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• Comparing angles and working out the difference

  - by Thomas O

  I want to compare angles and get an idea of the distance between them. For this application, I'm working in degrees, but it would also work for radians and grads. The problem with angles is that they depend on modular arithmetic, i.e. 0-360 degrees. Say one angle is at 15 degrees and one is at 45. The difference is 30 degrees, and the 45 degree angle is greater than the 15 degree one. But, this breaks down when you have, say, 345 degrees and 30 degrees. Although they compare properly, the difference between them is 315 degrees instead of the correct 45 degrees. How can I solve this? I could write algorithmic code: if(angle1 > angle2) delta_theta = 360 - angle2 - angle1; else delta_theta = angle2 - angle1; But I'd prefer a solution that avoids compares/branches, and relies entirely on arithmetic.

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• Safe zone implementation in Asteroids

  - by Moaz

  I would like to implement a safe zone for asteroids so that when the ship gets destroyed, it shouldn't be there unless it is safe from other asteroids. I tried to check the distance between each asteroid and the ship, and if it is above threshold, it sets a flag to the ship that's a safe zone, but sometimes it work and sometimes it doesn't. What am I doing wrong? Here's my code: for (list<Asteroid>::iterator itr_astroid = asteroids.begin(); itr_astroid!=asteroids.end(); ) { if(currentShip.m_state == Ship::Ship_Dead) { float distance = itr_astroid->getCenter().distance(Vec2f(getWindowWidth()/2,getWindowHeight()/2)); if( distance>200) { currentShip.m_saveField = true; break; } else { currentShip.m_saveField = false; itr_astroid++; } } else { itr_astroid++; } } At ship's death: if(m_state == Ship_Dead && m_saveField==true) { --m_lifeSpan; } if(m_lifeSpan<=0 && m_saveField == true) { m_state = Ship_Alive; m_Vel = Vec2f(0,0); m_Pos.x = app::getWindowWidth()/2; m_Pos.y = app::getWindowHeight()/2; m_lifeSpan = 100; }

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• Move projectile in direction the gun is facing

  - by Manderin87

  I am attempting to have a projectile follow the direction a gun is facing. When using the following code I am unable to make the projectile go in the right direction. float speed = .5f; float dX = (float) -Math.cos(Math.toRadians(degree)) * speed; float dY = (float) Math.sin(Math.toRadians(degree)) * speed; Can anyone tell me what I am doing wrong? The degree is the direction the gun is facing in degree's.

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• Drawing an outline around an arbitrary group of hexagons

  - by Perky

  Is there an algorithm for drawing an outline around around an arbitrary group of hexagons? The polygon outline drawn may be concave. See the images below, the green line is what I am trying to achieve. The hexagons are stored as vertices and drawn as polygons. Edit: I've uploaded images that should explain more. I want to favour convex hulls because it's conveys an area of control more quickly. Each hexagon is stored in a multidimensional array so they all have x and y coordinates, I can easily find adjacent hexagons and the opposite vertex, i.e. adjacentHexagon = getAdjacentHexagon( someHexagon, NORTHWEST ) if there isn't a hexagon immediately adjacent it will continue to search in that direction until it finds one or hits the map edges.

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• How can I generate a texture that looks like left-over tea leaves?

  - by Jedidja

  We are working on a project for iPhone and Windows Phone 7 where we'd like to be able to generate tea leaves at the bottom of a cup. It doesn't have to look photo-realistic, and actually cartoon-y is ok. What sort of techniques should we research to accomplish this? Are there any libraries (preferably in C, but we can translate) that would be helpful? Here are some samples pulled from a Google Image search

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• Starting out with OpenGL when most tutorials are out of date

  - by AUTO

  I'm sure there are already a bunch of questions like this asked, but the constant updating of the OpenGL library throws them all away, and in a month or two, the answers here will be worthless again. I am ready to start programming in OpenGL using C++. I've got a working compiler (DevCpp; do NOT ask me to switch to VC++, and don't ask me why). Now I'm just looking for a solid tutorial on how to program with OpenGL. My assistant found the tutorial provided by NeHe Productions, but as I've come to find out, it's WAY OUT OF DATE! (although I did pull together a basic window to support an OpenGL canvas) Then I went online, and found the OpenGL SuperBible, which apparently uses freeglut? But what I'd like to know is whether or not SuperBible 5th edition is up to date any longer. The suggestion to freeglut I found said the latest version was 2.6.0 but now it's 2.8.0! Is the OpenGL SuperBible still a good, and fairly up-to-date place to start? Is there a better place to go to learn OpenGL? Am I allowed to simply store freeglut in the DevCpp include directory (maybe in GL), or is there some important procedure? Are there any comments or suggestions that I didn't think to ask since I'm only just beginning? @dreta cleared some things up for me, so now I have a better idea of what to ask: I think I'd like to start out with OpenGL using a wrapper library instead of directly accessing OpenGL.I just think that, for a beginner, it would be easier for me to program and get good results, while I don't yet have to understand all the grimy details (as @stephelton mentioned). The problem is, I can't find any library that doesn't have undefined references to no longer supported functions. Freeglut sounds operational, but it still uses GLU.Does anyone know what I can do?Also, I tried compiling the first SuperBible's source, but I got errors since GLAPI is not being defined as a type, the error originating in the GLU library. I'd like to use the SuperBible, but I don't know how to fix this.

