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• Most efficient AABB - Ray intersection algorithm for input/output distance calculation

  - by Tobbey

  Thanks to the following thread : most efficient AABB vs Ray collision algorithms I have seen very fast algorithm for ray/AABB intersection point computation. Unfortunately, most of the recent algorithm are accelerated by omitting the "output" intersection point of the box. In my application, I would interested in getting both the the distance from source ray to input: t0 and source ray to output of bounding box: t1. I have seen for instance Eisemann designed a very fast version regarding plucker, smits, ... , but it does not compare the case when both input/output distance should be computed see: http://www.cg.cs.tu-bs.de/publications/Eisemann07FRA/ Does someone know where I can find more information on algorithm performances for the specific input/output problem ? Thank you in advance

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• Most efficient way to implement delta time

  - by Starkers

  Here's one way to implement delta time: /// init /// var duration = 5000, currentTime = Date.now(); // and create cube, scene, camera ect ////// function animate() { /// determine delta /// var now = Date.now(), deltat = now - currentTime, currentTime = now, scalar = deltat / duration, angle = (Math.PI * 2) * scalar; ////// /// animate /// cube.rotation.y += angle; ////// /// update /// requestAnimationFrame(render); ////// } Could someone confirm I know how it works? Here what I think is going on: Firstly, we set duration at 5000, which how long the loop will take to complete in an ideal world. With a computer that is slow/busy, let's say the animation loop takes twice as long as it should, so 10000: When this happens, the scalar is set to 2.0: scalar = deltat / duration scalar = 10000 / 5000 scalar = 2.0 We now times all animation by twice as much: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 2.0; angle = (Math.PI * 4) // which is 2 rotations When we do this, the cube rotation will appear to 'jump', but this is good because the animation remains real-time. With a computer that is going too quickly, let's say the animation loop takes half as long as it should, so 2500: When this happens, the scalar is set to 0.5: scalar = deltat / duration scalar = 2500 / 5000 scalar = 0.5 We now times all animation by a half: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 0.5; angle = (Math.PI * 1) // which is half a rotation When we do this, the cube won't jump at all, and the animation remains real time, and doesn't speed up. However, would I be right in thinking this doesn't alter how hard the computer is working? I mean it still goes through the loop as fast as it can, and it still has render the whole scene, just with different smaller angles! So this a bad way to implement delta time, right? Now let's pretend the computer is taking exactly as long as it should, so 5000: When this happens, the scalar is set to 1.0: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 1; angle = (Math.PI * 2) // which is 1 rotation When we do this, everything is timsed by 1, so nothing is changed. We'd get the same result if we weren't using delta time at all! My questions are as follows Mostly importantly, have I got the right end of the stick here? How do we know to set the duration to 5000 ? Or can it be any number? I'm a bit vague about the "computer going too quickly". Is there a way loop less often rather than reduce the animation steps? Seems like a better idea. Using this method, do all of our animations need to be timesed by the scalar? Do we have to hunt down every last one and times it? Is this the best way to implement delta time? I think not, due to the fact the computer can go nuts and all we do is divide each animation step and because we need to hunt down every step and times it by the scalar. Not a very nice DSL, as it were. So what is the best way to implement delta time? Below is one way that I do not really get but may be a better way to implement delta time. Could someone explain please? // Globals INV_MAX_FPS = 1 / 60; frameDelta = 0; clock = new THREE.Clock(); // In the animation loop (the requestAnimationFrame callback)… frameDelta += clock.getDelta(); // API: "Get the seconds passed since the last call to this method." while (frameDelta >= INV_MAX_FPS) { update(INV_MAX_FPS); // calculate physics frameDelta -= INV_MAX_FPS; } How I think this works: Firstly we set INV_MAX_FPS to 0.01666666666 How we will use this number number does not jump out at me. We then intialize a frameDelta which stores how long the last loop took to run. Come the first loop frameDelta is not greater than INV_MAX_FPS so the loop is not run (0 = 0.01666666666). So nothing happens. Now I really don't know what would cause this to happen, but let's pretend that the loop we just went through took 2 seconds to complete: We set frameDelta to 2: frameDelta += clock.getDelta(); frameDelta += 2.00 Now we run an animation thanks to update(0.01666666666). Again what is relevance of 0.01666666666?? And then we take away 0.01666666666 from the frameDelta: frameDelta -= INV_MAX_FPS; frameDelta = frameDelta - INV_MAX_FPS; frameDelta = 2 - 0.01666666666 frameDelta = 1.98333333334 So let's go into the second loop. Let's say it took 2(? Why not 2? Or 12? I am a bit confused): frameDelta += clock.getDelta(); frameDelta = frameDelta + clock.getDelta(); frameDelta = 1.98333333334 + 2 frameDelta = 3.98333333334 This time we enter the while loop because 3.98333333334 = 0.01666666666 We run update We take away 0.01666666666 from frameDelta again: frameDelta -= INV_MAX_FPS; frameDelta = frameDelta - INV_MAX_FPS; frameDelta = 3.98333333334 - 0.01666666666 frameDelta = 3.96666666668 Now let's pretend the loop is super quick and runs in just 0.1 seconds and continues to do this. (Because the computer isn't busy any more). Basically, the update function will be run, and every loop we take away 0.01666666666 from the frameDelta untill the frameDelta is less than 0.01666666666. And then nothing happens until the computer runs slowly again? Could someone shed some light please? Does the update() update the scalar or something like that and we still have to times everything by the scalar like in the first example?

