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• determining the starting speed for an accelerated animation (in flash/actionscript but it's a math question)

  - by vulkanino

  This question burns my brain. I have an object on a plane, but for the sake of simplicity let's work just on a single dimension, thus the object has a starting position xs. I know the ending position xe. The object has to move from starting to ending position with an accelerated (acceleration=a) movement. I know the velocity the object has to have at the ending position (=ve). In my special case the ending speed is zero, but of course I need a general formula. The only unknown is the starting velocity vs. The objects starts with vs in xs and ends with ve in xe, moving along a space x with an acceleration a in a time t. Since I'm working with flash, space is expressed in pixels, time is expressed in frames (but you can reason in terms of seconds, it's easy to convert knowing the frames-per-second). In the animation loop (think onEnterFrame) I compute the new velocity and the new position with (a=0.4 for example): vx *= a (same for vy) x += vx (same for y) I want the entire animation to last, say, 2 seconds, which at 30 fps is 60 frames. Now you know that in 60 frames my object has to move from xs to xe with a constant deceleration so that the ending speed is 0. How do I compute the starting speed vs? Maybe there's a simpler way to do this in Flash, but I am now interested in the math/physics behind this.

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• What are some of the more commonly used projectile rendering techniques?

  - by KlashnikovKid

  couldn't find a duplicate question (bit surprising to me) but anywho I'm starting to get near implementing the rendering of projectiles for my game. My question is what are some good techniques for efficiently rendering projectiles? I would like emphasis on techniques that leave room for the projectiles to be "rich" and dynamic (Cool to look at!) I'm also using DX11 for my rendering engine so bleeding edge techniques that can make use of that would be much appreciated too. Thanks!

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• Javascript phsyics in a 2d space

  - by eroo

  So, I am working on teaching myself Canvas (HTML5) and have most of a simple game engine coded up. It is a 2d representation of a space scene (planets, stars, celestial bodies, etc). My default "Sprite" class has a frame listener like such: "baseClass" contains a function that allows inheritance and applies "a" to "this.a". So, "var aTest = new Sprite({foo: 'bar'});" would make "aTest.foo = 'bar'". This is how I expose my objects to each other. { Sprite = baseClass.extend({ init: function(a){ baseClass.init(this, a); this.fields = new Array(); // list of fields of gravity one is in. Not sure if this is a good idea. this.addFL(function(tick){ // this will change to be independent of framerate soon. // and this is where I need help // gobjs is an array of all the Sprite objects in the "world". for(i = 0; i < gobjs.length; i++){ // Make sure its got setup correctly, make sure it -wants- gravity, and make sure it's not -this- sprite. if(typeof(gobjs[i].a) != undefined && !gobjs[i].a.ignoreGravity && gobjs[i].id != this.id){ // Check if it's within a certain range (obviously, gravity doesn't work this way... But I plan on having a large "space" area, // And I can't very well have all objects accounted for at all times, can I? if(this.distanceTo(gobjs[i]) < this.s.size*10 && gobjs[i].fields.indexOf(this.id) == -1){ gobjs[i].fields.push(this.id); } } } for(i = 0; i < this.fields.length; i++){ distance = this.distanceTo(gobjs[this.fields[i]]); angletosun = this.angleTo(gobjs[this.fields[i]])*(180/Math.PI); // .angleTo works very well, returning the angle in radians, which I convert to degrees here. // I have no idea what should happen here, although through trial and error (and attempting to read Maths papers on gravity (eeeeek!)), this sort of mimics gravity. // angle is its orientation, currently I assign a constant velocity to one of my objects, and leave the other static (it ignores gravity, but still emits it). this.a.angle = angletosun+(75+(distance*-1)/5); //todo: omg learn math if(this.distanceTo(gobjs[this.fields[i]]) > gobjs[this.fields[i]].a.size*10) this.fields.splice(i); // out of range, stop effecting. } }); } }); } Thanks in advance. The real trick is that one line: { this.a.angle = angletosun+(75+(distance*-1)/5); } This is more a physics question than Javascript, but I've searched and searched and read way to many wiki articles on orbital mathematics. It gets over my head very quickly. Edit: There is a weirdness with the SO formatting; forgives me, I is noobie.

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• Mass Ball-to-Ball Collision Handling (as in, lots of balls)

