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  • Boolean checks with a single quadtree, or multiple quadtrees?

    - by Djentleman
    I'm currently developing a 2D sidescrolling shooter game for PC (think metroidvania but with a lot more happening at once). Using XNA. I'm utilising quadtrees for my spatial partitioning system. All objects will be encompassed by standard bounding geometry (box or sphere) with possible pixel-perfect collision detection implemented after geometry collision (depends on how optimised I can get it). These are my collision scenarios, with < representing object overlap (multiplayer co-op is the reason for the player<player scenario): Collision scenarios (true = collision occurs): Player <> Player = false Enemy <> Enemy = false Player <> Enemy = true PlayerBullet <> Enemy = true PlayerBullet <> Player = false PlayerBullet <> EnemyBullet = true PlayerBullet <> PlayerBullet = false EnemyBullet <> Player = true EnemyBullet <> Enemy = false EnemyBullet <> EnemyBullet = false Player <> Environment = true Enemy <> Environment = true PlayerBullet <> Environment = true EnemyBullet <> Environment = true Going off this information and the fact that were will likely be several hundred objects rendering on-screen at any given time, my question is as follows: Which method is likely to be the most efficient/optimised and why: Using a single quadtree with boolean checks for collision between the different types of objects. Using three quadtrees at once (player, enemy, environment), only testing the player and enemy trees against each other while testing both the player and enemy trees against the environment tree.

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  • algorithim for simple colision detection in Java

    - by Bob Twinkles
    I'm not very experienced with Java, just started a couple weeks ago, but I have a simple applet that has two user controlled balls, drawn through java.awt and I need a way to detect a collision with between them. I have an algorithm for detecting collision with the walls: while (true){ if (xPositon > (300 - radius)){ xSpeed = -xSpeed; } else if (xPositon < radius){ xSpeed = -xSpeed; } else if (yPositon > (300 - radius)) { ySpeed = -ySpeed; } else if (yPositon < radius){ ySpeed = -ySpeed; } xPositon += xSpeed; yPositon += ySpeed; and for the second ball if (xPositon2 > (300 - radius)){ xSpeed2 = -xSpeed2; } else if (xPositon2 < radius){ xSpeed2 = -xSpeed2; } else if (yPositon2 > (300 - radius)) { ySpeed2 = -ySpeed2; } else if (yPositon2 < radius){ ySpeed2 = -ySpeed2; } xPositon2 += xSpeed2; yPositon2 += ySpeed2; the applet is 300 pixels by 300 pixels radius stores the radius of the circles xPositon and xPositon2 store the x cordanents for the two balls yPositon and yPositon store the y cordanents for the two balls xSpeed and xSpeed2 store the x velocities for the two balls ySpeed and ySpeed2 store the y velocities for the two balls I've only taken algebra 1 so please no advanced math or physics.

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  • Sub Rectangle or ROI problem in opencv

    - by iva123
    Hi, I'm trying to convert this c code(http://nashruddin.com/OpenCV_Eye_Detection) to the python code, but in c style, he used cvROI thing, since ROI functions are not supported by python-opencv, I tried cvGetSubRect so Here is the eye detection part of the code : eye_region = cvGetSubRect(image,cvRect(face.x,int(face.y + (face.height/4)),face.width,int(face.height/2))) eyes = cvHaarDetectObjects(eye_region,eyeCascade,memo,1.15,3,0,cvSize(25,15)) for e in eyes: cvRectangle(image, cvPoint( int(e.x), int(e.y)), cvPoint(int(e.x + e.width), int(e.y + e.height)), CV_RGB(0, 255, 0), 1, 8, 0) return image; When I run this code, It draws rectangles irrelevant places. I thought, eye_region coordinates are wrong, and tried some coordinates, but it didn't work. Any idea ? Note :Face detection method works very well, and it's code is same with the eye detection method.

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  • Adaboost algorithm and its usage in face detection

    - by Hani
    I am trying to understand Adaboost algorithm but i have some troubles. After reading about Adaboost i realized that it is a classification algorithm(somehow like neural network). But i could not know how the weak classifiers are chosen (i think they are haar-like features for face detection) and how finally the H result which is the final strong classifier can be used. I mean if i found the alpha values and compute the H ,how am i going to benefit from it as a value (one or zero) for new images. Please is there an example describes it in a perfect way? i found the plus and minus example that is found in most adaboost tutorials but i did not know how exactly hi is chosen and how to adopt the same concept on face detection. I read many papers and i had many ideas but until now my ideas are not well arranged. Thanks....

