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• Simulating smooth movement along a line after calculating a collision containing a restitution of zero in 2D

  - by Casey

  [for tl;dr see after listing] //...Code to determine shapes types involved in collision here... //...Rectangle-Line collision detected. if(_rbTest->GetCollisionShape()->Intersects(*_ground->GetCollisionShape())) { //Convert incoming shape to a line. a2de::Line l(*dynamic_cast<a2de::Line*>(_ground->GetCollisionShape())); //Get line's normal. a2de::Vector2D normal_vector(l.GetSlope().GetY(), -l.GetSlope().GetX()); a2de::Vector2D::Normalize(normal_vector); //Accumulate forces involved. a2de::Vector2D intermediate_forces; a2de::Vector2D normal_force = normal_vector * _rbTest->GetMass() * _world->GetGravityHandler()->GetGravityValue(); intermediate_forces += normal_force; //Calculate final velocity: See [1] double Ma = _rbTest->GetMass(); a2de::Vector2D Ua = _rbTest->GetVelocity(); double Mb = _ground->GetMass(); a2de::Vector2D Ub = _ground->GetVelocity(); double mCr = Mb * _ground->GetRestitution(); a2de::Vector2D collision_velocity( ((Ma * Ua) + (Mb * Ub) + ((mCr * Ub) - (mCr * Ua))) / (Ma + Mb)); //Calculate reflection vector: See [2] a2de::Vector2D reflect_velocity( -collision_velocity + 2 * (a2de::Vector2D::DotProduct(collision_velocity, normal_vector)) * normal_vector ); //Affect velocity to account for restitution of colliding bodies. reflect_velocity *= (_ground->GetRestitution() * _rbTest->GetRestitution()); _rbTest->SetVelocity(reflect_velocity); //THE ULTIMATE ISSUE STEMS FROM THE FOLLOWING LINE: //Move object away from collision one pixel to prevent constant collision. _rbTest->SetPosition(_rbTest->GetPosition() + normal_vector); _rbTest->ApplyImpulse(intermediate_forces); } Sources: (1) Wikipedia: Coefficient of Restitution: Speeds after impact (2) Wikipedia: Specular Reflection: Direction of reflection First, I have a system in place to account for friction (that is, a coefficient of friction) but is not used right now (in addition, it is zero, which should not affect the math anyway). I'll deal with that after I get this working. Anyway, when the restitution of either object involved in the collision is zero the object stops as required, but if movement along the same direction (again, irrespective of the friction value that isn't used) as the line is attempted the object moves as if slogging through knee deep snow. If I remove the line of code in question and the object is not push away one pixel the object barely moves at all. All because the object collides, is stopped, is pushed up, collides, is stopped...etc. OR collides, is stopped, collides, is stopped, etc... TL;DR How do I only account for a collision ONCE for restitution purposes (BONUS: but CONTINUALLY for frictional purposes, to be implemented later)

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• GetContactList stops reporting collisions on welded bodies

  - by Henrique Jung

  I have some strange problem with my game which uses Box2D as physics engine and I'm out of ideas on what I can do to solve it. My game is a class assignment where I need to build a simple game where the main character moves in a 2D environment while square blocks comes from below him. Each time a collision occurs, that block is attached to the character using a weld joint, when three blocks of the same colors are together, they annihilate themselves(an effect similar to Bejeweled). I'm using a recursive function to iterate through all the attached blocks of a given block to see if there are enough blocks for them to be deleted. I'm using GetContactList function to iterate through the list of contacts to see which blocks are adjacent to each other. The results are quite disappointing, the blocks only get annihilated in few cases. After a lot of debugging, I found the issue, but I still don't know how to solve. My issue is: after some time, GetContactList STOPS returning contacts (return NULL) to blocks that were already attached for some time. I spent some time reading the Box2D manual as well as some tutorials and still didn't find any clue of what is happening. Below there's some simplified version of the code that I wrote. for(int a = 0; a < blocksList.size(); a++) { blocksList[a].BuildConnections(); } And on BuildConnections b2ContactEdge* edge = body->GetContactList(); while(edge != NULL) { if (long_check_to_see_if_there's_a_block_nearby) { // add itself to the list to be anihilated globalList.push_back(this); //if there's, call BuildConnections again on the adjacent block adjacentBody->GetUserData()->BuildConnections; } edge = edge->next; } I know that there's another issue related to circular inclusions, but I fairly sure that this problem isn't causing the problem with the collisions. You can download my entire code from this page if you'd like http://code.google.com/p/fellz/source/list

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• How to correctly export UV coordinates from Blender

  - by KlashnikovKid

  Alright, so I'm just now getting around to texturing some assets. After much trial and error I feel I'm pretty good at UV unwrapping now and my work looks good in Blender. However, either I'm using the UV data incorrectly (I really doubt it) or Blender doesn't seem to export the correct UV coordinates into the obj file because the texture is mapped differently in my game engine. And in Blender I've played with the texture panel and it's mapping options and have noticed it doesn't appear to affect the exported obj file's uv coordinates. So I guess my question is, is there something I need to do prior to exporting in order to bake the correct UV coordinates into the obj file? Or something else that needs to be done to massage the texture coordinates for sampling. Or any thoughts at all of what could be going wrong? (Also here is a screen shot of my diffused texture in blender and the game engine. As you can see in the image, I have the same problem with a simple test cube not getting correct uv's either) http://www.digitalinception.net/blenderSS.png http://www.digitalinception.net/gameSS.png

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• Ensuring that saved data has not been edited in a game with both offline and online components

  - by Omar Kooheji

  I'm in the pre-planning phase of coming up with a game design and I was wondering if there was a sensible way to stop people from editing saves in a game with offline and online components. The offline component would allow the player to play through the game and the online component would allow them to play against other players, so I would need to make sure that people hadn't edited the source code/save files while offline to gain an advantage while online. Game likely to be developed in either .Net or Java, both of which are unfortunately easy to decompile.