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• Skip the first RenderTarget when writing to MRT with Opaque blending

  - by cubrman

  I am writing to three rendertargets and whant to know how to tell a GPU not to write to the first RT. When you write a shader you can simply output less data than you have RTs (like output a single float4 when writing to three RTs) and only the first RTs will be affected, but you cannot specify to output this data anywhere else but to COLOR0, then 1, etc. Is there a way to write to several RTs but skip the first target? If I output zeroes, the data in the target will become zeroes, but I need it to remain untuched in the first target and only change in the specified ones. The reason I need this is to prevent data loss when calling SetRendertarget() with DiscardContents RTs. I write to all the RTs at one point and I need to write to only the specified ones afterwards. It must be the first texture as I have a depth buffer linked to it (XNA 4.0). Thanks.

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• How to use the float value from Noise function in voxel terrain?

  - by therealjohn

  Im using Unity, although this question is not really specific to that engine. Im also using an asset from the store called Coherent Noise. It has some neat noise functionality built it. I am using those functions to produce some noise values. I am getting a value between 0 and 1 (floats). I have an array of blocks (for minecraft like voxel terrain) and I am confused on how to use this float value for terrain? Do I do something like <= 0 == Solid block etc etc? I am confused on how to use the floating values that the noise functions produce to use for height values of an array of say a height of 16. Thanks for any guidance.

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• Isometric algorithm producing tiles in wrong draw order

  - by David

  I've been toying with isometric and I just cant get the tiles to be in the right order. I'm probably missing something obvious and I just can't see it. Even at the risk of looking stupid, here's my code: for (int i = 0; i < Tile.MapSize; i++) { for (int j = 0; j < Tile.MapSize; j++) { spriteBatch.Draw( Tile.TileSetTexture, new Rectangle( (-j * Tile.TileWidth / 2) + (i * Tile.TileWidth / 2), (i * (Tile.TileHeight - 9) / 2) - (-j * (Tile.TileHeight - 9) / 2), Tile.TileWidth, Tile.TileHeight), Tile.GetSourceRectangle(tileID), Color.White, 0.0f, new Vector2(-350, -60), SpriteEffects.None, 1.0f); } } And here's what I end up with: messed up map Yep, bit of an issue. If anyone could help, I'd appreciate it.

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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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• D3D9 Alpha Blending on the surfaces

  - by Indeera

  I have a surface (OffScreenPlain or RenderTarget with D3DFMT_A8R8G8B8) which I copy pixels (ARGB) to, from a third party function. Before pixel copying, Bits are accessed by LockRect. This surface is then StretchRect to the Backbuffer which is (D3DFMT_A8R8G8B8). Surface and Backbuffer are different dimensions. Filtering is set to D3DTEXF_NONE. Just after creating the d3d device I've set following RenderState settings D3DRS_ALPHABLENDENABLE -> TRUE D3DRS_BLENDOP -> D3DBLENDOP_ADD D3DRS_SRCBLEND -> D3DBLEND_SRCALPHA D3DRS_DESTBLEND -> D3DBLEND_INVSRCALPHA But I see no alpha blending happening. I've verified that alpha is specified in pixels. I've done a simple test by creating a vertex buffer and drawing a triangle (DrawPrimitive) which displays with alpha blending. In this test surface was StretchRect first and then DrawPrimitive, and the surface content displays without alpha blending and the triangle displays with alpha blending. What am I missing here? Thanks

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• How does a BSP tree work for Z sorting?

  - by Jenko

  I'm developing a 3D engine in software, and so I must compute Z sorting manually. I'm currently using the painters algorithm to sort triangles and then drawing them back-to-front. This causes artifacts that I'm trying to correct. Would using a dynamic BSP-tree ensure "correct Z sorting" of triangles? Why? Because the bounding volumes of triangles would be similar? Since I would have a single "world" BSP tree, would I have to remove and re-add any moved/scaled/rotated object into the tree? Is it possible to add triangles into a BSP tree without the expensive cutting process? Why do you need to cut triangles on the axis planes anyway? Is it faster to traverse a BSP tree from any angle, than to sort all tris each draw like the painters algorithm?

