 0.02 Maximum Allowed Tir = 0.333
There is no difference between running the game in editor player and on Android
No. It looks OK when I set 0.01
My Paddle is Box Collider without Rigidbody, walls are the same
There are all in same layer (when speed is normal it all works) value in PhysicsManager are the default (same like in image) exept "Solver Interation Co..." = 50
No. When I change speed it pass other wall
I am using standard cube but I expand/shrink it to fit my screen and other objects, when I expand wall more then it's OK it bouncing
No. It's simple project simple example from Video http://www.youtube.com/watch?v=edfd1HJmKPY
I don't use gravity

See:
Similar SO Question
A community script that uses ray tracing to help manage fast objects
UnityAnswers post leading to the script in (2)
You could also try changing the fixed time step for physics. The smaller this value, the more times Unity calculates the physics of a scene. But be warned, making this value too small, say <= 0.005, will likely result in an unstable game, especially on a portable device.
The script above is best for bullets or small objects. You can manually force rigid body collisions tests:
public class example : MonoBehaviour {
public RaycastHit hit;
void Update() {
if (rigidbody.SweepTest(transform.forward, out hit, 10))
Debug.Log(hit.distance + "mts distance to obstacle");
}
}

I think the main problem is the manipulation of Rigidbody's velocity. I would try the following to solve the problem.
Redesign your code to ensure that IncreaseBallVelocity and every other manipulation of Rigidbody is called within FixedUpdate. Check that there are no other manipulations to Transform.position.
Try to replace setting velocity directly by using AddForce or similar methods so the physics engine has a higher chance to calculate all dependencies.
If there are more items (main player character, ...) involved related to the physics calculation, ensure that their code runs in FixedUpdate too.
Another point I stumbled upon were meshes that are scaled very much. Having a GameObject with scale <= 0.01 or >= 100 has definitely a negative impact on physics calculation. According to the docs and this Unity forum entry from one of the gurus you should avoid Transform.scale values != 1
Still not happy? OK then the next test is starting with high velocities but no acceleration. At this phase we want to know, if the high velocity itself or the acceleration is to blame for the problem. It would be interesting to know the velocities' values at which the physics engine starts to fail - please post them so that we can compare them.
EDIT: Some more things to investigate
6.7 m/sec does not sound that much so that I guess there is a special reason or a combination of reasons why things go wrong.
Is your Maximum Allowed Timestep high enough? For testing I suggest 5 to 10x Fixed Timestep. Note that this might kill the frame rate but that can be dfixed later.
Is there any difference between running the game in editor player and on Android?
Did you notice any drops in frame rate because of the 0.01 FixedTimestep? This would indicate that the physics engine might be in trouble.
Could it be that there are static colliders (objects having a collider but no Rigidbody) that are moved around or manipulated otherwise? This would cause heavy recalculations within PhysX.
What about the layers: Are all walls on the same layer resp. are the involved layers are configured appropriately in collision detection matrix?
Does the no-bounce effect always happen at the same wall? If so, can you just copy the 1st wall and put it in place of the second one to see if there is something wrong with this specific wall.
If not to much effort, I would try to set up some standard cubes as walls just to be sure that transform.scale is not to blame for it (I made really bad experience with this).
Do you manipulate gravity or TimeManager.timeScale from within a script?
BTW: are you using gravity? (Should be no problem just

How to add sprite as child sprite to another sprite in andengine?

I am developing game using andengine. I want to add a sprite as a child to another sprite so that sprite will rotate along with another sprite. Since I am new to andengine I didn't know how to add sprite as a child. By rotating main sprite the child has to rotate with it.
Some of them suggest to call sprite.attachChild() method to add as child but I can't get this method. I am extending BaseGameActivity.
Edited: Some of them says it's due to old version of andengine. Would anyone give me link for download new version of andengine?

AnimatedSpriteHelicopter mSpriteHelicopter = new AnimatedSpriteHelicopter(0, 0, this.mTRHelicopter);
mSpriteHelicopter.animate(50);
this.mScene.getChild(GameLayers.HELICPTER_LAYER).attachChild(mSpriteHelicopter);
this.mScene.registerTouchArea(mSpriteHelicopter);
this.mScene.setTouchAreaBindingEnabled(true);
// ==========================
// Missile
// ===========================
AnimatedSpriteMissile mMissile = new AnimatedSpriteMissile(0, 0, this.mTRMissile);
mMissile.animate(100);
mSpriteHelicopter.attachChild(mMissile);
return this.mScene;
Just a sample code. now missile will move with helicopter sprite :) very simple.
I have my own classes extended with AnimatedSprite.

The source code is located at http://code.google.com/p/andengine/ and indeed sprite composition is a feature in the most recent version of AndEngine as verified in this forum thread.
I'm using it and can personally verify that it's functional.