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• Unexpected results for projection on to plane

  - by ravenspoint

  I want to use this projection matrix: GLfloat shadow[] = { -1,0,0,0, 1,0,-1,1, 0,0,-1,0, 0,0,0,-1 }; It should cast object shadows onto the y = 0 plane from a point light at 1,1,-1. I create a rectangle in the x = 0.5 plane glBegin( GL_QUADS ); glVertex3f( 0.5,0.2,-0.5); glVertex3f( 0.5,0.2,-1.5); glVertex3f( 0.5,0.5,-1.5); glVertex3f( 0.5,0.5,-0.5); glEnd(); Now if I manually multiply these vertices with the matrix, I get. glBegin( GL_QUADS ); glVertex3f( 0.375,0,-0.375); glVertex3f( 0.375,0,-1.625); glVertex3f( 0,0,-2); glVertex3f( 0,0,0); glEnd(); Which produces a reasonable display ( camera at 0,5,0 looking down y axis ) So rather than do the calculation manually, I should be able to use the opengl model transormation. I write this code: glMatrixMode (GL_MODELVIEW); GLfloat shadow[] = { -1,0,0,0, 1,0,-1,1, 0,0,-1,0, 0,0,0,-1 }; glLoadMatrixf( shadow ); glBegin( GL_QUADS ); glVertex3f( 0.5,0.2,-0.5); glVertex3f( 0.5,0.2,-1.5); glVertex3f( 0.5,0.5,-1.5); glVertex3f( 0.5,0.5,-0.5); glEnd(); But this produces a blank screen! What am I doing wrong? Is there some debug mode where I can print out the transformed vertices, so I can see where they are ending up? Note: People have suggested that using glMultMatrixf() might make a difference. It doesn't. Replacing glLoadMatrixf( shadow ); with glLoadIdentity(); glMultMatrixf( shadow ); gives the identical result ( of course! )

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• xbox thumbstick used to rotate sprite, basic formula makes it "stick" or feel "sticky" at 90 degree intervals! how do get smooth rotation?

  - by Hugh

  Context: C#, XNA game I am using a very basic formula to calculate what angle my sprite (spaceship for example) should be facing based on the xbox controller thumbstick ie. you use the thumbstick to rotate the ship! in my main update method: shuttleAngle = (float) Math.Atan2(newGamePadState.ThumbSticks.Right.X, newGamePadState.ThumbSticks.Right.Y); in my main draw method: spriteBatch.Draw(shuttle, shuttleCoords, sourceRectangle, Color.White, shuttleAngle, origin, 1.0f, SpriteEffects.None, 1); as you can see its quite simple, i take the current radians from the thumbstick and store it in a float "shuttleAngle" and then use this as the rotation angle (in radians) arguement for drawing the shuttle. For some reason when i rotate the sprint it feels sticky at 0, 90, 180 and 270 degrees angles, it wants to settle at those angles. its not giving me a smooth and natural rotation like i would feel in a game that uses a similar mechanic. PS: my xbox controller is fine!

