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• Meaning of offset in pygame Mask.overlap methods

  - by Alan

  I have a situation in which two rectangles collide, and I have to detect how much did they collide so so I can redraw the objects in a way that they are only touching each others edges. It's a situation in which a moving ball should hit a completely unmovable wall and instantly stop moving. Since the ball sometimes moves multiple pixels per screen refresh, it it possible that it enters the wall with more that half its surface when the collision is detected, in which case i want to shift it position back to the point where it only touches the edges of the wall. Here is the conceptual image it: I decided to implement this with masks, and thought that i could supply the masks of both objects (wall and ball) and get the surface (as a square) of their intersection. However, there is also the offset parameter which i don't understand. Here are the docs for the method: Mask.overlap Returns the point of intersection if the masks overlap with the given offset - or None if it does not overlap. Mask.overlap(othermask, offset) -> x,y The overlap tests uses the following offsets (which may be negative): +----+----------.. |A | yoffset | +-+----------.. +--|B |xoffset | | : :

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• Java 2D Rectangle Collision? [on hold]

  - by Andreas Elia

  I am just wanting to know of another (longer OR shorter) way of getting 100% effective collisions on a 2D plat-former. The current collision system that is in place works from coords on the level and does not always work reliably. Thank you in advance for any help/support. The current system draws a rectangle and is checking to see if any two points collide. From testing, the system can sometimes "glitch" and allow the player to collide into walls etc. Player Class http://pastebin.com/2zE8vz8R Main Class http://pastebin.com/A6Utb3ti

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• Setting up collision using a tilemap and cocos2d

  - by James

  I'm building my first platformer using cocos2d and a tilemap. I'm having trouble coming up with a decent way of determining if the character is colliding with an object. More specifically, in which direction is the character colliding with an object. Following the tutorial here, I have made a separate "meta" layer of collidable tiles. The problem is that unless the character is in the tile, you can't detect the collision. Also, there's no way of telling WHERE the collision is occurring. The best solution would be one that could tell me if a character is up against a wall, or walking on top of a platform. However, I can't seem to figure out a good technique for this.

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• How to fetch only the sprites in the player's range of motion for collision testing? (2D, axis aligned sprites)

  - by Twodordan

  I am working on a 2D sprite game for educational purposes. (In case you want to know, it uses WebGl and Javascript) I've implemented movement using the Euler method (and delta time) to keep things simple. Now I'm trying to tackle collisions. The way I wrote things, my game only has rectangular sprites (axis aligned, never rotated) of various/variable sizes. So I need to figure out what I hit and which side of the target sprite I hit (and I'm probably going to use these intersection tests). The old fashioned method seems to be to use tile based grids, to target only a few tiles at a time, but that sounds silly and impractical for my game. (Splitting the whole level into blocks, having each sprite's bounding box fit multiple blocks I might abide. But if the sprites change size and move around, you have to keep changing which tiles they belong to, every frame, it doesn't sound right.) In Flash you can test collision under one point, but it's not efficient to iterate through all the elements on stage each frame. (hence why people use the tile method). Bottom line is, I'm trying to figure out how to test only the elements within the player's range of motion. (I know how to get the range of motion, I have a good idea of how to write a collisionCheck(playerSprite, targetSprite) function. But how do I know which sprites are currently in the player's vicinity to fetch only them?) Please discuss. Cheers!

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• Turning on collision crashes game

