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  • XNA 4.0 SpriteFont not displaying all Characters

    - by Iain Brown
    Am looking for a little help and trying to use SpriteFont in my XNA 4.0 game but the problem is am displaying to string "This is a test" but all that's displayed on the screen is "This is st" so the "a te" are missing from the screen. The space is there for the characters but the letters are not. The code am using is: spriteBatch.Begin(SpriteSortMode.BackToFront, BlendState.AlphaBlend); spriteBatch.DrawString(font,"this is a test",new Vector2(692,372),Color.White); spriteBatch.Draw(texture,new Rectangle(0,0,100,100),Color.White); spriteBatch.End(); Any help with this would be great!

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  • getting bone base and tip positions from a transform matrix?

    - by ddos
    I need this for a Blender3d script, but you don't really need to know Blender to answer this. I need to get bone head and tip positions from a transform matrix read from a file. The position of base is the location part of the matrix, length of the bone (distance from base to tip) is the scale, position of the tip is calculated from the scale (distance from bone base) and rotation part of the matrix. So how to calculate these? bone.base([x,y,z]) # x,y,z - floats bone.tip([x,y,z])

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  • Fixed-Function vs Shaders: Which for beginner?

    - by Rob Hays
    I'm currently going to college for computer science. Although I do plan on utilizing an existing engine at some point to create a small game, my aim right now is towards learning the fundamentals: namely, 3D programming. I've already done some research regarding the choice between DirectX and OpenGL, and the general sentiment that came out of that was that whether you choose OpenGL or DirectX as your training-wheels platform, a lot of the knowledge is transferrable to the other platform. Therefore, since OpenGL is supported by more systems (probably a silly reason to choose what to learn), I decided that I'm going to learn OpenGL first. After I made this decision to learn OpenGL, I did some more research and found out about a dichotomy that I was somewhere unaware of all this time: fixed-function OpenGL vs. modern programmable shader-based OpenGL. At first, I thought it was an obvious choice that I should choose to learn shader-based OpenGL since that's what's most commonly used in the industry today. However, I then stumbled upon the very popular Learning Modern 3D Graphics Programming by Jason L. McKesson, located here: http://www.arcsynthesis.org/gltut/ I read through the introductory bits, and in the "About This Book" section, the author states: "First, much of what is learned with this approach must be inevitably abandoned when the user encounters a graphics problem that must be solved with programmability. Programmability wipes out almost all of the fixed function pipeline, so the knowledge does not easily transfer." yet at the same time also makes the case that fixed-functionality provides an easier, more immediate learning curve for beginners by stating: "It is generally considered easiest to teach neophyte graphics programmers using the fixed function pipeline." Naturally, you can see why I might be conflicted about which paradigm to learn: Do I spend a lot of time learning (and then later unlearning) the ways of fixed-functionality, or do I choose to start out with shaders? My primary concern is that modern programmable shaders somehow require the programmer to already understand the fixed-function pipeline, but I doubt that's the case. TL;DR == As an aspiring game graphics programmer, is it in my best interest to learn 3D programming through fixed-functionality or modern shader-based programming?

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

    - by user1075940
    In my game the water movement is done in a shader using Gerstner equations. The water movement looks realistic enough for a school project but I encounter serious problem when I wanted to do sailing on waves (similar to this). I managed to do collision with land by calculating quad's vertices and normals beneath ship, however same method can not be applied to water because XZ are displaced and Y is calculated in a shader :( How to approach this problem ? Is it possible to retrieve transformed grid from shader? Unfortunately no external physics libraries can be used.

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  • Workaround the flip queue (AKA pre-rendered frames) in OpenGL?

    - by user41500
    It appears that some drivers implement a "flip queue" such that, even with vsync enabled, the first few calls to swap buffers return immediately (queuing those frames for later use). It is only after this queue is filled that buffer swaps will block to synchronize with vblank. This behavior is detrimental to my application. It creates latency. Does anyone know of a way to disable it or a workaround for dealing with it? The OpenGL Wiki on Swap Interval suggests a call to glFinish after the swap but I've had no such luck with that trick.