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• Are there any preexisting maps for a Minecraft-like level I could use in my engine?

  - by Rishav Sharan

  I am working on a tiny cube-based engine like Minecraft. I was wondering if there is a way for me to get large blocky terrain in a text format that I can use for rendering on my engine? I don't want to start on procedural generation now, I just want a resource where I can get the coord list for a pretty looking terrain. Alternatively, is it possible for me to parse the Minecraft world files and use that data to generate terrain/buildings in my code?

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• Gap in parallaxing background loop

  - by CinetiK

  The bug here is that my background kind of offset a bit itself from where it should draw and so I have this line. I have some troubles understanding why I get this bug when I set a speed that is different then 1,2,4,8,16,... In main class I set the speed depending on the player speed bgSpeed = -(int)playerMoveSpeed.X / 10; and here's my background class class ParallaxingBackground { Texture2D texture; Vector2[] positions; public int Speed { get; set;} public void Initialize(ContentManager content, String texturePath, int screenWidth, int speed) { texture = content.Load<Texture2D>(texturePath); this.Speed = speed; positions = new Vector2[screenWidth / texture.Width + 2]; for (int i = 0; i < positions.Length; i++) { positions[i] = new Vector2(i * texture.Width, 0); } } public void Update() { for (int i = 0; i < positions.Length; i++) { positions[i].X += Speed; if (Speed <= 0) { if (positions[i].X <= -texture.Width) { positions[i].X = texture.Width * (positions.Length - 1); } } else { if (positions[i].X >= texture.Width*(positions.Length - 1)) { positions[i].X = -texture.Width; } } } } public void Draw(SpriteBatch spriteBatch) { for (int i = 0; i < positions.Length; i++) { spriteBatch.Draw(texture, positions[i], Color.White); } } }

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• Frames per Second and Updates per Second [on hold]

  - by matt murray

  So this is more a general resources question, as I am seeking knowledge on how best to conserve resources in a game (I am writing in Java, and please this is not a thread on what language I should write it in, I have already chosen Java) so that the updates and frames per second could be the highest they could be. In general I am just searching for any articles you may have, any personal experience, anything what so ever that could be of use to a pretty new Java game developer on the subject! Thanks in advance!

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• Trouble with touch events on iPhone

  - by MrDatabase

  I'm making a simple 2D game for iPhone. Think of the game as a ball on the screen that goes up while the user is touching the screen and falls down when the user stops touching the screen. The ball starts moving up in touchesBegan:withEvent and starts moving down in touchesEnded:withEvent. This works fine almost all the time. However on occasion the ball will keep moving up after the user stops touching... or the ball will keep moving down while the user is touching. Why is this happening? Just fyi the ball is drawn on a UIWindow. The taps are handled by a UIImageview subclass that's clearColor and takes up the entire screen. This "touchLayer" is also moved to the front of the window in the game loop. Any idea why this control scheme occasionally fails? Perhaps the touch events just aren't firing? Or they're fired out of order? Cheers!

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• Implmenting RLE into a tilemap or how to create a large 3D array?

  - by Smallbro

  Currently I've been using a 3D array for my tiles in a 2D world but the 3D side comes in when moving down into caves and whatnot. Now this is not memory efficient and I switched over to a 2D array and can now have much larger maps. The only issue I'm having now is that it seems that my tiles cannot occupy the same space as a tile on the same z level. My current structure means that each block has its own z variable. This is what it used to look like: map.blockData[x][y][z] = new Block(); however now it works like this map.blockData[x][y] = new Block(z); I'm not sure why but if I decide to use the same space on say the floor below it wont allow me to. Does anyone have any ideas on how I can add a z-axis to my 2D array? I'm using java but I reckon the concept carries across different languages. Edit: As Will posted, RLE sounds like the best method for achieving a fast 3D array. However I'm struggling to understand how I would even start to implement it? Would I create a 4D array the 4th being something which controls how many to skip? Or would the x-axis simply change altogether and have large gaps in between - for example [5][y][z] would skip 5 tiles? Is there something really obvious here which I am missing? The number of z levels I'm trying to have is around 66, it would be preferably that I can have up to or more than 1000 in x and y.