  - by MomentumGaming

  I am getting a null pointer excecption to both my sprite and level. I am working on my mob class, and when I try to move him and the move function is called, the game crashes after checking collision with a null pointer excecption. Taking out the one line that actually checks if the tile located in front of it fixes the problem. Also, if i keep collision ON but don't move the position of the mob (the spider) the game works fine. I will have collision, and the spider appears on the screen, only problem is, getting it to move causes this nasty error that i just can't fix. true Exception in thread "Display" java.lang.NullPointerException at com.apcompsci.game.entity.mob.Mob.collision(Mob.java:67) at com.apcompsci.game.entity.mob.Mob.move(Mob.java:38) at com.apcompsci.game.entity.mob.spider.update(spider.java:58) at com.apcompsci.game.level.Level.update(Level.java:55) at com.apcompsci.game.Game.update(Game.java:128) at com.apcompsci.game.Game.run(Game.java:106) at java.lang.Thread.run(Unknown Source) Here is my renderMob mehtod: public void renderMob(int xp,int yp,Sprite sprite,int flip) { xp -= xOffset; yp-=yOffset; for(int y = 0; y<32; y++) { int ya = y + yp; int ys = y; if(flip == 2||flip == 3)ys = 31-y; for(int x = 0; x<32; x++) { int xa = x + xp; int xs = x; if(flip == 1||flip == 3)xs = 31-x; if(xa < -32 || xa >=width || ya<0||ya>=height) break; if(xa<0) xa =0; int col = sprite.pixels[xs+ys*32]; if(col!= 0x000000) pixels[xa+ya*width] = col; } } } My spider class which determines the sprite and where I control movement, also rendering the spider onto the screen, when I increment ya to move the sprite, I get the crash, but without ya++, it runs flawlessly with a spider sprite on screen: package com.apcompsci.game.entity.mob; import com.apcompsci.game.entity.mob.Mob.Direction; import com.apcompsci.game.graphics.Screen; import com.apcompsci.game.graphics.Sprite; import com.apcompsci.game.level.Level; public class spider extends Mob{ Direction dir; private Sprite sprite; private boolean walking; public spider(int x, int y) { this.x = x <<4; this.y = y <<4; sprite = sprite.spider_forward; } public void update() { int xa = 0, ya = 0; ya++; if(ya<0) { sprite = sprite.spider_forward; dir = Direction.UP; } if(ya>0) { sprite = sprite.spider_back; dir = Direction.DOWN; } if(xa<0) { sprite = sprite.spider_side; dir = Direction.LEFT; } if(xa>0) { sprite = sprite.spider_side; dir = Direction.LEFT; } if(xa!= 0 || ya!= 0) { System.out.println("true"); move(xa,ya); walking = true; } else{ walking = false; } } public void render(Screen screen) { screen.renderMob(x, y, sprite, 0); } } This is th mob class that contains the move() method that is called in the spider class above. This move method calls the collision method. tile and sprite comes up null in the debugger: package com.apcompsci.game.entity.mob; import java.util.ArrayList; import java.util.List; import com.apcompsci.game.entity.Entity; import com.apcompsci.game.entity.projectile.DemiGodProjectile; import com.apcompsci.game.entity.projectile.Projectile; import com.apcompsci.game.graphics.Sprite; public class Mob extends Entity{ protected Sprite sprite; protected boolean moving = false; protected enum Direction { UP,DOWN,LEFT,RIGHT } protected Direction dir; public void move(int xa,int ya) { if(xa != 0 && ya != 0) { move(xa,0); move(0,ya); return; } if(xa>0) dir = Direction.RIGHT; if(xa<0) dir = Direction.LEFT; if(ya>0)dir = Direction.DOWN; if(ya<0)dir = Direction.UP; if(!collision(xa,ya)){ x+= xa; y+=ya; } } public void update() { } public void shoot(int x, int y, double dir) { //dir = Math.toDegrees(dir); Projectile p = new DemiGodProjectile(x, y,dir); level.addProjectile(p); } public boolean collision(int xa,int ya) { boolean solid = false; for(int c = 0; c<4; c++) { int xt = ((x+xa) + c % 2 * 14 - 8 )/16; int yt = ((y+ya) + c / 2 * 12 +3 )/16; if(level.getTile(xt, yt).solid()) solid = true; } return solid; } public void render() { } } Finally, here is the method in which i call the add() method for the spider to add it to the level: protected void loadLevel(String path) { try{ BufferedImage image = ImageIO.read(SpawnLevel.class.getResource(path)); int w = width =image.getWidth(); int h = height = image.getHeight(); tiles = new int[w*h]; image.getRGB(0, 0, w,h, tiles,0, w); } catch(IOException e){ e.printStackTrace(); System.out.println("Exception! Could not load level file!"); } add(new spider(20,45)); } I don't think i need to include the level class but just in case, I have provided a gistHub link for better context. It contains all of the full classes listed above , plus my entity class and maybe another. Thanks for the help if you decide to do so, much appreciated! Also, please tell me if i'm in the wrong section of stackeoverflow, i figured that since this is the gamign section that it belonged but debugging code normally goes into the general section.

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• Camera Collision inside the room model

  - by sanddy

  I am having a problem in Calculating the camera collision for my Room model which consists of sofa, tables and other models. The users shall be moving the camera front, back, rotating so i need to make sure that the camera does not collide with any of the models with in the room. I have treated all my models inside the room by BoundingBox[] and the camera by BoundingSphere. So, far i have implemented collision by looking into the tutorial from http://www.toymaker.info/Games/XNA/html/xna_model_collisions.html which was great. But, I guess the problem lies in the Transformation part. I debugged and found some points to be at Vector(-XXX,-XXX,-XXX) where X is digit. Also i found my radius of some models where too large(in thousand, i just looked into its radius value before converting to BoundingBox). Do I need to scale the model for collision??? Below are my code:- On My LoadContent(): Matrix[] transforms = new Matrix[myModel.Bones.Count]; myModel.CopyAbsoluteBoneTransformsTo(transforms); int index = 0; box = new List<BoundingBox>(); BoundingBox worldModel = Utility.CalculateBoundingBox(myModel); foreach (ModelMesh mesh in myModel.Meshes) { Vector3[] obb = new Vector3[8]; worldModel.GetCorners(obb); Vector3[] asdf = (Vector3[])obb.Clone(); Vector3.Transform(obb, ref transforms[mesh.ParentBone.Index], obb); BoundingBox worldBox = BoundingBox.CreateFromPoints(obb); box.Add(worldBox); index++; } On CameraPosition Update: BoundingSphere bs = new BoundingSphere(this.cameraPos, 5.0f); if (RoomWalkthrough.Utility.CheckCollision(bs, bb)) { // Do Something } Please Help.

