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• What are the semantics of glRotate and glTranslate's parameters?

  - by Zarkopafilis

  I have been trying to play with OpenGL after watching some tutorials and I don't understand how the glTranslatef and glRotatef functions work. I believe a simple picture would help me. I understand that glTranslatef changes the position of the "camera" (but does it change the position in wich the shapes are getting drawn)? However, I don't understand the rotation concept at all. If I do glRotatef(1,0,0,1) it makes my quad spin around. If I just do glRotatef(1,0,0,0) it makes the quad smaller (further away) but if I try to rotate around the X or Y axis, I get a black screen. I don't understand the angle either. Help would be appreciated.

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• How does a single programmer make a game?

  - by Mike

  I have always been a software developer, but lately I've been wanting to get into games. The only thing stopping me is the fact that I'm a programmer, not an artist. I've made some simple stuff, Tetris, 2D chess things like that but I can't do much art and that's really what holds me back. Now the problem is, I've yet to go to college so most commercial projects wouldn't accept me even to work for free and learn a bit especially with my lack of experience in games and any indie projects I've looked into really have an issue with responding to people interested, or actually completing (or starting really, most don't get past the ideas on paper) the project they want to do. I've looked around locally for artists, anyone who can do modeling, textures or animating or even anyone with some ability to make some more advanced 2D assets to get something like a side-scrolling RPG or something but haven't been able to find anyone. So how do you guys do it? Do I really just have to wait until I can go to college to see if I like working with games or is there some way I can get art (for free, anything I do is just going to be for fun so I don't want to have to sink money into it) and just start messing around on my own? Or am I just having bad luck and not looking in the right places for other people interested in having me help? I'm not looking for anything in particular, just something to fill some time with and see if I like making games. If not, well I'll go back to my software projects. I just have one more year of highschool and I'd like to try a few different areas before I go to college.

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• What are some ways to texture map a terrain?

  - by ApocKalipsS

  I'm working with XNA on a 3D Game, and I'm trying to have a proper and nice environnement. I actually followed a tutorial to create a terrain from a heightmap. To texture it, I just apply a grass texture on it and tile it a number of times. But what I want to do is to have a really realistic texturing, but also generate it automatically (for example if I want to use Perlin noise to generate a terrain and then texture it). I already learned about multi-texturing, loading a map file with different colors for different textures, but I don't think this is really efficient, for instance for cliffs or very steep areas it will tile a texture badly as it's a view from the top. (Also, I don't know how I'll draw roads or dirt paths with that.) I'm looking for an efficient solution to realistically texture mapping procedurally-generated terrain.

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• Pseudo-magnet implementation with chipmunk

  - by Eimantas

  How should I go about implementing "natural" magnet on a certain body in chipmunk space? Context is of simple bodies lying in the space (think chessboard). When one of the figures is activated as a magnet - others should start moving towards it. Currently I'm applying force (cpBodyApplyForce)to the other figures with vector calculated towards the activated figure. However this doesn't really feel "natural". Are there any known algorithms for imitating magnets?

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• Re-sizing the form without scaling the GUI

  - by Bmoore

  I am writing a turn based strategy game in C#. My GUI implementation consists of class that extends Form containing a class that extends Panel. When I render the GUI I draw to the paint method in the panel. I am trying to figure out what is the best way for handling form re-size events. I know I want a minimum window size, but I would prefer to not have a maximum or a set size. Ideally the GUI would reveal more/less of the map as the user changes the window size. I would like to avoid scaling the graphics if at all possible. What is the best way to handle re-size events?