  - by BlueThen

  Update: Found out that I was using the radius as the diameter, which was why the mtd was overcompensating. Hi, StackOverflow. I've written a Processing program awhile back simulating ball physics. Basically, I have a large number of balls (1000), with gravity turned on. Detection works great, but my issue is that they start acting weird when they're bouncing against other balls in all directions. I'm pretty confident this involves the handling. For the most part, I'm using Jay Conrod's code. One part that's different is if (distance > 1.0) return; which I've changed to if (distance < 1.0) return; because the collision wasn't even being performed with the first bit of code, I'm guessing that's a typo. The balls overlap when I use his code, which isn't what I was looking for. My attempt to fix it was to move the balls to the edge of each other: float angle = atan2(y - collider.y, x - collider.x); float distance = dist(x,y, balls[ID2].x,balls[ID2].y); x = collider.x + radius * cos(angle); y = collider.y + radius * sin(angle); This isn't correct, I'm pretty sure of that. I tried the correction algorithm in the previous ball-to-ball topic: // get the mtd Vector2d delta = (position.subtract(ball.position)); float d = delta.getLength(); // minimum translation distance to push balls apart after intersecting Vector2d mtd = delta.multiply(((getRadius() + ball.getRadius())-d)/d); // resolve intersection -- // inverse mass quantities float im1 = 1 / getMass(); float im2 = 1 / ball.getMass(); // push-pull them apart based off their mass position = position.add(mtd.multiply(im1 / (im1 + im2))); ball.position = ball.position.subtract(mtd.multiply(im2 / (im1 + im2))); except my version doesn't use vectors, and every ball's weight is 1. The resulting code I get is this: PVector delta = new PVector(collider.x - x, collider.y - y); float d = delta.mag(); PVector mtd = new PVector(delta.x * ((radius + collider.radius - d) / d), delta.y * ((radius + collider.radius - d) / d)); // push-pull apart based on mass x -= mtd.x * 0.5; y -= mtd.y * 0.5; collider.x += mtd.x * 0.5; collider.y += mtd.y * 0.5; This code seems to over-correct collisions. Which doesn't make sense to me because in no other way do I modify the x and y values of each ball, other than this. Some other part of my code could be wrong, but I don't know. Here's the snippet of the entire ball-to-ball collision handling I'm using: if (alreadyCollided.contains(new Integer(ID2))) // if the ball has already collided with this, then we don't need to reperform the collision algorithm return; Ball collider = (Ball) objects.get(ID2); PVector collision = new PVector(x - collider.x, y - collider.y); float distance = collision.mag(); if (distance == 0) { collision = new PVector(1,0); distance = 1; } if (distance < 1) return; PVector velocity = new PVector(vx,vy); PVector velocity2 = new PVector(collider.vx, collider.vy); collision.div(distance); // normalize the distance float aci = velocity.dot(collision); float bci = velocity2.dot(collision); float acf = bci; float bcf = aci; vx += (acf - aci) * collision.x; vy += (acf - aci) * collision.y; collider.vx += (bcf - bci) * collision.x; collider.vy += (bcf - bci) * collision.y; alreadyCollided.add(new Integer(ID2)); collider.alreadyCollided.add(new Integer(ID)); PVector delta = new PVector(collider.x - x, collider.y - y); float d = delta.mag(); PVector mtd = new PVector(delta.x * ((radius + collider.radius - d) / d), delta.y * ((radius + collider.radius - d) / d)); // push-pull apart based on mass x -= mtd.x * 0.2; y -= mtd.y * 0.2; collider.x += mtd.x * 0.2; collider.y += mtd.y * 0.2; Thanks. (Apologies for lack of sources, stackoverflow thinks I'm a spammer)

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• RevoluteJoint Stop Rotating when Some Physics Body Collide in Andengine + Box2d?

  - by Nikhil Lamba

  I am making a Game from andengine + box2d in Which i am using RevoluteJoint in that case i am facing some problem that when physics body or Sprite Collide with this Revolute joint body then Revolute body stop rotating then after some time it start rotating I am using below code for this : this.mPhysicsWorld.registerPhysicsConnector(new PhysicsConnector(movingFace, movingBody, true, true)); final RevoluteJointDef revoluteJointDef = new RevoluteJointDef(); revoluteJointDef.initialize(anchorBody, movingBody, anchorBody.getWorldCenter()); revoluteJointDef.enableMotor = true; revoluteJointDef.motorSpeed = 100; revoluteJointDef.maxMotorTorque = 200; this.mPhysicsWorld.createJoint(revoluteJointDef); EDIT Here is a screenshot:

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• How can I simulate objects floating on water without a physics engine?

  - by user1075940

  In my game the water movement is done in a shader using Gerstner equations. The water movement looks realistic enough for a school project but I encounter serious problem when I wanted to do sailing on waves (similar to this). I managed to do collision with land by calculating quad's vertices and normals beneath ship, however same method can not be applied to water because XZ are displaced and Y is calculated in a shader :( How to approach this problem ? Is it possible to retrieve transformed grid from shader? Unfortunately no external physics libraries can be used.

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• How to simulate objects floating on water without a physics engine?

  - by user1075940

  In my game the water movement is done in a shader using Gerstner equations. The water movement looks realistic enough for a school project but I encounter serious problem when I wanted to do sailing on waves (similar to this). I managed to do collision with land by calculating quad's vertices and normals beneath ship, however same method can not be applied to water because XZ are displaced and Y is calculated in a shader :( How to approach this problem ? Is it possible to retrieve transformed grid from shader? Unfortunately no external physics libraries can be used.