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• Updating physics for animated models

  - by Mathias Hölzl

  For a new game we have do set up a scene with a minimum of 30 bone animated models.(shooter) The problem is that the update process for the animated models takes too long. Thats what I do: Each character has ~30 bones and for every update tick the animation gets calculated and every bone fires a event with the new matrix. The physics receives the event with the new matrix and updates the collision shape for that bone. The time that it takes to build the animation isn't that bad (0.2ms for 30 Bones - 6ms for 30 models). But the main problem is that the physic engine (Bullet) uses a diffrent matrix for transformation and so its necessary to convert it. Code for matrix conversion: (~0.005ms) btTransform CLEAR_PHYSICS_API Mat_to_btTransform( Mat mat ) { btMatrix3x3 bulletRotation; btVector3 bulletPosition; XMFLOAT4X4 matData = mat.GetStorage(); // copy rotation matrix for ( int row=0; row<3; ++row ) for ( int column=0; column<3; ++column ) bulletRotation[row][column] = matData.m[column][row]; for ( int column=0; column<3; ++column ) bulletPosition[column] = matData.m[3][column]; return btTransform( bulletRotation, bulletPosition ); } The function for updating the transform(Physic): void CLEAR_PHYSICS_API BulletPhysics::VKinematicMove(Mat mat, ActorId aid) { if ( btRigidBody * const body = FindActorBody( aid ) ) { btTransform tmp = Mat_to_btTransform( mat ); body->setWorldTransform( tmp ); } } The real problem is the function FindActorBody(id): ActorIDToBulletActorMap::const_iterator found = m_actorBodies.find( id ); if ( found != m_actorBodies.end() ) return found->second; All physic actors are stored in m_actorBodies and thats why the updating process takes to long. But I have no idea how I could avoid this. Friendly greedings, Mathias

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• Collision resolution - Character walking on ascendent ground

  - by marcg11

  I don't know if the solution to this problem is quite straight-foward but I really don't know how to handle collision resolution on a game where the player walks on an ascendent floor which is not flat. How can the player position itself on the y axis depend on the ground x and z (opengl coords)? What if the floor's slope is too much and the player can't go up, how do you handle that? I don't need any code, just a simple explanation would be great.

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• 2D Collision masks for handling slopes

  - by JiminyCricket

  I've been looking at the example at: http://create.msdn.com/en-US/education/catalog/tutorial/collision_2d_perpixel and am trying to figure out how to adjust the sprite once a collision has been detected. As David suggested at XNA 4.0 2D sidescroller variable terrain heightmap for walking/collision, I made a few sensor points (feet, sides, bottom center, etc.) and can easily detect when these points actually collide with non-transparent portions of a second texture (simple slope). I'm having trouble with the algorithm of how I would actually adjust the sprite position based on a collision. Say I detect a collision with the slope at the sprite's right foot. How can I scan the slope texture data to find the Y position to place the sprite's foot so it is no longer inside the slope? The way it is stored as a 1D array in the example is a bit confusing, should I try to store the data as a 2D array instead? For test purposes, I'm thinking of just using the slope texture alpha itself as a primitive and easy collision mask (no grass bits or anything besides a simple non-linear slope). Then, as in the example, I find the coordinates of any collisions between the slope texture and the sprite's sensors and mark these special sensor collisions as having occurred. Finally, in the case of moving up a slope, I would scan for the first transparent pixel above (in the texture's Ys at that X) the right foot collision point and set that as the new height of the sprite. I'm a little unclear also on when I should make these adjustments. Collisions are checked on every game.update() so would I quickly change the position of the sprite before the next update is called? I also noticed several people mention that it's best to separate collision checks horizontally and vertically, why is that exactly? Open to any suggestions if this is an inefficient or inaccurate way of handling this. I wish MSDN had provided an example of something like this, I didn't know it would be so much more complex than NES Mario style pure box platforming!

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• How can I convert a 2D bitmap (Used for terrain) to a 2D polygon mesh for collision?

  - by Megadanxzero

  So I'm making an artillery type game, sort of similar to Worms with all the usual stuff like destructible terrain etc... and while I could use per-pixel collision that doesn't give me collision normals or anything like that. Converting it all to a mesh would also mean I could use an existing physics library, which would be better than anything I can make by myself. I've seen people mention doing this by using Marching Squares to get contours in the bitmap, but I can't find anything which mentions how to turn these into a mesh (Unless it refers to a 3D mesh with contour lines defining different heights, which is NOT what I want). At the moment I can get a basic Marching Squares contour which looks something like this (Where the grid-like lines in the background would be the Marching Squares 'cells'): That needs to be interpolated to get a smoother, more accurate result but that's the general idea. I had a couple ideas for how to turn this into a mesh, but many of them wouldn't work in certain cases, and the one which I thought would work perfectly has turned out to be very slow and I've not even finished it yet! Ideally I'd like whatever I end up using to be fast enough to do every frame for cases such as rapidly-firing weapons, or digging tools. I'm thinking there must be some kind of existing algorithm/technique for turning something like this into a mesh, but I can't seem to find anything. I've looked at some things like Delaunay Triangulation, but as far as I can tell that won't correctly handle concave shapes like the above example, and also wouldn't account for holes within the terrain. I'll go through the technique I came up with for comparison and I guess I'll see if anyone has a better idea. First of all interpolate the Marching Squares contour lines, creating vertices from the line ends, and getting vertices where lines cross cell edges (Important). Then, for each cell containing vertices create polygons by using 2 vertices, and a cell corner as the 3rd vertex (Probably the closest corner). Do this for each cell and I think you should have a mesh which accurately represents the original bitmap (Though there will only be polygons at the edges of the bitmap, and large filled in areas in between will be empty). The only problem with this is that it involves lopping through every pixel once for the initial Marching Squares, then looping through every cell (image height + 1 x image width + 1) at least twice, which ends up being really slow for any decently sized image...

