Develop Reference

How to avoid sluggish d3 force layout on Android?

We're using a d3.layout.force on a web app, and I've been investigating a bug report that it is sluggish on Android: it feels like the nodes are in oil, compared to how it works on desktop browsers, or iOS.
(By the way, we only ever have between 4 and 9 nodes, and the sluggishness does not feel different between 4 and 9.)
We set size(), linkDistance() and charge(); so we're using the defaults for friction, theta, alpha, gravity, etc. I experimented with these to try and reproduce the effect on desktop, but couldn't. (friction(0.67), instead of default of 0.9, was closest, but still felt different, somehow.)
I then set up an FPS meter (based on calls to the tick() function). We get 60fps on desktop, and it seems in the 40s and 50s on an ipad. But on Android Chrome (on a Nexus 7) it seems capped at 30fps, and is often half that. Android Firefox was in the 20s normally, but sometimes into the 30s.
So, is it a reasonable hypothesis that are Android devices are just slower? Could there be a cap of 30fps in Android Chrome?
Then how can I fix this? I believe d3.js uses requestAnimationFrame(). Often animation libraries take the time between calls to requestAnimationFrame() to decide how far to move objects (so when the CPU gets overloaded the animation becomes jerkier, but takes the same amount of time to complete). But it appears that d3.js does not do this, and moves everything the same amount by tick, not by elapsed time. What can I do about this?
(Ideally I'd like a solution based on how slow/fast the machine is, rather than having to sniff the browser.)

Curiously, adding more calls to force.tick() in my own requestAnimationFrame() handler (see https://stackoverflow.com/a/26189110/841830), does increase the FPS. That suggests it is not CPU bound, but instead a limit that Android is enforcing (perhaps to save battery?).
Here is the code I'm using, that tries to adapt dynamically to the current fps; it ain't beautiful but seems to be getting the job done in my test android devices, without changing the behaviour in iOS or desktop.
First, where you set up the force layout:
var ticksPerRender = 0;
var animStartTime,animFrameCount;
force.on('start',function start(){
animStartTime = new Date();animFrameCount=0;
});
requestAnimationFrame(function render() {
for(var i = 0;i < ticksPerRender;i++)force.tick();
if(force.alpha() > 0)requestAnimationFrame(render);
});
The above does two things:
sets up the fps counter
sets up our own animation callback, which does nothing by default (ticksPerRender starts off as zero).
Then at the end of your tick handler:
++animFrameCount;
if(animFrameCount>=15){ //Wait for 15, to get an accurate count
var now = new Date();
var fps = (animFrameCount / (now - animStartTime))*1000;
if(fps < 30){
ticksPerRender++;
animStartTime = now;animFrameCount = 0; //Reset the fps counter
}
if(fps > 60 && ticksPerRender >= 1){
ticksPerRender--;
animStartTime = now;animFrameCount = 0; //Reset the fps counter
}
}
This says that if the FPS is low (below 30), do an extra call to tick() on each animation frame. And if it goes high (over 60), remove that extra call.
Each time ticksPerRender is changed, we measure the FPS from scratch.

Parallel image detection and camera preview OpenCV Android

I'm using OpenCV to detect an image. Here is my problem: my function detect_image(mRgba) needs some time to perform operations and give some results. While function is computing camera preview is frozen because it only shows image when code reaches return inputFrame.rgba() I would like to know how to make those operation parallel, function will be computing in a background while camera preview is working with normal speed.
public Mat onCameraFrame(CvCameraViewFrame inputFrame) {
mRgba = inputFrame.rgba();
detect_image(mRgba);
return inputFrame.rgba();
}

To just get a taste at parallelization, the simple approach would be to just use an AsyncTask to process your images:
AsyncTask reference page
A more friendly introduction can be found here:
http://android-developers.blogspot.co.il/2010/07/multithreading-for-performance.html
while this:
http://developer.att.com/developer/forward.jsp?passedItemId=11900176
is a nice all-around introduction to multi-threading on Android.
If you want to just get started, a simple algorithm should work like this:
from within your "onCameraFrame" method check if you have an AsyncThread for processing the image which is already running
if the answer is "yes", just show mRgba in the preview window and return
if the answer is "no" start a new AsyncThread and let it run "detectImage" on mRgba, making sure that the results are saved in the onPostExecute method.
With this algorithm, if your system can detect 4 images per second while taking a preview at 60fps (for example), you will be able to get a smooth video with a new result about each 20-30 frames on a single processor device, under the realistic assumption that detect_image is CPU intensive while the camera preview/display are I/O intensive.
Capture: x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x....
Processing: 1.......1.......1.......1.....1.......1....
time ------------------------------------>
Starting with HoneyComb, a more refined approach would be to account for the number of cores in your CPU (multicore phones/tablets are becoming increasingly common) and start N AsyncTask in parallel (one for each core), feeding a different preview image to each one (maybe using a thread pool...).
If you separate each thread by a fixed delay (about the duration of detectImage/N ), you should get a constant stream of results with a frequency that should be a multiple of the single threaded version.
Capture: x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x.x....
Processing: 1.2.3.4.1.2.3.4.1.2.3.4.1.2.3.4.1.2.3.4....
time ------------------------------------>
Hope this helps

Background image taking too long to draw (Canvas) Jerky Sprites......?

