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• Trouble with SAT style vector projection in C#/XNA

  - by ssb

  Simply put I'm having a hard time working out how to work with XNA's Vector2 types while maintaining spatial considerations. I'm working with separating axis theorem and trying to project vectors onto an arbitrary axis to check if those projections overlap, but the severe lack of XNA-specific help online combined with pseudo code everywhere that omits key parts of the algorithm, googling has left me little help. I'm aware of HOW to project a vector, but the way that I know of doing it involves the two vectors starting from the same point. Particularly here: http://www.metanetsoftware.com/technique/tutorialA.html So let's say I have a simple rectangle, and I store each of its corners in a list of Vector2s. How would I go about projecting that onto an arbitrary axis? The crux of my problem is that taking the dot product of say, a vector2 of (1, 0) and a vector2 of (50, 50) won't get me the dot product I'm looking for.. or will it? Because that (50, 50) won't be the vector of the polygon's vertex but from whatever XNA calculates. It's getting the calculation from the right starting point that's throwing me off. I'm sorry if this is unclear, but my brain is fried from trying to think about this. I need a better understanding of how XNA calculates Vector2s as actual vectors and not just as random points.

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• XNA hlsl tex2D() only reads 3 channels from normal maps and specular maps

  - by cubrman

  Our engine uses deferred rendering and at the main draw phase gathers plenty of data from the objects it draws. In order to save on tex2D calls, we packed our objects' specular maps with all sorts of data, so three out of four channels are already taken. To make it clear: I am talking about the assets that come with the models and are stored in their material's Specular Level channel, not about the RenderTarget. So now I need another information to be stored in the alpha channel, but I cannot make the shader to read it properly! Nomatter what I write into alpha it ends up being 1 (255)! I tried: saving the textures in PNG/TGA formats. turning off pre-computed alpha in model's properties. Out of every texture available to me (we use Diffuse map, Normal Map and Specular Map) I was only able to read alpha successfully from the Diffuse Map! Here is how I add specular and normal maps to my model's material in the content processor: if (geometry.Material.Textures.ContainsKey(normalMapKey)) { ExternalReference<TextureContent> texRef = geometry.Material.Textures[normalMapKey]; geometry.Material.Textures.Remove("NormalMap"); geometry.Material.Textures.Add("NormalMap", texRef); } ... foreach (KeyValuePair<String, ExternalReference<TextureContent>> texture in material.Textures) { if ((texture.Key == "Texture") || (texture.Key == "NormalMap") || (texture.Key == "SpecularMap")) mat.Textures.Add(texture.Key, texture.Value); } In the shader I obviously use: float4 data = tex2D(specularMapSampler, TexCoords); so data.a is always 1 in my case, could you suggest a reason?

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• 3d trajectory - calculate initial velocity

  - by Skoder

  Hey, I've got a 2D projectile code sample working, but would like to extend it to 3D. How would I calculate the initial velocity of the Z-axis? At the moment, I've got: initVel.X = (float)Math.Cos(45.0); initVel.Y = (float)Math.Sin(45.0); How would I convert this to work in 3D (and add the initial velocity for the Z-axis)? In my example, X is across, Y is up down and Z is going into the screen. I also normalize the vector and multiply it by the speed. Thanks

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• When mapping the surface of a sphere with tiles, how might you deal with polar distortion?

  - by clweeks

  It's easy to deal with the way locations interact on a clean Cartesian grid. It's just vanilla math. And you can kind of ignore the geometry of the sphere's surface for a bunch of it if you want to just truncate the poles or something. But I keep coming up with ideas for games where the polar space matters. Geo-coded ARGs and global roguelikes and stuff. I want square(ish?) locations -- reasonably representable by square tiles of the same size across the globe, anyway. This has to be a solved problem, right? What are the solutions? ETA: At the equator -- and assuming that your square locations are reasonably small, it's close enough to true that you can get away with having one square in the rows north and south of the most equatorial row. And you could probably get away with that by just hand-waving the difference up to like 45-degrees or so. But eventually, you need to have fewer squares in a pole-ward circumferential row. If I reduce the length of the row by one and offset the squares by 1/2 then they're just like hexes and it's relatively easy to do the coding to keep track of the connections. But as you get pole-ward, it gets more and more extreme. Projecting the surface of the world onto the surface of a cube is tempting. But I figured there must be more elegant solutions already in use. If I did the cube thing (not dissecting it further through geodesy) Are there any pros and cons related to placing the pole at the center of a face or at the vertex of three sides?

