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• Game physics presentation by Richard Lord, some questions

  - by Steve

  I been implementing (in XNA) the examples in this physics presentation by Richard Lord where he discusses various integration techniques. Bearing in mind that I am a newcomer to game physics (and physics in general) I have some questions. 15 slides in he shows ActionScript code for a gravity example and an animation showing a bouncing ball. The ball bounces higher and higher until it is out of control. I implemented the same in C# XNA but my ball appeared to be bouncing at a constant height. The same applies to the next example where the ball bounces lower and lower. After some experimentation I found that if I switched to a fixed timestep and then on the first iteration of Update() I set the time variable to be equal to elapsed milliseconds (16.6667) I would see the same behaviour. Doing this essentially set the framerate, velocity and acceleration to zero for the first update and introduced errors(?) into the algorithm causing the ball's velocity to increase (or decrease) over time. I think! My question is, does this make the integration method used poor? Or is it demonstrating that it is poor when used with variable timestep because you can't pass in a valid value for the first lot of calculations? (because you cannot know the framerate in advance). I will continue my research into physics but can anyone suggest a good method to get my feet wet? I would like to experiment with variable timestep, acceleration that changes over time and probably friction. Would the Time Corrected Verlet be OK for this?

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• AABB Sweeping, algorithm to solve "stacking box" problem

  - by Ivo Wetzel

  I'm currently working on a simple AABB collision system and after some fiddling the sweeping of a single box vs. another and the calculation of the response velocity needed to push them apart works flawlessly. Now on to the new problem, imagine I'm having a stack of boxes which are falling towards a ground box which isn't moving: Each of these boxes has a vertical velocity for the "gravity" value, let's say this velocity is 5. Now, the result is that they all fall into each other: The reason is obvious, since all the boxes have a downward velocity of 5, this results in no collisions when calculating the relative velocity between the boxes during sweeping. Note: The red ground box here is static (always 0 velocity, can utilize spatial partitioning ), and all dynamic static collisions are resolved first, thus the fact that the boxes stop correctly at this ground box. So, this seems to be simply an issue with the order the boxes are sweept against each other. I imagine that sorting the boxes based on their x and y velocities and then sweeping these groups correctly against each other may resolve this issues. So, I'm looking for algorithms / examples on how to implement such a system. The code can be found here: https://github.com/BonsaiDen/aabb The two files which are of interest are [box/Dynamic.lua][3] and [box/Manager.lua][4]. The project is using Love2D in case you want to run it.

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• Interpolate air drag for my game?

  - 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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• Minecraft-style player-gound collision detection

  - by khyperia

  The title pretty much says it all... (Minecraft is a game consisting of evenly-spaced cubes for terrain, like voxels) Note: I am using C# XNA. I am pretty sure AABB is the way to go, yet I don't know how to implement it. I admit, I'm almost looking for code, but theories/ideas are very welcome. Important capabilities of my code: I have a function that can get a block anywhere in the world, and get a BoundingBox for that cube. Hence, I have created a BoundingBox for the player to collide with those cubes. My idea was to get the blocks around the player (maybe 4x6x4) and test against those. The problems I have been having: Say the world is a flat plane. If I use the method of go the shortest distance out, then if the player is slightly clipped into the ground (from gravity), but even slighter into the next block over, then the player will be pushed sideways (and so cannot walk along ground). Of course, this is assuming I react to every block intersected. Another problem is knowing which direction to go (aka negative x or positive). That takes me to my final problem- Getting the amount of intersection, in the correct direction (+ or -) has been tough for me. I hope I haven't been too hard to understand, I'm not too good at explaining things... And if this question has already been asked, I'm sorry, I looked for it... for 3 days straight. One last thing, if someone knows exactly how minecraft does it, or has source (I know MC modders have the source, how else would they mod), please point me to it.