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• Scanline filling of polygons that share edges and vertices

  - by Belgin

  In this picture (a perspective projection of an icosahedron), the scanline (red) intersects that vertex at the top. In an icosahedron each edge belongs to two triangles. From edge a, only one triangle is visible, the other one is in the back. Same for edge d. Also, in order to determine what color the current pixel should be, each polygon has a flag which can either be 'in' or 'out', depending upon where on the scanline we currently are. Flags are flipped according to the intersection of the scanline with the edges. Now, as we go from a to d (because all edges are intersected with the scanline at that vertex), this happens: the triangle behind triangle 1 and triangle 1 itself are set 'in', then 2 is set in and 1 is 'out', then 3 is set 'in', 2 is 'out' and finally 3 is 'out' and the one behind it is set 'in', which is not the desired behavior because we only need the triangles which are facing us to be set 'in', the rest should be 'out'. How do process the edges in the Active Edge List (a list of edges that are currently intersected by the scanline) so the right polys are set 'in'? Also, I should mention that the edges are unique, which means there exists an array of edges in the data structure of the icosahedron which are pointed to by edge pointers in each of the triangles.

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• Unity Frustum Culling Issue

  - by N0xus

  I'm creating a game that utilizes off center projection. I've got my game set up in a CAVE being rendered in a cluster, over 8 PC's with 4 of these PC's being used for each eye (this creates a stereoscopic effect). To help with alignment in the CAVE I've implemented an off center projection class. This class simply tells the camera what its top left, bottom left & bottom right corners are. From here, it creates a new projection matrix showing the the player the left and right of their world. However, inside Unity's editor, the camera is still facing forwards and, as a result the culling inside Unity isn't rendering half of the image that appears on the left and right screens. Does anyone know of a way to to either turn off the culling in Unity, or find a way to fix the projection matrix issue?

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• Libnoise producing completely random noise

  - by Doodlemeat

  I am using libnoise in C++ taken and I have some problems with getting coherent noise. I mean, the noise produced now are completely random and it doesn't look like a noise. Here's a to the image produced by my game. I am diving the map into several chunks, but I can't seem to find any problem doing that since libnoise supports tileable noise. The code can be found below. Every chunk is 8x8 tiles large. Every tile is 64x64 pixels. I am also providing a link to download the entire project. It was made in Visual Studio 2013. Download link This is the code for generating a chunk Chunk *World::loadChunk(sf::Vector2i pPosition) { sf::Vector2i chunkPos = pPosition; pPosition.x *= mChunkTileSize.x; pPosition.y *= mChunkTileSize.y; sf::FloatRect bounds(static_cast<sf::Vector2f>(pPosition), sf::Vector2f(static_cast<float>(mChunkTileSize.x), static_cast<float>(mChunkTileSize.y))); utils::NoiseMap heightMap; utils::NoiseMapBuilderPlane heightMapBuilder; heightMapBuilder.SetSourceModule(mNoiseModule); heightMapBuilder.SetDestNoiseMap(heightMap); heightMapBuilder.SetDestSize(mChunkTileSize.x, mChunkTileSize.y); heightMapBuilder.SetBounds(bounds.left, bounds.left + bounds.width - 1, bounds.top, bounds.top + bounds.height - 1); heightMapBuilder.Build(); Chunk *chunk = new Chunk(this); chunk->setPosition(chunkPos); chunk->buildChunk(&heightMap); chunk->setTexture(&mTileset); mChunks.push_back(chunk); return chunk; } This is the code for building the chunk void Chunk::buildChunk(utils::NoiseMap *pHeightMap) { // Resize the tiles space mTiles.resize(pHeightMap->GetWidth()); for (int x = 0; x < mTiles.size(); x++) { mTiles[x].resize(pHeightMap->GetHeight()); } // Set vertices type and size mVertices.setPrimitiveType(sf::Quads); mVertices.resize(pHeightMap->GetWidth() * pHeightMap->GetWidth() * 4); // Get the offset position of all tiles position sf::Vector2i tileSize = mWorld->getTileSize(); sf::Vector2i chunkSize = mWorld->getChunkSize(); sf::Vector2f offsetPositon = sf::Vector2f(mPosition); offsetPositon.x *= chunkSize.x; offsetPositon.y *= chunkSize.y; // Build tiles for (int x = 0; x < mTiles.size(); x++) { for (int y = 0; y < mTiles[x].size(); y++) { // Sometimes libnoise can return a value over 1.0, better be sure to cap the top and bottom.. float heightValue = pHeightMap->GetValue(x, y); if (heightValue > 1.f) heightValue = 1.f; if (heightValue < -1.f) heightValue = -1.f; // Instantiate a new Tile object with the noise value, this doesn't do anything yet.. mTiles[x][y] = new Tile(this, pHeightMap->GetValue(x, y)); // Get a pointer to the current tile's quad sf::Vertex *quad = &mVertices[(y + x * pHeightMap->GetWidth()) * 4]; quad[0].position = sf::Vector2f(offsetPositon.x + x * tileSize.x, offsetPositon.y + y * tileSize.y); quad[1].position = sf::Vector2f(offsetPositon.x + (x + 1) * tileSize.x, offsetPositon.y + y * tileSize.y); quad[2].position = sf::Vector2f(offsetPositon.x + (x + 1) * tileSize.x, offsetPositon.y + (y + 1) * tileSize.y); quad[3].position = sf::Vector2f(offsetPositon.x + x * tileSize.x, offsetPositon.y + (y + 1) * tileSize.y); // find out which type of tile to render, atm only air or stone TileStop *tilestop = mWorld->getTileStopAt(heightValue); sf::Vector2i texturePos = tilestop->getTexturePosition(); // define its 4 texture coordinates quad[0].texCoords = sf::Vector2f(texturePos.x, texturePos.y); quad[1].texCoords = sf::Vector2f(texturePos.x + 64, texturePos.y); quad[2].texCoords = sf::Vector2f(texturePos.x + 64, texturePos.y + 64); quad[3].texCoords = sf::Vector2f(texturePos.x, texturePos.y + 64); } } } All the code that uses libnoise in some way are World.cpp, World.h and Chunk.cpp, Chunk.h in the project.