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• AI agents with FSM: a question regarding this

  - by Prog

  Finite State Machines implemented with the State design pattern are a common way to design AI agents. I am familiar with the State design pattern and know how to implement it. However I have a question regarding how this is used in games to design AI agents. Please consider a class Monster that represents an AI agent. Simplified it looks like this: class Monster{ State state; // other fields omitted public void update(){ // called every game-loop cycle state.execute(this); } public void setState(State state){ this.state = state; } // irrelevant stuff omitted } There are several State subclasses that implement execute() differently. So far classic State pattern. Here's my question: AI agents are subject to environmental effects and other objects communicating with them. For example an AI agent might tell another AI agent to attack (i.e. agent.attack()). Or a fireball might tell an AI agent to fall down. This means that the agent must have methods such as attack() and fallDown(), or commonly some message receiving mechanism to understand such messages. My question is divided to two parts: 1- Please say if this is correct: With an FSM, the current State of the agent should be the one taking care of such method calls - i.e. the agent delegates to the current state upon every event. Correct? Or wrong? 2- If correct, than how is this done? Are all states obligated by their superclass) to implement methods such as attack(), fallDown() etc., so the agent can always delegate to them on almost every event? Or is it done in some other way?

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• Are there any reasons to use Legacy (2.X) OpenGL?

  - by user27886

  The benefits are well documented of the Modern OpenGL 3.X & 4.X API's, but I'm wondering if there are ANY benefits to keeping with the old OpenGL, Or if learning OpenGL 2.X is a complete waste of time now no matter what? Particularly I've wondered if using the OpenGL 2.X API is appropriate if the target platform had graphics hardware capable of only up to OpenGL 2.X. Would a driver update on said target platform allow programs compiled using the Modern OpenGL API's to be released on this old platform? If they both work, which would be faster? Thanks

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• Character coding / programming

  - by Jery

  Lately I tryed a few times to create characters for some games, but at some certain point (especially when collision detection came in) everything became messy and the interaction between chars, the world and certain items had a lot of bugs. So here is my question, how do you ussualy keep track of actions that your character is allowed to do, or more in general do you have some links / advices how to set up a char efficiantly? I´m working on a char right now, who should at least be able to run, jump, pick items up and use different fighting animations. Most ideas I came up with until now use some kind of action.priority / action.duration system to determain whats possible and what not, or a "action-manager" which defines for every action what is possible from that action on but it all doesnt work that well together.

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• How do I optimize searching for the nearest point?

  - by Rootosaurus

  For a little project of mine I'm trying to implement a space colonization algorithm in order to grow trees. The current implementation of this algorithm works fine. But I have to optimize the whole thing in order to make it generate faster. I work with 1 to 300K of random attraction points to generate one tree, and it takes a lot of time to compute and compare distances between attraction points and tree node in order to keep only the closest treenode for an attraction point. So I was wondering if some solutions exist (I know they must exist) in order to avoid the time loss looping on each tree node for each attraction point to find the closest... and so on until the tree is finished.

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• Creating shooting arrow class [on hold]

  - by I.Hristov

  OK I am trying to write an XNA game with one controllable by the player entity, while the rest are bots (enemy and friendly) wondering around and... shooting each other from range. Now the shooting I suppose should be done with a separate class Arrow (for example). The resulting object would be the arrow appearing on screen moving from shooting entity to target entity. When target is reached arrow is no longer active, probably removed from the list. I plan to make a class with fields: Vector2 shootingEntity; Vector2 targetEntity; float arrowSpeed; float arrowAttackSpeed; int damageDone; bool isActive; Then when enemy entities get closer than a int rangeToShoot (which each entity will have as a field/prop) I plan to make a list of arrows emerging from each entity and going to the closest opposite one. I wonder if that logic will enable me later to make possible many entities to be able to shoot independently at different enemy entities at the same time. I know the question is broad but it would be wise to ask if the foundations of the idea are correct.

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• How can I locate the frames of a spritesheet PNG based on this PLIST data?

  - by kitsune

  Someone asked me to reskin a certain game. Now he only sent me the whole sprite PNG and PLIST files of the sprites. He instructed me to rename each sprite with the same name corresponding to each original sprite. The problem is, he gave me the whole sprite sheet instead of each individual sprite and the PLIST. Now yes, I can read the PNG filenames from the PLIST, but I cannot rename the reskin sprites I did because I'm not sure which sprite is boy_gun_3_3.png; there are multiple guns, I don't know which is which. Is there a way to extract individual accurately named individual PNG files from the single sprite sheet using the PLIST?

