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• Zooming in isometric engine using XNA

  - by Yheeky

  I´m currently working on an isometric game engine and right now I´m looking for help concerning my zoom function. On my tilemap there are several objects, some of them are selectable. When a house (texture size 128 x 256) is placed on the map I create an array containing all pixels (= 32768 pixels). Therefore each pixel has an alpha value I check if the value is bigger than 200 so it seems to be a pixel which belongs to the building. So if the mouse cursor is on this pixel the building will be selected - PixelCollision. Now I´ve already implemented my zooming function which works quite well. I use a scale variable which will change my calculation on drawing all map items. What I´m looking for right now is a precise way to find out if a zoomed out/in house is selected. My formula works for values like 0,5 (zoomed out) or 2 (zoomed in) but not for in between. Here is the code I use for the pixel index: var pixelIndex = (int)(((yPos / (Scale * Scale)) * width) + (xPos / Scale) + 1); Example: Let´s assume my mouse is over pixel coordinate 38/222 on the original house texture. Using the code above we get the following pixel index. var pixelIndex = ((222 / (1 * 1)) * 128) + (38 / 1) + 1; = (222 * 128) + 39 = 28416 + 39 = 28455 If we now zoom out to scale 0,5, the texture size will change to 64 x 128 and the amount of pixels will decrease from 32768 to 8192. Of course also our mouse point changes by the scale to 19/111. The formula makes it easy to calculate the original pixelIndex using our new coordinates: var pixelIndex = ((111 / (0.5 * 0.5)) * 64) + (19 / 0.5) + 1; = (444 * 64) + 39 = 28416 + 39 = 28455 But now comes the problem. If I zoom out just to scale 0.75 it does not work any more. The pixel amount changes from 32768 to 18432 pixels since texture size is 96 x 192. Mouse point is transformed to point 28/166. The formula gives me a wrong pixelIndex. var pixelIndex = ((166 / (0.75 * 0.75)) * 96) + (28 / 0.75) + 1; = (295.11 * 96) + 38.33 = 28330.66 + 38.33 = 28369 Does anyone have a clue what´s wrong in my code? Must be the first part (28330.66) which causes the calculation problem. Thanks! Yheeky

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• Sending state diffs (deltas) and unreliable connections

  - by spaceOwl

  We're building a realtime multiplayer game, in which each player is responsible for reporting its state on every iteration of the game loop. The state updates are broadcasted using unreliable UDP. To minimize state data sending, we've come up with a system that will send only deltas (whatever state data that was changed). This method however is flawed, since a lost packet will mean that other players will not receive the delta, making the game behave in an unexpected way. For example: Assume that state is comprised of: { positionX, positionY, health } Frame 1 - positionX changed --> send a packet with positionX only. Frame 2 - health changed // lost ! Frame 3 - positionY changed --> send a packet with positionY only. // Other players don't know about health change. How can one overcome this issue then? sending the entire data is not always feasible.

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• How can I plot a radius of all reachable points with pathfinding for a Mob?

  - by PugWrath

  I am designing a tactical turn based game. The maps are 2d, but do have varying level-layers and blocking objects/terrain. I'm looking for an algorithm for pathfinding which will allow me to show an opaque shape representing all of the possible max-distance pixels that a mob can move to, knowing the mob's max pixel distance. Any thoughts on this, or do I just need to write a good pathfinding algorithm and use it to find the cutoff points for any direction in which an obstacle exists?

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• Structuring game world entities and their rendering objects

  - by keithjgrant

  I'm putting together a simple 2d tile-based game. I'm finding myself spinning circles on some design decisions, and I think I'm in danger of over-engineering. After all, the game is simple enough that I had a working prototype inside of four hours with fewer than ten classes, it just wasn't scalable or flexible enough for a polished game. My question is about how to structure flow of control between game entity objects and their rendering objects. Should each renderer have a reference to their entity or vice-versa? Or both? Should the entity be in control of calling the render() method, or be completely oblivious? I know there are several valid approaches here, but I'm kind of feeling decision paralysis. What are the pros and cons of each approach?