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• Drawing particles with CPU instead of GPU (XNA)

  - by Helix

  I'm trying out modifications to the following particle system. http://create.msdn.com/en-US/education/catalog/sample/particle_3d I have a function such that when I press Space, all the particles have their positions and velocities set to 0. for (int i = 0; i < particles.GetLength(0); i++) { particles[i].Position = Vector3.Zero; particles[i].Velocity = Vector3.Zero; } However, when I press space, the particles are still moving. If I go to FireParticleSystem.cs I can turn settings.Gravity to 0 and the particles stop moving, but the particles are still not being shifted to (0,0,0). As I understand it, the problem lies in the fact that the GPU is processing all the particle positions, and it's calculating where the particles should be based on their initial position, their initial velocity and multiplying by their age. Therefore, all I've been able to do is change the initial position and velocity of particles, but I'm unable to do it on the fly since the GPU is handling everything. I want the CPU to calculate the positions of the particles individually. This is because I will be later implementing some sort of wind to push the particles around. How do I stop the GPU from taking over? I think it's something to do with VertexBuffers and the draw function, but I don't know how to modify it to make it work.

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• How do I choose the scaling factor of a 3D game world?

  - by concept3d

  I am making a 3D tank game prototype with some physics simulation, am using C++. One of the decisions I need to make is the scale of the game world in relation to reality. For example, I could consider 1 in-game unit of measurement to correspond to 1 meter in reality. This feels intuitive, but I feel like I might be missing something. I can think of the following as potential problems: 3D modelling program compatibility. (?) Numerical accuracy. (Does this matter?) Especially at large scales, how games like Battlefield have huge maps: How don't they lose numerical accuracy if they use 1:1 mapping with real world scale, since floating point representation tend to lose more precision with larger numbers (e.g. with ray casting, physics simulation)? Gameplay. I don't want the movement of units to feel slow or fast while using almost real world values like -9.8 m/s^2 for gravity. (This might be subjective.) Is it ok to scale up/down imported assets or it's best fit with a world with its original scale? Rendering performance. Are large meshes with the same vertex count slower to render? I'm wondering if I should split this into multiple questions...

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• Bullet Physic: Transform body after adding

  - by Mathias Hölzl

  I would like to transform a rigidbody after adding it to the btDiscreteDynamicsWorld. When I use the CF_KINEMATIC_OBJECT flag I am able to transform it but it's static (no collision response/gravity). When I don't use the CF_KINEMATIC_OBJECT flag the transform doesn't gets applied. So how to I transform non-static objects in bullet? DemoCode: btBoxShape* colShape = new btBoxShape(btVector3(SCALING*1,SCALING*1,SCALING*1)); /// Create Dynamic Objects btTransform startTransform; startTransform.setIdentity(); btScalar mass(1.f); //rigidbody is dynamic if and only if mass is non zero, otherwise static bool isDynamic = (mass != 0.f); btVector3 localInertia(0,0,0); if (isDynamic) colShape->calculateLocalInertia(mass,localInertia); btDefaultMotionState* myMotionState = new btDefaultMotionState(); btRigidBody::btRigidBodyConstructionInfo rbInfo(mass,myMotionState,colShape,localInertia); btRigidBody* body = new btRigidBody(rbInfo); body->setCollisionFlags(body->getCollisionFlags()|btCollisionObject::CF_KINEMATIC_OBJECT); body->setActivationState(DISABLE_DEACTIVATION); m_dynamicsWorld->addRigidBody(body); startTransform.setOrigin(SCALING*btVector3( btScalar(0), btScalar(20), btScalar(0) )); body->getMotionState()->setWorldTransform(startTransform);

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• Integration error in high velocity

  - by Elektito

  I've implemented a simple simulation of two planets (simple 2D disks really) in which the only force is gravity and there is also collision detection/response (collisions are completely elastic). I can launch one planet into orbit of the other just fine. The collision detection code though does not work so well. I noticed that when one planet hits the other in a free fall it speeds backward and goes much higher than its original position. Some poking around convinced me that the simplistic Euler integration is causing the error. Consider this case. One object has a mass of 1kg and the other has a mass equal to earth. Say the object is 10 meters above ground. Assume that our dt (delta t) is 1 second. The object goes to the height of 9 meters at the end of the first iteration, 7 at the end of the second, 4 at the end of the third and 0 at the end of the fourth iteration. At this points it hits the ground and bounces back with the speed of 10 meters per second. The problem is with dt=1, on the first iteration it bounces back to a height of 10. It takes several more steps to make the object change its course. So my question is, what integration method can I use which fixes this problem. Should I split dt to smaller pieces when velocity is high? Or should I use another method altogether? What method do you suggest? EDIT: You can see the source code here at github:https://github.com/elektito/diskworld/