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  • How do I have to take into account the direction in which the camera is facing when creating a first person strafe (left/right) movement

    - by Chris
    This is the code I am currently using, and it works great, except for the strafe always causes the camera to move along the X axis which is not relative to the direction in which the camera is actually facing. As you can see currently only the x location is updated: [delta * -1, 0, 0] How should I take into account the direction in which the camera is facing (I have the camera's target x,y,z) when creating a first person strafe (left/right) movement? case 'a': var eyeOriginal = g_eye; var targetOriginal = g_target; var viewEye = g_math.subVector(g_eye, g_target); var viewTarget = g_math.subVector(g_target, g_eye); viewEye = g_math.addVector([delta * -1, 0, 0], viewEye); viewTarget = g_math.addVector([delta * -1, 0, 0], viewTarget); g_eye = g_math.addVector(viewEye, targetOriginal); g_target = g_math.addVector(viewTarget, eyeOriginal); break; case 'd': var eyeOriginal = g_eye; var targetOriginal = g_target; var viewEye = g_math.subVector(g_eye, g_target); var viewTarget = g_math.subVector(g_target, g_eye); viewEye = g_math.addVector([delta, 0, 0], viewEye); viewTarget = g_math.addVector([delta, 0, 0], viewTarget); g_eye = g_math.addVector(viewEye, targetOriginal); g_target = g_math.addVector(viewTarget, eyeOriginal); break;

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  • Regulating how much to draw based on how much was drawn last frame.

    - by Mike Howard
    I have a 3D game world on an iPhone (limited graphics speed), and I'm already regulating whether I draw each shape on the screen based on it's size and distance from the camera. Something like... if (how_big_it_looks_from_the_camera > constant) then draw What I want to do now is also take into account how many shapes are being drawn, so that in busier areas of the game world I can draw less than I otherwise would. I tried to do this by dividing how_big_it_looks by the number of shapes that were drawn last frame (well, the square root of this but I'm simplifying - the problem is the same). if (how_big_it_looks / shapes_drawn > constant2) then draw But the check happens at the level of objects which represent many drawn shapes, and if an object containing many shapes is switched on, it increases shapes_drawn lots and switches itself back off the next frame. It flickers on and off. I tried keeping a kind of weighted average of previous values, by each frame doing something like shapes_drawn_recently = 0.9 * shapes_drawn_recently + 0.1 * shapes_just_drawn, but of course it only slows the flickering down because of the nature of the feedback loop. Is there a good way of solving this? My project is in Objective-C, but a general algorithm or pseudo-code is good too. Thanks.

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  • Efficiently representing a dynamic transform hierarchy

    - by Mattia
    I'm looking for a way to represent a dynamic transform hierarchy (i.e. one where nodes can be inserted and removed arbitrarily) that's a bit more efficient than using a standard tree of pointers . I saw the answers to this question ( Efficient structure for representing a transform hierarchy. ), but as far as I can determine the tree-as-array approach only works for static hierarchies or dynamic ones where nodes have a fixed number of children (both deal-breakers for me). I'm probably wrong about that but could anyone point out how? If I'm not wrong are there other alternatives that work for dynamic hierarchies?

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  • What is a good way to measure game virality?

    - by Chris Garrett
    I have added some social features to an iPhone game (Lexitect if you're curious), such as email, Twitter, and Facebook integration for sharing high scores. Along with these features, I am measuring how many times users make it to each step. The goal of these features are to make the game more viral, and I am trying to get to a measure of game virality. I would think that a game virality metric would produce a number based on 1.0, where 1.0 = zero viral growth, and 1.01 would represent 1% viral growth over some unit of time. How is virality normally measured, and in what units? How is time capped on the metric? i.e. if I gave each player a year to determine how many recommendations they make, I wouldn't get any real numbers for a year from the time I start tracking it. Are there any standards for tracking virality in a meaningful way?

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  • Is chess-like AI really inapplicable in turn-based strategy games?

    - by Joh
    Obviously, trying to apply the min-max algorithm on the complete tree of moves works only for small games (I apologize to all chess enthusiasts, by "small" I do not mean "simplistic"). For typical turn-based strategy games where the board is often wider than 100 tiles and all pieces in a side can move simultaneously, the min-max algorithm is inapplicable. I was wondering if a partial min-max algorithm which limits itself to N board configurations at each depth couldn't be good enough? Using a genetic algorithm, it might be possible to find a number of board configurations that are good wrt to the evaluation function. Hopefully, these configurations might also be good wrt to long-term goals. I would be surprised if this hasn't been thought of before and tried. Has it? How does it work?

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  • Problem with Ogre::Camera lookAt function when target is directly below.