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• Trouble using Ray.Intersect method on bounding boxes in a 2D XNA game

  - by getsauce

  I am trying to use a ray and bounding box to determine if a box is between the player and the mouse pointer in 2D space. When I try testing the code, the collision will return true when pointed at the box but it also returns true under other circumstances where it shouldn't. For instance. If I have a player on the left and a box directly to the right, I can put the mouse pointer a few hundred pixels above the box or a few hundred below and it will still return true. Also, I can put my mouse pointer to the left of the player and in a certain area it will still return true. Does anyone have any idea what might cause this? I have left out definitions for some of my members and properties just to make this code sample easier to read. The position property is just a Vector2 for where each object is located. ray = new Ray(new Vector3(player.Position, 0), new Vector3(mouse.Position, 0); box = new BoundingBox(new Vector3(box.Position, 0), new Vector3( new Vector2(box.Position + box.Width, box.Position + box.Height), 0); if (ray.Intersects(box) != null) collision = true; else collision = false;

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• The underlying mechanism in 'yield return www' of Unity3D Game Engine

  - by thyandrecardoso

  In the Unity3D game engine, a common code sequence for getting remote data is this: WWW www = new WWW("http://remote.com/data/location/with/texture.png"); yield return www; What is the underlying mechanism here? I know we use the yield mechanism in order to allow the next frame to be processed, while the download is being completed. But what is going on under the hood when we do the yield return www ? What method is being called (if any, on the WWW class)? Is Unity using threads? Is the "upper" Unity layer getting hold of www instance and doing something?

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• Use PathModifier of MoveModifier for Tower of Defense Game

  - by Siddharth

  In my game I want to move enemy on the fixed path so that I have establish manual grid structure for that purpose not used tile map. Game contain multiple level and the path will be different for each level and also multiple fixed path exist for each level. So my question is, What I have to use MoveModifier or PathModifier for my game ? Also mention I have to use WayPoint or not. Further detail you all are free to ask. Please help me to decide what to do.

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• Client-Server MMOG & data structures sync when joining / playing

  - by plang

  After reading a few articles on MMOG architecture, there is still one point on which I cannot find much information: it has to do with how you keep in sync server data on the client, when you join, and while you play. A pretty vague question, I agree. Let me refine it: Let's say we have an MMOG virtual world subdivided into geographical cells. A player in a cell is mostly interested in what happens in the cell itself, and all the surrounding cells, not more. When joining the game for the first time, the only thing we can do is send some sort of "database dump" of the interesting cells to the client. When playing, I guess it would be very inefficient to do the same thing regularly. I imagine the best thing to do is to send "deltas" to the client, which would allow keeping the local database in sync. Now let's say the player moves, and arrives in another cell. Surrounding cells change, and for all the new cells the player subscribes, the same technique as used when joining the game has to be used: some sort of "database dump". This mechanic of joining/moving in a cell-based MMOG virtual world interests me, and I was wondering if there were tried and tested techniques in this domain. Thanks!

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• Logic / Render phases with a single thread

  - by DevilWithin

  The question I have may generate different opinions from different developers, but I'd still like to have an answer on this. Its all about the updating and rendering steps of the game loop, and their use under multi and single threaded environments. Currently, there is one thread running, which takes care of sequentially executing events , logic and rendering. Sometimes, the logic part may wish to change the game state to something else, and in between do some loading of files. The result is that the game hangs completely while loading, and then proceeds to normal rendering of the new state. To go around this, i could make another thread, do the loading there while the main thread renders a smooth loading animation, and then proceed normally. The real question is about if i don't create another thread. I could refresh the screen from the logic thread, and provide some basic loading screen, which could be not so smoothly updated while the files load. In fact, this approach is not loved by a lot of developers, as it scrambles render code in the logic step, which may cause problems of different sorts.. Hope its clear!

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• Space invaders clone not moving properly