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• How does Starcraft 2 load it's metadata?

  - by chobok

  Lets say you are playing Starcraft 2 melee map. The game loads the map. Melee maps have the following dependencies: Liberty (Mod) Liberty Multi (Mod) I think the game engine will load the data from Liberty (Mod) first, then from Liberty Multi (Mod). For data that exists in both dependencies, the engine will use the one from Liberty Multi (Mod). Is this correct? Liberty Multi (Mod) is updated with each patch of Starcraft 2. Does the game engine load just the latest version of Liberty Multi (Mod)? or Does the game engine load all the versions and overwrite duplicate data with the latest version?

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• Can't get sprite to rotate correctly?

  - by rphello101

  I'm attempting to play with graphics using Java/Slick 2d. I'm trying to get my sprite to rotate to wherever the mouse is on the screen and then move accordingly. I figured the best way to do this was to keep track of the angle the sprite is at since I have to multiply the cosine/sine of the angle by the move speed in order to get the sprite to go "forwards" even if it is, say, facing 45 degrees in quadrant 3. However, before I even worry about that, I'm having trouble even getting my sprite to rotate in the first place. Preliminary console tests showed that this code worked, but when applied to the sprite, it just kind twitches. Anyone know what's wrong? int mX = Mouse.getX(); int mY = HEIGHT - Mouse.getY(); int pX = sprite.x; int pY = sprite.y; int tempY, tempX; double mAng, pAng = sprite.angle; double angRotate=0; if(mX!=pX){ tempY=pY-mY; tempX=mX-pX; mAng = Math.toDegrees(Math.atan2(Math.abs((tempY)),Math.abs((tempX)))); if(mAng==0 && mX<=pX) mAng=180; } else{ if(mY>pY) mAng=270; else mAng=90; } //Calculations if(mX<pX&&mY<pY){ //If in Q2 mAng = 180-mAng; } if(mX<pX&&mY>pY){ //If in Q3 mAng = 180+mAng; } if(mX>pX&&mY>pY){ //If in Q4 mAng = 360-mAng; } angRotate = mAng-pAng; sprite.angle = mAng; sprite.image.setRotation((float)angRotate);

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• How can I prevent seams from showing up on objects using lower mipmap levels?

  - by Shivan Dragon

  Disclaimer: kindly right click on the images and open them separately so that they're at full size, as there are fine details which don't show up otherwise. Thank you. I made a simple Blender model, it's a cylinder with the top cap removed: I've exported the UVs: Then imported them into Photoshop, and painted the inner area in yellow and the outer area in red. I made sure I cover well the UV lines: I then save the image and load it as texture on the model in Blender. Actually, I just reload it as the image where the UVs are exported, and change the viewport view mode to textured. When I look at the mesh up-close, there's yellow everywhere, everything seems fine: However, if I start zooming out, I start seeing red (literally and metaphorically) where the texture edges are: And the more I zoom, the more I see it: Same thing happends in Unity, though the effect seems less pronounced. Up close is fine and yellow: Zoom out and you see red at the seams: Now, obviously, for this simple example a workaround is to spread the yellow well outside the UV margins, and its fine from all distances. However this is an issue when you try making a complex texture that should tile seamlessly at the edges. In this situation I either make a few lines of pixels overlap (in which case it looks bad from upclose and ok from far away), or I leave them seamless and then I have those seams when seeing it from far away. So my question is, is there something I'm missing, or some extra thing I must do to have my texture look seamless from all distances?

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• How do I get the child of a unique parent in ActionScript?