    - by PigBen
    I am trying to make a class which controls a camera. It's pretty basic right now, it looks like this: class HoveringCameraController { public: void init(Ogre::Camera & camera, AnimatedBody & target, Ogre::Real height); void update(Ogre::Real time_delta); private: Ogre::Camera * camera_; AnimatedBody * target_; Ogre::Real height_; }; HoveringCameraController.cpp void HoveringCameraController::init(Ogre::Camera & camera, AnimatedBody & target, Ogre::Real height) { camera_ = &camera; target_ = &target; height_ = height; update(0.0); } void HoveringCameraController::update(Ogre::Real time_delta) { auto position = target_->getPosition(); position.y += height_; camera_->setPosition(position); camera_->lookAt(target_->getPosition()); } AnimatedBody is just a class that encapsulates an entity, it's animations and a scene node. The getPosition function is simply forwarded to it's scene node. What I want(for now) is for the camera to simply follow the AnimatedBody overhead at the distance given(the height parameter), and look down at it. It follows the object around, but it doesn't look straight down, it's tilted quite a bit in the positive Z direction. Does anybody have any idea why it would do that? If I change this line: position.y += height_; to this: position.x += height_; or this: position.z += height_; it does exactly what I would expect. It follows the object from the side or front, and looks directly at it.

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  • Implementing a FSM with ActionScript 2 without using classes?

    - by Up2u
    I have seen several references of A.I. and FSM, but sadly I still can't understand the point of an FSM in AS2.0. Is it a must to create a class for each state? I have a game-project which also it has an A.I., the A.I. has 3 states: distanceCheck, ChaseTarget, and Hit the target. It's an FPS game and played via mouse. I have created the A.I. successfully, but I want to convert it to FSM method... My first state is CheckDistanceState() and in that function I look for the nearest target and trigger the function ChaseState(), there I insert the Hit() function to destroy the enemy, The 3 functions that I created are being called in AI_cursor.onEnterframe. Is there any chance to implement an FSM without the need to create a class? From what I've read before, you have to create a class. I prefer to write the code on frames in flash and I still don't understand how to have external classes.

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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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  • Android Loading Screen: How do I use a stack to load elements?

    - by tom_mai78101
    I have some problems with figuring out what value I should put in the function: int value_needed_to_figure_out = X; ProgressBar.incrementProgressBy(value_needed_to_figure_out); I've been researching about loading screens and how to use them. Some examples I've seen have implemented Thread.sleep() in a Handler.post(new Runnable()) function. To me, I got most of that concept of using the Handler to update the ProgressBar, while pretending to do some heavy crunching work. So, I kept looking. I have read this thread here: How do I load chunks of data from an assest manager during a loading screen? It said that I can try using a stack it needs to load, and adding a size counter as I add elements to the stack. What does it mean? This is the part where I'm totally stumped. If anyone would provide some hints, I'll gladly appreciate it. Thanks in advance.

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  • How to spawn a character at certain point and walk to a set point

    - by Robert H.
    I am making a game where I have a background image of a neighborhood. Each location has a different number of customers that are generated to walk on sidewalks. They all walk to a specific location (like a stand or cart that sells stuff), after they get to location I want them to interact with the cart. However, if another customer is already in a sale interaction then the others get in line in order of arrival. After the transaction the customers walk off screen. Any information on how I can do this and what game engine would be needed? Any one have any idea where I should go for this. I already have my game done up through Eclipse/Java without any game engine.

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  • How do I properly use multithreading with Nvidia PhysX?

    - by xcrypt
    I'm having a multithreading problem with Nvidia PhysX. the SDK requires that you call Simulate() (starts computing new physics positions within a new thread) and FetchResults() (waits 'till the physics computations are done). Inbetween Simulate() and FetchResults() you may not "compute new physics". It is proposed (in a sample) that we create a game loop as such: Logic (you may calculate physics here and other stuff) Render + Simulate() at start of Render call and FetchResults at end of Render() call However, this has given me various little errors that stack up: since you actually render the scene that was computed in the previous iteration in the game loop. Does anyone have a solution to this?