  - by ThePlan

  I'm trying to make a basic space invaders clone in allegro 5, I've got my game set up, basic events and such, here is the code: #include <allegro5/allegro.h> #include <allegro5/allegro_image.h> #include <allegro5/allegro_primitives.h> #include <allegro5/allegro_font.h> #include <allegro5/allegro_ttf.h> #include "Entity.h" // GLOBALS ========================================== const int width = 500; const int height = 500; const int imgsize = 3; bool key[5] = {false, false, false, false, false}; bool running = true; bool draw = true; // FUNCTIONS ======================================== void initSpaceship(Spaceship &ship); void moveSpaceshipRight(Spaceship &ship); void moveSpaceshipLeft(Spaceship &ship); void initInvader(Invader &invader); void moveInvaderRight(Invader &invader); void moveInvaderLeft(Invader &invader); void initBullet(Bullet &bullet); void fireBullet(); void doCollision(); void updateInvaders(); void drawText(); enum key_t { UP, DOWN, LEFT, RIGHT, SPACE }; enum source_t { INVADER, DEFENDER }; int main(void) { if(!al_init()) { return -1; } Spaceship ship; Invader invader; Bullet bullet; al_init_image_addon(); al_install_keyboard(); al_init_font_addon(); al_init_ttf_addon(); ALLEGRO_DISPLAY *display = al_create_display(width, height); ALLEGRO_EVENT_QUEUE *event_queue = al_create_event_queue(); ALLEGRO_TIMER *timer = al_create_timer(1.0 / 60); ALLEGRO_BITMAP *images[imgsize]; ALLEGRO_FONT *font1 = al_load_font("arial.ttf", 20, 0); al_register_event_source(event_queue, al_get_keyboard_event_source()); al_register_event_source(event_queue, al_get_display_event_source(display)); al_register_event_source(event_queue, al_get_timer_event_source(timer)); images[0] = al_load_bitmap("defender.bmp"); images[1] = al_load_bitmap("invader.bmp"); images[2] = al_load_bitmap("explosion.bmp"); al_convert_mask_to_alpha(images[0], al_map_rgb(0, 0, 0)); al_convert_mask_to_alpha(images[1], al_map_rgb(0, 0, 0)); al_convert_mask_to_alpha(images[2], al_map_rgb(0, 0, 0)); initSpaceship(ship); initBullet(bullet); initInvader(invader); al_start_timer(timer); while(running) { ALLEGRO_EVENT ev; al_wait_for_event(event_queue, &ev); if(ev.type == ALLEGRO_EVENT_TIMER) { draw = true; if(key[RIGHT] == true) moveSpaceshipRight(ship); if(key[LEFT] == true) moveSpaceshipLeft(ship); } else if(ev.type == ALLEGRO_EVENT_DISPLAY_CLOSE) running = false; else if(ev.type == ALLEGRO_EVENT_KEY_DOWN) { switch(ev.keyboard.keycode) { case ALLEGRO_KEY_ESCAPE: running = false; break; case ALLEGRO_KEY_LEFT: key[LEFT] = true; break; case ALLEGRO_KEY_RIGHT: key[RIGHT] = true; break; case ALLEGRO_KEY_SPACE: key[SPACE] = true; break; } } else if(ev.type == ALLEGRO_KEY_UP) { switch(ev.keyboard.keycode) { case ALLEGRO_KEY_LEFT: key[LEFT] = false; break; case ALLEGRO_KEY_RIGHT: key[RIGHT] = false; break; case ALLEGRO_KEY_SPACE: key[SPACE] = false; break; } } if(draw && al_is_event_queue_empty(event_queue)) { draw = false; al_draw_bitmap(images[0], ship.pos_x, ship.pos_y, 0); al_flip_display(); al_clear_to_color(al_map_rgb(0, 0, 0)); } } al_destroy_font(font1); al_destroy_event_queue(event_queue); al_destroy_timer(timer); for(int i = 0; i < imgsize; i++) al_destroy_bitmap(images[i]); al_destroy_display(display); } // FUNCTION LOGIC ====================================== void initSpaceship(Spaceship &ship) { ship.lives = 3; ship.speed = 2; ship.pos_x = width / 2; ship.pos_y = height - 20; } void initInvader(Invader &invader) { invader.health = 100; invader.count = 40; invader.speed = 0.5; invader.pos_x = 300; invader.pos_y = 300; } void initBullet(Bullet &bullet) { bullet.speed = 10; } void moveSpaceshipRight(Spaceship &ship) { ship.pos_x += ship.speed; if(ship.pos_x >= width) ship.pos_x = width-30; } void moveSpaceshipLeft(Spaceship &ship) { ship.pos_x -= ship.speed; if(ship.pos_x <= 0) ship.pos_x = 0+30; } However it's not behaving the way I want it to behave, in fact the behavior for the ship movement is un-normal. Basically I specified that the ship only moves when the right/left key is down, however the ship is moving constantly to the direction of the key pressed, it never stops although it should only move while my key is down. Even more weird behavior, when I press the opposite key the ship completely stops no matter what else I press. What's wrong with the code? Why does the ship move constantly even after I specified it only moves when a key is down?

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• Platform game collisions with Block

  - by Sri Harsha Chilakapati

  I am trying to create a platform game and doing wrong collision detection with the blocks. Here's my code // Variables GTimer jump = new GTimer(1000); boolean onground = true; // The update method public void update(long elapsedTime){ MapView.follow(this); // Add the gravity if (!onground && !jump.active){ setVelocityY(4); } // Jumping if (isPressed(VK_SPACE) && onground){ jump.start(); setVelocityY(-4); onground = false; } if (jump.action(elapsedTime)){ // jump expired jump.stop(); } // Horizontal movement setVelocityX(0); if (isPressed(VK_LEFT)){ setVelocityX(-4); } if (isPressed(VK_RIGHT)){ setVelocityX(4); } } // The collision method public void collision(GObject other){ if (other instanceof Block){ // Determine the horizontal distance between centers float h_dist = Math.abs((other.getX() + other.getWidth()/2) - (getX() + getWidth()/2)); // Now the vertical distance float v_dist = Math.abs((other.getY() + other.getHeight()/2) - (getY() + getHeight()/2)); // If h_dist > v_dist horizontal collision else vertical collision if (h_dist > v_dist){ // Are we moving right? if (getX()<other.getX()){ setX(other.getX()-getWidth()); } // Are we moving left? else if (getX()>other.getX()){ setX(other.getX()+other.getWidth()); } } else { // Are we moving up? if (jump.active){ jump.stop(); } // We are moving down else { setY(other.getY()-getHeight()); setVelocityY(0); onground = true; } } } } The problem is that the object jumps well but does not fall when moved out of platform. Here's an image describing the problem. I know I'm not checking underneath the object but I don't know how. The map is a list of objects and should I have to iterate over all the objects??? Thanks