  - by Koen

  My question is about targeting a child with a unique parent. For example. Let's say I have a box people can move called box_mc and 3 platforms it can jump on called: Platform_1 Platform_2 Platform_3 All of these platforms have a child element called hit. Platform_1 Hit Platform_2 Hit Platform_3 Hit I use an array and a for each statement to detect if box_mc hits one of the platforms childs. var obj_arr:Array = [Platform_1, Platform_2, Platform_3]; for each(obj in obj_arr){ if(box_mc.hitTestObject(obj.hit)){ trace(obj + " " + obj.hit); box_mc.y = obj.hit.y - box_mc.height; } } obj seems to output the unique parent it is hitting but obj.hit ouputs hit, so my theory is that it is applying the change of y to all the childs called hit in the stage. Would it be possible to only detect the child of that specific parent?

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• How to detect which edges of a rectange touch when they collide in iOS

  - by Mike King

  I'm creating a basic "game" in iOS 4.1. The premise is simple, there is a green rectangle ("disk") that moves/bounces around the screen, and red rectangle ("bump") that is stationary. The user can move the red "bump" by touching another coordinate on the screen, but that's irrelevant to this question. Each rectangle is a UIImageView (I will replace them with some kind of image/icon once I get the mechanics down). I've gotten as far as detecting when the rectangles collide, and I'm able to reverse the direction of the green "disk" on the Y axis if they do. This works well when the green "disk" approaches the red "bump" from top or bottom, it bounces off in the other direction. But when it approaches from the side, the bounce is incorrect; I need to reverse the X direction instead. Here's the timer I setup: - (void)viewDidLoad { xSpeed = 3; ySpeed = -3; gameTimer = [NSTimer scheduledTimerWithTimeInterval:0.05 target:self selector:@selector(mainGameLoop:) userInfo:nil repeats:YES]; [super viewDidLoad]; } Here's the main game loop: - (void) mainGameLoop:(NSTimer *)theTimer { disk.center = CGPointMake(disk.center.x + xSpeed, disk.center.y + ySpeed); // make sure the disk does not travel off the edges of the screen // magic number values based on size of disk's frame // startAnimating causes the image to "pulse" if (disk.center.x < 55 || disk.center.x > 265) { xSpeed = xSpeed * -1; [disk startAnimating]; } if (disk.center.y < 55 || disk.center.y > 360) { ySpeed = ySpeed * -1; [disk startAnimating]; } // check to see if the disk collides with the bump if (CGRectIntersectsRect(disk.frame, bump.frame)) { NSLog(@"Collision detected..."); if (! [disk isAnimating]) { ySpeed = ySpeed * -1; [disk startAnimating]; } } } So my question is: how can I detect whether I need to flip the X speed or the Y speed? ie: how can I calculate which edge of the bump was collided with?

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• Split vector vs matrix notation for transformation

  - by seahorse

  Some rendering engines like Ogre prefer to use a individual vector based notation for transformations like the following Split vector notation: Net Transformation is represented by Scale vector = sx, sy, sz Transformation vector = tx, ty, tz Rotation Quaternion Vector = w,x,y,z Matrix notation: There are other engines which simply use a net combined transformation matrix. What are the advantages of the first notation over the second? Also for animation interpolation does it work in the first notation that we interpolate across the individual components and use the interpolated parts to get the net transformation? Is this another advantage?

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• glColor3f Setting colour

  - by Aaron

  This draws a white vertical line from 640 to 768 at x512: glDisable(GL_TEXTURE_2D); glBegin(GL_LINES); glColor3f((double)R/255,(double)G/255,(double)B/255); glVertex3f(SX, -SPosY, 0); // origin of the line glVertex3f(SX, -EPosY, 0); // ending point of the line glEnd(); glEnable(GL_TEXTURE_2D); This works, but after having a problem where it wouldn't draw it white (Or to any colour passed) I discovered that disabling GL_TEXTURE_2D Before drawing the line, and the re-enabling it afterwards for other things, fixed it. I want to know, is this a normal step a programmer might take? Or is it highly inefficient? I don't want to be causing any slow downs due to a mistake =) Thanks

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• Unable to access jar. Why?