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• Cocos2d score resetting is messing up (long post warning)

  - by Jhon Doe

  The score is not resetting right at all,I am trying to make a high score counter where every time you passed previous high score it will update.However, right now it is resetting during the game. For example if I had high score of 2 during the game it will take 3 points just to put it up to 3 as high score instead of keep going up until it is game over. I have came to the conclusion that I need to reset it in gameoverlayer so it won't reset during game. I have been trying to to do this but no luck. hello world ./h #import "cocos2d.h" // HelloWorldLayer @interface HelloWorldLayer : CCLayer { int _score; int _oldScore; CCLabelTTF *_scoreLabel; } @property (nonatomic, assign) CCLabelTTF *scoreLabel; hello world init ./m _score = [[NSUserDefaults standardUserDefaults] integerForKey:@"score"]; _oldScore = -1; self.scoreLabel = [CCLabelTTF labelWithString:@"" dimensions:CGSizeMake(100, 50) alignment:UITextAlignmentRight fontName:@"Marker Felt" fontSize:32]; _scoreLabel.position = ccp(winSize.width - _scoreLabel.contentSize.width, _scoreLabel.contentSize.height); _scoreLabel.color = ccc3(255,0,0); [self addChild:_scoreLabel z:1]; hello world implement ./m - (void)update:(ccTime)dt { NSMutableArray *projectilesToDelete = [[NSMutableArray alloc] init]; CGRect projectileRect = CGRectMake( projectile.position.x - (projectile.contentSize.width/2), projectile.position.y - (projectile.contentSize.height/2), projectile.contentSize.width, projectile.contentSize.height); BOOL monsterHit = FALSE; NSMutableArray *targetsToDelete = [[NSMutableArray alloc] init]; for (CCSprite *target in _targets) { CGRect targetRect = CGRectMake( target.position.x - (target.contentSize.width/2), target.position.y - (target.contentSize.height/2), target.contentSize.width, target.contentSize.height); if (CGRectIntersectsRect(projectileRect, targetRect)) { CCParticleFire* explosion = [[CCParticleFire alloc] initWithTotalParticles:200]; explosion.texture =[[CCTextureCache sharedTextureCache] addImage:@"sun.png"]; explosion.autoRemoveOnFinish = YES; explosion.startSize = 20.0f; explosion.speed = 70.0f; explosion.anchorPoint = ccp(0.5f,0.5f); explosion.position = target.position; explosion.duration = 1.0f; [self addChild:explosion z:11]; [explosion release]; monsterHit = TRUE; Monster *monster = (Monster *)target; monster.hp--; if (monster.hp <= 0) { [targetsToDelete addObject:target]; [[SimpleAudioEngine sharedEngine] playEffect:@"splash.wav"]; _score ++; } break; } } for (CCSprite *target in targetsToDelete) { [_targets removeObject:target]; [self removeChild:target cleanup:YES]; } if (targetsToDelete.count > 0) { [ projectilesToDelete addObject:projectile]; } [targetsToDelete release]; if (_score > _oldScore) { _oldScore = _score; [_scoreLabel setString:[NSString stringWithFormat:@"score%d", _score]]; [[NSUserDefaults standardUserDefaults] setInteger:_oldScore forKey:@"score"]; _score = 0; } } - (void)update:(ccTime)dt { NSMutableArray *projectilesToDelete = [[NSMutableArray alloc] init]; CGRect projectileRect = CGRectMake( projectile.position.x - (projectile.contentSize.width/2), projectile.position.y - (projectile.contentSize.height/2), projectile.contentSize.width, projectile.contentSize.height); BOOL monsterHit = FALSE; NSMutableArray *targetsToDelete = [[NSMutableArray alloc] init]; for (CCSprite *target in _targets) { CGRect targetRect = CGRectMake( target.position.x - (target.contentSize.width/2), target.position.y - (target.contentSize.height/2), target.contentSize.width, target.contentSize.height); if (CGRectIntersectsRect(projectileRect, targetRect)) { CCParticleFire* explosion = [[CCParticleFire alloc] initWithTotalParticles:200]; explosion.texture =[[CCTextureCache sharedTextureCache] addImage:@"sun.png"]; explosion.autoRemoveOnFinish = YES; explosion.startSize = 20.0f; explosion.speed = 70.0f; explosion.anchorPoint = ccp(0.5f,0.5f); explosion.position = target.position; explosion.duration = 1.0f; [self addChild:explosion z:11]; [explosion release]; monsterHit = TRUE; Monster *monster = (Monster *)target; monster.hp--; if (monster.hp <= 0) { [targetsToDelete addObject:target]; [[SimpleAudioEngine sharedEngine] playEffect:@"splash.wav"]; _score ++; } break; } } for (CCSprite *target in targetsToDelete) { [_targets removeObject:target]; [self removeChild:target cleanup:YES]; } if (targetsToDelete.count > 0) { [projectilesToDelete addObject:projectile]; } [targetsToDelete release]; if (_score > _oldScore) { _oldScore = _score; [_scoreLabel setString:[NSString stringWithFormat:@"score%d", _score]]; [[NSUserDefaults standardUserDefaults] setInteger:_oldScore forKey:@"score"]; _score = 0; } The game overlayer .h file game over @interface GameOverLayer : CCLayerColor { CCLabelTTF *_label; CCSprite * background; int _score; int _oldScore; } @property (nonatomic, retain) CCLabelTTF *label; @end @interface GameOverScene : CCScene { GameOverLayer *_layer; } @property (nonatomic, retain) GameOverLayer *layer; @end .m file gameover #import "GameOverLayer.h" #import "HelloWorldLayer.h" #import "MainMenuScene.h" @implementation GameOverScene @synthesize layer = _layer; - (id)init { if ((self = [super init])) { self.layer = [GameOverLayer node]; [self addChild:_layer]; } return self; } - (void)dealloc { [_layer release]; _layer = nil; [super dealloc]; } @end @implementation GameOverLayer @synthesize label = _label; -(id) init { if( (self=[super initWithColor:ccc4(0,0,0,0)] )) { CGSize winSize = [[CCDirector sharedDirector] winSize]; self.label = [CCLabelTTF labelWithString:@"" fontName:@"Arial" fontSize:32]; _label.color = ccc3(225,0,0); _label.position = ccp(winSize.width/2, winSize.height/2); [self addChild:_label]; [self runAction:[CCSequence actions: [CCDelayTime actionWithDuration:3], [CCCallFunc actionWithTarget:self selector:@selector(gameOverDone)], nil]]; _score=0; }