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• Frame Independent Movement

  - by ShrimpCrackers

  I've read two other threads here on movement: Time based movement Vs Frame rate based movement?, and Fixed time step vs Variable time step but I think I'm lacking a basic understanding of frame independent movement because I don't understand what either of those threads are talking about. I'm following along with lazyfoo's SDL tutorials and came upon the frame independent lesson. http://lazyfoo.net/SDL_tutorials/lesson32/index.php I'm not sure what the movement part of the code is trying to say but I think it's this (please correct me if I'm wrong): In order to have frame independent movement, we need to find out how far an object (ex. sprite) moves within a certain time frame, for example 1 second. If the dot moves at 200 pixels per second, then I need to calculate how much it moves within that second by multiplying 200 pps by 1/1000 of a second. Is that right? The lesson says: "velocity in pixels per second * time since last frame in seconds. So if the program runs at 200 frames per second: 200 pps * 1/200 seconds = 1 pixel" But...I thought we were multiplying 200 pps by 1/1000th of a second. What is this business with frames per second? I'd appreciate if someone could give me a little bit more detailed explanation as to how frame independent movement works. Thank you.

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• How can I select an audio output device in directshow

  - by Vibhore Tanwer

  I was wondering how I can select the output device for audio in directshow. I am able to get available audio output devices in directshow. But how can I make one of these to be audio output device. Its always going for the default audio device. I want to be able to output audio on my choice of device. I have been struggling through google but couldn't find anything useful. All I could get was this link but it doesn't really solve my problem. Any help will be really helpful for me.

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• How can I achieve a 3D-like effect with spritebatch's rotation and scale parameters

  - by Alic44

  I'm working on a 2d game with a top-down perspective similar to Secret of Mana and the 2D Final Fantasy games, with one big difference being that it's an action rpg using a 3-dimensional physics engine. I'm trying to draw an aimer graphic (basically an arrow) at my characters' feet when they're aiming a ranged weapon. At first I just converted the character's aim vector to radians and passed that into spritebatch, but there was a problem. The position of every object in my world is scaled for perspective when it's drawn to the screen. So if the physics engine coordinates are (1, 0, 1), the screen coords are actually (1, .707) -- the Y and Z axis are scaled by a perspective factor of .707 and then added together to get the screen coordinates. This meant that the direction the aimer graphic pointed (thanks to its rotation value passed into spritebatch) didn't match up with the direction the projectile actually traveled over time. Things looked fine when the characters fired left, right, up, or down, but if you fired on a diagonal the perspective of the physics engine didn't match with the simplistic way I was converting the character's aim direction to a screen rotation. Ok, fast forward to now: I've got the aimer's rotation matched up with the path the projectile will actually take, which I'm doing by decomposing a transform matrix which I build from two rotation matrices (one to represent the aimer's rotation, and one to represent the camera's 45 degree rotation on the x axis). My question is, is there a way to get not just rotation from a series of matrix transformations, but to also get a Vector2 scale which would give the aimer the appearance of being a 3d object, being warped by perspective? Orthographic perspective is what I'm going for, I think. So, the aimer arrow would get longer when facing sideways, and shorter when facing north and south because of the perspective. At the same time, it would get wider when facing north and south, and less wide when facing right or left. I'd like to avoid actually drawing the aimer texture in 3d because I'm still using spritebatch's layerdepth parameter at this point in my project, and I don't want to have to figure out how to draw a 3d object within the depth sorting system I already have. I can provide code and more details if this is too vague as a question... This is my first post on stack exchange. Thanks a lot for reading! Note: (I think) I realize it can't be a technically correct 3D perspective, because the spritebatch's vector2 scaling argument doesn't allow for an object to be skewed the way it actually should be. What I'm really interested in is, is there a good way to fake the effect, or should I just drop it and not scale at all? Edit to clarify without the help of a picture (apparently I can't post them yet): I want the aimer arrow to look like it has been painted on the ground at the character's feet, so it should appear to be drawn on the ground plane (in my case the XZ plane) which should be tilted at a 45 degree angle (around the X axis) from the viewing perspective. Alex