  - by SystemNetworks

  I was making a game in java and exported it as jar file. Then after that, I opeed jar splice. I added the libaries and exported jar. I added the natives then i made a main class. I created a fat jar and put it on my desktop. I'm using Mac OS X 10.8 Mountain Lion. When I put in the terminal, java -jar System Front.jar it says unable to access System Front.jar Even if i double click on the file, it doesen't show up! Help! I'm using slick. I added slick and lwjgl as libraries for the jar splice at the jars.

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• Bomberman clone, how to do bombs?

  - by hustlerinc

  I'm playing around with a bomberman clone to learn game-developement. So far I've done tiles, movement, collision detection, and item pickup. I also have pseudo bombplacing (just graphics and collision, no real functionality). I've made a jsFiddle of the game with the functionality I currently have. The code in the fiddle is very ugly though. Scroll past the map and you find how I place bombs. Anyway, what I would like to do is an object, that has the general information about bombs like: function Bomb(){ this.radius = player.bombRadius; this.placeBomb = function (){ if(player.bombs != 0){ // place bomb } } this.explosion = function (){ // Explosion } } I don't really know how to fit it into the code though. Everytime I place a bomb, do I do var bomb = new Bomb(); or do i need to constantly have that in the script to be able to access it. How does the bomb do damage? Is it as simple as doing X,Y in all directions until radius runs out or object stops it? Can I use something like setTimeout(bomb.explosion, 3000) as timer? Any help is appreciated, be it a simple explanation of the theory or code examples based on the fiddle. When I tried the object way it breaks the code.

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• How can I do Mouse Selection In OpenGL 3.0?

  - by NoobScratcher

  Hello I'm pretty good programmer I've made my own 2D games in SDL and made a gui in 3D using Old OpenGL and Modern OpenGL but.. I'm having problems with trying to click 3D models with opengl I have no idea what to do too be honest. Do I read the area that I've clicked? or what do I do? 100% shore this has been asked before but I just don't know what to do...?? using : OpenGL 3.0 WIN32 API C++

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• Error in my Separating Axis Theorem collision code

  - by Holly

  The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; int x; int y; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } public void update(int xPos, int yPos){ x = xPos; y = yPos; } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(new Vect(vertices[0].x+x, vertices[0].y+y)); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(new Vect(vertices[i].x+x, vertices[i].y+y)); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if(y > other.x && other.y > x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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• Multiplayer game communication framework for mac/ios

  - by ishaq

  (Cross post from stackoverflow) I am creating a multiplayer 2D game for Mac and iOS devices. I'll be using cocso2d for graphics/game engine, however I am largely blank on what to use for multiplayer communication. Please note that I cannot use central severs e.g. SmartFox, RedDwarf, etc since I want the players to "host" games for others and be able to play it on their LAN, VPN or my own servers. Any pointers? I checked lidgren but it's for .NET only and hence not an option for me. EDIT: just in case it wasn't clear, the messaging has to be real time hence it's probably going to be over UDP

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• XNA CustomModelAnimationSample problem

  - by Mentoliptus

  I downloaded the official tutorial from:CustomModelAnimationSample It works fine but when I try to replicate it in my project, it fails to load the Tag property in my model. Is found that the probelm is in the line: skinnedModel = Content.Load<Model>("DudeWalk"); This line loads the model from the DudeWalk.fbx file and with the custom SkinnedModelProcessor. It loads the animations data in the model. After the line the Tag property is full. I stepped into the method and it went to the custom ModelData class. I copied everything from the projects CustomModelAnimationWindows and CustomModelAnimationPipeline to my solution and set all the references. I tried the same line of code and couldn't step in the method. It called the default method or model constructor and after the line the model's Tag propetry was null. I have to load the model through my custom SkinnedModelProcessor class, but how I tell the game to use this class? In the tutroail CustomModelClass the line is changed to: model = Content.Load<CustomModel>("tank"); So I assumed that I have to set the generic type to a custom model class, but the first example works without it. If anyone has some useful advice or some other helpful link, I'll be happy to try it.