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• From simple physics with a ball, to a more complicated shape

  - by Maximus

  Hello fellow game devs and stack overflowers... I recently made a transition from OpenGL ES 1.1 to 2.0 (on Android via NDK) and things are going well so far. I'm working on doing a dice rolling application (gaming dice up to 20 sided, not just regular 6 sided die) as a way to learn more about how physics is implemented in a gaming environment. I've explored implementing existing engine options (such as Bullet) and I don't think I need to implement something quite so sophisticated. I've found several tutorials that handle a lot of the general physics involved with initial trajectory, velocity, angle of contact and reflection angle, etc. I'm confident that I'd be able to implement ball-like behavior without much trouble. My question lies in when I attempt to make the interaction of the die shape with another surface more "realistic," for example... the die strikes the floor surface at such an angle where only one corner makes contact with the floor. In my mind, the center of gravity of the object would play a part in determining how the die bounces away, possibly even spinning it it faster, etc... but I am not sure what the actual math involved is. Are there any recommended resources for getting into this level of detail? Initial searches haven't turned up much... Thanks to everyone in the community, -Jeremiah

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• If statement causing xna sprites to draw frame by frame

  - by user1489599

  I’m a bit new to XNA but I wanted to write a simple program that would fire a cannon ball from a cannon at a 45 degree angle. It works fine outside of my keyboard i/o if statement, but when I encapsulate the code around an if statement checking to see if the user hits the space bar, the sprite will draw one frame at a time every time the space bar is hit. This is the code in question if (currentKeyboardState.IsKeyUp(Keys.Space) && previousKeyboardState.IsKeyDown(Keys.Space) && !skullBall.Alive) { //works outside the keyboard input if statement //{ skullBall.Position = cannon.Position; skullBall.DeltaY = -(float)(Math.Sin(MathHelper.ToRadians(45)) * 50/*39.7577*/ * time + 0.5 * (gravity * (time * time))); skullBall.DeltaX = (float)(Math.Cos(MathHelper.ToRadians(45)) * 50/*39.7577*/ * time); skullBall.Alive = true; //} } The skull ball represents the cannon ball and the cannon is just the starting point. DeltaX and DeltaY are the values I’m using to update the cannon balls position per update. I know it's dumb to have the cannon ball start at the cannons position every time the update is called but it’s not really noticeable right now. I was wondering if after examining my code, if anyone noticed any errors that would cause the sprite to display frame by frame instead of drawing it as a full animation of the cannon ball leaving the cannon and moving from there.

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• Representing heightmaps, on disk and when drawing

  - by gardian06

  This is a conglomeration question when answering please specify which part you are addressing. I am looking at creating a maze type game that utilizes elevation. I have a few features I would like to have, but am unsure as to some of the implementation. I have done work doing fileIO maze generation (using a key to read the file, and then generate the level based on that file), but I am unsure how to think about this with elevation in the mix. I think height maps might be a good approach, but don't know how to represent them effectively. for a height map which is more beneficial XML(containing h[u,v] data and key definition), CSV (item1 is key reference, item2 is elevation), or another approach that I have not thought of yet? When it comes to placing the elevation values themselves what kind of deltah values are appropriate to have it noticeable at about a 60degree angle while not really effecting gravity driven physics (assuming some effect while moving up/down hill)? I am thinking of maybe going to procedural generation at some point, but am wondering if it is practical to have a procedurally generated grid (wall squares possibly same dimensions as the open space squares), or if designing to a thin wall open spaces is better? this decision will effect the amount of work need on the graphics end for uniform vs. irregular walls. EDIT: Game will be a elevation maze shooter. Levels/maps will be mazes with elevation the player has to negotiate. Elevations will have effects on "combat" vision, and movement.