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• Linear search vs Octree (Frustum cull)

  - by Dave

  I am wondering whether I should look into implementing an octree of some kind. I have a very simple game which consists of a 3d plane for the floor. There are multiple objects scattered around on the ground, each one has an aabb in world space. Currently I just do a loop through the list of all these objects and check if its bounding box intersects with the frustum, it works great but I am wondering if if it would be a good investment in an octree. I only have max 512 of these objects on the map and they all contain bounding boxes. I am not sure if an octree would make it faster since I have so little objects in the scene.

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• Programming bots in games

  - by Bane

  I'm interested in how bots are usually written. Here's my situation: I plan to make an online 2D mecha game in HTML5, and the server-side will be done with node. It is intended to be multiplayer, but I also want to make bots in case there aren't enough players. How does my game logic see them, as players or as bots? Is there a standard by which I should make them? Also, any general tips and hints will be OK.

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• How are components properly instantiated and used in XNA 4.0?

  - by Christopher Horenstein

  I am creating a simple input component to hold on to actions and key states, and a short history of the last ten or so states. The idea is that everything that is interested in input will ask this component for the latest input, and I am wondering where I should create it. I am also wondering how I should create components that are specific to my game objects - I envision them as variables, but then how do their Update/Draw methods get called? What I'm trying to ask is, what are the best practices for adding components to the proper collections? Right now I've added my input component in the main Game class that XNA creates when everything is first initialized, saying something along the lines of this.Components.Add(new InputComponent(this)), which looks a little odd to me, and I'd still want to hang onto that reference so I can ask it things. An answer to my input component's dilemma is great, but also I'm guessing there is a right way to do this in general in XNA.

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• Switching songs - MediaPlayer lags the game

  - by Fibericon

  When the player encounters a boss in the game I'm working on, I want to have the music change. It seems simple enough with the MediaPlayer class to fade out the current song, switch to another, and then fade the new song in. However, at the point where the second song starts, the game freezes for a split second. The songs in question aren't particularly large either - the first song is 1.7mb and the second song is 3.1mb, both mp3 format. This is the code I'm using to do it: protected void switchSong(GameTime gameTime) { if (!bossSongPlaying) { MediaPlayer.Volume -= ((float)gameTime.ElapsedGameTime.TotalSeconds/10); if (MediaPlayer.Volume < 0.05f) { MediaPlayer.Play(bossSong); MediaPlayer.Volume = 1.0f; bossSongPlaying = true; } } } What can I do to eliminate that momentary hang?

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• Whats a good setup/toolchain for a project?

  - by acidzombie24

  I was thinking, what is needed for a good setup and what are good (free) tools to use? Some of what i came up with are Bug tracking Some good (distributed:P) source control (which means no svn fellas) automated nightly builds or a continuous integration (or anything that automates builds and possibly sends emails when there are build errors) wiki to document decisions, road map or milestones. Something to backup assets (art, sound, etc) What else? and do you have suggestions for any of the above? i pretty much clueless of all of these except for source control