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  • What is better: CSS hacks or browser detection?

    - by Darryl Hein
    Commonly when I look around the Internet, I find that people are generally using CSS hacks to make their website look the same in all browsers. Personally, I have found this to be quite time consuming to find all of these hacks and test them; each change you make you have to test in 4+ browsers to make sure it didn't break anything else. About a year ago, I looked around the Internet for what other major sites are using (Yahoo, Google, BBC, etc) and found that most of them are doing some form of browser detection (JS, HTML if statements, server based). I have started doing this as well. On almost all of the sites I have worked on recently, I use jQuery, so I use the built in browser detection. Is there a reason you use or don't use either of these?

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  • XNA - 3D AABB collision detection and response

    - by fastinvsqrt
    I've been fiddling around with 3D AABB collision in my voxel engine for the last couple of days, and every method I've come up with thus far has been almost correct, but each one never quite worked exactly the way I hoped it would. Currently what I do is get two bounding boxes for my entity, one modified by the X translation component and the other by the Z component, and check if each collides with any of the surrounding chunks (chunks have their own octrees that are populated only with blocks that support collision). If there is a collision, then I cast out rays into that chunk to get the shortest collision distance, and set the translation component to that distance if the component is greater than the distance. The problem is that sometimes collisions aren't even registered. Here's a video on YouTube that I created showing what I mean. I suspect the problem may be with the rays that I cast to get the collision distance not being where I think they are, but I'm not entirely sure what would be wrong with them if they are indeed the problem. Here is my code for collision detection and response in the X direction (the Z direction is basically the same): // create the XZ offset vector Vector3 offsXZ = new Vector3( ( _translation.X > 0.0f ) ? SizeX / 2.0f : ( _translation.X < 0.0f ) ? -SizeX / 2.0f : 0.0f, 0.0f, ( _translation.Z > 0.0f ) ? SizeZ / 2.0f : ( _translation.Z < 0.0f ) ? -SizeZ / 2.0f : 0.0f ); // X physics BoundingBox boxx = GetBounds( _translation.X, 0.0f, 0.0f ); if ( _translation.X > 0.0f ) { foreach ( Chunk chunk in surrounding ) { if ( chunk.Collides( boxx ) ) { float dist = GetShortestCollisionDistance( chunk, Vector3.Right, offsXZ ) - 0.0001f; if ( dist < _translation.X ) { _translation.X = dist; } } } } else if ( _translation.X < 0.0f ) { foreach ( Chunk chunk in surrounding ) { if ( chunk.Collides( boxx ) ) { float dist = GetShortestCollisionDistance( chunk, Vector3.Left, offsXZ ) - 0.0001f; if ( dist < -_translation.X ) { _translation.X = -dist; } } } } And here is my implementation for GetShortestCollisionDistance: private float GetShortestCollisionDistance( Chunk chunk, Vector3 rayDir, Vector3 offs ) { int startY = (int)( -SizeY / 2.0f ); int endY = (int)( SizeY / 2.0f ); int incY = (int)Cube.Size; float dist = Chunk.Size; for ( int y = startY; y <= endY; y += incY ) { // Position is the center of the entity's bounding box Ray ray = new Ray( new Vector3( Position.X + offs.X, Position.Y + offs.Y + y, Position.Z + offs.Z ), rayDir ); // Chunk.GetIntersections(Ray) returns Dictionary<Block, float?> foreach ( var pair in chunk.GetIntersections( ray ) ) { if ( pair.Value.HasValue && pair.Value.Value < dist ) { dist = pair.Value.Value; } } } return dist; } I realize some of this code can be consolidated to help with speed, but my main concern right now is to get this bit of physics programming to actually work.

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  • Surface Detection in 2d Game?