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• Asking Box2d if a collision happened

  - by Rosarch

  I'm using Box2dx (ported to C#; optimized for XNA). It handles collision resolution, but how can I tell if two objects are currently colliding? This is the function I'm trying to write: public bool IsColliding(GameObjectController collider1, GameObjectController collider2) Where collider1.Model.Body is the Box2d Body, and collider1.Model.BodyDef is the Box2d BodyDef. (The same goes for collider2, of course.) UPDATE: Looks like contact listeners or this could be useful: AABB collisionBox; model.Body.GetFixtureList().GetAABB(out collisionBox); Why does GetFixtureList() return one fixture?

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• Box2dx: Usage of World.QueryAABB?

  - by Rosarch

  I'm using Box2dx with C#/XNA. I'm trying to write a function that determines if a body could exist in a given point without colliding with anything: /// <summary> /// Can gameObject exist with start Point without colliding with anything? /// </summary> internal bool IsAvailableArea(GameObjectModel model, Vector2 point) { Vector2 originalPosition = model.Body.Position; model.Body.Position = point; // less risky would be to use a deep clone AABB collisionBox; model.Body.GetFixtureList().GetAABB(out collisionBox); // how is this supposed to work? physicsWorld.QueryAABB(x => true, ref collisionBox); model.Body.Position = originalPosition; return true; } Is there a better way to go about doing this? How is World.QueryAABB supposed to work? Here is an earlier attempt. It is broken; it always returns false. /// <summary> /// Can gameObject exist with start Point without colliding with anything? /// </summary> internal bool IsAvailableArea(GameObjectModel model, Vector2 point) { Vector2 originalPosition = model.Body.Position; model.Body.Position = point; // less risky would be to use a deep clone AABB collisionBox; model.Body.GetFixtureList().GetAABB(out collisionBox); ICollection<GameObjectController> gameObjects = worldQueryEngine.GameObjectsForPredicate(x => ! x.Model.Passable); foreach (GameObjectController controller in gameObjects) { AABB potentialCollidingBox; controller.Model.Body.GetFixtureList().GetAABB(out potentialCollidingBox); if (AABB.TestOverlap(ref collisionBox, ref potentialCollidingBox)) { model.Body.Position = originalPosition; return false; // there is something that will collide at this point } } model.Body.Position = originalPosition; return true; }

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• Kalman Filter for Android

  - by Johnny

  Is there a Kalman filter implementation I can use to fliter my gyroscope and acceleration data from an Android Phone?

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• What is the most platform- and Python-version-independent way to make a fast loop for use in Python?

  - by Statto

  I'm writing a scientific application in Python with a very processor-intensive loop at its core. I would like to optimise this as far as possible, at minimum inconvenience to end users, who will probably use it as an uncompiled collection of Python scripts, and will be using Windows, Mac, and (mainly Ubuntu) Linux. It is currently written in Python with a dash of NumPy, and I've included the code below. Is there a solution which would be reasonably fast which would not require compilation? This would seem to be the easiest way to maintain platform-independence. If using something like Pyrex, which does require compilation, is there an easy way to bundle many modules and have Python choose between them depending on detected OS and Python version? Is there an easy way to build the collection of modules without needing access to every system with every version of Python? Does one method lend itself particularly to multi-processor optimisation? (If you're interested, the loop is to calculate the magnetic field at a given point inside a crystal by adding together the contributions of a large number of nearby magnetic ions, treated as tiny bar magnets. Basically, a massive sum of these.) # calculate_dipole # ------------------------- # calculate_dipole works out the dipole field at a given point within the crystal unit cell # --- # INPUT # mu = position at which to calculate the dipole field # r_i = array of atomic positions # mom_i = corresponding array of magnetic moments # --- # OUTPUT # B = the B-field at this point def calculate_dipole(mu, r_i, mom_i): relative = mu - r_i r_unit = unit_vectors(relative) #4pi / mu0 (at the front of the dipole eqn) A = 1e-7 #initalise dipole field B = zeros(3,float) for i in range(len(relative)): #work out the dipole field and add it to the estimate so far B += A*(3*dot(mom_i[i],r_unit[i])*r_unit[i] - mom_i[i]) / sqrt(dot(relative[i],relative[i]))**3 return B

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• point light illumination using Phong model