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• Move a 2D square on y axis on android GLES2

  - by Dan

  I am trying to create a simple game for android, to start i am trying to make the square move down the y axis but the way i am doing it dosent move the square at all and i cant find any tutorials for GLES20 The on draw frame function in the render class updates the users position based on accleration dew to gravity, gets the transform matrix from the user class which is used to move the square down, then the program draws it. All that happens is that the square is drawn, no motion happens public void onDrawFrame(GL10 gl) { user.update(0.0, phy.AccelerationDewToGravity); GLES20.glClear(GLES20.GL_COLOR_BUFFER_BIT | GLES20.GL_DEPTH_BUFFER_BIT); // Re draws black background GLES20.glVertexAttribPointer(maPositionHandle, 3, GLES20.GL_FLOAT, false, 12, user.SquareVB);//triangleVB); GLES20.glEnableVertexAttribArray(maPositionHandle); GLES20.glUniformMatrix4fv(maPositionHandle, 1, false, user.getTransformMatrix(), 0); GLES20.glDrawArrays(GLES20.GL_TRIANGLE_STRIP, 0, 4); } The update function in the player class is public void update(double vh, double vv) { Vh += vh; // Increase horrzontal Velosity Vv += vv; // Increase vertical velosity //Matrix.translateM(mMMatrix, 0, (int)Vh, (int)Vv, 0); Matrix.translateM(mMMatrix, 0, mMMatrix, 0, (float)Vh, (float)Vv, 0); }

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• What kind of physics to choose for our arcade 3D MMO?

  - by Nick

  We're creating an action MMO using Three.js (WebGL) with an arcadish feel, and implementing physics for it has been a pain in the butt. Our game has a terrain where the character will walk on, and in the future 3D objects (a house, a tree, etc) that will have collisions. In terms of complexity, the physics engine should be like World of Warcraft. We don't need friction, bouncing behaviour or anything more complex like joints, etc. Just gravity. I have managed to implement terrain physics so far by casting a ray downwards, but it does not take into account possible 3D objects. Note that these 3D objects need to have convex collisions, so our artists create a 3D house and the player can walk inside but can't walk through the walls. How do I implement proper collision detection with 3D objects like in World of Warcraft? Do I need an advanced physics engine? I read about Physijs which looks cool, but I fear that it may be overkill to implement that for our game. Also, how does WoW do it? Do they have a separate raycasting system for the terrain? Or do they treat the terrain like any other convex mesh? A screenshot of our game so far:

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• Vector vs Scalar velocity?

  - by Serguei Fedorov

  I am revamping an engine I have been working on and off on for the last few weeks to use a directional vector to dictate direction; this way I can dictate the displacement based on a direction. However, the issue I am trying to overcome is the following problem; the speed towards X and speed towards Y are unrelated to one another. If gravity pulls the object down by an increasing velocity my velocity towards the X should not change. This is very easy to implement if my speed is broken into a Vector datatype, Vector.X dictates one direction Vector.Y dictates the other (assuming we are not concerned about the Z axis). However, this defeats the purpose of the directional vector because: SpeedX = 10 SpeedY = 15 [1, 1] normalized = ~[0.7, 0.7] [0.7, 0.7] * [10, 15] = [7, 10.5] As you can see my direction is now "scaled" to my speed which is no longer the direction that I want to be moving in. I am very new to vector math and this is a learning project for me. I looked around a little bit on the internet but I still want to figure out things on my own (not just look at an example and copy off it). Is there way around this? Using a directional vector is extremely useful but I am a little bit stumped at this problem. I am sorry if my mathematical understanding maybe completely wrong.