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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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• Blender to 3ds max to cal3d format

  - by Kaliber64

  There are quite a few questions on cal3d but they are old and don't apply anymore. In Blender(must be 2.49a for python script to work!!!): I have a scene with 7 meshes, 1 armature, 10 bones. I tried going to one mesh to simplify it but doesn't change anything. I found a small blend file that was used for cal3d and it exported just fine. So I tried to copy it's setup with no success. EDIT*8/13/2012 In the last week here is what I have found so far. I made the mesh in the newest blender(2.62?) and exported it to import it in the old one(2.49a). Did an animation in the old one because importing new blend files to old blenders, its just said it would lose keyframe data and all was good. And then you get the last problem of it not exporting meshes. BUT I found that meshes made in the old one export regardless. I can't find any that won't export. So if I used the old blender to remake my model I could get it to export :) At this point I found a modified release of cal3d (because the most core model variable would not initiate as I made a really small test subject in old blender instead of remaking my big one which took 4 hours.) which fixes the morph objects and adds what cal3d left off with. Under their license they have to release the modification but it has no documentation so I have to figure it out on my own. Its mostly the same. But with this lib it came with a 3ds max exporter. My question now is how do I transfer armature and mesh information from blender to 3ds max in order to export into cal3d format. Every time I try the models are see through and small and there are no bones. The formats I have tried to import are .3ds .obj(mesh only) and COLLADA. In all of them the mesh is invisible and no bones. It says the default texture is on so I should be able to see it. All the vertices are present I found a vertex highlighter so I can see those. If any of this is confusing let me know so I can clear it up. Its late .<=sleep.

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• 3D rotation matrices deform object while rotating

  - by Kevin

  I'm writing a small 3D renderer (using an orthographic projection right now). I've run into some trouble with my 3D rotation matrices. They seem to squeeze my 3D object (a box primitive) at certain angles. Here's a live demo (only tested in Google Chrome): http://dl.dropbox.com/u/109400107/3D/index.html The box is viewed from the top along the Y axis and is rotating around the X and Z axis. These are my 3 rotation matrices (Only rX and rZ are being used): var rX = new Matrix([ [1, 0, 0], [0, Math.cos(radiants), -Math.sin(radiants)], [0, Math.sin(radiants), Math.cos(radiants)] ]); var rY = new Matrix([ [Math.cos(radiants), 0, Math.sin(radiants)], [0, 1, 0], [-Math.sin(radiants), 0, Math.cos(radiants)] ]); var rZ = new Matrix([ [Math.cos(radiants), -Math.sin(radiants), 0], [Math.sin(radiants), Math.cos(radiants), 0], [0, 0, 1] ]); Before projecting the verticies I multiply them by rZ and rX like so: vert1.multiply(rZ); vert1.multiply(rX); vert2.multiply(rZ); vert2.multiply(rX); vert3.multiply(rZ); vert3.multiply(rX); The projection itself looks like this: bX = (pos.x + (vert1.x*scale)); bY = (pos.y + (vert1.z*scale)); Where "pos.x" and "pos.y" is an offset for centering the box on the screen. I just can't seem to find a solution to this and I'm still relativly new to working with Matricies. You can view the source-code of the demo page if you want to see the whole thing.

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• Bouncing ball slowing down over time

  - by user46610

  I use the unreal engine 4 to bounce a ball off of walls in a 2D space, but over time the ball gets slower and slower. Movement happens in the tick function of the ball FVector location = GetActorLocation(); location.X += this->Velocity.X * DeltaSeconds; location.Y += this->Velocity.Y * DeltaSeconds; SetActorLocation(location, true); When a wall gets hit I get a Hit Event with the normal of the collision. This is how I calculate the new velocity of the ball: FVector2D V = this->Velocity; FVector2D N = FVector2D(HitNormal.X, HitNormal.Y); FVector2D newVelocity = -2 * (V.X * N.X + V.Y * N.Y) * N + V; this->Velocity = newVelocity; Over time, the more the ball bounced around, the velocity gets smaller and smaller. How do I prevent speed loss when bouncing off walls like that? It's supposed to be a perfect bounce without friction or anything.

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• Can I use PBOs for textures in iOS?

