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• Algorithm to shoot at a target in a 3d game

  - by Sebastian Bugiu

  For those of you remembering Descent Freespace it had a nice feature to help you aim at the enemy when shooting non-homing missiles or lasers: it showed a crosshair in front of the ship you chased telling you where to shoot in order to hit the moving target. I tried using the answer from http://stackoverflow.com/questions/4107403/ai-algorithm-to-shoot-at-a-target-in-a-2d-game?lq=1 but it's for 2D so I tried adapting it. I first decomposed the calculation to solve the intersection point for XoZ plane and saved the x and z coordinates and then solving the intersection point for XoY plane and adding the y coordinate to a final xyz that I then transformed to clipspace and put a texture at those coordinates. But of course it doesn't work as it should or else I wouldn't have posted the question. From what I notice the after finding x in XoZ plane and the in XoY the x is not the same so something must be wrong. float a = ENG_Math.sqr(targetVelocity.x) + ENG_Math.sqr(targetVelocity.y) - ENG_Math.sqr(projectileSpeed); float b = 2.0f * (targetVelocity.x * targetPos.x + targetVelocity.y * targetPos.y); float c = ENG_Math.sqr(targetPos.x) + ENG_Math.sqr(targetPos.y); ENG_Math.solveQuadraticEquation(a, b, c, collisionTime); First time targetVelocity.y is actually targetVelocity.z (the same for targetPos) and the second time it's actually targetVelocity.y. The final position after XoZ is crossPosition.set(minTime * finalEntityVelocity.x + finalTargetPos4D.x, 0.0f, minTime * finalEntityVelocity.z + finalTargetPos4D.z); and after XoY crossPosition.y = minTime * finalEntityVelocity.y + finalTargetPos4D.y; Is my approach of separating into 2 planes and calculating any good? Or for 3D there is a whole different approach? sqr() is square not sqrt - avoiding a confusion.

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• Drawing texture does not work anymore with a small amount of triangles

  - by Paul

  When i draw lines, the vertices are well connected. But when i draw the texture inside the triangles, it only works with i<4 in the for loop, otherwise with i<5 for example, there is a EXC_BAD_ACCESS message, at @synthesize textureImage = _textureImage. I don't understand why. (The generatePolygons method seems to work fine as i tried to draw lines with many vertices as in the second image below. And textureImage remains the same for i<4 or i<5 : it's a 512px square image). Here are the images : What i want to achieve is to put the red points and connect them to the y-axis (the green points) and color the area (the green triangles) : If i only draw lines, it works fine : Then with a texture color, it works for i<4 in the loop (the red points in my first image, plus the fifth one to connect the last y) : But then, if i set i<5, the debug tool says EXC_BAD_ACCESS at the synthesize of _textureImage. Here is my code : I set a texture color in HelloWordLayer.mm with : CCSprite *textureImage = [self spriteWithColor:color3 textureSize:512]; _terrain.textureImage = textureImage; Then in the class Terrain, i create the vertices and put the texture in the draw method : @implementation Terrain @synthesize textureImage = _textureImage; //EXC_BAD_ACCESS for i<5 - (void)generatePath2{ CGSize winSize = [CCDirector sharedDirector].winSize; float x = 40; float y = 0; for(int i = 0; i < kMaxKeyPoints+1; ++i) { _hillKeyPoints[i] = CGPointMake(x, y); x = 150 + (random() % (int) 30); y += 30; } } -(void)generatePolygons{ _nPolyVertices = 0; float x1 = 0; float y1 = 0; int keyPoints = 0; for (int i=0; i<4; i++){ /* HERE : 4 = OK / 5 = crash */ //V0: at (0,0) _polyVertices[_nPolyVertices] = CGPointMake(x1, y1); _polyTexCoords[_nPolyVertices++] = CGPointMake(x1, y1); //V1: to the first "point" _polyVertices[_nPolyVertices] = CGPointMake(_hillKeyPoints[keyPoints].x, _hillKeyPoints[keyPoints].y); _polyTexCoords[_nPolyVertices++] = CGPointMake(_hillKeyPoints[keyPoints].x, _hillKeyPoints[keyPoints].y); keyPoints++; //from point at index 0 to 1 //V2, same y as point n°2: _polyVertices[_nPolyVertices] = CGPointMake(0, _hillKeyPoints[keyPoints].y); _polyTexCoords[_nPolyVertices++] = CGPointMake(0, _hillKeyPoints[keyPoints].y); //V1 again _polyVertices[_nPolyVertices] = _polyVertices[_nPolyVertices-2]; _polyTexCoords[_nPolyVertices++] = _polyVertices[_nPolyVertices-2]; //V2 again _polyVertices[_nPolyVertices] = _polyVertices[_nPolyVertices-2]; _polyTexCoords[_nPolyVertices++] = _polyVertices[_nPolyVertices-2]; //V3 = same x,y as point at index 1 _polyVertices[_nPolyVertices] = CGPointMake(_hillKeyPoints[keyPoints].x, _hillKeyPoints[keyPoints].y); _polyTexCoords[_nPolyVertices] = CGPointMake(_hillKeyPoints[keyPoints].x, _hillKeyPoints[keyPoints].y); y1 = _polyVertices[_nPolyVertices].y; _nPolyVertices++; } } - (id)init { if ((self = [super init])) { [self generatePath2]; [self generatePolygons]; } return self; } - (void) draw { //glDisable(GL_TEXTURE_2D); glDisableClientState(GL_COLOR_ARRAY); glDisableClientState(GL_TEXTURE_COORD_ARRAY); glBindTexture(GL_TEXTURE_2D, _textureImage.texture.name); glColor4f(1, 1, 1, 1); glVertexPointer(2, GL_FLOAT, 0, _polyVertices); glTexCoordPointer(2, GL_FLOAT, 0, _polyTexCoords); glDrawArrays(GL_TRIANGLE_STRIP, 0, (GLsizei)_nPolyVertices); glColor4f(1, 1, 1, 1); for(int i = 1; i < 40; ++i) { ccDrawLine(_polyVertices[i-1], _polyVertices[i]); } // restore default GL states glEnable(GL_TEXTURE_2D); glEnableClientState(GL_COLOR_ARRAY); glEnableClientState(GL_TEXTURE_COORD_ARRAY); } Do you see anything wrong in this code? Thanks for your help