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• Physics System ignores collision in some rare cases

  - by Gajoo

  I've been developing a simple physics engine for my game. since the game physics is very simple I've decided to increase accuracy a little bit. Instead of formal integration methods like fourier or RK4, I'm directly computing the results after delta time "dt". based on the very first laws of physics : dx = 0.5 * a * dt^2 + v0 * dt dv = a * dt where a is acceleration and v0 is object's previous velocity. Also to handle collisions I've used a method which is somehow different from those I've seen so far. I'm detecting all the collision in the given time frame, stepping the world forward to the nearest collision, resolving it and again check for possible collisions. As I said the world consist of very simple objects, so I'm not loosing any performance due to multiple collision checking. First I'm checking if the ball collides with any walls around it (which is working perfectly) and then I'm checking if it collides with the edges of the walls (yellow points in the picture). the algorithm seems to work without any problem except some rare cases, in which the collision with points are ignored. I've tested everything and all the variables seem to be what they should but after leaving the system work for a minute or two the system the ball passes through one of those points. Here is collision portion of my code, hopefully one of you guys can give me a hint where to look for a potential bug! void PhysicalWorld::checkForPointCollision(Vec2 acceleration, PhysicsComponent& ball, Vec2& collisionNormal, float& collisionTime, Vec2 target) { // this function checks if there will be any collision between a circle and a point // ball contains informations about the circle (it's current velocity, position and radius) // collisionNormal is an output variable // collisionTime is also an output varialbe // target is the point I want to check for collisions Vec2 V = ball.mVelocity; Vec2 A = acceleration; Vec2 P = ball.mPosition - target; float wallWidth = mMap->getWallWidth() / (mMap->getWallWidth() + mMap->getHallWidth()) / 2; float r = ball.mRadius / (mMap->getWallWidth() + mMap->getHallWidth()); // r is ball radius scaled to match actual rendered object. if (A.any()) // todo : I need to first correctly solve the collisions in case there is no acceleration return; if (V.any()) // if object is not moving there will be no collisions! { float D = P.x * V.y - P.y * V.x; float Delta = r*r*V.length2() - D*D; if(Delta < eps) return; Delta = sqrt(Delta); float sgnvy = V.y > 0 ? 1: (V.y < 0?-1:0); Vec2 c1(( D*V.y+sgnvy*V.x*Delta) / V.length2(), (-D*V.x+fabs(V.y)*Delta) / V.length2()); Vec2 c2(( D*V.y-sgnvy*V.x*Delta) / V.length2(), (-D*V.x-fabs(V.y)*Delta) / V.length2()); float t1 = (c1.x - P.x) / V.x; float t2 = (c2.x - P.x) / V.x; if(t1 > eps && t1 <= collisionTime) { collisionTime = t1; collisionNormal = c1; } if(t2 > eps && t2 <= collisionTime) { collisionTime = t2; collisionNormal = c2; } } } // this function should step the world forward by dt. it doesn't check for collision of any two balls (components) // it just checks if there is a collision between the current component and 4 points forming a rectangle around it. void PhysicalWorld::step(float dt) { for (unsigned i=0;i<mObjects.size();i++) { PhysicsComponent &current = *mObjects[i]; Vec2 acceleration = current.mForces * current.mInvMass; float rt=dt; // stores how much more the world should advance while(rt > eps) { float collisionTime = rt; Vec2 collisionNormal = Vec2(0,0); float halfWallWidth = mMap->getWallWidth() / (mMap->getWallWidth() + mMap->getHallWidth()) / 2; // we check if there is any collision with any of those 4 points around the ball // if there is a collision both collisionNormal and collisionTime variables will change // after these functions collisionTime will be exactly the value of nearest collision (if any) // and if there was, collisionNormal will report in which direction the ball should return. checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2(floor(current.mPosition.x) + halfWallWidth,floor(current.mPosition.y) + halfWallWidth)); checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2(floor(current.mPosition.x) + halfWallWidth, ceil(current.mPosition.y) - halfWallWidth)); checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2( ceil(current.mPosition.x) - halfWallWidth,floor(current.mPosition.y) + halfWallWidth)); checkForPointCollision(acceleration,current,collisionNormal,collisionTime,Vec2( ceil(current.mPosition.x) - halfWallWidth, ceil(current.mPosition.y) - halfWallWidth)); // either if there is a collision or if there is not we step the forward since we are sure there will be no collision before collisionTime current.mPosition += collisionTime * (collisionTime * acceleration * 0.5 + current.mVelocity); current.mVelocity += collisionTime * acceleration; // if the ball collided with anything collisionNormal should be at least none zero in one of it's axis if (collisionNormal.any()) { collisionNormal *= Dot(collisionNormal, current.mVelocity) / collisionNormal.length2(); current.mVelocity -= 2 * collisionNormal; // simply reverse velocity along collision normal direction } rt -= collisionTime; } // reset all forces for current object so it'll be ready for later game event current.mForces.zero(); } }

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• Stencil buffer appears to not be decrementing values correctly