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• Parenting Opengl with Groups in LibGDX

  - by Rudy_TM

  I am trying to make an object child of a Group, but this object has a draw method that calls opengl to draw in the screen. Its class its this public class OpenGLSquare extends Actor { private static final ImmediateModeRenderer renderer = new ImmediateModeRenderer10(); private static Matrix4 matrix = null; private static Vector2 temp = new Vector2(); public static void setMatrix4(Matrix4 mat) { matrix = mat; } @Override public void draw(SpriteBatch batch, float arg1) { // TODO Auto-generated method stub renderer.begin(matrix, GL10.GL_TRIANGLES); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x0, y0, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x0, y1, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x1, y1, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x1, y1, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x1, y0, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x0, y0, 0f); renderer.end(); } } In my screen class I have this, i call it in the constructor MyGroupClass spriteLab = new MyGroupClass(spriteSheetLab); OpenGLSquare square = new OpenGLSquare(); square.setX0(100); square.setY0(200); square.setX1(400); square.setY1(280); square.color.set(Color.BLUE); square.setSize(); //spriteLab.addActorAt(0, clock); spriteLab.addActor(square); stage.addActor(spriteLab); And the render in the screen I have @Override public void render(float arg0) { this.gl.glClear(GL10.GL_COLOR_BUFFER_BIT |GL10.GL_DEPTH_BUFFER_BIT); stage.draw(); stage.act(Gdx.graphics.getDeltaTime()); } The problem its that when i use opengl with parent, it resets all the other chldren to position 0,0 and the opengl renderer paints the square in the exact position of the screen and not relative to the parent. I tried using batch.enableBlending() and batch.disableBlending() that fixes the position problem of the other children, but not the relative position of the opengl drawing and it also puts alpha to the glDrawing. What am i doing wrong?:/

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• Triangle Picking Picking Back faces

  - by Tangeleno

  I'm having a bit of trouble with 3D picking, at first I thought my ray was inaccurate but it turns out that the picking is happening on faces facing the camera and faces facing away from the camera which I'm currently culling. Here's my ray creation code, I'm pretty sure the problem isn't here but I've been wrong before. private uint Pick() { Ray cursorRay = CalculateCursorRay(); Vector3? point = Control.Mesh.RayCast(cursorRay); if (point != null) { Tile hitTile = Control.TileMesh.GetTileAtPoint(point); return hitTile == null ? uint.MaxValue : (uint)(hitTile.X + hitTile.Y * Control.Generator.TilesWide); } return uint.MaxValue; } private Ray CalculateCursorRay() { Vector3 nearPoint = Control.Camera.Unproject(new Vector3(Cursor.Position.X, Control.ClientRectangle.Height - Cursor.Position.Y, 0f)); Vector3 farPoint = Control.Camera.Unproject(new Vector3(Cursor.Position.X, Control.ClientRectangle.Height - Cursor.Position.Y, 1f)); Vector3 direction = farPoint - nearPoint; direction.Normalize(); return new Ray(nearPoint, direction); } public Vector3 Camera.Unproject(Vector3 source) { Vector4 result; result.X = (source.X - _control.ClientRectangle.X) * 2 / _control.ClientRectangle.Width - 1; result.Y = (source.Y - _control.ClientRectangle.Y) * 2 / _control.ClientRectangle.Height - 1; result.Z = source.Z - 1; if (_farPlane - 1 == 0) result.Z = 0; else result.Z = result.Z / (_farPlane - 1); result.W = 1f; result = Vector4.Transform(result, Matrix4.Invert(ProjectionMatrix)); result = Vector4.Transform(result, Matrix4.Invert(ViewMatrix)); result = Vector4.Transform(result, Matrix4.Invert(_world)); result = Vector4.Divide(result, result.W); return new Vector3(result.X, result.Y, result.Z); } And my triangle intersection code. Ripped mainly from the XNA picking sample. public float? Intersects(Ray ray) { float? closestHit = Bounds.Intersects(ray); if (closestHit != null && Vertices.Length == 3) { Vector3 e1, e2; Vector3.Subtract(ref Vertices[1].Position, ref Vertices[0].Position, out e1); Vector3.Subtract(ref Vertices[2].Position, ref Vertices[0].Position, out e2); Vector3 directionCrossEdge2; Vector3.Cross(ref ray.Direction, ref e2, out directionCrossEdge2); float determinant; Vector3.Dot(ref e1, ref directionCrossEdge2, out determinant); if (determinant > -float.Epsilon && determinant < float.Epsilon) return null; float inverseDeterminant = 1.0f/determinant; Vector3 distanceVector; Vector3.Subtract(ref ray.Position, ref Vertices[0].Position, out distanceVector); float triangleU; Vector3.Dot(ref distanceVector, ref directionCrossEdge2, out triangleU); triangleU *= inverseDeterminant; if (triangleU < 0 || triangleU > 1) return null; Vector3 distanceCrossEdge1; Vector3.Cross(ref distanceVector, ref e1, out distanceCrossEdge1); float triangleV; Vector3.Dot(ref ray.Direction, ref distanceCrossEdge1, out triangleV); triangleV *= inverseDeterminant; if (triangleV < 0 || triangleU + triangleV > 1) return null; float rayDistance; Vector3.Dot(ref e2, ref distanceCrossEdge1, out rayDistance); rayDistance *= inverseDeterminant; if (rayDistance < 0) return null; return rayDistance; } return closestHit; } I'll admit I don't fully understand all of the math behind the intersection and that is something I'm working on, but my understanding was that if rayDistance was less than 0 the face was facing away from the camera, and shouldn't be counted as a hit. So my question is, is there an issue with my intersection or ray creation code, or is there another check I need to perform to tell if the face is facing away from the camera, and if so any hints on what that check might contain would be appreciated.