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• Setting uniform value of a vertex shader for different sprites in a SpriteBatch

  - by midasmax

  I'm using libGDX and currently have a simple shader that does a passthrough, except for randomly shifting the vertex positions. This shift is a vec2 uniform that I set within my code's render() loop. It's declared in my vertex shader as uniform vec2 u_random. I have two different kind of Sprites -- let's called them SpriteA and SpriteB. Both are drawn within the same SpriteBatch's begin()/end() calls. Prior to drawing each sprite in my scene, I check the type of the sprite. If sprite instance of SpriteA: I set the uniform u_random value to Vector2.Zero, meaning that I don't want any vertex changes for it. If sprite instance of SpriteB, I set the uniform u_random to Vector2(MathUtils.random(), MathUtils.random(). The expected behavior was that all the SpriteA objects in my scene won't experience any jittering, while all SpriteB objects would be jittering about their positions. However, what I'm experiencing is that both SpriteA and SpriteB are jittering, leading me to believe that the u_random uniform is not actually being set per Sprite, and being applied to all sprites. What is the reason for this? And how can I fix this such that the vertex shader correctly accepts the uniform value set to affect each sprite individually? passthrough.vsh attribute vec4 a_color; attribute vec3 a_position; attribute vec2 a_texCoord0; uniform mat4 u_projTrans; uniform vec2 u_random; varying vec4 v_color; varying vec2 v_texCoord; void main() { v_color = a_color; v_texCoord = a_texCoord0; vec3 temp_position = vec3( a_position.x + u_random.x, a_position.y + u_random.y, a_position.z); gl_Position = u_projTrans * vec4(temp_position, 1.0); } Java Code this.batch.begin(); this.batch.setShader(shader); for (Sprite sprite : sprites) { Vector2 v = Vector2.Zero; if (sprite instanceof SpriteB) { v.x = MathUtils.random(-1, 1); v.y = MathUtils.random(-1, 1); } shader.setUniformf("u_random", v); sprite.draw(this.batch); } this.batch.end();

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• Prevent collisions between mobs/npcs/units piloted by computer AI : How to avoid mobile obstacles?

  - by Arthur Wulf White

  Lets says we have character a starting at point A and character b starting at point B. character a is headed to point B and character b is headed to point A. There are several simple ways to find the path(I will be using Dijkstra). The question is, how do I take preventative action in the code to stop the two from colliding with one another? case2: Characters a and b start from the same point in different times. Character b starts later and is the faster of the two. How do I make character b walk around character a without going through it? case3:Lets say we have m such characters in each side and there is sufficient room to pass through without the characters overlapping with one another. How do I stop the two groups of characters from "walking on top of one another" and allow them pass around one another in a natural organic way. A correct answer would be any algorithm, that given the path to the destination and a list of mobile objects that block the path, finds an alternative path or stops without stopping all units when there is sufficient room to traverse.

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• Direct3D - Zooming into Mouse Position