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• Is '@' Error Suppression a Valid Technique for Testing for an Optional Array Key?

  - by MikeSchinkel

  Rarst and I were debating offline about the use of the '@' error suppression operator in PHP, specifically for use to test for existence of "optional" array keys, i.e. array keys that are being used as a switch here a their lack of existence in the array is functionally equivalent to the array having the key with a value equaling false. Here is pseudo-code for this scenario: function do_something( $args = array() ) { if ( @$args['switch'] ) { // Do something with this switch } // continue on... } vs. this approach: function do_something( $args = array() ) { if ( ! empty( $args['switch'] ) && $args['switch'] ) { // Do something with this switch } // continue on... } Of course in most use-cases, suppressing errors would not be A Good Thing(tm). However in this use-case where an array is passed with an optional element, it seems to me that it is actually a very good technique but I could be wrong and would like to hear other's opinions on the subject before I make up my mind. I do know that there are alleged performance hits for using the former approach but I'd like to know how they compare with the alternative and if they performance hits really matter in real world scenarios? P.S. I decided to post this because, after debating this offline with Rarst, he asked a more general question here on Programmers but didn't actually give a detailed example of the specific use-case we were debating. And since I'm pretty sure he'll want to use the out-of-context answers on that other question as justification for why the above is "bad" I decided I needed to get opinions on this specific use-case.

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• 2D object-aligned bounding-box intersection test

  - by AshleysBrain

  Hi all, I have two object-aligned bounding boxes (i.e. not axis aligned, they rotate with the object). I'd like to know if two object-aligned boxes overlap. (Edit: note - I'm using an axis-aligned bounding box test to quickly discard distant objects, so it doesn't matter if the quad routine is a little slower.) My boxes are stored as four x,y points. I've searched around for answers, but I can't make sense of the variable names and algorithms in examples to apply them to my particular case. Can someone help show me how this would be done, in a clear and simple way? Thanks. (The particular language isn't important, C-style pseudo code is OK.)

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• Physics System ignores collision in some rare cases