  - by Alex Ames

  I'm attempting to use the stencil buffer as a clipper for my UI system, but I'm having trouble debugging a problem I'm running in to. This is what I'm doing: A widget can pass a rectangle to the the stencil clipper functions, which will increment the stencil buffer values that it covers. Then it will draw its children, which will only get drawn in the stencilled area (so that if they extend outside they'll be clipped). After a widget is done drawing its children, it pops that rectangle from the stack and in the process decrements the values in the stencil buffer that it has previously incremented. The slightly simplified code is below: static void drawStencil(Rect& rect, unsigned int ref) { // Save previous values of the color and depth masks GLboolean colorMask[4]; GLboolean depthMask; glGetBooleanv(GL_COLOR_WRITEMASK, colorMask); glGetBooleanv(GL_DEPTH_WRITEMASK, &depthMask); // Turn off drawing glColorMask(0, 0, 0, 0); glDepthMask(0); // Draw vertices here ... // Turn everything back on glColorMask(colorMask[0], colorMask[1], colorMask[2], colorMask[3]); glDepthMask(depthMask); // Only render pixels in areas where the stencil buffer value == ref glStencilFunc(GL_EQUAL, ref, 0xFF); glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP); } void pushScissor(Rect rect) { // increment things only at the current stencil stack level glStencilFunc(GL_EQUAL, s_scissorStack.size(), 0xFF); glStencilOp(GL_KEEP, GL_INCR, GL_INCR); s_scissorStack.push_back(rect); drawStencil(rect, states, s_ScissorStack.size()); } void popScissor() { // undo what was done in the previous push, // decrement things only at the current stencil stack level glStencilFunc(GL_EQUAL, s_scissorStack.size(), 0xFF); glStencilOp(GL_KEEP, GL_DECR, GL_DECR); Rect rect = s_scissorStack.back(); s_scissorStack.pop_back(); drawStencil(rect, states, s_scissorStack.size()); } And this is how it's being used by the Widgets if (m_clip) pushScissor(m_rect); drawInternal(target, states); for (auto child : m_children) target.draw(*child, states); if (m_clip) popScissor(); This is the result of the above code: There are two things on the screen, a giant test button, and a window with some buttons and text areas on it. The text area scroll box is set to clip its children (so that the text doesn't extend outside the scroll box). The button is drawn after the window and should be on top of it completely. However, for some reason the text area is appearing on top of the button. The only reason I can think of that this would happen is if the stencil values were not getting decremented in the pop, and when it comes time to render the button, since those pixels don't have the right stencil value it doesn't draw over. But I can't figure out whats wrong with my code that would cause that to happen.

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• C++ property system interface for game editors (reflection system)

  - by Cristopher Ismael Sosa Abarca

  I have designed an reusable game engine for an project, and their functionality is like this: Is a completely scripted game engine instead of the usual scripting languages as Lua or Python, this uses Runtime-Compiled C++, and an modified version of Cistron (an component-based programming framework).to be compatible with Runtime-Compiled C++ and so on. Using the typical GameObject and Component classes of the Component-based design pattern, is serializable via JSON, BSON or Binary useful for selecting which objects will be loaded the next time. The main problem: We want to use our custom GameObjects and their components properties in our level editor, before used hardcoded functions to access GameObject base class virtual functions from the derived ones, if do you want to modify an property specifically from that class you need inside into the code, this situation happens too with the derived classes of Component class, in little projects there's no problem but for larger projects becomes tedious, lengthy and error-prone. I've researched a lot to find a solution without luck, i tried with the Ogitor's property system (since our engine is Ogre-based) but we find it inappropiate for the component-based design and it's limited only for the Ogre classes and can lead to performance overhead, and we tried some code we find in the Internet we tested it and worked a little but we considered the macro and lambda abuse too horrible take a look (some code omitted): IWE_IMPLEMENT_PROP_BEGIN(CBaseEntity) IWE_PROP_LEVEL_BEGIN("Editor"); IWE_PROP_INT_S("Id", "Internal id", m_nEntID, [](int n) {}, true); IWE_PROP_LEVEL_END(); IWE_PROP_LEVEL_BEGIN("Entity"); IWE_PROP_STRING_S("Mesh", "Mesh used for this entity", m_pModelName, [pInst](const std::string& sModelName) { pInst->m_stackMemUndoType.push(ENT_MEM_MESH); pInst->m_stackMemUndoStr.push(pInst->getModelName()); pInst->setModel(sModelName, false); pInst->saveState(); }, false); IWE_PROP_VECTOR3_S("Position", m_vecPosition, [pInst](float fX, float fY, float fZ) { pInst->m_stackMemUndoType.push(ENT_MEM_POSITION); pInst->m_stackMemUndoVec3.push(pInst->getPosition()); pInst->saveState(); pInst->m_vecPosition.Get()[0] = fX; pInst->m_vecPosition.Get()[1] = fY; pInst->m_vecPosition.Get()[2] = fZ; pInst->setPosition(pInst->m_vecPosition); }, false); IWE_PROP_QUATERNION_S("Orientation (Quat)", m_quatOrientation, [pInst](float fW, float fX, float fY, float fZ) { pInst->m_stackMemUndoType.push(ENT_MEM_ROTATE); pInst->m_stackMemUndoQuat.push(pInst->getOrientation()); pInst->saveState(); pInst->m_quatOrientation.Get()[0] = fW; pInst->m_quatOrientation.Get()[1] = fX; pInst->m_quatOrientation.Get()[2] = fY; pInst->m_quatOrientation.Get()[3] = fZ; pInst->setOrientation(pInst->m_quatOrientation); }, false); IWE_PROP_LEVEL_END(); IWE_IMPLEMENT_PROP_END() We are finding an simplified way to this, without leading confusing the programmers, (will be released to the public) i find ways to achieve this but they are only available for the common scripting as Lua or editors using C#. also too portable, we can write "wrappers" for different GUI toolkits as Qt or GTK, also i'm thinking to using Boost.Wave to get additional macro functionality without creating my own compiler. The properties designed to use in the editor they are removed in the game since the save file contains their data and loads it using an simple 'load' function to reduce unnecessary code bloat may will be useful if some GameObject property wants to be hidden instead. In summary, there's a way to implement an reflection(property) system for a level editor based in properties from derived classes? Also we can use C++11 and Boost (restricted only to Wave and PropertyTree)

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• How to display a hierarchical skill tree in php