  - by roohan

  I'm trying to implement my camera class for a simulation. But I cant figure out how to zoom into my world based on the mouse position. I mean the object under the mouse cursor should remain at the same screen position. My zooming looks like this: VOID ZoomIn(D3DXMATRIX& WorldMatrix, FLOAT const& MouseX, FLOAT const& MouseY) { this->Position.z = this->Position.z * 0.9f; D3DXMatrixLookAtLH(&this->ViewMatrix, &this->Position, &this->Target, &this->UpDirection); } I passed the world matrix to the function because I had the idea to move my drawing origin according to the mouse position. But I cant find out how to calculate the offset in to move my drawing origin. Anyone got an idea how to calculate this? Thanks in advance. SOLVED Ok I solved my problem. Here is the code if anyone is interested: VOID CAMERA2D::ZoomIn(FLOAT const& MouseX, FLOAT const& MouseY) { // Get the setting of the current view port. D3DVIEWPORT9 ViewPort; this->Direct3DDevice->GetViewport(&ViewPort); // Convert the screen coordinates of the mouse to world space coordinates. D3DXVECTOR3 VectorOne; D3DXVECTOR3 VectorTwo; D3DXVec3Unproject(&VectorOne, &D3DXVECTOR3(MouseX, MouseY, 0.0f), &ViewPort, &this->ProjectionMatrix, &this->ViewMatrix, &WorldMatrix); D3DXVec3Unproject(&VectorTwo, &D3DXVECTOR3(MouseX, MouseY, 1.0f), &ViewPort, &this->ProjectionMatrix, &this->ViewMatrix, &WorldMatrix); // Calculate the resulting vector components. float WorldZ = 0.0f; float WorldX = ((WorldZ - VectorOne.z) * (VectorTwo.x - VectorOne.x)) / (VectorTwo.z - VectorOne.z) + VectorOne.x; float WorldY = ((WorldZ - VectorOne.z) * (VectorTwo.y - VectorOne.y)) / (VectorTwo.z - VectorOne.z) + VectorOne.y; // Move the camera into the screen. this->Position.z = this->Position.z * 0.9f; D3DXMatrixLookAtLH(&this->ViewMatrix, &this->Position, &this->Target, &this->UpDirection); // Calculate the world space vector again based on the new view matrix, D3DXVec3Unproject(&VectorOne, &D3DXVECTOR3(MouseX, MouseY, 0.0f), &ViewPort, &this->ProjectionMatrix, &this->ViewMatrix, &WorldMatrix); D3DXVec3Unproject(&VectorTwo, &D3DXVECTOR3(MouseX, MouseY, 1.0f), &ViewPort, &this->ProjectionMatrix, &this->ViewMatrix, &WorldMatrix); // Calculate the resulting vector components. float WorldZ2 = 0.0f; float WorldX2 = ((WorldZ2 - VectorOne.z) * (VectorTwo.x - VectorOne.x)) / (VectorTwo.z - VectorOne.z) + VectorOne.x; float WorldY2 = ((WorldZ2 - VectorOne.z) * (VectorTwo.y - VectorOne.y)) / (VectorTwo.z - VectorOne.z) + VectorOne.y; // Create a temporary translation matrix for calculating the origin offset. D3DXMATRIX TranslationMatrix; D3DXMatrixIdentity(&TranslationMatrix); // Calculate the origin offset. D3DXMatrixTranslation(&TranslationMatrix, WorldX2 - WorldX, WorldY2 - WorldY, 0.0f); // At the offset to the cameras world matrix. this->WorldMatrix = this->WorldMatrix * TranslationMatrix; } Maybe someone has even a better solution than mine.

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• Inputting cheat codes - hidden keyboard input

  - by Fibericon

  Okay, here's what I want to do - when the player is at the main menu, I want them to be able to type in cheat codes. That's the only place I want it to work. I don't want to give them a text box to type into. Rather, I want them to simply type in a word (let's say "cheat", just for simplicity sake) that activates the cheat code. I only need to capture keyboard input when the window is in focus. What can I do to accomplish this?

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• How can I get my first-person character in Unity to move to a ledge with an animation?

  - by BallzOfSteel

  I'm trying to get this to happen: The character walks up to a large crate, the player presses a button, and an animation starts playing where the character climbs up on to the crate. (all in first person view). So far I tried this with normal "First Person Controller" Prefab in Unity. My code so far: function OnTriggerStay(other : Collider){ if(other.tag == "GrabZone"){ if(Input.GetKeyDown("e")){ animation.Play("JumpToLedge"); } } } However when i use this on The FPC it will always play from the position the animation is created on. I also tried to create an empty game object, placing the FPC in there. Gives same effect. I also tried just animating the graphics of the FPC alone. This seems to work but since the Character Controller itself is not animated that stays onthe ground. So the whole FPC wont work anymore. Is there anyway i could let this animation play on the local position the player is on at that time? Or can you think of any other logical solution for a grab and climb?