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  • Understanding how OpenGL blending works

    - by yuumei
    I am attempting to understand how OpenGL (ES) blending works. I am finding it difficult to understand the documentation and how the results of glBlendFunc and glBlendEquation effect the final pixel that is written. Do the source and destination out of glBlendFunc get added together with GL_FUNC_ADD by default? This seems wrong because "basic" blending of GL_ONE, GL_ONE would output 2,2,2,2 then (Source giving 1,1,1,1 and dest giving 1,1,1,1). I have written the following pseudo-code, what have I got wrong? struct colour { float r, g, b, a; }; colour blend_factor( GLenum factor, colour source, colour destination, colour blend_colour ) { colour colour_factor; float i = min( source.a, 1 - destination.a ); // From http://www.khronos.org/opengles/sdk/docs/man/xhtml/glBlendFunc.xml switch( factor ) { case GL_ZERO: colour_factor = { 0, 0, 0, 0 }; break; case GL_ONE: colour_factor = { 1, 1, 1, 1 }; break; case GL_SRC_COLOR: colour_factor = source; break; case GL_ONE_MINUS_SRC_COLOR: colour_factor = { 1 - source.r, 1 - source.g, 1 - source.b, 1 - source.a }; break; // ... } return colour_factor; } colour blend( colour & source, colour destination, GLenum source_factor, // from glBlendFunc GLenum destination_factor, // from glBlendFunc colour blend_colour, // from glBlendColor GLenum blend_equation // from glBlendEquation ) { colour source_colour = blend_factor( source_factor, source, destination, blend_colour ); colour destination_colour = blend_factor( destination_factor, source, destination, blend_colour ); colour output; // From http://www.khronos.org/opengles/sdk/docs/man/xhtml/glBlendEquation.xml switch( blend_equation ) { case GL_FUNC_ADD: output = add( source_colour, destination_colour ); case GL_FUNC_SUBTRACT: output = sub( source_colour, destination_colour ); case GL_FUNC_REVERSE_SUBTRACT: output = sub( destination_colour, source_colour ); } return output; } void do_pixel() { colour final_colour; // Blending if( enable_blending ) { final_colour = blend( current_colour_output, framebuffer[ pixel ], ... ); } else { final_colour = current_colour_output; } } Thanks!

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  • Breakout... Getting the ball reflection X angle when htitting paddle / bricks

    - by Steven Wilson
    Im currently creating a breakout clone for my first ever C# / XNA game. Currently Ive had little trouble creating the paddle object, ball object, and all the bricks. The issue im currently having is getting the ball to bounce off of the paddle and bricks correctly based off of where the ball touches the object. This is my forumala thus far: if (paddleLocation.Intersects(ballLocation)) { position.Y = paddleLocation.Y - texture.Height; motion.Y *= -1; // determine X motion.X = 1 - 2 * (ballLocation.X - paddleLocation.X) / (paddleLocation.Width / 2); } The problem is, the ball goes the opposite direction then its supposed to. When the ball hits the left side of the paddle, instead of bouncing back to the left, it bounces right, and vise versa. Does anyone know what the math equation is to fix this?

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  • Unity Occlusion Portals: What and How?

    - by Nick Wiggill
    (Here I eat my words on Meta about posting Unity questions on Unity Answers... since that site is less responsive than this one.) Unity provides cell-based Occlusion Culling (via Umbra, I believe). However, a newer feature that it supports is Occlusion Portals. The question is, if BSP-based occlusion culling is already a feature of Unity, what do portals add, and how? PS. This question is not "What are portals?" -- I'm aware of the original Quake BSP-style portals -- which is partly why I find the explicit portal concept in Unity odd, since it uses BSP anyway.

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  • How could you model "scent trails" in a game?

    - by Sebastien Diot
    Say you want to create a 3D game, and have either players, or mobiles, be able to tract other entity by following their scent trails. Is there any known data-structure that matches this use case? If you have only few individuals going about, you can probably do something like a map of 3D coord to entity ID, but real scent works differently, because it fades over time, but slowly. And most of the time, you can only know approximately what went there, and approximately how many things of that type went there. And the approximation becomes worst with time, until it's gone. I imagine it's kind of like starting with an exact number, and slowly loosing the least significant digits, until you loose the most significant digit too. But that doesn't really help me, because entity IDs aren't normally encoded to contain the entity type, in addition to it's individual ID.