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• backface culling error

  - by acrilige

  I write simple software renderer. In my pipeline i have stage of backface culling. But looks like it has some error (see picture). I perform culling right after world transformation. (i can't insert picture in post coz i don't have enough points, so i just upload it (cube model): http://imageshack.us/photo/my-images/705/bcerror.png/) Vector3F view_dir(0.0f, 0.0f, 1.0f); std::vector<Triangle> to_remove; for (Triangle &t : m_triangles) { Vector4F e1 = t.v2 - t.v1; Vector4F e2 = t.v3 - t.v1; Vector3F normal( e1.y * e2.z - e1.z * e2.y, e1.z * e2.x - e1.x * e2.z, e1.x * e2.y - e1.y * e2.x ); normal.Normalize(); float dot = Dot(view_dir, normal); if (dot <= 0) to_remove.push_back(t); } for (Triangle& t : to_remove) m_triangles.erase(std::remove(m_triangles.begin(), m_triangles.end(), t), m_triangles.end()); Camera sits in origin and points in screen (RH). What is the reason?

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• Map format for 3d open world

  - by Pacha

  I am making an open world 3d platformer in Ogre3D, and I have no idea on what kind of 3d map file format I should use for it. I want to make low-polygon blocky-style objects. Probably rectangles and other geometrical figures that don't have circular edges. Some of those blocks will have properties, like climbable or they might move. I was wondering what would be the best thing to do to make the map (just one level, as it is open).

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• How to handle loading and keeping many bitmaps in an Android 2D game

  - by Lumis

  In an Android 2D game which is using SurfaceView where its onDraw is driven by a loop from a Thread, I use many bitmap sprites (sprite sheets) and two background size bitmaps, which are all loaded into memory at the start. It all works fine, however, when the activity is onPause or after reloading it few times, Android shows a tendency to wipe out the big bitmaps only, probably to free memory. Sometimes this happens even in the middle of loading this very activity. In order to counter this, I made a check in the onDraw method to test if the big bitmaps are still there and reload them if they are forcefully recycled by Android, before drawing them on Canvas. This solution may not be the most stable, and since I know that there are much more accomplished android game programmers here than myself, I hope you can reveal some tricks or secrets or at least provide some good hints, how to overcome this.

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• SDL mouse wheel not picking up

  - by Chris

  Running Ubuntu 11.04, SDL 1.2 trying to pickup mouse wheel up/down movement with this (stripped down) code: int main( int argc, char **argv ) { SDL_MouseButtonEvent *mousebutton = NULL; while ( !done ) { if(mousebutton != NULL && mousebutton->button == SDL_BUTTON_LEFT) yrot += 0.75f; else if(mousebutton != NULL && mousebutton->button == SDL_BUTTON_RIGHT) yrot -= 0.75f; else if(mousebutton != NULL && mousebutton->button == SDL_BUTTON_WHEELUP){ xrot += 0.75f; }else if(mousebutton != NULL && mousebutton->button == SDL_BUTTON_WHEELDOWN){ xrot -= 0.75f; } while ( SDL_PollEvent( &event ) ) { switch( event.type ) { case SDL_MOUSEBUTTONDOWN: mousebutton = &event.button; break; case SDL_MOUSEBUTTONUP: mousebutton = NULL; break; default: break; } } } return 0; } strange thing is, scrolling with the mouse button does nothing, but if I hold down a mouse button or two and then move the mouse it hits the SDL_BUTTON_WHEEL code occasionally. This honestly reeks of a pointer issue, which would make sense since I've been spoiled with C# for the past couple years, but I am just not seeing it. How do i correctly find mouse scroll events in SDL?

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• How do you get the total asset size (or total resource size) in an Android game?

  - by tom_mai78101

  In an Android Java project, there are two folders, asset and res. To me, I usually put some stuffs, like PNG files, sound files, etc. in either one of the two folder. When resources are increasingly becoming more and more in those folders, the time it takes to load them will increase. Therefore, a loading screen is a must in these situation. The total size is to be used in a loading screen, so that I can guess the average time it takes to load each resources, from 0 bytes to its individual resource file size. I only know that by adding all individual sizes in a respective order, I will then obtain the total asset or res folder size, simply by adding them up. So, when it comes to getting the total file size from either folder, how do you obtain their individual resource/object sizes, respectively? Thanks in advance.