  - by Gajoo

  I've been developing a simple physics engine for my game. since the game physics is very simple I've decided to increase accuracy a little bit. Instead of formal integration methods like fourier or RK4, I'm directly computing the results after delta time "dt". based on the very first laws of physics : dx = 0.5 * a * dt^2 + v0 * dt dv = a * dt where a is acceleration and v0 is object's previous velocity. Also to handle collisions I've used a method which is somehow different from those I've seen so far. I'm detecting all the collision in the given time frame, stepping the world forward to the nearest collision, resolving it and again check for possible collisions. As I said the world consist of very simple objects, so I'm not loosing any performance due to multiple collision checking. First I'm checking if the ball collides with any walls around it (which is working perfectly) and then I'm checking if it collides with the edges of the walls (yellow points in the picture). the algorithm seems to work without any problem except some rare cases, in which the collision with points are ignored. I've tested everything and all the variables seem to be what they should but after leaving the system work for a minute or two the system the ball passes through one of those points. Here is collision portion of my code, hopefully one of you guys can give me a hint where to look for a potential bug! void PhysicalWorld::checkForPointCollision(Vec2 acceleration, PhysicsComponent& ball, Vec2& collisionNormal, float& collisionTime, Vec2 target) { // this function checks if there will be any collision between a circle and a point // ball contains informations about the circle (it's current velocity, position and radius) // collisionNormal is an output variable // collisionTime is also an output varialbe // target is the point I want to check for collisions Vec2 V = ball.mVelocity; Vec2 A = acceleration; Vec2 P = ball.mPosition - target; float wallWidth = mMap->getWallWidth() / (mMap->getWallWidth() + mMap->getHallWidth()) / 2; float r = ball.mRadius / (mMap->getWallWidth() + mMap->getHallWidth()); // r is ball radius scaled to match actual rendered object. if (A.any()) // todo : I need to first correctly solve the collisions in case there is no acceleration return; if (V.any()) // if object is not moving there will be no collisions! { float D = P.x * V.y - P.y * V.x; float Delta = r*r*V.length2() - D*D; if(Delta < eps) return; Delta = sqrt(Delta); float sgnvy = V.y > 0 ? 1: (V.y < 0?-1:0); Vec2 c1(( D*V.y+sgnvy*V.x*Delta) / V.length2(), (-D*V.x+fabs(V.y)*Delta) / V.length2()); Vec2 c2(( D*V.y-sgnvy*V.x*Delta) / V.length2(), (-D*V.x-fabs(V.y)*Delta) / V.length2()); float t1 = (c1.x - P.x) / V.x; float t2 = (c2.x - P.x) / V.x; if(t1 > eps && t1 <= collisionTime) { collisionTime = t1; collisionNormal = c1; } if(t2 > eps && t2 <= collisionTime) { collisionTime = t2; collisionNormal = c2; } } } // this function should step the world forward by dt. it doesn't check for collision of any two balls (components) // it just checks if there is a collision between the current component and 4 points forming a rectangle around it. void PhysicalWorld::step(float dt) { for (unsigned i=0;i<mObjects.size();i++) { PhysicsComponent &current = *mObjects[i]; Vec2 acceleration = current.mForces * current.mInvMass; float rt=dt; // stores how much more the world should advance while(rt > eps) { float collisionTime = rt; Vec2 collisionNormal = Vec2(0,0); float halfWallWidth = mMap->getWallWidth() / (mMap->getWallWidth() + mMap->getHallWidth()) / 2; // we check if there is any collision with any of those 4 points around the ball // if there is a collision both collisionNormal and collisionTime variables will change // after these functions collisionTime will be exactly the value of nearest collision (if any) // and if there was, collisionNormal will report in which direction the ball should return. checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2(floor(current.mPosition.x) + halfWallWidth,floor(current.mPosition.y) + halfWallWidth)); checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2(floor(current.mPosition.x) + halfWallWidth, ceil(current.mPosition.y) - halfWallWidth)); checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2( ceil(current.mPosition.x) - halfWallWidth,floor(current.mPosition.y) + halfWallWidth)); checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2( ceil(current.mPosition.x) - halfWallWidth, ceil(current.mPosition.y) - halfWallWidth)); // either if there is a collision or if there is not we step the forward since we are sure there will be no collision before collisionTime current.mPosition += collisionTime * (collisionTime * acceleration * 0.5 + current.mVelocity); current.mVelocity += collisionTime * acceleration; // if the ball collided with anything collisionNormal should be at least none zero in one of it's axis if (collisionNormal.any()) { collisionNormal *= Dot(collisionNormal, current.mVelocity) / collisionNormal.length2(); current.mVelocity -= 2 * collisionNormal; // simply reverse velocity along collision normal direction } rt -= collisionTime; } // reset all forces for current object so it'll be ready for later game event current.mForces.zero(); } }

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• How can I test if my rotated rectangle intersects a corner?

  - by Raven Dreamer

  I have a square, tile-based collision map. To check if one of my (square) entities is colliding, I get the vertices of the 4 corners, and test those 4 points against my collision map. If none of those points are intersecting, I know I'm good to move to the new position. I'd like to allow entities to rotate. I can still calculate the 4 corners of the square, but once you factor in rotation, those 4 corners alone don't seem to be enough information to determine if the entity is trying to move to a valid state. For example: In the picture below, black is unwalkable terrain, and red is the player's hitbox. The left scenario is allowed because the 4 corners of the red square are not in the black terrain. The right scenario would also be (incorrectly) allowed, because the player, cleverly turned at a 45* angle, has its corners in valid spaces, even if it is (quite literally) cutting the corner. How can I detect scenarios similar to the situation on the right?

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• How can I perform 2D side-scroller collision checks in a tile-based map?

  - by bill

  I am trying to create a game where you have a player that can move horizontally and jump. It's kind of like Mario but it isn't a side scroller. I'm using a 2D array to implement a tile map. My problem is that I don't understand how to check for collisions using this implementation. After spending about two weeks thinking about it, I've got two possible solutions, but both of them have some problems. Let's say that my map is defined by the following tiles: 0 = sky 1 = player 2 = ground The data for the map itself might look like: 00000 10002 22022 For solution 1, I'd move the player (the 1) a complete tile and update the map directly. This make the collision easy because you can check if the player is touching the ground simply by looking at the tile directly below the player: // x and y are the tile coordinates of the player. The tile origin is the upper-left. if (grid[x][y+1] == 2){ // The player is standing on top of a ground tile. } The problem with this approach is that the player moves in discrete tile steps, so the animation isn't smooth. For solution 2, I thought about moving the player via pixel coordinates and not updating the tile map. This will make the animation much smoother because I have a smaller movement unit per frame. However, this means I can't really accurately store the player in the tile map because sometimes he would logically be between two tiles. But the bigger problem here is that I think the only way to check for collision is to use Java's intersection method, which means the player would need to be at least a single pixel "into" the ground to register collision, and that won't look good. How can I solve this problem?