    - by GamiShini
    I'm working on a 2D Platform game, and I was wondering what's the best (performance-wise) way to implement Surface (Collision) Detection. So far I'm thinking of constructing a list of level objects constructed of a list of lines, and I draw tiles along the lines. ( http://img375.imageshack.us/img375/1704/lines.png ). I'm thinking every object holds the ID of the surface that he walks on, in order to easily manipulate his y position while walking up/downhill. Something like this: //Player/MovableObject class MoveLeft() { this.Position.Y = Helper.GetSurfaceById(this.SurfaceId).GetYWhenXIs(this.Position.X) } So the logic I use to detect "droping/walking on surface" is a simple point (player's lower legs)-touches-line (surface) check (with some safety approximation - let`s say 1-2 pixels over the line). Is this approach OK? I`ve been having difficulty trying to find reading material for this problem, so feel free to drop links/advice.

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  • C# XNA 2D Multiple boxes collision detection and movement

    - by zini
    Hi, I've been making simple game where you shoot boxes that are coming towards you. All game objects are simple rectangles. Now I have problem with collision detection; how to check where the collision comes so I can change the coordinates right? I have this kind of situation: http://imgur.com/8yjfW Imagine that all of those blocks are moving towards you (green box). If those orange boxes collide with each other, they should "avoid" themselves and not go through each other. I have class Enemy which has properties x, y and such. Now I'm doing the collision like this: // os.Count is an amount of other enemies colliding with this enemy if (os.Count == 0) { // If enemy doesn't collide with other enemy lasty = y; lastx = x; slope = (x - player.x) / (y - player.y); x += slope * l; // l is "movement speed" of enemy (float) if (y > player.y) { y = lasty; } else if (y < player.y) { y += l; } } else { foreach(Enemy b in os) { if (b.y > this.y) { // If some colliding enemy is closer player than this enemy, that closer one will be moved towards the player b.lasty = b.y; if (!BiggestY(os)) { // BiggestY returns true if this enemy has the biggest Y b.y += b.l; } b.x = b.lastx; } } } But this is very, very bad way to do this. I know it, but I just can't figure out other way. And as a matter in fact, this method doesn't even work pretty good; if multiple enemies are colliding same enemy they go through each other. I explained this pretty badly, but I hope that you understand this. And to sum up, as I said: How to check where the collision comes so I can change the coordinates right?

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  • Facial recognition/detection PHP or software for photo and video galleries

    - by Peter
    I have a very large photo gallery with thousands of similar people, objects, locations, things. The majority of the people in the photos have their own user accounts and avatar photos to match. There are also logical short lists of people potentially in the photo based on additional data available for each photo. I allow users to tag photos with their friends and people they know but an automated process would be better. I've used photo tagger/finder from face.com integrating with Facebook photos and the Google Picasa photo tagger for personal albums also does the same thing and is exactly what I'm looking to do. Is there a PHP script, API for Google Picasa, face.com or other recognition service or any other open source project that provides server-side facial recognition and/or grouping photos by similarity? Examples: As you can see, various photo sharing sites offer the feature, but are there any that provide an API for images stored on my own server or something extensive enough to link into my own gallery and tagging system? viewdle - Face recognition/Tagging for video PHP - Face detection in pure PHP Xarg OpenCV Face.com - app for finding and tagging photos in Facebook Google Picasa - photo sharing TeraSnaps - photo sharing site Google Portrait - photo grouping from Google Image results FaceOnIt - Video face recognition PittPatt - Detection, Recognition, Video Face Mining BetaFace ChaosFace - Real-time Face Detector

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  • Android - How to approach fall detection algorithm

    - by bobby123
    I want to be able to feature a fairly simple fall detection algorithm in my application. At the moment in onSensorChanged(), I am getting the absolute value of the current x,x,z values and subtracting SensorManager.GRAVITY_EARTH (9.8 m/s) from this. The resulting value has to be bigger than a threshold value 10 times in a row to set a flag saying a fall has been detected by the accelerometer, the threshold value is about 8m/s. Also I'm comparing the orientation of the phone as soon as the threshold has been passed and the orienation of it when the threshold is no longer being passed, this sets another flag saying the orientation sensor has detected a fall. When both flags are set, an event occurs to check is user ok, etc etc. My problem is with the threshold, when the phone is held straight up the absolute value of accelerometer is about 9.8 m/s, but when i hold it still at an angle it can be over 15m/s. This is causing other events to trigger the fall detection, and if i increase the threshold to avoid that, it won't detect falls. Can anyone give me some advice here with what possible values i should use or how to even improve my method? Many thanks.