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• In concept how is Animation done?

  - by sharethis

  The first approaches in animation for my game relied mostly on sine and cosine functions with the time as parameter. As a jump a perfect sine function is acceptable but for motions of arms, weapons or face it would look quite unnatural. Moreover patching every animation out of sine and cosine is stretched to its limits soon. I head of skeletons and rigging already. Although I could not implement skeletal animations I can't imagine that quite natural animations in major games are made of static predefined motion states. So how in general is animation done today?

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• Picking a suitable resolution for a modern low-res game?

  - by MrKatSwordfish

  I'm working on a 2D game project right now (using SFML+OpenGL and C++) and I'm trying to figure out how to go about choosing a resolution. I want my game to have a pixel resolution that is around that of classic '16bit' era consoles like the Super Nintendo or Neo Geo. However, I'd also like to have my game fit the 16:9 aspect ratio that most modern PC monitors use. Finally I'd like to be able to include an option for running full screen. I know that I could create my own low-res 16:9 resolution that is more-or-less around the size of SNES or NeoGeo games. However, the problem seems to be that doing so would leave me with a non-standard resolution that my monitor would not be able to support in fullscreen mode. For example, if i divide the common 16:9 resolution 1920x1080 by 4, I would get a 16:9 resolution that is relatively close to the resolution used by 16bit era games; 480x270. That would be fine in a windowed mode, but I don't think that it would be supported in fullscreen mode. How can I choose a resolution that suits my needs? Can I use something like 480x270? If so, how would I go about getting fullscreen mode to work with such a non-standard resolution? (I'm guessing OpenGL/SFML might have a way of up-scaling...but..)

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• Why can't I compare two Texture2D's?

  - by Fiona

  I am trying to use an accessor, as it seems to me that that is the only way to accomplish what I want to do. Here is my code: Game1.cs public class GroundTexture { private Texture2D dirt; public Texture2D Dirt { get { return dirt; } set { dirt = value; } } } public class Main : Game { public static Texture2D texture = tile.Texture; GroundTexture groundTexture = new GroundTexture(); public static Texture2D dirt; protected override void LoadContent() { Tile tile = (Tile)currentLevel.GetTile(20, 20); dirt = Content.Load<Texture2D>("Dirt"); groundTexture.Dirt = dirt; Texture2D texture = tile.Texture; } protected override void Update(GameTime gameTime) { if (texture == groundTexture.Dirt) { player.TileCollision(groundBounds); } base.Update(gameTime); } } I removed irrelevant information from the LoadContent and Update functions. On the following line: if (texture == groundTexture.Dirt) I am getting the error Operator '==' cannot be applied to operands of type 'Microsoft.Xna.Framework.Graphics.Texture2D' and 'Game1.GroundTexture' Am I using the accessor correctly? And why do I get this error? "Dirt" is Texture2D, so they should be comparable. This using a few functions from a program called Realm Factory, which is a tile editor. The numbers "20, 20" are just a sample of the level I made below: tile.Texture returns the sprite, which here is the content item Dirt.png Thank you very much! (I posted this on the main Stackoverflow site, but after several days didn't get a response. Since it has to do mainly with Texture2D, I figured I'd ask here.)