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• Tile map collision is not working properly

  - by Sigh-AniDe

  I am having problems setting collision between my sprite and the tiles. I have only done the code for colision for moving upwards but some places on the map it moves up and some places it doesn't. Here is what I have so far: Vector2 position; private static float scalingFactor = 32; static int tileWidth = 32; static int tileHeight = 32; int[ , ] map = { {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, {0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, }, }; // This is in turtle.update if ( keyboardState.IsKeyDown( Keys.Up ) ) { if ( position.Y > screenHeight / 4 ) { //// current position of the turtle on the tiles int mapX = ( int )( position.X / scalingFactor ); int mapY = ( int )( position.Y / scalingFactor ) - 1; if ( isMovable( mapX , mapY , map ) ) { position.Y = position.Y - scalingFactor; } } else { MoveUp(); } } private void MoveUp() { motion.Y = -1; } public bool isMovable( int mapX , int mapY , int[ , ] map ) { if ( mapX < 0 || mapX > 19 || mapY < 0 || mapY > 20 ) { return false; } int tile = map[ mapX , mapY ]; if ( tile == 0 ) { return false; } return true; } protected override void Update( GameTime gameTime ) { turtle.Update( screenHeight , scalingFactor , map ); base.Update( gameTime ); }

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• Platformer Starter Kit - Collision Issues

  - by Cyral

  I'm having trouble with my game that is based off the XNA Platformer starter kit. My game uses smaller tiles (16x16) then the original (32x40) which I'm thinking may be having an effect on collision (Being it needs to be more precise). Standing on the edge of a tile and jumping causes the player to move off the the tile when he lands. And 80% of the time, when the player lands, he goes flying though SOLID tiles in a diagonal fashion. This is very annoying as it is almost impossible to test other features, when spawning and jumping will result in the player landing in another part of the level or falling off the edge completely. The code is as follows: /// <summary> /// Updates the player's velocity and position based on input, gravity, etc. /// </summary> public void ApplyPhysics(GameTime gameTime) { float elapsed = (float)gameTime.ElapsedGameTime.TotalSeconds; Vector2 previousPosition = Position; // Base velocity is a combination of horizontal movement control and // acceleration downward due to gravity. velocity.X += movement * MoveAcceleration * elapsed; velocity.Y = MathHelper.Clamp(velocity.Y + GravityAcceleration * elapsed, -MaxFallSpeed, MaxFallSpeed); velocity.Y = DoJump(velocity.Y, gameTime); // Apply pseudo-drag horizontally. if (IsOnGround) velocity.X *= GroundDragFactor; else velocity.X *= AirDragFactor; // Prevent the player from running faster than his top speed. velocity.X = MathHelper.Clamp(velocity.X, -MaxMoveSpeed, MaxMoveSpeed); // Apply velocity. Position += velocity * elapsed; Position = new Vector2((float)Math.Round(Position.X), (float)Math.Round(Position.Y)); // If the player is now colliding with the level, separate them. HandleCollisions(); // If the collision stopped us from moving, reset the velocity to zero. if (Position.X == previousPosition.X) velocity.X = 0; if (Position.Y == previousPosition.Y) velocity.Y = 0; } /// <summary> /// Detects and resolves all collisions between the player and his neighboring /// tiles. When a collision is detected, the player is pushed away along one /// axis to prevent overlapping. There is some special logic for the Y axis to /// handle platforms which behave differently depending on direction of movement. /// </summary> private void HandleCollisions() { // Get the player's bounding rectangle and find neighboring tiles. Rectangle bounds = BoundingRectangle; int leftTile = (int)Math.Floor((float)bounds.Left / Tile.Width); int rightTile = (int)Math.Ceiling(((float)bounds.Right / Tile.Width)) - 1; int topTile = (int)Math.Floor((float)bounds.Top / Tile.Height); int bottomTile = (int)Math.Ceiling(((float)bounds.Bottom / Tile.Height)) - 1; // Reset flag to search for ground collision. isOnGround = false; // For each potentially colliding tile, for (int y = topTile; y <= bottomTile; ++y) { for (int x = leftTile; x <= rightTile; ++x) { // If this tile is collidable, ItemCollision collision = Level.GetCollision(x, y); if (collision != ItemCollision.Passable) { // Determine collision depth (with direction) and magnitude. Rectangle tileBounds = Level.GetBounds(x, y); Vector2 depth = RectangleExtensions.GetIntersectionDepth(bounds, tileBounds); if (depth != Vector2.Zero) { float absDepthX = Math.Abs(depth.X); float absDepthY = Math.Abs(depth.Y); // Resolve the collision along the shallow axis. if (absDepthY < absDepthX || collision == ItemCollision.Platform) { // If we crossed the top of a tile, we are on the ground. if (previousBottom <= tileBounds.Top) isOnGround = true; // Ignore platforms, unless we are on the ground. if (collision == ItemCollision.Impassable || IsOnGround) { // Resolve the collision along the Y axis. Position = new Vector2(Position.X, Position.Y + depth.Y); // Perform further collisions with the new bounds. bounds = BoundingRectangle; } } else if (collision == ItemCollision.Impassable) // Ignore platforms. { // Resolve the collision along the X axis. Position = new Vector2(Position.X + depth.X, Position.Y); // Perform further collisions with the new bounds. bounds = BoundingRectangle; } } } } } // Save the new bounds bottom. previousBottom = bounds.Bottom; } It also tends to jitter a little bit sometimes, I'm solved some of this with some fixes I found here on stackexchange, But Ive only seen one other case of the flying though blocks problem. This question seems to have a similar problem in the video, but mine is more crazy. Again this is a very annoying bug! Any help would be greatly appreciated! EDIT: Speed stuff // Constants for controling horizontal movement private const float MoveAcceleration = 13000.0f; private const float MaxMoveSpeed = 1750.0f; private const float GroundDragFactor = 0.48f; private const float AirDragFactor = 0.58f; // Constants for controlling vertical movement private const float MaxJumpTime = 0.35f; private const float JumpLaunchVelocity = -3500.0f; private const float GravityAcceleration = 3400.0f; private const float MaxFallSpeed = 550.0f; private const float JumpControlPower = 0.14f;