  - by user3587554

  If I have skill data set up in a tree format (where earlier skills are prerequisites for later ones), how would I display it as a tree, using php? The parent would be on top and have 3 children. Each of these children can then have one more child so its parent would be directly above it. I'm having trouble figuring out how to add the root element in the middle of the top div, and the child of the children below each child of the root. I'm not looking for code, but an explanation of how to do it. My data in array form is this: Data: Array ( [1] => Array ( [id] => 1 [title] => Jutsu [description] => Skill that makes you awesomer at using ninjutsu [tiers] => 1 [prereq] => [image] => images/skills/jutsu.png [children] => Array ( [2] => Array ( [id] => 2 [title] => fireball [description] => Increase your damage with fire jutsu and weapons [tiers] => 5 [prereq] => 1 [image] => images/skills/fireball.png [children] => Array ( [5] => Array ( [id] => 5 [title] => pin point [description] => Increases jutsu accuracy [tiers] => 5 [prereq] => 2 [image] => images/skills/pinpoint.png ) ) ) [3] => Array ( [id] => 3 [title] => synergy [description] => Reduce the amount of chakra needed to use ninjutsu [tiers] => 1 [prereq] => 1 [image] => images/skills/synergy.png ) [4] => Array ( [id] => 4 [title] => ebb & flow [description] => Increase the damage of water jutsu, water weapons, and reduce the damage of jutsu and weapons that use water element [tiers] => 5 [prereq] => 1 [image] => images/skills/ebbandflow.png [children] => Array ( [6] => Array ( [id] => 6 [title] => IQ [description] => Decrease the time it takes to learn a jutsu [tiers] => 5 [prereq] => 4 [image] => images/skills/iq.png ) ) ) ) ) ) An example would be this demo image minus the hover stuff.

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• Solving 2D Collision Detection Issues with Relative Velocities

  - by Jengerer

  Imagine you have a situation where two objects are moving parallel to one-another and are both within range to collide with a static wall, like this: A common method used in dynamic collision detection is to loop through all objects in arbitrary order, solve for pair-wise collision detection using relative velocities, and then move the object to the nearest collision, if any. However, in this case, if the red object is checked first against the blue one, it would see that the relative velocity to the blue object is -20 m/s (and would thereby not collide this time frame). Then it would see that the red object would collide with the static wall, and the solution would be: And the red object passes through the blue one. So it appears to be a matter of choosing the right order in which you check collisions; but how can you determine which order is correct? How can this passing through of objects be avoided? Is ignoring relative velocity and considering every object as static during pair-wise checks a better idea for this reason?

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• Java 2D Rectangle Collision? [on hold]

  - by Andreas Elia

  I am just wanting to know of another (longer OR shorter) way of getting 100% effective collisions on a 2D plat-former. The current collision system that is in place works from coords on the level and does not always work reliably. Thank you in advance for any help/support. The current system draws a rectangle and is checking to see if any two points collide. From testing, the system can sometimes "glitch" and allow the player to collide into walls etc. Player Class http://pastebin.com/2zE8vz8R Main Class http://pastebin.com/A6Utb3ti

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• Voice artist for a game for kids

  - by devmiles.com

  We're making a game for kids which should include about 50 spoken phrases. I'm asking for help in finding the right voice artist / studio for this. I've tried searching the web but couldn't find anything that would make me sure that it would work for us or games in general. So I'm looking for references from those of you who had a successful collaboration with artists or studios. Any help would be appreciated.

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• What methods should save/load a game state

  - by vedi

  There are a lot of articles about how to save a state of a game and they are pretty good. But I have one conceptual misunderstanding where should I save the state? My game has number of screens and pair of them are MainMenuScreen and MainSceneScreen these are inherited from Screen class. MainMenuScreen is shown at start of the game the MainSceneScreen little later. What is the problem? I navigated to MainSceneScreen, forced Android to stop the application (I change a language settings on the device to achieve it, please let me know if I'm wrong). After that I select the application again and I can see MainMenuScreen is shown. But I want MainSceneScreen to be shown. I suppose I should override resume method. But what class I should override? I have class PsGame that extends Game class of libgdx. I put breakpoints to its resume method and it turned out that method was not called. I investigated the problem and I've found little strange code in onResume method of AndroidApplication class of libgdx: if (!firstResume) graphics.resume(); else firstResume = false; My debugger said firstResume was true and didn't go to *graphics.resume()*line. Sorry for a lot of words but could you answer following question: What did I do wrong? What methods should I override? Thank you in advance.

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• Most efficient way to implement delta time