  - by Myx

  Hello: I wish to render a scene that contains one box and a point light source using the Phong illumination scheme. The following are the relevant code snippets for my calculation: R3Rgb Phong(R3Scene *scene, R3Ray *ray, R3Intersection *intersection) { R3Rgb radiance; if(intersection->hit == 0) { radiance = scene->background; return radiance; } ... // obtain ambient term ... // this is zero for my test // obtain emissive term ... // this is also zero for my test // for each light in the scene, obtain calculate the diffuse and specular terms R3Rgb intensity_diffuse(0,0,0,1); R3Rgb intensity_specular(0,0,0,1); for(unsigned int i = 0; i < scene->lights.size(); i++) { R3Light *light = scene->Light(i); R3Rgb light_color = LightIntensity(scene->Light(i), intersection->position); R3Vector light_vector = -LightDirection(scene->Light(i), intersection->position); // check if the light is "behind" the surface normal if(normal.Dot(light_vector)<=0) continue; // calculate diffuse reflection if(!Kd.IsBlack()) intensity_diffuse += Kd*normal.Dot(light_vector)*light_color; if(Ks.IsBlack()) continue; // calculate specular reflection ... // this I believe to be irrelevant for the particular test I'm doing } radiance = intensity_diffuse; return radiance; } R3Rgb LightIntensity(R3Light *light, R3Point position) { R3Rgb light_intensity; double distance; double denominator; if(light->type != R3_DIRECTIONAL_LIGHT) { distance = (position-light->position).Length(); denominator = light->constant_attenuation + (light->linear_attenuation*distance) + (light->quadratic_attenuation*distance*distance); } switch(light->type) { ... case R3_POINT_LIGHT: light_intensity = light->color/denominator; break; ... } return light_intensity; } R3Vector LightDirection(R3Light *light, R3Point position) { R3Vector light_direction; switch(light->type) { ... case R3_POINT_LIGHT: light_direction = position - light->position; break; ... } light_direction.Normalize(); return light_direction; } I believe that the error must be somewhere in either LightDirection(...) or LightIntensity(...) functions because when I run my code using a directional light source, I obtain the desired rendered image (thus this leads me to believe that the Phong illumination equation is correct). Also, in Phong(...), when I computed the intensity_diffuse and while debugging, I divided light_color by 10, I was obtaining a resulting image that looked more like what I need. Am I calculating the light_color correctly? Thanks.

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• Friction in Box2d

  - by Rosarch

  I am using Box2d for a topdown game. The "ground" is a series of tiles, where each tile is a static body with a sensor shape. Can I make friction take effect for this, even though the objects aren't really "colliding" with the ground? If Box2d won't let me do this, I considered trying to implement my own by detecting what force is currently moving the object, and applying a force opposite to it, but I'm not quite sure how to detect that force.

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• Pool Billiard AI

  - by Sebi

  Im implementing a pool billiard game in Java and it all works fine. It is a multiplayer game, but nevertheless, it should also be possible to play it alone. For this purpose I'm trying to implement a simple KI. At the moment, the KI choose just randomly a direction and a random intensity of the impulse (don't know the correct english word for that). Of course this AI is very poor and unlikely to ever challenge a player. So i thought about improving the KI, but there are several hard to solve problems. First I thought of just choosing the nearest ball and to try to put it directly into the nearest hole. This isn't that bad, but if there other balls in the line between, it isn't really working anymore. Additionally this dosn't solve te problem of calculating the intensity of the impulse. So are there any general advice? Or any ideas? Best practices?

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• Can't create an OgreBullet Trimesh

  - by Nathan Baggs

  I'm using Ogre and Bullet for a project and I currently have a first person camera set up with a Capsule Collision Shape. I've created a model of a cave (which will serve as the main part of the level) and imported it into my game. I'm now trying to create an OgreBulletCollisions::TriangleMeshCollisionShape of the cave. The code I've got so far is this but it isn't working. It compiles but the Capsule shape passes straight through the cave shape. Also I have debug outlines on and there are none being drawn around the cave mesh. Entity *cave = mSceneMgr->createEntity("Cave", "pCube1.mesh"); SceneNode *caveNode = mSceneMgr->getRootSceneNode()->createChildSceneNode(); caveNode->setPosition(0, 10, 250); caveNode->setScale(10, 10, 10); caveNode->rotate(Quaternion(0.5, 0.5, -0.5, 0.5)); caveNode->attachObject(cave); OgreBulletCollisions::StaticMeshToShapeConverter *smtsc = new OgreBulletCollisions::StaticMeshToShapeConverter(); smtsc->addEntity(cave); OgreBulletCollisions::TriangleMeshCollisionShape *tri = smtsc->createTrimesh(); OgreBulletDynamics::RigidBody *caveBody = new OgreBulletDynamics::RigidBody("cave", mWorld); caveBody->setStaticShape(tri, 0.1, 0.8); mShapes.push_back(tri); mBodies.push_back(caveBody); Any suggestions are welcome. To clarify. It compiles but the Capsule shape passes straight through the cave shape. Also I have debug outlines on and there are none being drawn around the cave mesh

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• Python/Biophysics- Trying to code a simple stochastic simulation!