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• Efficient mapping layout in 2D side-scroller, and collisions between character and the world

  - by Jack

  I haven't touched Visual Studio for a couple months now, but I was playing a game from the '90s toady and had an epiphany: I was looking for something what i didn't need, and I wasn't using what I knew correctly. One of those realizations was collision, so let me tell you a bit about my project that I was working on. The project's graphics looks like Mario or Dangerous Dave, etc., you get the idea - old-school pixels. So anyway I remember trying to think of something else than AABB for character form, but I couldn't think of anything. Perhaps I could get a suggestion for this? Another thing is the world - I don't want it to be just linear world, I want mountains, etc.. My idea is to use triangles, and no idea yet what to do if I want just part of the cube, say 3/4 or 2/4 or whatever. Hard-coding such things seems inefficient. P.S. I am not looking at the precision level offered by Box2D. Actually I remember trying to implement it at first, but I failed as my understanding of C++ wasn't advanced enough, as it'll be mentioned below. P.P.S. I am programming in C++, and I haven't done it for a couple months now. I have no means of testing it either, as my PC is broken down, and this one can barely run games from late '90s, not to speak about a compiler or a program with inefficient resource management... I am also not an expert (obviously), I don't even know if I can consider myself an average programmer. In short, I am simply curious about my thoughts and my past experience when programming the game. I may come back to it when my PC is fixed, I'm already filling a note about these things.

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• Calculating 2D (screen) coordinates from 3D positions in XNA 4.0

  - by NDraskovic

  I have a program that draws some items to the scene by loading their positions from a file. Now I want to place a Ray on the same location where the items are drawn. So my question is how can I calculate the position of the ray (it's 2D components) by using 3D coordinates of each particular item? The items don't move anywhere, so once they are placed they stay until the end of the programs execution. Thanks.

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• SAT and then what?

  - by Marek

  I am on my way to make another Arkanoid game but this time I decided that I want it a little bit more realistic than just checking intersections between AABB and inverting one vector's component on collision. So I found SAT but I don't know how can I change direction of the ball in realistic matter. Maybe I'm wrong but it seems like knowing MTV doesn't give me much. So my question is what algorithms should I use to make it realistic? I also care about possibility of spinning ball with a pallet. I don't know how to do it exactly but I guess I will need to consider acceleration of the pallet.

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• Platform jumping problems with AABB collisions