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• OpenGL ES 2.0 texture distortion on large geometry

  - by Spruce

  OpenGL ES 2.0 has serious precision issues with texture sampling - I've seen topics with a similar problem, but I haven't seen a real solution to this "distorted OpenGL ES 2.0 texture" problem yet. This is not related to the texture's image format or OpenGL color buffers, it seems like it's a precision error. I don't know what specifically causes the precision to fail - it doesn't seem like it's just the size of geometry that causes this distortion, because simply scaling vertex position passed to the the vertex shader does not solve the issue. Here are some examples of the texture distortion: Distorted Texture (on OpenGL ES 2.0): http://i47.tinypic.com/3322h6d.png What the texture normally looks like (also on OpenGL ES 2.0): http://i49.tinypic.com/b4jc6c.png The texture issue is limited to small scale geometry on OpenGL ES 2.0, otherwise the texture sampling appears normal, but the grainy effect gradually worsens the further the vertex data is from the origin of XYZ(0,0,0) These texture issues do not occur on desktop OpenGL (works fine under Windows XP, Windows 7, and Mac OS X) I've only seen the problem occur on Android, iPhone, or WebGL(which is similar to OpenGL ES 2.0) All textures are power of 2 but the problem still occurs Scaling the vertex data - The values of a vertex's X Y Z location are in the range of: -65536 to +65536 floating point I realized this was large, so I tried dividing the vertex positions by 1024 to shrink the geometry and hopefully get more accurate floating point precision, but this didn't fix or lessen the texture distortion issue Scaling the modelview or scaling the projection matrix does not help Changing texture filtering options does not help Disabling mipmapping, or using GL_NEAREST/GL_LINEAR does nothing Enabling/disabling anisotropic does nothing The banding effect still occurs even when using GL_CLAMP Dividing the texture coords passed to the vertex shader and then multiplying them back to the correct values in the fragment shader, also does not work precision highp sampler2D, highp float, highp int - in the fragment or the vertex shader didn't change anything (lowp/mediump did not work either) I'm thinking this problem has to have been solved at one point - Seeing that OpenGL ES 2.0 -based games have been able to render large-scale, highly detailed geometry

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• Collision Resolution

  - by CiscoIPPhone

  I know quite well how to check for collisions, but I don't know how to handle the collision in a good way. Simplified, if two objects collide I use some calculations to change the velocity direction. If I don't move the two objects they will still overlap and if the velocity is not big enough they will still collide after next update. This can cause objects to get stuck in each other. But what if I try to move the two objects so they do not overlap. This sounds like a good idea but I have realised that if there is more than two objects this becomes very complicated. What if I move the two objects and one of them collides with other objects so I have to move them too and they may collide with walls etc. I have a top down 2D game in mind but I don't think that has much to do with it. How are collisions usually handled? This question is asked on behalf of Wooh

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• strange behavior in Box2D+LibGDX when applying impulse

  - by Z0lenDer

  I have been playing around with Box2D and LibGDX and have been using a sample code from DecisionTreeGames as the testing ground. Now I have a screen with four walls and a rectangle shape, lets call it a brick. When I use applyLinearImpulse to the brick, it starts bouncing right and left without any pattern and won't stop! I tried adding friction and increasing the density, but the behavior still remains the same. Here are some of the code that might be useful: method for applying the impulse: center = brick.getWorldCenter(); brick.applyLinearImpulse(20, 0, center.x, center.y); Defining the brick: brick_bodyDef.type = BodyType.DynamicBody; brick_bodyDef.position.set(pos); // brick is initially on the ground brick_bodyDef.angle = 0; brick_body = world.createBody(brick_bodyDef); brick_body.setBullet(true); brick_bodyShape.setAsBox(w,h); brick_fixtureDef.density = 0.9f; brick_fixtureDef.restitution = 1; brick_fixtureDef.shape = brick_bodyShape; brick_fixtureDef.friction=1; brick_body.createFixture(fixtureDef); Walls are defined the same only their bullet value is set to false I would really appreciate it if you could help me have a change this code to have a realistic behavior (i.e. when I apply impulse to the brick it should trip a few times and then stop completely).

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