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• Random enemy placement on a 2d grid

  - by Robb

  I want to place my items and enemies randomly (or as randomly as possible). At the moment I use XNA's Random class to generate a number between 800 for X and 600 for Y. It feels like enemies spawn more towards the top of the map than in the middle or bottom. I do not seed the generator, maybe that is something to consider. Are there other techniques described that can improve random enemy placement on a 2d grid?

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• Problem with Update(GameTime) Methods and Pause implementation

  - by Adam

  I have the pause function implemented and it works correctly in that it dims the player screen and stops updating the gameplay. The problem is that GameTime continues to increase while it is paused, so my method that checks gameTime versus previousSpawnTime before spawning another enemy gets messed up and if the game is paused too long it is noticeable that the next enemy draws far too early. Here is my code for the enemy update. private void UpdateEnemies(GameTime gameTime) { // Spawn a new enemy every 1.5 seconds if (gameTime.TotalGameTime - previousSpawnTime > enemySpawnTime) { previousSpawnTime = gameTime.TotalGameTime; // Add an Enemy AddEnemy(); } ... I also have other methods that depend on gameTime. I've tried getting the total pause time and subtracting that from the total game time, but I can't seem to get it to work correctly if that is the way I should go about solving this. If you need to see any other code let me know. Thank you.

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• libGDX using Stage and Actor produces different camera angles on desktop and Android Phone

  - by Brandon

  libGDX using Stage and Actor produces different camera angles on desktop and Android Phone. Here are pictures demonstrating the problem: http://brandonyuh.minus.com/mFpdTSgN17VUq On the desktop version, the image takes up most all the screen. On the Android phone it only takes up a bit of the screen. Here's the code (not my actual project but I isolated the problem): package com.me.mygdxgame2; import com.badlogic.gdx.*; import com.badlogic.gdx.graphics.*; import com.badlogic.gdx.graphics.Texture.TextureFilter; import com.badlogic.gdx.graphics.g2d.*; import com.badlogic.gdx.scenes.scene2d.*; public class MyGdxGame2 implements ApplicationListener { private Stage stage; public void create() { stage = new Stage(); stage.addActor(new ActorHi()); } public void render() { Gdx.gl.glClearColor(0, 1, 0, 1); Gdx.gl.glClear(GL10.GL_COLOR_BUFFER_BIT); stage.draw(); } public void dispose() {} public void resize(int width, int height) {} public void pause() {} public void resume() {} public class ActorHi extends Actor { private Sprite sprite; public ActorHi() { Texture texture = new Texture(Gdx.files.internal("data/hi.png")); texture.setFilter(TextureFilter.Linear, TextureFilter.Linear); sprite = new Sprite(new TextureRegion(texture, 0, 0, 128, 128)); sprite.setBounds(0, 0, 300.0f, 300.0f); } public void draw(SpriteBatch batch, float parentAlpha) { sprite.draw(batch); } } } hi.png is included in the above link Thank you very much for answering my question. I've spent 3 days trying to figure it out.

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• BoundingBox Intersection Problems