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• Extremely simple online multiplayer game

  - by Postscripter

  I am considering creating a simple multiplayer game, which focuses on physics and can accommodate up to 30 players per session. Very simple graphics, but smart physics (pushing, weight and gravity, balance) is required. After some research I found a good java script (framework ??) called box2d.js I found the demo to be excellent. this is is kind of physics am looking for in my game. Now, what other frameworks will I need? Node.js?? Prototype.js?? (btw, I found the latest versoin of protoype.js to be released in 2010...?? is this still supported? Should I avoid using it?) What bout HTML 5 and Canvas? would I need them? websockets? Am a beginner in web programming + game programming world. but I will learn fast, am computer science graduate. (but no much web expeience but know essentionals javascript, html, css..). I just need a guiding path to build my game. Thanks

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• Platform game collisions with Block

  - by Sri Harsha Chilakapati

  I am trying to create a platform game and doing wrong collision detection with the blocks. Here's my code // Variables GTimer jump = new GTimer(1000); boolean onground = true; // The update method public void update(long elapsedTime){ MapView.follow(this); // Add the gravity if (!onground && !jump.active){ setVelocityY(4); } // Jumping if (isPressed(VK_SPACE) && onground){ jump.start(); setVelocityY(-4); onground = false; } if (jump.action(elapsedTime)){ // jump expired jump.stop(); } // Horizontal movement setVelocityX(0); if (isPressed(VK_LEFT)){ setVelocityX(-4); } if (isPressed(VK_RIGHT)){ setVelocityX(4); } } // The collision method public void collision(GObject other){ if (other instanceof Block){ // Determine the horizontal distance between centers float h_dist = Math.abs((other.getX() + other.getWidth()/2) - (getX() + getWidth()/2)); // Now the vertical distance float v_dist = Math.abs((other.getY() + other.getHeight()/2) - (getY() + getHeight()/2)); // If h_dist > v_dist horizontal collision else vertical collision if (h_dist > v_dist){ // Are we moving right? if (getX()<other.getX()){ setX(other.getX()-getWidth()); } // Are we moving left? else if (getX()>other.getX()){ setX(other.getX()+other.getWidth()); } } else { // Are we moving up? if (jump.active){ jump.stop(); } // We are moving down else { setY(other.getY()-getHeight()); setVelocityY(0); onground = true; } } } } The problem is that the object jumps well but does not fall when moved out of platform. Here's an image describing the problem. I know I'm not checking underneath the object but I don't know how. The map is a list of objects and should I have to iterate over all the objects??? Thanks

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• MVC design in Cocoa - are all 3 always necessary? Also: naming conventions, where to put Controller

  - by Nektarios

  I'm new to MVC although I've read a lot of papers and information on the web. I know it's somewhat ambiguous and there are many different interpretations of MVC patterns.. but the differences seem somewhat minimal My main question is - are M, V, and C always going to be necessary to be doing this right? I haven't seen anyone address this in anything I've read. Examples (I'm working in Cocoa/Obj-c although that shouldn't much matter).. 1) If I have a simple image on my GUI, or a text entry field that is just for a user's convenience and isn't saved or modified, these both would be V (view) but there's no M (no data and no domain processing going on), and no C to bridge them. So I just have some aspects that are "V" - seems fine 2) I have 2 different and visible windows that each have a button on them labeled as "ACTIVATE FOO" - when a user clicks the button on either, both buttons press in and change to say "DEACTIVATE FOO" and a third window appears with label "FOO". Clicking the button again will change the button on both windows to "ACTIVATE FOO" and will remove the third "FOO" window. In this case, my V consists of the buttons on both windows, and I guess also the third window (maybe all 3 windows). I definitely have a C, my Controller object will know about these buttons and windows and will get their clicks and hold generic states regarding windows and buttons. However, whether I have 1 button or 10 button, my window is called "FOO" or my window is called "BAR", this doesn't matter. There's no domain knowledge or data here - just control of views. So in this example, I really have "V" and "C" but no "M" - is that ok? 3) Final example, which I am running in to the most. I have a text entry field as my View. When I enter text in this, say a number representing gravity, I keep it in a Model that may do things like compute physics of a ball while taking in to account my gravity parameter. Here I have a V and an M, but I don't understand why I would need to add a C - a controller would just accept the signals from the View and pass it along to the Model, and vice versa. Being as the C is just a pure passthrough, it's really "junk" code and isn't making things any more reusable in my opinion. In most situations, when something changes I will need to change the C and M both in nearly identical ways. I realize it's probably an MVC beginner's mistake to think most situations call for only V and M.. leads me in to next subject 4) In Cocoa / Xcode / IB, I guess my Controllers should always be an instantiated object in IB? That is, I lay all of my "V" components in IB, and for each collection of View objects (things that are related) I should have an instantiated Controller? And then perhaps my Models should NOT be found in IB, and instead only found as classes in Xcode that tie in with Controller code found there. Is this accurate? This could explain why you'd have a Controller that is not really adding value - because you are keeping consistent.. 5) What about naming these things - for my above example about FOO / BAR maybe something that ends in Controller would be the C, like FancyWindowOpeningController, etc? And for models - should I suffix them with like GravityBallPhysicsModel etc, or should I just name those whatever I like? I haven't seen enough code to know what's out there in the wild and I want to get on the right track early on Thank you in advance for setting me straight or letting me know I'm on the right track. I feel like I'm starting to get it and most of what I say here makes sense, but validation of my guessing would help me feel confident..