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  • eclipse 3.4 (ganymede) package collision with type

    - by Monis Iqbal
    We have a package that ends with exception e.g. package a.b.c.exception; Our code base had no issues up till eclipse 3.3, however when we shifted to eclipse 3.4, it started giving errors related to this package: "The package a.b.c.exception collides with a type" When I refactor the package name to a.b.c.exceptions, there are no issues. Is this due to a bug in eclipse 3.4 or is there some setting to rectify this behavior?

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  • Collision detection, alternatives to "push out"

    - by LaZe
    I'm moving a character (ellipsoid) around in my physics engine. The movement must be constrained by the static geometry, but should slide on the edges, so it won't be stuck. My current approach is to move it a little and then push it back out of the geometry. It seems to work, but I think it's mostly because of luck. I fear there must be some corner cases where this method will go haywire. For example a sharp corner where two walls keeps pushing the character into each other. How would a "state of the art" game engine solve this?

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  • Collision of dot and line in 2D space

    - by Anderiel
    So i'm trying to make my first game on android. The thing is i have a small moving ball and i want it to bounce from a line that i drew. For that i need to find if the x,y of the ball are also coordinates of one dot from the line. I tried to implement these equations about lines x=a1 + t*u1 y=a2 + t*u2 = (x-a1)/u1=(y-a2)/u2 (t=t which has to be if the point is on the line) where x and y are the coordinates im testing, dot[a1,a2] is a dot that is on the line and u(u1,u2) is the vector of the line. heres the code: public boolean Collided() { float u1 =Math.abs(Math.round(begin_X)-Math.round(end_X)); float u2 =Math.abs(Math.round(begin_Y)-Math.round(end_Y)); float t_x =Math.round((elect_X - begin_X)/u1); float t_y =Math.round((elect_Y - begin_Y)/u2); if(t_x==t_y) { return true; } else { return false; } } points [begin_X,end_X] and [begin_Y,end_Y] are the two points from the line and [elect_X,elect_Y] are the coordinates of the ball theoreticaly it should work, but in the reality the ball most of the time just goes straigth through the line or bounces somewhere else where it shouldnt

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  • Opinions on platform game actor/background collision resolving

    - by Kawa
    Imagine the following scenario: I have a level whose physical structure is built up from a collection of bounding rectangles, combined with prerendered bitmap backgrounds. My actors, including the player character, all have their own bounding rectangle. If an actor manages to get stuck inside a level block, partially or otherwise, it'll need to be shifted out again, so that it is flush against the block. The untested technique I thought up during bio break is as follows: If an actor's box is found to intersect a level box, determine where the centerpoints of each rect are. If the actor's center is higher than the level box's, move the actor so that the bottom of the actor's rect is flush with the top of the level's rect, and vice versa if it's lower. Then do a similar thing horizontally. Opinions on that? Suggestions on better methods? Actually, the bounding rects are XNA BoundingBlocks with their Z spanning from -1 to 1, but it's still 2D gameplay.

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  • Collision detection problems...

    - by thyrgle
    Hi, I have written the following: -(void) checkIfLineCollidesWithAll { float slope = ((160-L1Circle1.position.y)-(160-L1Circle2.position.y))/((240-L1Circle1.position.x)-(240-L1Circle2.position.x)); float b = (160-L1Circle1.position.y) - slope * (240-L1Circle1.position.x); if ((240-L1Sensor1.position.x) < (240-L1Circle1.position.x) && (240-L1Sensor1.position.x) < (240-L1Circle2.position.x) || ((240-L1Sensor1.position.x) > (240-L1Circle1.position.x) && (240-L1Sensor1.position.x) > (240-L1Circle2.position.x))) { [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorOk.png"]]; } else if (slope == INFINITY || slope == -INFINITY) { if (L1Circle1.position.y + 16 >= L1Sensor1.position.y || L1Circle1.position.y - 16 <= L1Sensor1.position.y) { [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorBad.png"]]; } else { [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorOk.png"]]; } } else if (160-L1Sensor1.position.y + 12 >= slope*(240-L1Sensor1.position.x) + b && 160-L1Sensor1.position.y - 12 <= slope*(240-L1Sensor1.position.x) + b) { [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorBad.png"]]; } else { [L1Sensor1 setTexture:[[CCTextureCache sharedTextureCache] addImage:@"SensorOk.png"]]; } } Basically what this does is finds m and b in the well known equation: y = mx + b and then substitutes coordinates of the L1Sensor1 (the circle I'm trying to detect if it it intersects with the line segment) to see if y = mx + b hold true. But, there are two problems, first, when slope approaches infinity the range of what the L1Sensor1 should "react" to (it "reacts" by changing its image) becomes smaller. Also, the code that should handle infinity is not working. Thanks for the help in advanced.