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• Hydraulics in game

  - by Mungoid

  I'm not completely sure if this would be better in the Physics site or not as this question is more about how hydraulics should work in game as opposed to how they really work (although that is taken into account) - So I apologize if this is in the wrong place. A project we are on, we have a machine with hydraulics that are powered (They don't just look like they move something, they are the only thing moving/turning/lifting something) - However, the hydraulic extends the same speed no matter what it is pushing. So, say there is a 10 ton object attached to one end of the hydraulic and the other end is attached to a plate on the ground. In real life it takes a few seconds to build up pressure depending on how heavy the object is, but in our project the hydraulics don't care about that. It will lift a 100 ton object the same speed as a 10 ton object. We have a way to fake the hydraulic pressurizing by reducing the 'drive amount' (how fast or slow the hydraulic extends) when we sense that it is touching the ground and that does a relatively decent job but we would like to be able to take other things into account like engine speed, ratios, loads, etc. but we aren't too sure what we need to think about. I'm kinda wondering if anyone here has any experience with this and could offer some suggestions on what to take into account?

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• Class Design - Space Simulator

  - by Peteyslatts

  I have pretty much taught myself everything I know about programming, so while I know how to teach myself (books, internet and reading API's), I'm finding that there hasn't been a whole lot in the way of good programming. So I have two questions: First the broad one: Does anyone have suggestions as to sources for learning about good programming habits and techniques? I'd prefer it if the resource wasn't a 5000 page tome. The more I can read it in installments the better. More specifically: I am finishing up learning the basics of XNA and I want to create a space simulator to test my knowledge. This isn't a full scale simulator, but just something that covers everything I learned. It's also going to be modular so I can build on it, after I get the basics down. One of the early features I want to implement is AI. And I want to take this into account as I'm designing my classes so I can minimize rewriting code. So my question: How should I design ship classes so that both the player and AI can use them? The only idea I have so far is: Create a ship class that contains stats, models, textures, collision data etc. The player and AI would then have the data for position, rotation, health, etc and would base their status off of the ship stats.

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• Getting to math applications gradually

  - by den-javamaniac

  I'm currently getting a formal degree related to computation, in particular my current focus is numerical programming, scientific computing and machine learning. I'd love to apply that knowledge in game dev and expand it with statistics, probability theory, and graph theory (probably even linear algebra). The question is: which spheres of gamedev are filled with such math stuff, is it possible to advance in those without being a part of a group of people and how to get to it gradually? P.S.: I've got experience with commercial java dev and am getting my hands on C/C++ at the moment, however, I'm opened to go ahead and try Unity3D and etc.

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• HLSL: An array of textures and sampler states

  - by nate142

  The shader must switch between multiple textures depending on the Alpha value of the original texture for each pixel. Now this would word fine if I didn't have to worry about SamplerStates. I have created my array of textures and can select a texture based on the Alpha value of the pixel. But how do I create an Array of SamplerStates and link it to my array of textures? I attempted to treat the SamplerState as a function by adding the (int i) but that didn't work. Also I can't use Texture.Sample since this is shader model 2.0. //shader model 2.0 (DX9) texture subTextures[255]; SamplerState MeshTextureSampler(int i) { Texture = (subTextures[i]); }; float4 SampleCompoundTexture(float2 texCoord, float4 diffuse) { float4 SelectedColor = SAMPLE_TEXTURE(Texture, texCoord); int i = SelectedColor.a; texture SelectedTx = subTextures[i]; return tex2D(MeshTextureSampler(i), texCoord) * diffuse; }

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• Why does my code dividing a 2D array into chunks fail?