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• Why is CS never a topic of conversation of the layman? [closed]

  - by hydroparadise

  Granted, every profession has it's technicalities. If you are an MD, you better know the anatomy of the human body, and if you are astronomer, you better know your calculus. Yet, you don't have to know these more advance topics to know that smoking might give you lung cancer because of carcinogens or the moon revolves around the earth because of gravity (thank you Discovery Channel). There's sort of a common knowledge (at least in more developed countries) of these more advanced topics. With that said, why are things like recursive descent parsing, BNF, or Turing machines hardly ever mentioned outsided 3000 or 4000 level classes in a university setting or between colleagues? Even back in my days before college in my pursuit of knowledge on how computers work, these very important topics (IMHO) never seem to get the light of day. Many different sources and sites go into "What is a processor?" or "What is RAM?", or "What is an OS?". You might get lucky and discover something about programming languages and how they play a role in how applications are created, but nothing about the tools for creating the language itself. To extend this idea, Dennis Ritchie died shortly after Steve Jobs, yet Dennis Ritchie got very little press compared to Steve Jobs. So, the heart of my question: Does the public in general not care to hear about computer science topics that make the technology in their lives work, or does the computer science community not lend itself to the general public to close the knowledge gap? Am I wrong to think the general public has the same thirst for knowledge on how things work as I do? Please consider the question carefully before answering or vote closing please.

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• generating maps

  - by gardian06

  This is a conglomeration question when answering please specify which part you are addressing. I am looking at creating a maze type game that utilizes elevation. I have a few features I would like to have, but am unsure as to some of the implementation. I have done work doing fileIO maze generation (using a key to read the file, and then generate the level based on that file), but I am unsure how to think about this with elevation in the mix. I think height maps might be a good approach, but don't know how to represent them effectively. for a height map which is more beneficial XML(containing h[u,v] data and key definition), CSV (item1 is key reference, item2 is elevation), or another approach that I have not thought of yet? When it comes to placing the elevation values themselves what kind of deltah values are appropriate to have it noticeable at about a 60degree angle while not really effecting gravity driven physics (assuming some effect while moving up/down hill)? I am thinking of maybe going to procedural generation at some point, but am wondering if it is practical to have a procedurally generated grid (wall squares possibly same dimensions as the open space squares), or if designing to a thin wall open spaces is better? this decision will effect the amount of work need on the graphics end for uniform vs. irregular walls. EDIT: game will be a elevation maze shooter. levels/maps will be mazes with elevation the player has to negotiate. elevations will have effects on "combat" vision, and movement

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• Dynamic Jump spot

  - by Pasquale Sada

  I have an initial velocity V(Vx,Vy,VZ) and a spot where he stands still at S(Sx,Sy,Sz). What I'm trying to achieve is a jump on a spot E(Ex,Ey,Ez) where you have clicked on(only lower or higher spot, because I've in place a simple steering behavior for even terrains). There are no obstacle around. I've implemented a formula that can make him jump in a precise way on a spot but you need to declare an angle: the problem arise when the selected spot is straight above your head. It' pretty lame that the char hang there and can reach a thing that is 1cm above is head. I'll share the code I'm using: Vector3 dir = target - transform.position; // get target direction float h = dir.y; // get height difference dir.y = 0; // retain only the horizontal direction float dist = dir.magnitude ; // get horizontal distance float a = angle * Mathf.Deg2Rad; // convert angle to radians dir.y = dist * Mathf.Tan(a); // set dir to the elevation angle dist += h / Mathf.Tan(a); // correct for small height differences // calculate the velocity magnitude float vel = Mathf.Sqrt(dist * Physics.gravity.magnitude / Mathf.Sin(2 *a)); return vel * dir.normalized;