  - by user359597

  Hey guys- I'm trying to figure out what to make of the following code- this is not the clear, intuitive python I've been learning. Was it written in C or something then wrapped in a python fxn? The code I wrote (not shown) is using the same math, but I couldn't figure out how to write a conditional loop. If anyone could explain/decipher/clean this up, I'd be really appreciative. I mean- is this 'good' python- or does it look funky? I'm brand new to this- but it's like the order of the fxns is messed up? I understand Gillespie's- I've successfully coded several simpler simulations. So in a nutshell- good code-(pythonic)? order? c? improvements? am i being an idiot? The code shown is the 'answer,' to the following question from a biophysics text (petri-net not shown and honestly not necessary to understand problem): "In a programming language of your choice, implement Gillespie’s First Reaction Algorithm to study the temporal behaviour of the reaction A---B in which the transition from A to B can only take place if another compound, C, is present, and where C dynamically interconverts with D, as modelled in the Petri-net below. Assume that there are 100 molecules of A, 1 of C, and no B or D present at the start of the reaction. Set kAB to 0.1 s-1 and both kCD and kDC to 1.0 s-1. Simulate the behaviour of the system over 100 s." def sim(): # Set the rate constants for all transitions kAB = 0.1 kCD = 1.0 kDC = 1.0 # Set up the initial state A = 100 B = 0 C = 1 D = 0 # Set the start and end times t = 0.0 tEnd = 100.0 print "Time\t", "Transition\t", "A\t", "B\t", "C\t", "D" # Compute the first interval transition, interval = transitionData(A, B, C, D, kAB, kCD, kDC) # Loop until the end time is exceded or no transition can fire any more while t <= tEnd and transition >= 0: print t, '\t', transition, '\t', A, '\t', B, '\t', C, '\t', D t += interval if transition == 0: A -= 1 B += 1 if transition == 1: C -= 1 D += 1 if transition == 2: C += 1 D -= 1 transition, interval = transitionData(A, B, C, D, kAB, kCD, kDC) def transitionData(A, B, C, D, kAB, kCD, kDC): """ Returns nTransition, the number of the firing transition (0: A->B, 1: C->D, 2: D->C), and interval, the interval between the time of the previous transition and that of the current one. """ RAB = kAB * A * C RCD = kCD * C RDC = kDC * D dt = [-1.0, -1.0, -1.0] if RAB > 0.0: dt[0] = -math.log(1.0 - random.random())/RAB if RCD > 0.0: dt[1] = -math.log(1.0 - random.random())/RCD if RDC > 0.0: dt[2] = -math.log(1.0 - random.random())/RDC interval = 1e36 transition = -1 for n in range(len(dt)): if dt[n] > 0.0 and dt[n] < interval: interval = dt[n] transition = n return transition, interval if __name__ == '__main__': sim()

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• Detecting Acceleration in a car (iPhone Accelerometer)

  - by TheGazzardian

  Hello, I am working on an iPhone app where we are trying to calculate the acceleration of a moving car. Similar apps have accomplished this (Dynolicious), but the difference is that this app is designed to be used during general city driving, not on a drag strip. This leads us to one big concern that Dynolicious was luckily able to avoid: hills. Yes, hills. There are two important stages to this: calibration, and actual driving. Our initial run was simple and suffered the consequences. During the calibration stage, I took the average force on the phone, and during running, I just subtracted the average force from the current force to get the current acceleration this frame. The problem with this is that the typical car receives much more force than just the forward force - everything from turning to potholes was causing the values to go out of sync with what was really happening. The next run was to add the condition that the iPhone must be oriented in such a way that the screen was facing toward the back of the car. Using this method, I attempted to follow only force on the z-axis, but this obviously lead to problems unless the iPhone was oriented directly upright, because of gravity. Some trigonometry later, and I had managed to work gravity out of the equation, so that the car was actually being read very, very well by the iPhone. Until I hit a slope. As soon as the angle of the car changed, suddenly I was receiving accelerations and decelerations that didn't make sense, and we were once again going out of sync. Talking with someone a lot smarter than me at math lead to a solution that I have been trying to implement for longer than I would like to admit. It's steps are as follows: 1) During calibration, measure gravity as a vector instead of a size. Store that vector. 2) When the car initially moves forward, take the vector of motion and subtract gravity. Use this as the forward momentum. (Ignore, for now, the user cases where this will be difficult and let's concentrate on the math :) 3) From the forward vector and the gravity vector, construct a plane. 4) Whenever a force is received, project it onto said plane to get rid of sideways force/etc. 5) Then, use that force, the known magnitude of gravity, and the known direction of forward motion to essentially solve a triangle to get the forward vector. The problem that is causing the most difficulty in this new system is not step 5, which I have gotten to the point where all the numbers look as they should. The difficult part is actually the detection of the forward vector. I am selecting vectors whose magnitude exceeds gravity, and from there, averaging them and subtracting gravity. (I am doing some error checking to make sure that I am not using a force just because the iPhone accelerometer was off by a bit, which happens more frequently than I would like). But if I plot these vectors that I am using, they actually vary by an angle of about 20-30 degrees, which can lead to some strong inaccuracies. The end result is that the app is even more inaccurate now than before. So basically - all you math and iPhone brains out there - any glaring errors? Any potentially better solutions? Any experience that could be useful at all? Award: offering a bounty of $250 to the first answer that leads to a solution.