  - by Starkers

  Here's one way to implement delta time: /// init /// var duration = 5000, currentTime = Date.now(); // and create cube, scene, camera ect ////// function animate() { /// determine delta /// var now = Date.now(), deltat = now - currentTime, currentTime = now, scalar = deltat / duration, angle = (Math.PI * 2) * scalar; ////// /// animate /// cube.rotation.y += angle; ////// /// update /// requestAnimationFrame(render); ////// } Could someone confirm I know how it works? Here what I think is going on: Firstly, we set duration at 5000, which how long the loop will take to complete in an ideal world. With a computer that is slow/busy, let's say the animation loop takes twice as long as it should, so 10000: When this happens, the scalar is set to 2.0: scalar = deltat / duration scalar = 10000 / 5000 scalar = 2.0 We now times all animation by twice as much: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 2.0; angle = (Math.PI * 4) // which is 2 rotations When we do this, the cube rotation will appear to 'jump', but this is good because the animation remains real-time. With a computer that is going too quickly, let's say the animation loop takes half as long as it should, so 2500: When this happens, the scalar is set to 0.5: scalar = deltat / duration scalar = 2500 / 5000 scalar = 0.5 We now times all animation by a half: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 0.5; angle = (Math.PI * 1) // which is half a rotation When we do this, the cube won't jump at all, and the animation remains real time, and doesn't speed up. However, would I be right in thinking this doesn't alter how hard the computer is working? I mean it still goes through the loop as fast as it can, and it still has render the whole scene, just with different smaller angles! So this a bad way to implement delta time, right? Now let's pretend the computer is taking exactly as long as it should, so 5000: When this happens, the scalar is set to 1.0: angle = (Math.PI * 2) * scalar; angle = (Math.PI * 2) * 1; angle = (Math.PI * 2) // which is 1 rotation When we do this, everything is timsed by 1, so nothing is changed. We'd get the same result if we weren't using delta time at all! My questions are as follows Mostly importantly, have I got the right end of the stick here? How do we know to set the duration to 5000 ? Or can it be any number? I'm a bit vague about the "computer going too quickly". Is there a way loop less often rather than reduce the animation steps? Seems like a better idea. Using this method, do all of our animations need to be timesed by the scalar? Do we have to hunt down every last one and times it? Is this the best way to implement delta time? I think not, due to the fact the computer can go nuts and all we do is divide each animation step and because we need to hunt down every step and times it by the scalar. Not a very nice DSL, as it were. So what is the best way to implement delta time? Below is one way that I do not really get but may be a better way to implement delta time. Could someone explain please? // Globals INV_MAX_FPS = 1 / 60; frameDelta = 0; clock = new THREE.Clock(); // In the animation loop (the requestAnimationFrame callback)… frameDelta += clock.getDelta(); // API: "Get the seconds passed since the last call to this method." while (frameDelta >= INV_MAX_FPS) { update(INV_MAX_FPS); // calculate physics frameDelta -= INV_MAX_FPS; } How I think this works: Firstly we set INV_MAX_FPS to 0.01666666666 How we will use this number number does not jump out at me. We then intialize a frameDelta which stores how long the last loop took to run. Come the first loop frameDelta is not greater than INV_MAX_FPS so the loop is not run (0 = 0.01666666666). So nothing happens. Now I really don't know what would cause this to happen, but let's pretend that the loop we just went through took 2 seconds to complete: We set frameDelta to 2: frameDelta += clock.getDelta(); frameDelta += 2.00 Now we run an animation thanks to update(0.01666666666). Again what is relevance of 0.01666666666?? And then we take away 0.01666666666 from the frameDelta: frameDelta -= INV_MAX_FPS; frameDelta = frameDelta - INV_MAX_FPS; frameDelta = 2 - 0.01666666666 frameDelta = 1.98333333334 So let's go into the second loop. Let's say it took 2(? Why not 2? Or 12? I am a bit confused): frameDelta += clock.getDelta(); frameDelta = frameDelta + clock.getDelta(); frameDelta = 1.98333333334 + 2 frameDelta = 3.98333333334 This time we enter the while loop because 3.98333333334 = 0.01666666666 We run update We take away 0.01666666666 from frameDelta again: frameDelta -= INV_MAX_FPS; frameDelta = frameDelta - INV_MAX_FPS; frameDelta = 3.98333333334 - 0.01666666666 frameDelta = 3.96666666668 Now let's pretend the loop is super quick and runs in just 0.1 seconds and continues to do this. (Because the computer isn't busy any more). Basically, the update function will be run, and every loop we take away 0.01666666666 from the frameDelta untill the frameDelta is less than 0.01666666666. And then nothing happens until the computer runs slowly again? Could someone shed some light please? Does the update() update the scalar or something like that and we still have to times everything by the scalar like in the first example?

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• Can't read .cso files but I can read their .hlsl versions?

  - by Jader J Rivera

  Well I've been trying to read a .cso file to use as a shader for a DirectX program I'm currently making. Problem is no matter how I implemented a way to read the file it never worked. And after fidgeting around I discover that it's only the .cso files I can't read. I can read anything else (which means it works) even their .hlsl files. Which is strange because the .hlsl (high level shader language) files are supposed to turn into .cso (compiled shader object) files. What I'm currently doing is: vector<byte> Read(string File){ vector<byte> Text; fstream file(File, ios::in | ios::ate | ios::binary); if(file.is_open()){ Text.resize(file.tellg()); file.seekg(0 , ios::beg); file.read(reinterpret_cast<char*>(&Text[0]), Text.size()); file.close(); } return Text; }; If I then implement it. Read("VertexShader.hlsl"); //Works Read("VertexShader.cso"); //Doesn't Works?!?! And I need the .cso version of the shader to draw my sexy triangles. Without it my life and application will never continue and I have no idea what could be wrong. (I've also asked this at stack overflow but still no answers.)

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• MiniMax not working properly(for checkers game)

  - by engineer

  I am creating a checkers game but My miniMax is not functioning properly,it is always switching between two positions for its move(index 20 and 17).Here is my code: public double MiniMax(int[] board, int depth, int turn, int red_best, int black_best) { int source; int dest; double MAX_SCORE=-INFINITY,newScore; int MAX_DEPTH=3; int[] newBoard=new int[32]; generateMoves(board,turn); System.arraycopy(board, 0, newBoard, 0, 32); if(depth==MAX_DEPTH) { return Evaluation(turn,board);} for(int z=0;z<possibleMoves.size();z+=2){ source=Integer.parseInt(possibleMoves.elementAt(z).toString()); System.out.println("SOURCE= "+source); dest=Integer.parseInt(possibleMoves.elementAt(z+1).toString());//(int[])possibleMoves.elementAt(z+1); System.out.println("DEST = "+dest); applyMove(newBoard,source,dest); newScore=MiniMax(newBoard,depth+1,opponent(turn),red_best, black_best); if(newScore>MAX_SCORE) {MAX_SCORE=newScore;maxSource=source; maxDest=dest;}//maxSource and maxDest will be used to perform the move. if (MAX_SCORE > black_best) { if (MAX_SCORE >= red_best) break; /* alpha_beta cutoff */ else black_best = (int) MAX_SCORE; //the_score } if (MAX_SCORE < red_best) { if (MAX_SCORE<= black_best) break; /* alpha_beta cutoff */ else red_best = (int) MAX_SCORE; //the_score } }//for ends return MAX_SCORE; } //end minimax I am unable to find out the logical mistake. Any idea what's going wrong?

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• What is the correct and most efficient approach of streaming vertex data?