  - by Vee

  See the diagram first: When my AABB physics engine resolves an intersection, it does so by finding the axis where the penetration is smaller, then "push out" the entity on that axis. Considering the "jumping moving left" example: If velocityX is bigger than velocityY, AABB pushes the entity out on the Y axis, effectively stopping the jump (result: the player stops in mid-air). If velocityX is smaller than velocitY (not shown in diagram), the program works as intended, because AABB pushes the entity out on the X axis. How can I solve this problem? Source code: public void Update() { Position += Velocity; Velocity += World.Gravity; List<SSSPBody> toCheck = World.SpatialHash.GetNearbyItems(this); for (int i = 0; i < toCheck.Count; i++) { SSSPBody body = toCheck[i]; body.Test.Color = Color.White; if (body != this && body.Static) { float left = (body.CornerMin.X - CornerMax.X); float right = (body.CornerMax.X - CornerMin.X); float top = (body.CornerMin.Y - CornerMax.Y); float bottom = (body.CornerMax.Y - CornerMin.Y); if (SSSPUtils.AABBIsOverlapping(this, body)) { body.Test.Color = Color.Yellow; Vector2 overlapVector = SSSPUtils.AABBGetOverlapVector(left, right, top, bottom); Position += overlapVector; } if (SSSPUtils.AABBIsCollidingTop(this, body)) { if ((Position.X >= body.CornerMin.X && Position.X <= body.CornerMax.X) && (Position.Y + Height/2f == body.Position.Y - body.Height/2f)) { body.Test.Color = Color.Red; Velocity = new Vector2(Velocity.X, 0); } } } } } public static bool AABBIsOverlapping(SSSPBody mBody1, SSSPBody mBody2) { if(mBody1.CornerMax.X <= mBody2.CornerMin.X || mBody1.CornerMin.X >= mBody2.CornerMax.X) return false; if (mBody1.CornerMax.Y <= mBody2.CornerMin.Y || mBody1.CornerMin.Y >= mBody2.CornerMax.Y) return false; return true; } public static bool AABBIsColliding(SSSPBody mBody1, SSSPBody mBody2) { if (mBody1.CornerMax.X < mBody2.CornerMin.X || mBody1.CornerMin.X > mBody2.CornerMax.X) return false; if (mBody1.CornerMax.Y < mBody2.CornerMin.Y || mBody1.CornerMin.Y > mBody2.CornerMax.Y) return false; return true; } public static bool AABBIsCollidingTop(SSSPBody mBody1, SSSPBody mBody2) { if (mBody1.CornerMax.X < mBody2.CornerMin.X || mBody1.CornerMin.X > mBody2.CornerMax.X) return false; if (mBody1.CornerMax.Y < mBody2.CornerMin.Y || mBody1.CornerMin.Y > mBody2.CornerMax.Y) return false; if(mBody1.CornerMax.Y == mBody2.CornerMin.Y) return true; return false; } public static Vector2 AABBGetOverlapVector(float mLeft, float mRight, float mTop, float mBottom) { Vector2 result = new Vector2(0, 0); if ((mLeft > 0 || mRight < 0) || (mTop > 0 || mBottom < 0)) return result; if (Math.Abs(mLeft) < mRight) result.X = mLeft; else result.X = mRight; if (Math.Abs(mTop) < mBottom) result.Y = mTop; else result.Y = mBottom; if (Math.Abs(result.X) < Math.Abs(result.Y)) result.Y = 0; else result.X = 0; return result; }

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• How can I monitor a website for malicious changes to the files

  - by rossmcm

  I had an occasion recently where our website was compromised - a link farm was added to a couple of the pages on one occasion, and on another occasion, a large and nasty aspx file was put on the server. I won't mention the host's name (Hostway), but I was pretty annoyed that someone was able to do this. No, it wasn't a leaky password - around 10 sites hosted by HW with consecutive IP addresses got trashed. Anyway. What I need is a utility or service (preferably free) that takes a snapshot of my websites contents, and then regularly monitors the files (size and datestamp) for unauthorized changes or additions, and alerts me. I've used web services that monitor one file for changes, but I'm looking for something a bit more aggressive.

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• Detect collision from a particular side

  - by Fabián

  I'm making a platform sidescrolling game. All I want to do is to detect if my character is on the floor: function OnCollisionStay (col : Collision){ if(col.gameObject.tag == "Floor"){ onFloor = true; } else {onFloor = false;} } function OnCollisionExit (col : Collision){ onFloor = false; } But I know this isn't the accurate way. If I hit a cube with a "floor" tag, in the air (no matter if with the character's feet or head) I would be able to jump. Is there a way to use the same box collision to detect if I'm touching something from a specific side?

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• Draw Rectangle To All Dimensions of Image

  - by opiop65

  I have some rudimentary collision code: public class Collision { static boolean isColliding = false; static Rectangle player; static Rectangle female; public static void collision(){ Rectangle player = Game.Playerbounds(); Rectangle female = Game.Femalebounds(); if(player.intersects(female)){ isColliding = true; }else{ isColliding = false; } } } And this is the rectangle code: public static Rectangle Playerbounds() { return(new Rectangle(posX, posY, 25, 25)); } public static Rectangle Femalebounds() { return(new Rectangle(femaleX, femaleY, 25, 25)); } My InputHandling class: public static void movePlayer(GameContainer gc, int delta){ Input input = gc.getInput(); if(input.isKeyDown(input.KEY_W)){ Game.posY -= walkSpeed * delta; walkUp = true; if(Collision.isColliding == true){ Game.posY += walkSpeed * delta; } } if(input.isKeyDown(input.KEY_S)){ Game.posY += walkSpeed * delta; walkDown = true; if(Collision.isColliding == true){ Game.posY -= walkSpeed * delta; } } if(input.isKeyDown(input.KEY_D)){ Game.posX += walkSpeed * delta; walkRight = true; if(Collision.isColliding == true){ Game.posX -= walkSpeed * delta; } } if(input.isKeyDown(input.KEY_A)){ Game.posX -= walkSpeed * delta; walkLeft = true; if(Collision.isColliding == true){ Game.posX += walkSpeed * delta; } } } The code works partially. Only the right and top side of the images collide. How do I correct the rectangle so it will draw on all sides? Thanks for any suggestions!

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• map data structure in pacman

  - by Sam Fisher

  i am trying to make a pacman game in c# using GDI+, i have done some basic work and i have previously replicated games like copter-it and minesweeper. but i am confused about how do i implement the map in pacman, i mean which datastructure to use, so i can use it for moving AI controlled objects and check collisions with walls. i thought of a 2d array of ints but that didnt make sense to me. looking for some help. thanks.

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