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• Animation with Initial Velocity

  - by abustin

  I've been trying to solve this problem for a number of days now but I must be missing something. Known Variables: vi = Initial Velocity t = Animation Duration d = Distance The function I'm trying to create: D(t) = the current distance for a given time Using this information I want to be able to create a smooth animation curve with varying velocity (ease-in/ease-out). The animation must be able ease-in from an initial velocity. The animation must be exactly t seconds and must be travel exactly d units. The curve should lean towards the average velocity with acceleration occurring at the beginning and the end portions of the curve. I'm open to extra configuration variables. The best I've been able to come up with is something that doesn't factor in the initial velocity. I'm hoping someone smarter can help me out. ;) Thank you! p.s. I'm working with an ECMAScript variant

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• Can my loop be optimized any more? (C++)

  - by Sagekilla

  Below is one of my inner loops that's run several thousand times, with input sizes of 20 - 1000 or more. Is there anything I can do to help squeeze any more performance out of this? I'm not looking to move this code to something like using tree codes (Barnes-Hut), but towards optimizing the actual calculations happening inside, since the same calculations occur in the Barnes-Hut algorithm. Any help is appreciated! typedef double real; struct Particle { Vector pos, vel, acc, jerk; Vector oldPos, oldVel, oldAcc, oldJerk; real mass; }; class Vector { private: real vec[3]; public: // Operators defined here }; real Gravity::interact(Particle *p, size_t numParticles) { PROFILE_FUNC(); real tau_q = 1e300; for (size_t i = 0; i < numParticles; i++) { p[i].jerk = 0; p[i].acc = 0; } for (size_t i = 0; i < numParticles; i++) { for (size_t j = i+1; j < numParticles; j++) { Vector r = p[j].pos - p[i].pos; Vector v = p[j].vel - p[i].vel; real r2 = lengthsq(r); real v2 = lengthsq(v); // Calculate inverse of |r|^3 real r3i = Constants::G * pow(r2, -1.5); // da = r / |r|^3 // dj = (v / |r|^3 - 3 * (r . v) * r / |r|^5 Vector da = r * r3i; Vector dj = (v - r * (3 * dot(r, v) / r2)) * r3i; // Calculate new acceleration and jerk p[i].acc += da * p[j].mass; p[i].jerk += dj * p[j].mass; p[j].acc -= da * p[i].mass; p[j].jerk -= dj * p[i].mass; // Collision estimation // Metric 1) tau = |r|^2 / |a(j) - a(i)| // Metric 2) tau = |r|^4 / |v|^4 real mij = p[i].mass + p[j].mass; real tau_est_q1 = r2 / (lengthsq(da) * mij * mij); real tau_est_q2 = (r2*r2) / (v2*v2); if (tau_est_q1 < tau_q) tau_q = tau_est_q1; if (tau_est_q2 < tau_q) tau_q = tau_est_q2; } } return sqrt(sqrt(tau_q)); }

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• Falling Sand simulation

  - by Erik Forbes

  I'm trying to re-create a 'falling sand' simulation, similar to those various web toys that are out there doing the same thing - and I'm failing pretty hard. I'm not really sure where to begin. I'm trying to use cellular automata to model the behavior of the sand particles, but I'm having trouble figuring out how to make the direction in which I update the 'world' not matter... For example, one of the particle types I'd like to have is Plant. When Plant comes in contact with Water, Plant turns that Water particle into another Plant particle. The problem here though is that if I'm updating the game world from top to bottom and left to right, then a Plant particle placed in the middle of a sea of Water particles will immediately cause all of the Water particles to the right and below that new Plant particle to turn into Plants. This is not the behavior I am expecting. =( I'm having difficulty explaining exactly my difficulty, so I'll try to add more information as best I can as I go along. Suffice it to say that this is very much outside my box, as it were, and I don't even know what to search for.

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• The Math of a Jump in a 2D game.

  - by ONi

  I have been all around with this question and I can't find the correct answer! So, behold, the description of my question: I'm working in J2ME, I have my gameloop that do the following: public void run() { Graphics g = this.getGraphics(); while (running) { long diff = System.currentTimeMillis() - lastLoop; lastLoop = System.currentTimeMillis(); input(); this.level.doLogic(); render(g, diff); try { Thread.sleep(10); } catch (InterruptedException e) { stop(e); } } } so it's just a basic gameloop, the doLogic() function calls for all the logic functions of the characters in the scene and render(g, diff) calls the animateChar function of every character on scene, following this, the animChar function in the Character class sets up everything in the screen as this: protected void animChar(long diff) { this.checkGravity(); this.move((int) ((diff * this.dx) / 1000), (int) ((diff * this.dy) / 1000)); if (this.acumFrame > this.framerate) { this.nextFrame(); this.acumFrame = 0; } else { this.acumFrame += diff; } } This ensures me that everything must to move according to the time that the machine takes to go from cycle to cycle (remember it's a phone, not a gaming rig). I'm sure it's not the most efficient way to achieve this behavior so I'm totally open for criticism of my programming skills in the comments, but here my problem: When I make I character jump, what I do is that I put his dy to a negative value, say -200 and I set the boolean jumping to true, that makes the character go up, and then I have this function called checkGravity() that ensure that everything that goes up has to go down, checkGravity also checks for the character being over platforms so I will strip it down a little for the sake of your time: public void checkGravity() { if (this.jumping) { this.jumpSpeed += 10; if (this.jumpSpeed > 0) { this.jumping = false; this.falling = true; } this.dy = this.jumpSpeed; } if (this.falling) { this.jumpSpeed += 10; if (this.jumpSpeed > 200) this.jumpSpeed = 200; this.dy = this.jumpSpeed; if (this.collidesWithPlatform()) { this.falling = false; this.standing = true; this.jumping = false; this.jumpSpeed = 0; this.dy = this.jumpSpeed; } } } So, the problem is, that this function updates the dy regardless of the diff, making the characters fly like Superman in slow machines, and I have no idea how to implement the diff factor so that when a character is jumping, his speed decrement in a proportional way to the game speed. Can anyone help me fix this issue? or give me pointers on how to make a 2D Jump in J2ME the right way. Thank you very much for your time.