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• Updating the jump in game

  - by Luka Tiger

  I am making a Java game and I want my game to run the same on any FPS so I'm using time delta between each update. This is the update method of the Player: public void update(long timeDelta) { //speed is the movement speed of a player on X axis //timeDelta is expressed in nano seconds so I'm dividing it with 1000000000 to express it in seconds if (Input.keyDown(37)) this.velocityX -= speed * (timeDelta / 1000000000.0); if (Input.keyDown(39)) this.velocityX += speed * (timeDelta / 1000000000.0); if(Input.keyPressed(38)) { this.velocityY -= 6; } velocityY += g * (timeDelta/1000000000.0); //applying gravity move(velocityX, velocityY); /*this is method which moves a player according to velocityX and velocityY, and checking the collision */ this.velocityX = 0.0; } The strange thing is that when I have unlimited FPS (and update number) my player is jumping about 10 blocks. It jumps even higher when the FPS is increasing. If I limit FPS it is jumping 4 blocks. (BLOCK: 32x32) I have just realized that the problem is this: if(Input.keyPressed(38)) { this.velocityY -= 6; } I add -6 to velocityY which increases player's Y proportionally to the update number and not to the time. But I don't know how to fix this.

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• Bending of track in a racing game

  - by caius

  I am trying to create a small racing game in which the track would be modeled using a BSpline curve for the path's center line and directional vectors to define the 'bending' of the track at each point. My problem is that I don't know how to calculate the correct bending / slope of the curve, in such a way that it would be optimal or at least visually nice for a car to 'bend in the corner'. My idea was to use the direction of the 2nd derivatives of the curve, however while this approach looks fine for most of the track, there are points in which the 2nd derivative makes sharp 'twists' / very quick 180 degree flips. I also read about 'knots' of bsplines, but I don't know if such 'twist' in 2nd derivatives is a knot or knots are something else. Can you tell me that using a BSpline: 1. How could I calculate a visually nice bending of a track for a racing game? 2. Is it possible to do this by using some simple calculations of centripertal force / gravity? 3. Is it possible to do this by using 1st, 2nd and 3rd derivatives of the BSpline curve? I am not looking for the 'physically correct' bending angle for the track, I would just like to create something which is visually pleasing in a simple game. I am using a framework which has a built-in class for BSpline, including support for 1st, 2nd and 3rd derivatives of the curve.

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• Wall jumping collision detection anomaly

  - by Nanor

  I'm creating a game where the player ascends a tower by wall jumping his way to the top. When the player has collided with the right wall they can only jump left and vice versa. Here is my current implementation: if(wallCollision() == "left"){ player.setPosX(0); player.setVelX(0); ignoreCollisions = true; player.setCanJump(true); player.setFacingLeft(false); } else if (wallCollision() == "right"){ player.setPosX(screenWidth-playerWidth*2); player.setVelX(0); ignoreCollisions = true; player.setCanJump(true); player.setFacingLeft(true); } else{ player.setVelY(player.getVelY() + gravity); } and private String wallCollision(){ if(player.getPosX() < playerWidth && !ignoreCollisions) return "left"; else if(player.getPosX() > screenWidth - playerWidth*2 && !ignoreCollisions) return "right"; else{ timeToJump += Gdx.graphics.getDeltaTime(); if(timeToJump > 0.50f){ timeToJump = 0; ignoreCollisions = false; } return "jumping"; } } If the player is colliding with the left wall it will switch between the states left and jumping repeatedly due to the varible ignoreCollisions being switched repeatedly in collision checks. This will give a chance to either jump as intended or simply ascend vertically instead of diagonally. I can't figure out an implementation that will reliably make sure the player jumps as intended. Does anyone have any pointers?