Hey all I'm at a crossroads with my app that I've been working on.
It's a game and an 'arcade / action' one at that, but I've coded it using Surfaceview rather than Open GL (it just turned out that way as the game changed drastically from it's original design).
I find myself plagued with performance issues and not even in the game, but just in the first activity which is an animated menu (full screen background with about 8 sprites floating across the screen).
Even with this small amount of sprites, I can't get perfectly smooth movement. They move smoothly for a while and then it goes 'choppy' or 'jerky' for a split second.
I noticed that (from what I can tell) the background (a pre-scaled image) is taking about 7 to 8 ms to draw. Is this reasonable? I've experimented with different ways of drawing such as:
canvas.drawBitmap(scaledBackground, 0, 0, null);
the above code produces roughly the same results as:
canvas.drawBitmap(scaledBackground, null, screen, null);
However, if I change my holder to:
getHolder().setFormat(PixelFormat.RGBA_8888);
The the drawing of the bitmap shoots up to about 13 MS (I am assuming because it then has to convert to RGB_8888 format.
The strange thing is that the rendering and logic move at a very steady 30fps, it doesn't drop any frames and there is no Garbage Collection happening during run-time.
I've tried pretty much everything I can think of to get my sprites moving smoothly
I recently incorporated interpolation into my gameloop:
float interpolation = (float)(System.nanoTime() + skipTicks - nextGameTick)
/ (float)(skipTicks);
I then pass this into my draw() method:
onDraw(interpolate)
I have had some success with this and it has really helped smooth things out, but I'm still not happy with the results.
Can any one give me any final tips on maybe reducing the time taken to draw my bitmaps or any other tips on what may be causing this or do you think it's simply a case of Surfaceview not being up to the task and therefore, should I scrap the app as it were and start again with Open GL?
This is my main game loop:
int TICKS_PER_SECOND = 30;
int SKIP_TICKS = 1000 / TICKS_PER_SECOND;
int MAX_FRAMESKIP = 10;
long next_game_tick = GetTickCount();
int loops;
bool game_is_running = true;
while( game_is_running ) {
loops = 0;
while( GetTickCount() > next_game_tick && loops < MAX_FRAMESKIP) {
update_game();
next_game_tick += SKIP_TICKS;
loops++;
}
interpolation = float( GetTickCount() + SKIP_TICKS - next_game_tick )
/ float( SKIP_TICKS );
display_game( interpolation );
}
Thanks

You shouldn't use Canvas to draw fast sprites, especially if you're drawing a fullscreen image. Takes way too long, I tell you from experience. I believe Canvas is not hardware accelerated, which is the main reason you'll never get good performance out of it. Even simple sprites start to move slow when there are ~15 on screen. Switch to OpenGL, make an orthographic projection and for every Sprite make a textured quad. Believe me, I did it, and it's worth the effort.
EDIT: Actually, instead of a SurfaceView, the OpenGL way is to use a GLSurfaceView. You create your own class, derive from it, implement surfaceCreated, surfaceDestroyed and surfaceChanged, then you derive from Renderer too and connect both. Renderer handles an onDraw() function, which is what will render, GLSurfaceView manages how you will render (bit depth, render modes, etc.)

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

Android real-time game - implement time unit

I'll try to explain what I mean.
I'm developing a 2d game. When I run the code below on the small screen it works more quickly than the same code on the big screen. I think it depends on an iteration of the game loop takes more time on the big screen than on the small. How can I implement time unit or something else to it doesn't depend on the iteration of the game loop?
private void createDebris(){
if(dx<=0) return;
if(stepDebris==2){
Debris debris = new Debris(gameActivity, dx-=1280*coefX/77, 800*coefY-50*coefY, coefX, coefY);
synchronized (necessaryObjects) {
necessaryObjects.add(debris);
}
stepDebris=-1;
Log.e("COUNT", (count++)+"");
}
stepDebris++;
}
P.S. Debris is visual object which is drawn on canvas. I'll appreciate your answers. Thanks.

If, stepDebris is the unit by which you move objects on the screen - then incrementing it per draw call is wrong, because it ties the rate of movement to the framerate.
What you want is something like this
stepDebris += elapsedMilliseconds * speedFactor
where elapsedMilliseconds is the time elapsed since the game started (in mS). Once you find the correct speedFactor for stepDebris - it will move at the same speed on different machines/resolutions irrespective of framerate.
Hope this helps!

You can make an 'iteration' take x milliseconds by measuring the time it takes to do the actual iteration (= y), and afterwards sleeping (x-y) millisecs.
See also step 3 of this tutorial

Android provies the Handler API, which implements timed event loops, to control the timing of computation. This article is pretty good.
You will save battery life by implementing a frame rate controller with this interface rather redrawing as fast as you can.