  - by Borog

  I have a 2D-Array representing my world. I want to divide this huge thing into smaller chunks to make collision detection easier. I have a Chunk class that consists only of another 2D Array with a specific width and height and I want to iterate through the world, create new Chunks and add them to a list (or maybe a Map with Coordinates as the key; we'll see about that). world = new World(8192, 1024); Integer[][] chunkArray; for(int a = 0; a < map.getHeight() / Chunk.chunkHeight; a++) { for(int b = 0; b < map.getWidth() / Chunk.chunkWidth; b++) { Chunk chunk = new Chunk(); chunkArray = new Integer[Chunk.chunkWidth][Chunk.chunkHeight]; for(int x = Chunk.chunkHeight*a; x < Chunk.chunkHeight*(a+1); x++) { for(int y = Chunk.chunkWidth*b; y < Chunk.chunkWidth*(b+1); y++) { // Yes, the tileMap actually is [height][width] I'll have // to fix that somewhere down the line -.- chunkArray[y][x] = map.getTileMap()[x*a][y*b]; // TODO:Attach to chunk } } chunkList.add(chunk); } } System.out.println(chunkList.size()); The two outer loops get a new chunk in a specific row and column. I do that by dividing the overall size of the map by the chunkSize. The inner loops then fill a new chunkArray and attach it to the chunk. But somehow my maths is broken here. Let's assume the chunkHeight = chunkWidth = 64. For the first Array I want to start at [0][0] and go until [63][63]. For the next I want to start at [64][64] and go until [127][127] and so on. But I get an out of bounds exception and can't figure out why. Any help appreciated! Actually I think I know where the problem lies: chunkArray[y][x] can't work, because y goes from 0-63 just in the first iteration. Afterwards it goes from 64-127, so sure it is out of bounds. Still no nice solution though :/ EDIT: if(y < Chunk.chunkWidth && x < Chunk.chunkHeight) chunkArray[y][x] = map.getTileMap()[y][x]; This works for the first iteration... now I need to get the commonly accepted formula.

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• Calculate velocity of a bullet ricocheting on a circle

  - by SteveL

  I made a picture to demostrate what I need,basecaly I have a bullet with velocity and I want it to bounce with the correct angle after it hits a circle Solved(look the accepted answer for explain): Vector.vector.set(bullet.vel); //->v Vector.vector2.setDirection(pos, bullet.pos); //->n normal from center of circle to bullet float dot=Vector.vector.dot(Vector.vector2); //->dot product Vector.vector2.mul(dot).mul(2); Vector.vector.sub(Vector.vector2); Vector.vector.y=-Vector.vector.y; //->for some reason i had to invert the y bullet.vel.set(Vector.vector);

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• 3D architecture app for Android or iPhone

  - by Manixate

  I want to make an app for 3D modeling on iPhone/Android. I cannot get the basic idea of how to get started. I have various options such as learning OpenGL ES, UDK or Unity3d but I want to create models(e.g architecture etc) in my app and then render them when user is finished modeling. I do not know if I am able to design models and then render them in the same app with various effects on the iPhone/Android using UDK or Unity3d. (Note: If you find this question unclear please ask, I may have skipped some vital information).

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• How to avoid game objects accidentally deleting themselves in C++

  - by Tom Dalling

  Let's say my game has a monster that can kamikaze explode on the player. Let's pick a name for this monster at random: a Creeper. So, the Creeper class has a method that looks something like this: void Creeper::kamikaze() { EventSystem::postEvent(ENTITY_DEATH, this); Explosion* e = new Explosion; e->setLocation(this->location()); this->world->addEntity(e); } The events are not queued, they get dispatched immediately. This causes the Creeper object to get deleted somewhere inside the call to postEvent. Something like this: void World::handleEvent(int type, void* context) { if(type == ENTITY_DEATH){ Entity* ent = dynamic_cast<Entity*>(context); removeEntity(ent); delete ent; } } Because the Creeper object gets deleted while the kamikaze method is still running, it will crash when it tries to access this->location(). One solution is to queue the events into a buffer and dispatch them later. Is that the common solution in C++ games? It feels like a bit of a hack, but that might just be because of my experience with other languages with different memory management practices. In C++, is there a better general solution to this problem where an object accidentally deletes itself from inside one of its methods?

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