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• How to refresh a GridView?

  - by Daniel

  Hello everyone, I have a GridView which is pretty similar to the Google tutorial, except that I want to add the ImageViews on runtime (via a subactivity). The results are okay, but the layout of the View is messed up: The GridView doesn't fill the content of its parent, what do I have to do to design it properly? Here the code of adding the children: public void initializeWorkbench(GridView gv, Vector<String> items) { Prototype.workbench.setDimension(screenWidth, divider.height()+workbenchArea.height()); Prototype.workbench.activateWorkbench(); // this measures the workbench correctly Log.d(Prototype.TAG, "workbench width: "+Prototype.workbench.getMeasuredWidth()); // 320 Log.d(Prototype.TAG, "workbench height: "+Prototype.workbench.getMeasuredHeight()); // 30 ImageAdapter imgAdapter = new ImageAdapter(this.getContext(), items); gv.setAdapter(imgAdapter); gv.measure(screenWidth, screenHeight); gv.requestLayout(); gv.forceLayout(); Log.d(Prototype.TAG, "gv width: "+gv.getMeasuredWidth()); // 22 Log.d(Prototype.TAG, "gv height: "+gv.getMeasuredHeight()); // 119 Prototype.workbench.setDimension(screenWidth, divider.height()+workbenchArea.height()); } } activateWorkbench, setDimension and measure in the workbench (LinearLayout above the GridView): public void activateWorkbench() { if(this.equals(Prototype.workbench)) { this.setOrientation(VERTICAL); show = true; measure(); } } public void setDimension(int w, int h) { width = w; height = h; this.setLayoutParams(new LinearLayout.LayoutParams(width, height)); this.invalidate(); } private void measure() { if (this.getOrientation() == LinearLayout.VERTICAL) { int h = 0; int w = 0; this.measureChildren(0, 0); for (int i = 0; i < this.getChildCount(); i++) { View v = this.getChildAt(i); h += v.getMeasuredHeight(); w = (w < v.getMeasuredWidth()) ? v.getMeasuredWidth() : w; } if (this.equals(Prototype.tagarea)) height = (h < height) ? height : h; if (this.equals(Prototype.tagarea)) width = (w < width) ? width : w; } this.setMeasuredDimension(width, height); } The ImageAdapter constructor: public ImageAdapter(Context c, Vector<String> items) { mContext = c; boolean mExternalStorageAvailable = false; boolean mExternalStorageWriteable = false; String state = Environment.getExternalStorageState(); if (Environment.MEDIA_MOUNTED.equals(state)) { // We can read and write the media mExternalStorageAvailable = mExternalStorageWriteable = true; } else if (Environment.MEDIA_MOUNTED_READ_ONLY.equals(state)) { // We can only read the media mExternalStorageAvailable = true; mExternalStorageWriteable = false; } else { // Something else is wrong. It may be one of many other states, but // all we need // to know is we can neither read nor write mExternalStorageAvailable = mExternalStorageWriteable = false; } if (mExternalStorageAvailable && mExternalStorageWriteable) { for (String item : items) { File f = new File(item); if (f.exists()) { try { FileInputStream fis = new FileInputStream(f); Bitmap b = BitmapFactory.decodeStream(fis); bitmaps.add(b); files.add(f); } catch (FileNotFoundException e) { Log.e(Prototype.TAG, "", e); } } } } } And the xml layout: <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:orientation="vertical" android:gravity="bottom" android:paddingLeft="0px" android:paddingTop="0px" android:paddingRight="0px"> <com.unimelb.pt3.ui.TransparentPanel android:id="@+id/workbench" android:layout_width="fill_parent" android:layout_height="10px" android:paddingTop="0px" android:paddingLeft="0px" android:paddingBottom="0px" android:paddingRight="0px"> <GridView xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/gridview" android:layout_width="fill_parent" android:layout_height="fill_parent" android:columnWidth="90dp" android:numColumns="auto_fit" android:verticalSpacing="10dp" android:horizontalSpacing="10dp" android:stretchMode="columnWidth" android:gravity="center" /> </com.unimelb.pt3.ui.TransparentPanel> </LinearLayout>

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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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