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• Accelerometer gravity components

  - by Dvd

  Hi, I know this question is definitely solved somewhere many times already, please enlighten me if you know of their existence, thanks. Quick rundown: I want to compute from a 3 axis accelerometer the gravity component on each of these 3 axes. I have used 2 axes free body diagrams to work out the accelerometer's gravity component in the world X-Z, Y-Z and X-Y axes. But the solution seems slightly off, it's acceptable for extreme cases when only 1 accelerometer axis is exposed to gravity, but for a pitch and roll of both 45 degrees, the combined total magnitude is greater than gravity (obtained by Xa^2+Ya^2+Za^2=g^2; Xa, Ya and Za are accelerometer readings in its X, Y and Z axis). More detail: The device is a Nexus One, and have a magnetic field sensor for azimuth, pitch and roll in addition to the 3-axis accelerometer. In the world's axis (with Z in the same direction as gravity, and either X or Y points to the north pole, don't think this matters much?), I assumed my device has a pitch (P) on the Y-Z axis, and a roll (R) on the X-Z axis. With that I used simple trig to get: Sin(R)=Ax/Gxz Cos(R)=Az/Gxz Tan(R)=Ax/Az There is another set for pitch, P. Now I defined gravity to have 3 components in the world's axis, a Gxz that is measurable only in the X-Z axis, a Gyz for Y-Z, and a Gxy for X-Y axis. Gxz^2+Gyz^2+Gxy^2=2*G^2 the 2G is because gravity is effectively included twice in this definition. Oh and the X-Y axis produce something more exotic... I'll explain if required later. From these equations I obtained a formula for Az, and removed the tan operations because I don't know how to handle tan90 calculations (it's infinity?). So my question is, anyone know whether I did this right/wrong or able to point me to the right direction? Thanks! Dvd

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• How to identify four sided polygon (not rectangle) collision detection?

  - by Chandan Shetty SP

  I am developing 2D game for iPhone, for that I need to handle collision detection. My need is: I have two polygons, each is a four-sided polygon (not a rectangle), I need to check whether they are collided or not.

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• Rewriting a for loop in pure NumPy to decrease execution time

  - by Statto

  I recently asked about trying to optimise a Python loop for a scientific application, and received an excellent, smart way of recoding it within NumPy which reduced execution time by a factor of around 100 for me! However, calculation of the B value is actually nested within a few other loops, because it is evaluated at a regular grid of positions. Is there a similarly smart NumPy rewrite to shave time off this procedure? I suspect the performance gain for this part would be less marked, and the disadvantages would presumably be that it would not be possible to report back to the user on the progress of the calculation, that the results could not be written to the output file until the end of the calculation, and possibly that doing this in one enormous step would have memory implications? Is it possible to circumvent any of these? import numpy as np import time def reshape_vector(v): b = np.empty((3,1)) for i in range(3): b[i][0] = v[i] return b def unit_vectors(r): return r / np.sqrt((r*r).sum(0)) def calculate_dipole(mu, r_i, mom_i): relative = mu - r_i r_unit = unit_vectors(relative) A = 1e-7 num = A*(3*np.sum(mom_i*r_unit, 0)*r_unit - mom_i) den = np.sqrt(np.sum(relative*relative, 0))**3 B = np.sum(num/den, 1) return B N = 20000 # number of dipoles r_i = np.random.random((3,N)) # positions of dipoles mom_i = np.random.random((3,N)) # moments of dipoles a = np.random.random((3,3)) # three basis vectors for this crystal n = [10,10,10] # points at which to evaluate sum gamma_mu = 135.5 # a constant t_start = time.clock() for i in range(n[0]): r_frac_x = np.float(i)/np.float(n[0]) r_test_x = r_frac_x * a[0] for j in range(n[1]): r_frac_y = np.float(j)/np.float(n[1]) r_test_y = r_frac_y * a[1] for k in range(n[2]): r_frac_z = np.float(k)/np.float(n[2]) r_test = r_test_x +r_test_y + r_frac_z * a[2] r_test_fast = reshape_vector(r_test) B = calculate_dipole(r_test_fast, r_i, mom_i) omega = gamma_mu*np.sqrt(np.dot(B,B)) # write r_test, B and omega to a file frac_done = np.float(i+1)/(n[0]+1) t_elapsed = (time.clock()-t_start) t_remain = (1-frac_done)*t_elapsed/frac_done print frac_done*100,'% done in',t_elapsed/60.,'minutes...approximately',t_remain/60.,'minutes remaining'

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