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• How to attach two XNA models together?

  - by jeangil

  I go back on unsolved question I asked about attaching two models together, could you give me some help on this ? For example, If I want to attach together Model1 (= Main model) & Model2 ? I have to get the transformation matrix of Model1 and after get the Bone index on Model1 where I want to attach Model2 and then apply some transformation to attach Model2 to Model1 I wrote some code below about this, but It does not work at all !! (6th line of my code seems to be wrong !?) Model1TransfoMatrix=New Matrix[Model1.Bones.Count]; Index=Model1.bone[x].Index; foreach (ModelMesh mesh in Model2.Meshes) { foreach(BasicEffect effect in mesh.effects) { matrix model2Transform = Matrix.CreateScale(0.1.0f)*Matrix.CreateFromYawPitchRoll(x,y,z); effect.World= model2Transform *Model1TransfoMatrix[Index]; effect.view = camera.View; effect.Projection= camera.Projection; } mesh.draw(); }

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• LOD in modern games

  - by Firas Assaad

  I'm currently working on my master's thesis about LOD and mesh simplification, and I've been reading many academic papers and articles about the subject. However, I can't find enough information about how LOD is being used in modern games. I know many games use some sort of dynamic LOD for terrain, but what about elsewhere? Level of Detail for 3D Graphics for example points out that discrete LOD (where artists prepare several models in advance) is widely used because of the performance overhead of continuous LOD. That book was published in 2002 however, and I'm wondering if things are different now. There has been some research in performing dynamic LOD using the geometry shader (this paper for example, with its implementation in ShaderX6), would that be used in a modern game? To summarize, my question is about the state of LOD in modern video games, what algorithms are used and why? In particular, is view dependent continuous simplification used or does the runtime overhead make using discrete models with proper blending and impostors a more attractive solution? If discrete models are used, is an algorithm used (e.g. vertex clustering) to generate them offline, do artists manually create the models, or perhaps a combination of both methods is used?

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• 2D Tile based Game Collision problem

  - by iNbdy

  I've been trying to program a tile based game, and I'm stuck at the collision detection. Here is my code (not the best ^^): void checkTile(Character *c, int **map) { int x1,x2,y1,y2; /* Character position in the map */ c->upY = (c->y) / TILE_SIZE; // Top left corner c->downY = (c->y + c->h) / TILE_SIZE; // Bottom left corner c->leftX = (c->x) / TILE_SIZE; // Top right corner c->rightX = (c->x + c->w) / TILE_SIZE; // Bottom right corner x1 = (c->x + 10) / TILE_SIZE; // 10px from left side point x2 = (c->x + c->w - 10) / TILE_SIZE; // 10px from right side point y1 = (c->y + 10) / TILE_SIZE; // 10px from top side point y2 = (c->y + c->h - 10) / TILE_SIZE; // 10px from bottom side point /* Top */ if (map[c->upY][x1] > 2 || map[c->upY][x2] > 2) c->topCollision = 1; else c->topCollision = 0; /* Bottom */ if ((map[c->downY][x1] > 2 || map[c->downY][x2] > 2)) c->downCollision = 1; else c->downCollision = 0; /* Left */ if (map[y1][c->leftX] > 2 || map[y2][c->leftX] > 2) c->leftCollision = 1; else c->leftCollision = 0; /* Right */ if (map[y1][c->rightX] > 2 || map[y2][c->rightX] > 2) c->rightCollision = 1; else c->rightCollision = 0; } That calculates 8 collision points My moving function is like that: void movePlayer(Character *c, int **map) { if ((c->dirX == LEFT && !c->leftCollision) || (c->dirX == RIGHT && !c->rightCollision)) c->x += c->vx; if ((c->dirY == UP && !c->topCollision) || (c->dirY == DOWN && !c->downCollision)) c->y += c->vy; checkPosition(c, map); } and the checkPosition: void checkPosition(Character *c, int **map) { checkTile(c, map); if (c->downCollision) { if (c->state != JUMPING) { c->vy = 0; c->y = (c->downY * TILE_SIZE - c->h); } } if (c->leftCollision) { c->vx = 0; c->x = (c->leftX) * TILE_SIZE + TILE_SIZE; } if (c->rightCollision) { c->vx = 0; c->x = c->rightX * TILE_SIZE - c->w; } } This works, but sometimes, when the player is landing on ground, right and left collision points become equal to 1. So it's as if there were collision coming from left or right. Does anyone know why this is doing this?