  - by Radu

  As far as I can see, there is no GL_PIXEL_UNPACK_BUFFER. Also, the OpenGL ES 2.0 specification (and as far as I know, no iOS device currently supports OpenGL ES 2.0) states that glMapBufferOES() can only use GL_ARRAY_BUFFER as a target, yet glTexImage2D() and glTexSubImage2D() only seem to use PBOs if GL_PIXEL_UNPACK_BUFFER is bound. The OpenGL documentation for glBindBuffer() also states that: GL_PIXEL_PACK_BUFFER and GL_PIXEL_UNPACK_BUFFER are available only if the GL version is 2.1 or greater. So, can I use PBOs for textures? Am I missing something obvious?

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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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• Fastest bit-blit in C# ?

  - by AttackingHobo

  I know there is Unity, and XNA that both use C#, but I am don't know what else I could use. The reason I say C# is that the syntax and style is similar to AS3, which I am familiar with, and I want to choose the correct framework to start learning with. What should I use to be able to do the most possible bit-blit(direct pixel copy) objects per frame. EDIT: I should not need to add this, but I am looking for the most possible amount of objects per frame because I am making a few Bullet-Hell SHMUPS. I need thousands and thousands of bullets, particles, and hundreds of enemies on the screen at once. I am looking for a solution to do as many bit-blit operations per frame, I am not looking for a general purpose engine. EDIT2: I want bit-blitting because I do not want to exclude people who have lower end video cards but a fast processor from playing my games.

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• Drawing a random x,y grid of objects within a prespective

  - by T Reddy

  I'm wrapping my head around OpenGL ES 2.0 and I think I'm trying to do something very simple, but I think the math may be eluding me. I created a simple, flat-ish cylinder in Blender that is 2 units in diameter. I want to create an arbitrary grid of these edge to edge (think of a checker board). I'm using a 3D perspective with GLKit: CGSize size = [[self view] bounds].size; _projectionMatrix = GLKMatrix4MakePerspective(GLKMathDegreesToRadians(45.0f), size.width/size.height, 0.1f, 100.0f); So, I managed to manually get all of these cylinders drawn on the screen just fine. However, I would like to understand how I can programmatically "fit" all of these cylinders on the screen at the same time given the camera location, screen size, cylinder diameter, and the number of rows/columns. So the net effect is that for small grids (i.e., 5x5) the objects are closer to the camera, but for large grids (i.e., 30x30) the objects are farther away. In either case, all of the cylinders are visible.

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• How exactly does XNA's SpriteBatch work?

  - by David Gouveia

  To be more precise, if I needed to recreate this functionality from scratch in another API (e.g. in OpenGL) what would it need to be capable of doing? I do have a general idea of some of the steps, such as how it prepares an orthographic projection matrix and creates a quad for each draw call. I'm not too familiar, however, with the batching process itself. Are all quads stored in the same vertex buffer? Does it need an index buffer? How are different textures handled? If possible I'd be grateful if you could guide me through the process from when SpriteBatch.Begin() is called until SpriteBatch.End(), at least when using the default Deferred mode.

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• In esenthel engine how can I remove some object from Gui class?

  - by Gajet

  I know many people in this site may not know esenthel engine at all and my question may be better answered at engine forum but I'm putting it here to share the name of a real easy to code gameengine with all of you: you can easily add a Button for example to your GUI class (gui is it's shared instance) with Gui += buttonInstance.create("click on me") but I'm just wondering how can you remove an on object from from Gui members. as far as I know there is no such a method as removeChild or getChildren or anything similar.

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• Role of an entity state in a component based system?

  - by Paul

  Component-based entity systems are all the rage these days; everyone seems to agree they are the way to go, but no one really has a definitive implementation of such a system. I was wondering, what role do entity states (walking-left, standing, jumping, etc) have in a CBS? Do they act like controllers (i.e. they handle events and change the entity's attributes based on those events)? What about cases where a state would, for example, require that the entity enters no-clip mode? Should, that state, when it enters, maybe set the CollisionComponent of the entity to a null pointer or something? (Then, on exit, the state should restore the entity's CollisionComponent to its previous state.) Also, I guess it's the current state's job to change the entity's state to something else, right?

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• Sharing VBO with multiple objects and fixed size buffer data

  - by Mark Ingram

  I'm just messing around with OpenGL and getting some basic structures in place and my first attempt resulted in each SceneObject class (just contains vertex information right now) having it's own VBO inside it, however I've read that it might be better to share VBOs across multiple objects. Also, I read that you should avoid resizing a VBO (repeated calls to glBufferData with different size parameters), and instead choose a fixed size for a VBO, and just try a range from the buffer. I don't think changing the size of the buffer data would happen too often, but surely it would be better to only allocate the data you need? Choosing an arbitrary value seems risky. I'm looking for some advice on working with individual objects in a scene and their associated buffer data.

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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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