  - by Deukalion

  When I try to render two cubes, same sizes, one beside the other. With the same proportions (XYZ). My problem is, why do a Box1.BoundingBox.Contains(Box2.BoundingBox) == ContaintmentType.Intersects - when it clearly doesn't? I'm trying to place objects with BoundingBoxes as "intersection" checking, but this simple example clearly shows that this doesn't work. Why is that? I also try checking height of the next object to be placed, by checking intersection, adding each boxes height += (Max.Y - Min.Y) to a Height value, so when I add a new Box it has a height value. This works, but sometimes due to strange behavior it adds extra values when there isn't anything there. This is an example of what I mean: BoundingBox box1 = GetBoundaries(new Vector3(0, 0, 0), new Vector3(128, 64, 128)); BoundingBox box2 = GetBoundaries(new Vector3(128, 0, 0), new Vector3(128, 64, 128)); if (box1.Contains(box2) == ContainmentType.Intersects) { // This will be executed System.Windows.Forms.MessageBox.Show("Intersects = True"); } if (box1.Contains(box2) == ContainmentType.Disjoint) { System.Windows.Forms.MessageBox.Show("Disjoint = True"); } if (box1.Contains(box2) == ContainmentType.Contains) { System.Windows.Forms.MessageBox.Show("Contains = True"); } Test Method: public BoundingBox GetBoundaries(Vector3 position, Vector3 size) { Vector3[] vertices = new Vector3[8]; vertices[0] = position + new Vector3(-0.5f, 0.5f, -0.5f) * size; vertices[1] = position + new Vector3(-0.5f, 0.5f, 0.5f) * size; vertices[2] = position + new Vector3(0.5f, 0.5f, -0.5f) * size; vertices[3] = position + new Vector3(0.5f, 0.5f, 0.5f) * size; vertices[4] = position + new Vector3(-0.5f, -0.5f, -0.5f) * size; vertices[5] = position + new Vector3(-0.5f, -0.5f, 0.5f) * size; vertices[6] = position + new Vector3(0.5f, -0.5f, -0.5f) * size; vertices[7] = position + new Vector3(0.5f, -0.5f, 0.5f) * size; return BoundingBox.CreateFromPoints(vertices); } Box 1 should start at x -64, Box 2 should start at x 64 which means they never overlap. If I add Box 2 to 129 instead it creates a small gap between the cubes which is not pretty. So, the question is how can I place two cubes beside eachother and make them understand that they do not overlap or actually intersect? Because this way I can never automatically check for intersections or place cube beside eachother.

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• Box2Dweb very slow on node.js

  - by Peteris

  I'm using Box2Dweb on node.js. I have a rotated box object that I apply an impulse to move around. The timestep is set at 50ms, however, it bumps up to 100ms and even 200ms as soon as I add any more edges or boxes. Here are the edges I would like to use as bounds around the playing area: // Computing the corners var upLeft = new b2Vec2(0, 0), lowLeft = new b2Vec2(0, height), lowRight = new b2Vec2(width, height), upRight = new b2Vec2(width, 0) // Edges bounding the visible game area var edgeFixDef = new b2FixtureDef edgeFixDef.friction = 0.5 edgeFixDef.restitution = 0.2 edgeFixDef.shape = new b2PolygonShape var edgeBodyDef = new b2BodyDef; edgeBodyDef.type = b2Body.b2_staticBody edgeFixDef.shape.SetAsEdge(upLeft, lowLeft) world.CreateBody(edgeBodyDef).CreateFixture(edgeFixDef) edgeFixDef.shape.SetAsEdge(lowLeft, lowRight) world.CreateBody(edgeBodyDef).CreateFixture(edgeFixDef) edgeFixDef.shape.SetAsEdge(lowRight, upRight) world.CreateBody(edgeBodyDef).CreateFixture(edgeFixDef) edgeFixDef.shape.SetAsEdge(upRight, upLeft) world.CreateBody(edgeBodyDef).CreateFixture(edgeFixDef) Can box2d really become this slow for even two bodies or is there some pitfall? It would be very surprising given all the demos which successfully use tens of objects.

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• How can I get a 2D texture to rotate like a compass in XNA?

  - by IronGiraffe

  I'm working on a small maze puzzle game and I'm trying to add a compass to make it somewhat easier for the player to find their way around the maze. The problem is: I'm using XNA's draw method to rotate the arrow and I don't really know how to get it to rotate properly. What I need it to do is point towards the exit from the player's position, but I'm not sure how I can do that. So does anyone know how I can do this? Is there a better way to do it?

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• How to set sprite source coordinates?