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• QuadTree: store only points, or regions?

  - by alekop

  I am developing a quadtree to keep track of moving objects for collision detection. Each object has a bounding shape, let's say they are all circles. (It's a 2D top-down game) I am unsure whether to store only the position of each object, or the whole bounding shape. If working with points, insertion and subdivision is easy, because objects will never span multiple nodes. On the other hand, a proximity query for an object may miss collisions, because it won't take the objects' dimensions into account. How to calculate the query region when you only have points? If working with regions, how to handle an object that spans multiple nodes? Should it be inserted in the nearest parent node that completely contains it, even if this exceeds the node's capacity? Thanks.

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• How to get scripted programs governing game entities run in parallel with a game loop?

  - by Jim

  I recently discovered Crobot which is (briefly) a game where each player codes a virtual robot in a pseudo-C language. Each robot is then put in an arena where it fights against other robots. A robots' source code has this shape : /* Beginning file robot.r */ main() { while (1) { /* Do whatever you want */ ... move(); ... fire(); } } /* End file robot.r */ You can see that : The code is totally independent from any library/include Some predefined functions are available (move, fire, etc…) The program has its own game loop, and consequently is not called every frame My question is: How to achieve a similar result using scripted languages in collaboration with a C/C++ main program ? I found a possible approach using Python, multi-threading and shared memory, although I am not sure yet that it is possible this way. TCP/IP seems a bit too complicated for this kind of application.

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• How to send multiple MVP matrices to a vertex shader in OpenGL ES 2.0

  - by Carbon Crystal

  I'm working my way through optimizing the rendering of sprites in a 2D game using OpenGL ES and I've hit the limit of my knowledge when it comes to GLSL and vertex shaders. I have two large float buffers containing my vertex coordinates and texture coordinates (eventually this will be one buffer) for multiple sprites in order to perform a single glDrawArrays call. This works but I've hit a snag when it comes to passing the transformation matrix into the vertex shader. My shader code is: uniform mat4 u_MVPMatrix; attribute vec4 a_Position; attribute vec2 a_TexCoordinate; varying vec2 v_TexCoordinate; void main() { v_TexCoordinate = a_TexCoordinate; gl_Position = u_MVPMatrix * a_Position; } In Java (Android) I am using a FloatBuffer to store the vertex/texture data and this is provided to the shader like so: mGlEs20.glVertexAttribPointer(mVertexHandle, Globals.GL_POSITION_VERTEX_COUNT, GLES20.GL_FLOAT, false, 0, mVertexCoordinates); mGlEs20.glVertexAttribPointer(mTextureCoordinateHandle, Globals.GL_TEXTURE_VERTEX_COUNT, GLES20.GL_FLOAT, false, 0, mTextureCoordinates); (The Globals.GL_POSITION_VERTEX_COUNT etc are just integers with the value of 2 right now) And I'm passing the MVP (Model/View/Projection) matrix buffer like this: GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mModelCoordinates); (mModelCoordinates is a FloatBuffer containing 16-float sequences representing the MVP matrix for each sprite) This renders my scene but all the sprites share the same transformation, so it's obviously only picking the first 16 elements from the buffer which makes sense since I am passing in "1" as the second parameter. The documentation for this method says: "This should be 1 if the targeted uniform variable is not an array of matrices, and 1 or more if it is an array of matrices." So I tried modifying the shader with a fixed size array large enough to accomodate most of my scenarios: uniform mat4 u_MVPMatrix[1000]; But this lead to an error in the shader: cannot convert from 'uniform array of 4X4 matrix of float' to 'Position 4-component vector of float' This just seems wrong anyway as it's not clear to me how the shader would know when to transition to the next matrix anyway. Anyone have an idea how I can get my shader to pick up a different MVP matrix (i.e. the NEXT 16 floats) from my MVP buffer for every 4 vertices it encounters? (I am using GL_TRIANGLE_STRIP so each sprite has 4 vertices). Thanks!