  - by Martijn Courteaux

  Usually, I do this in my current OpenGL ES project (for iOS): Initialization: Create two VBO's and one IndexBuffer (since I will use the same indices), same size. Create two VAO's and configure them, both bound to the same Index Buffer. Each frame: Choose a VBO/VAO couple. (Different from the previous frame, so I'm alternating.) Bind that VBO Upload new data using glBufferSubData(GL_ARRAY_BUFFER, ...). Bind the VAO Render my stuff using glDrawElements(GL_***, ...); Unbind the VAO However, someone told me to avoid uploading data (step 3) and render immediately the new data (step 5). I should avoid this, because the glDrawElements call will stall until the buffer is effectively uploaded to VRAM. So he suggested to draw all my geometry I uploaded the previous frame and upload in the current frame what will be drawn in the next frame. Thus, everything is rendered with the delay of one frame. Is this true or am I using the good approach to work with streaming vertex data? (I do know that the pipeline will stall the other way around. Ie: when you draw and immediately try to change the buffer data. But I'm not doing that, since I implemented double buffering.)

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• Actionscript 3.0 - Enemies do not move right in my platformer game

  - by Christian Basar

  I am making a side-scrolling platformer game in Flash (Actionscript 3.0). I have made lots of progress lately, but I have come across a new problem. I will give some background first. My game level's terrain (or 'floor') is referenced by a MovieClip variable called 'floor.' My desire is to have the Player and enemy characters walk along the terrain. I have gotten the Player character to move on the terrain just fine; he walks up/down hills and falls whenever there is no ground beneath him. Here is the code I created to allow the Player to follow the terrain correctly. Much more code is used to control the Player, but only this code deals with the Player character's following of the terrain and gravity. // If the Player's not on the ground (not touching the 'floor' MovieClip)... if (!onGround) { // Disable ducking downKeyPressed = false; // Increase the Player's 'y' position by his 'y' velocity player.y += playerYVel; } // Increase the 'playerYVel' variable so that the Player will fall // progressively faster down the screen. This code technically // runs "all the time" but in reality it only affects the player // when he's off the ground. playerYVel += gravity; // Give the Player a terminal velocity of 15 px/frame if (playerYVel > 15) { playerYVel = 15; } // If the Player has not hit the 'floor,' increase his falling //speed if (! floor.hitTestPoint(player.x, player.y, true)) { player.y += playerYVel; // The Player is not on the ground when he's not touching it onGround = false; } Since getting this code to work for the Player, I have created a 'SkullDemon' class, which is one of the planned enemies for my game. I want the 'SkullDemon' objects to move along the terrain like the Player does. With lots of great help, I have already coded the EventListeners, etc. necessary for the 'SkullDemons' to move. Unfortunately, I am having trouble getting them to move along the terrain. In fact, they do not touch the terrain at all; they move along the top of the boundary of the 'floor' MovieClip! I had a simple text diagram showing what I mean, but unfortunately Stackoverflow does not format it correctly. I hope my problem is clear from my description. Strangely enough, my code for the Player's movement and the 'SkullDemon's' movement is almost exactly the same, yet the 'SkullDemons' do not move like the Player does. Here is my code for the SkullDemon movement: // Move all of the Skull Demons using this method protected function moveSkullDemons():void { // Go through the whole 'skullDemonContainer' for (var skullDi:int = 0; skullDi < skullDemonContainer.numChildren; skullDi++) { // Set the SkullDemon 'instance' variable to equal the current SkullDemon skullDIns = SkullDemon(skullDemonContainer.getChildAt(skullDi)); // For now, just move the Skull Demons left at 5 units per second skullDIns.x -= 5; // If the Skull Demon has not hit the 'floor,' increase his falling //speed if (! floor.hitTestPoint(skullDIns.x, skullDIns.y, true)) { // Increase the Skull Demon's 'y' position by his 'y' velocity skullDIns.y += skullDIns.sdYVel; // The Skull Demon is not on the ground when he's not touching it skullDIns.sdOnGround = false; } // Increase the 'sdYVel' variable so that the Skull Demon will fall // progressively faster down the screen. This code technically // runs "all the time" but in reality it only affects the Skull Demon // when he's off the ground. if (! skullDIns.sdOnGround) { skullDIns.sdYVel += skullDIns.sdGravity; // Give the Skull Demon a terminal velocity of 15 px/frame if (skullDIns.sdYVel > 15) { skullDIns.sdYVel = 15; } } // What happens when the Skull Demon lands on the ground after a fall? // The Skull Demon is only on the ground ('onGround == true') when // the ground is touching the Skull Demon MovieClip's origin point, // which is at the Skull Demon's bottom centre for (var i:int = 0; i < 10; i++) { // The Skull Demon is only on the ground ('onGround == true') when // the ground is touching the Skull Demon MovieClip's origin point, // which is at the Skull Demon's bottom centre if (floor.hitTestPoint(skullDIns.x, skullDIns.y, true)) { skullDIns.y = skullDIns.y; // Set the Skull Demon's y-axis speed to 0 skullDIns.sdYVel = 0; // The Skull Demon is on the ground again skullDIns.sdOnGround = true; } } } } // End of 'moveSkullDemons()' function It is almost like the 'SkullDemons' are interacting with the 'floor' MovieClip using the hitTestObject() function, and not the hitTestPoint() function which is what I want, and which works for the Player character. I am confused about this problem and would appreciate any help you could give me. Thanks!

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• Updating games for iOS 6 and new iPhone/iPod Touch

  - by SundayMonday

  Say I have a game that runs full-screen on iPhone 4S and older devices. The balance of the game is just right for the 480 x 320 screen and associated aspect ratio. Now I want to update my game to run full-screen on the new iPhone/iPod Touch where the aspect ratio of the screen is different. It seems like this can be challenging for some games in terms of maintaining the "balance". For example if the extra screen space was just tacked onto the right side of Jet Pack Joyride the balance would be thrown off since the user now has more time to see and react to obstacles. Also it could be challenging in terms of code maintenance. Perhaps Jet Pack Joyride would slightly increase the speed of approaching obstacles when the game is played on newer devices. However this quickly becomes messy when extra conditional statements are added all over the code. One solution is to have some parameters that are set in once place at start-up depending on the device type. What are some strategies for updating iOS games to run on the new iPhone and iPod Touch?

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• How to expose game data in the game without a singelton?