  - by ChaosDev

  I am creating own sprite drawer with DX11 on C++. Works fine but I dont know how to apply source rectangle to texture coordinates of rendering surface(for animation sprite sheets) //source = (0,0,32,64); //RECT D3DXVECTOR2 t0 = D3DXVECTOR2( 1.0f, 0.0f); D3DXVECTOR2 t1 = D3DXVECTOR2( 1.0f, 1.0f); D3DXVECTOR2 t2 = D3DXVECTOR2( 0.0f, 1.0f); D3DXVECTOR2 t3 = D3DXVECTOR2( 0.0f, 1.0f); D3DXVECTOR2 t4 = D3DXVECTOR2( 0.0f, 0.0f); D3DXVECTOR2 t5 = D3DXVECTOR2( 1.0f, 0.0f); VertexPositionColorTexture vertices[] = { { D3DXVECTOR3( dest.left+dest.right, dest.top, z),D3DXVECTOR4(1,1,1,1), t0}, { D3DXVECTOR3( dest.left+dest.right, dest.top+dest.bottom, z),D3DXVECTOR4(1,1,1,1), t1}, { D3DXVECTOR3( dest.left, dest.top+dest.bottom, z),D3DXVECTOR4(1,1,1,1), t2}, { D3DXVECTOR3( dest.left, dest.top+dest.bottom, z),D3DXVECTOR4(1,1,1,1), t3}, { D3DXVECTOR3( dest.left , dest.top, z),D3DXVECTOR4(1,1,1,1), t4}, { D3DXVECTOR3( dest.left+dest.right, dest.top, z),D3DXVECTOR4(1,1,1,1), t5}, };

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• How do I interpolate air drag with a variable time step?

  - by Valentin Krummenacher

  So I have a little game which works with small steps, however those steps vary in time, so for example I sometimes have 10 Steps/second and then I have 20 Steps/second. This changes automatically depending on how many steps the user's computer can take. To avoid inaccurate positioning of the game's player object I use y=v0*dt+g*dt^2/2 to determine my objects y-position, where dt is the time since the last step, v0 is the velocity of my object in the beginning of my step and g is the gravity. To calculate the velocity in the end of a step I use v=v0+g*dt what also gives me correct results, independent of whether I use 2 steps with a dt of for example 20ms or one step with a dt of 40ms. Now I would like to introduce air drag. For simplicity's sake I use a=k*v^2 where a is the air drag's acceleration (I am aware that it would usually result in a force, but since I assume 1kg for my object's mass the force is the same as the resulting acceleration), k is a constant (in this case I'm using 0.001) and v is the speed. Now in an infinitely small time interval a is k multiplied by the velocity in this small time interval powered by 2. The problem is that v in the next time interval would depend on the drag of the last which again depends on the v of the last interval and so on... In other words: If I use a=k*v^2 I get different results for my position/velocity when I use 2 steps of 20ms than when I use one step of 40ms. I used to have this problem for my position too, but adding +g*dt^2/2 to the formula for my position fixed the problem since it takes into account that the position depends on the velocity which changes slightly in every infinitely small time interval. Does something like that exist for air drag too? And no, I dont mean anything like Adding air drag to a golf ball trajectory equation or similar, for that kind of method only gives correct results when all my steps are the same. (I hope you can understand my intermediate english, it's not my main language so I would like to say sorry for all the silly mistakes I might have made in my question)

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• Do I need the 'w' component in my Vector class?

  - by bobobobo

  Assume you're writing matrix code that handles rotation, translation etc for 3d space. Now the transformation matrices have to be 4x4 to fit the translation component in. However, you don't actually need to store a w component in the vector do you? Even in perspective division, you can simply compute and store w outside of the vector, and perspective divide before returning from the method. For example: // post multiply vec2=matrix*vector Vector operator*( const Matrix & a, const Vector& v ) { Vector r ; // do matrix mult r.x = a._11*v.x + a._12*v.y ... real w = a._41*v.x + a._42*v.y ... // perspective divide r /= w ; return r ; } Is there a point in storing w in the Vector class?

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