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• Java : 2D Collision Detection

  - by neko

  I'm been working on 2D rectangle collision for weeks and still cannot get this problem fixed. The problem I'm having is how to adjust a player to obstacles when it collides. I'm referencing this link. The player sometime does not get adjusted to obstacles. Also, it sometimes stuck in obstacle guy after colliding. Here, the player and the obstacle are inheriting super class Sprite I can detect collision between the two rectangles and the point by ; public Point getSpriteCollision(Sprite sprite, double newX, double newY) { // set each rectangle Rectangle spriteRectA = new Rectangle( (int)getPosX(), (int)getPosY(), getWidth(), getHeight()); Rectangle spriteRectB = new Rectangle( (int)sprite.getPosX(), (int)sprite.getPosY(), sprite.getWidth(), sprite.getHeight()); // if a sprite is colliding with the other sprite if (spriteRectA.intersects(spriteRectB)){ System.out.println("Colliding"); return new Point((int)getPosX(), (int)getPosY()); } return null; } and to adjust sprites after a collision: // Update the sprite's conditions public void update() { // only the player is moving for simplicity // collision detection on x-axis (just x-axis collision detection at this moment) double newX = x + vx; // calculate the x-coordinate of sprite move Point sprite = getSpriteCollision(map.getSprite().get(1), newX, y);// collision coordinates (x,y) if (sprite == null) { // if the player is no colliding with obstacle guy x = newX; // move } else { // if collided if (vx > 0) { // if the player was moving from left to right x = (sprite.x - vx); // this works but a bit strange } else if (vx < 0) { x = (sprite.x + vx); // there's something wrong with this too } } vx=0; y+=vy; vy=0; } I think there is something wrong in update() but cannot fix it. Now I only have a collision with the player and an obstacle guy but in future, I'm planning to have more of them and making them all collide with each other. What would be a good way to do it? Thanks in advance.

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• C# Collision test of a ship and asteriod, angle confusion

  - by Cherry

  We are trying to to do a collision detection for the ship and asteroid. If success than it should detect the collision before N turns. However it is confused between angle 350 and 15 and it is not really working. Sometimes it is moving but sometime it is not moving at all. On the other hand, it is not shooting at the right time as well. I just want to ask how to make the collision detection working??? And how to solve the angle confusion problem? // Get velocities of asteroid Console.WriteLine("lol"); // IF equation is between -2 and -3 if (equation1a <= -2) { // Calculate no. turns till asteroid hits float turns_till_hit = dx / vx; // Calculate angle of asteroid float asteroid_angle_rad = (float)Math.Atan(Math.Abs(dy / dx)); float asteroid_angle_deg = (float)(asteroid_angle_rad * 180 / Math.PI); float asteroid_angle = 0; // Calculate angle if asteroid is in certain positions if (asteroid.Y > ship.Y && asteroid.X > ship.X) { asteroid_angle = asteroid_angle_deg; } else if (asteroid.Y < ship.Y && asteroid.X > ship.X) { asteroid_angle = (360 - asteroid_angle_deg); } else if (asteroid.Y < ship.Y && asteroid.X < ship.X) { asteroid_angle = (180 + asteroid_angle_deg); } else if (asteroid.Y > ship.Y && asteroid.X < ship.X) { asteroid_angle = (180 - asteroid_angle_deg); } // IF turns till asteroid hits are less than 35 if (turns_till_hit < 50) { float angle_between = 0; // Calculate angle between if asteroid is in certain positions if (asteroid.Y > ship.Y && asteroid.X > ship.X) { angle_between = ship_angle - asteroid_angle; } else if (asteroid.Y < ship.Y && asteroid.X > ship.X) { angle_between = (360 - Math.Abs(ship_angle - asteroid_angle)); } else if (asteroid.Y < ship.Y && asteroid.X < ship.X) { angle_between = ship_angle - asteroid_angle; } else if (asteroid.Y > ship.Y && asteroid.X < ship.X) { angle_between = ship_angle - asteroid_angle; } // If angle less than 0, add 360 if (angle_between < 0) { //angle_between %= 360; angle_between = Math.Abs(angle_between); } // Calculate no. of turns to face asteroid float turns_to_face = angle_between / 25; if (turns_to_face < turns_till_hit) { float ship_angle_left = ShipAngle(ship_angle, "leftKey", 1); float ship_angle_right = ShipAngle(ship_angle, "rightKey", 1); float angle_between_left = Math.Abs(ship_angle_left - asteroid_angle); float angle_between_right = Math.Abs(ship_angle_right - asteroid_angle); if (angle_between_left < angle_between_right) { leftKey = true; } else if (angle_between_right < angle_between_left) { rightKey = true; } } if (angle_between > 0 && angle_between < 25) { spaceKey = true; } } }

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• Easiest Way To Implement "Slow Motion" and variable game speed in XNA?

  - by TerryB

  I have an XNA 4.0 game that I want to be able to switch into slow motion and back again to full speed every now and then. So if you kill an enemy the game switches into slow motion as they explode and then goes back to normal. What is the easiest way to do this in XNA 4.0 without having to alter all my existing code that relies on GameTime? I have some code that relies on the TotalGameTime, which will be wrong unless I get XNA to slow down. Is there anyway to avoid refactoring that code? Thanks!

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