  - by zardon

  I'm quite new to cocos2d and games programming, and am currently I am writing a game that is currently in Prototype stage. Everything is going okay, but I've realized a potentially big problem and I am not sure how to solve it. I am using a singelton to store a bunch of arrays for everything, a global list of planets, a global list of troops, a global list of products, etc. And only now I'm realizing that all of this will be in memory and this is the wrong way to do it. I am not storing files or anything on the disk just yet, with exception to a save/load state, which is a capture of everything. My game makes use of a map which allows you to select a planet, then it will give you a breakdown of that planets troops and resources, Lets use this scenario: My game has 20 planets. On which you can have 20 troops. Straight away that's an array of 400! This does not add the NPC, which is another 10. So, 20x10 = 200 So, now we have 600 all in arrays inside a Singelton. This is obviously very bad, and very wrong. Especially as the game scales in the amount of data. But I need to expose pretty much everything, especially on the map page, and I am not sure how else to do it. I've been told that I can use a controller for the map page which has the information I need for each planet, and other controllers for other items I require global display for. I've also thought about storing each planet's data in a save file, using initWithCoder however there could be a boatload of files on the user's device? I really don't want to use a database, mainly because I would need to translate NSObjects and non-NSObjects like CGRects and CGPoints and Colors into/from SQL. I am open to other ideas on how to store and read game data to prevent using a singelton to store everything, everywhere. Thanks for your time.

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• I need to move an entity to the mouse location after i rightclick

  - by I.Hristov

  Well I've read the related questions-answers but still cant find a way to move my champion to the mouse position after a right-button mouse-click. I use this code at the top: float speed = (float)1/3; And this is in my void Update: //check if right mouse button is clicked if (mouse.RightButton == ButtonState.Released && previousButtonState == ButtonState.Pressed) { // gets the position of the mouse in mousePosition mousePosition = new Vector2(mouse.X, mouse.Y); //gets the current position of champion (the drawRectangle) currentChampionPosition = new Vector2(drawRectangle.X, drawRectangle.Y); // move champion to mouse position: //handles the case when the mouse position is really close to current position if (Math.Abs(currentChampionPosition.X - mousePosition.X) <= speed && Math.Abs(currentChampionPosition.Y - mousePosition.Y) <= speed) { drawRectangle.X = (int)mousePosition.X; drawRectangle.Y = (int)mousePosition.Y; } else if (currentChampionPosition != mousePosition) { drawRectangle.X += (int)((mousePosition.X - currentChampionPosition.X) * speed); drawRectangle.Y += (int)((mousePosition.Y - currentChampionPosition.Y) * speed); } } previousButtonState = mouse.RightButton; What that code does at the moment is on a click it brings the sprite 1/3 of the distance to the mouse but only once. How do I make it move consistently all the time? It seems I am not updating the sprite at all. EDIT I added the Vector2 as Nick said and with speed changed to 50 it should be OK. I tried it with if ButtonState.Pressed and it works while pressing the button. Thanks. However I wanted it to start moving when single mouse clicked. It should be moving until reaches the mousePosition. The Edit of Nick's post says to create another Vector2, But I already have the one called mousePosition. Not sure how to use another one. //gets a Vector2 direction to move *by Nick Wilson Vector2 direction = mousePosition - currentChampionPosition; //make the direction vector a unit vector direction.Normalize(); //multiply with speed (number of pixels) direction *= speed; // move champion to mouse position if (currentChampionPosition != mousePosition) { drawRectangle.X += (int)(direction.X); drawRectangle.Y += (int)(direction.Y); } } previousButtonState = mouse.RightButton;

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• Light mask map and camera for static lights in XNA Platformer

  - by JiminyCricket

  Using the example for some basic light maps found here : http://blog.josack.com/2011/07/xna-2d-dynamic-lighting.html, I've managed to create a lightmap texture using individual lightmaps and display it over a 2D tiled world as in the Platformer example. I'm using the very basic 2D camera example as found here : http://www.david-amador.com/2009/10/xna-camera-2d-with-zoom-and-rotation/, and the problem is that the lightmap texture scrolls with the player sprite. This looks pretty good and would be excellent for lighting the player sprite as it moves. But, I also want to be able to place static lights (or some initial position for the lights) that do not move with the player or camera. When I turn off the camera or give it a static position, it works as a series of static lights so I believe it's probably caused by the camera transformation matrix following the player around. I'm using RenderTarget2Ds, one for the main game screen after all the backgrounds and tiles are rendered, and one for the "lightmap" which consists of a black background and a bunch of lighting textures which are merged with it using additive blending. For now, I'm doing all of this in PlatformerGame.cs where the camera transformation and position is set and the level.Draw() call is made. I can't figure out how to separate the drawing of the lightmap and the camera following the player. I was thinking it would be better to render the shadows and lighting directly in the drawing of the level itself, but I'm not sure how to do that either because this technique requires RenderTarget2Ds and calling SpriteBatch.Begin()/End().

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• Finding direction of travel in a world with wrapped edges

  - by crazy

  I need to find the shortest distance direction from one point in my 2D world to another point where the edges are wrapped (like asteroids etc). I know how to find the shortest distance but am struggling to find which direction it's in. The shortest distance is given by: int rows = MapY; int cols = MapX; int d1 = abs(S.Y - T.Y); int d2 = abs(S.X - T.X); int dr = min(d1, rows-d1); int dc = min(d2, cols-d2); double dist = sqrt((double)(dr*dr + dc*dc)); Example of the world : : T : :--------------:--------- : : : S : : : : : : T : : : :--------------: In the diagram the edges are shown with : and -. I've shown a wrapped repeat of the world at the top right too. I want to find the direction in degrees from S to T. So the shortest distance is to the top right repeat of T. but how do I calculate the direction in degreed from S to the repeated T in the top right? I know the positions of both S and T but I suppose I need to find the position of the repeated T however there more than 1. The worlds coordinates system starts at 0,0 at the top left and 0 degrees for the direction could start at West. It seems like this shouldn’t be too hard but I haven’t been able to work out a solution. I hope somone can help? Any websites would be appreciated.

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