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  • Foreach loop with 2d array of objects

    - by Jacob Millward
    I'm using a 2D array of objects to store data about tiles, or "blocks" in my gameworld. I initialise the array, fill it with data and then attempt to invoke the draw method of each object. foreach (Block block in blockList) { block.Draw(spriteBatch); } I end up with an exception being thrown "Object reference is not set to an instance of an object". What have I done wrong? EDIT: This is the code used to define the array Block[,] blockList; Then blockList = new Block[screenRectangle.Width, screenRectangle.Height]; // Fill with dummy data for (int x = 0; x <= screenRectangle.Width / texture.Width; x++) { for (int y = 0; y <= screenRectangle.Height / texture.Width; y++) { if (y >= screenRectangle.Height / (texture.Width*2)) { blockList[x, y] = new Block(1, new Rectangle(x * 16, y * 16, texture.Width, texture.Height), texture); } else { blockList[x, y] = new Block(0, new Rectangle(x * 16, y * 16, texture.Width, texture.Height), texture); } } }

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  • Keep 3d model facing the camera at all angles

    - by Sparky41
    I'm trying to keep a 3d plane facing the camera at all angles but while i have some success with this: Vector3 gunToCam = cam.cameraPosition - getWorld.Translation; Vector3 beamRight = Vector3.Cross(torpDirection, gunToCam); beamRight.Normalize(); Vector3 beamUp = Vector3.Cross(beamRight, torpDirection); shipeffect.beamWorld = Matrix.Identity; shipeffect.beamWorld.Forward = (torpDirection) * 1f; shipeffect.beamWorld.Right = beamRight; shipeffect.beamWorld.Up = beamUp; shipeffect.beamWorld.Translation = shipeffect.beamPosition; *Note: Logic not wrote by me i just found this rather useful It seems to only face the camera at certain angles. For example if i place the camera behind the plane you can see it that only Roll's around the axis like this: http://i.imgur.com/FOKLx.png (imagine if you are looking from behind where you have fired from. Any idea what to what the problem is (angles are not my specialty) shipeffect is an object that holds this class variables: public Texture2D altBeam; public Model beam; public Matrix beamWorld; public Matrix[] gunTransforms; public Vector3 beamPosition;

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  • How to update entity states and animations in a component-based game

    - by mivic
    I'm trying to design a component-based entity system for learning purposes (and later use on some games) and I'm having some troubles when it comes to updating entity states. I don't want to have an update() method inside the Component to prevent dependencies between Components. What I currently have in mind is that components hold data and systems update components. So, if I have a simple 2D game with some entities (e.g. player, enemy1, enemy 2) that have Transform, Movement, State, Animation and Rendering components I think I should have: A MovementSystem that moves all the Movement components and updates the State components And a RenderSystem that updates the Animation components (the animation component should have one animation (i.e. a set of frames/textures) for each state and updating it means selecting the animation corresponding to the current state (e.g. jumping, moving_left, etc), and updating the frame index). Then, the RenderSystem updates the Render components with the texture corresponding to the current frame of each entity's Animation and renders everything on screen. I've seen some implementations like Artemis framework, but I don't know how to solve this situation: Let's say that my game has the following entities. Each entity have a set of states and one animation for each state: player: "idle", "moving_right", "jumping" enemy1: "moving_up", "moving_down" enemy2: "moving_left", "moving_right" What are the most accepted approaches in order to update the current state of each entity? The only thing that I can think of is having separate systems for each group of entities and separate State and Animation components so I would have PlayerState, PlayerAnimation, Enemy1State, Enemy1Animation... PlayerMovementSystem, PlayerRenderingSystem... but I think this is a bad solution and breaks the purpose of having a component-based system. As you can see, I'm quite lost here, so I'd very much appreciate any help.

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  • Moving in a diamond - enemy gets stuck

    - by Fibericon
    I have an enemy that I would like to move as follows: Start at (0, 200, 0) Move to (200, 0, 0) Move to (0, -200, 0) Move to (-200, 0, 0) Move to start point, repeat as long as it remains active. This is what I've done to achieve that: if (position.X < 200 && position.Y > 0) { Velocity = new Vector3(1, -1, 0) * speed; } else if (position.X >= 200 && position.Y <= 0 && position.Y > -200) { Velocity = new Vector3(-1, -1, 0) * speed; } else if (position.X <= 0 && position.Y <= -200) { Velocity = new Vector3(-1, 1, 0) * speed; } else { Velocity = new Vector3(1, 1, 0) * speed; } It moves to the second point, but then gets stuck and appears to vibrate in place. How should I be doing this?

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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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