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  • Collision Detection for arbitrarily sized, positioned and rotated rectangles in XNA

    - by Stefan
    I'm working with xna in C# and in my game I will have a variety of space ships flying all over the place. They will each have an arbitrary rotation, size and position in space and I need a method to determine when they collide. Ideally the method would take two Rectangles, two doubles and two Vector2s for size, rotation and position respectively and return a boolean that indicates whether they have intersected or not.

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  • Square collision detection problem (iPhone).

    - by thyrgle
    Hi, I know I've probably posted three questions related to this then deleted them, but thats only because I solved them before I got an answer. But, this one I can not solve and I don't believe it is that hard compared to the others. So, with out further ado, here is my problem: So I am using Cocos2d and one of the major problem is they don't have buttons. To compensate for there lack in buttons I am trying to detect if when a touch ended did it collide with a square (the button). Here is my code: - (void)ccTouchesEnded:(NSSet*)touches withEvent:(UIEvent*)event { UITouch *touch = [touches anyObject]; CGPoint location = [touch locationInView:touch.view]; NSLog(@"%f", 240-location.y); if (isReady == YES) { if (((240-location.y) <= (240-StartButton.position.x - 100) || -(240-location.y) >= (240-StartButton.position.x) + 100) && ((160-location.x) <= (160-StartButton.position.y) - 25 || (160-location.x) >= (160-StartButton.position.y) + 25)) { NSLog(@"Coll:%f", 240-StartButton.position.x); CCScene *scene = [PlayScene node]; [[CCDirector sharedDirector] replaceScene:[CCZoomFlipAngularTransition transitionWithDuration:2.0f scene:scene orientation:kOrientationRightOver]]; } } } Do you know what I am doing wrong?

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  • The how of a collision engine

    - by JXPheonix
    This is a very, very broad question - what is the general algorithm of how a collision engine works? No code in specific, but rather, just a general idea of how a collision engine does what it does, constantly refreshing the points of an object and comparing it to other objects? (see, I have the general gist of it here.) A collision engine is basically an engine used in games (generally) so that your player (call him Bob), whenever bob moves into a wall, Bob stops, Bob does not walk through the wall. They also generally handle the gravity in a game and environmental things like that.

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  • The how of a collision engine

    - by JXPheonix
    This is a very, very broad question - what is the general algorithm of how a collision engine works? No code in specific, but rather, just a general idea of how a collision engine does what it does, constantly refreshing the points of an object and comparing it to other objects? (see, I have the general gist of it here.) A collision engine is basically an engine used in games (generally) so that your player (call him Bob), whenever bob moves into a wall, Bob stops, Bob does not walk through the wall. They also generally handle the gravity in a game and environmental things like that.

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  • Motion detection in compressed domain (JPEG/Mpeg4/H264)

    - by paft
    everyone! I process video from IP cameras and have wrote a motion detection algorithm based on decompressed video analysis. But i really something more fast. I've found several papers about compressed domain analysis but have failed to find any implementations. Can anyone recommend me some code? found materials: http://www.ist-live.org/intranet/school-of-informatics-university-of-bradford001-7/41410206.pdf/view http://doc.rero.ch/lm.php?url=1000,43,4,20061128120121-NA/Bracamonte_Javier_-_A_Low_Complexity_Change_Detection_Algorithm_20061128.pdf

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