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• cocos2d-x simple shader usage [on hold]

  - by Narek

  I want to obtain color ramp effect from this tutorial: http://www.raywenderlich.com/10862/how-to-create-cool-effects-with-custom-shaders-in-opengl-es-2-0-and-cocos2d-2-x Here is my code in cocos2d-x 3: bool HelloWorld::init() { ////////////////////////////// // 1. super init first if ( !Layer::init() ) { return false; } Vec2 origin = Director::getInstance()->getVisibleOrigin(); sprite = Sprite::create("HelloWorld.png"); sprite->setAnchorPoint(Vec2(0, 0)); sprite->setRotation(3); sprite->setPosition(origin); addChild(sprite); std::string str = FileUtils::getInstance()->getStringFromFile("CSEColorRamp.fsh"); const GLchar * fragmentSource = str.c_str(); GLProgram* p = GLProgram::createWithByteArrays(ccPositionTextureA8Color_vert, fragmentSource); p->bindAttribLocation(GLProgram::ATTRIBUTE_NAME_POSITION, GLProgram::VERTEX_ATTRIB_POSITION); p->bindAttribLocation(GLProgram::ATTRIBUTE_NAME_TEX_COORD, GLProgram::VERTEX_ATTRIB_TEX_COORD); p->link(); p->updateUniforms(); sprite->setGLProgram(p); // 3 colorRampUniformLocation = glGetUniformLocation(sprite->getGLProgram()->getProgram(), "u_colorRampTexture"); glUniform1i(colorRampUniformLocation, 1); // 4 colorRampTexture = Director::getInstance()->getTextureCache()->addImage("colorRamp.png"); colorRampTexture->setAliasTexParameters(); // 5 sprite->getGLProgram()->use(); glActiveTexture(GL_TEXTURE1); glBindTexture(GL_TEXTURE_2D, colorRampTexture->getName()); glActiveTexture(GL_TEXTURE0); return true; } And here is the fragment shader as it is in the tutorial: #ifdef GL_ES precision mediump float; #endif // 1 varying vec2 v_texCoord; uniform sampler2D u_texture; uniform sampler2D u_colorRampTexture; void main() { // 2 vec3 normalColor = texture2D(u_texture, v_texCoord).rgb; // 3 float rampedR = texture2D(u_colorRampTexture, vec2(normalColor.r, 0)).r; float rampedG = texture2D(u_colorRampTexture, vec2(normalColor.g, 0)).g; float rampedB = texture2D(u_colorRampTexture, vec2(normalColor.b, 0)).b; // 4 gl_FragColor = vec4(rampedR, rampedG, rampedB, 1); } As a result I get a black screen with 2 draw calls. What is wrong? Do I miss something?

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• How does one specify raster operations in XNA?

  - by Corey Ogburn

  I'm looking for a way to add a sprite using a particular logic operation (like XOR). I can't find anything on Google and I'm not sure where to look in the documentation. I've looked into SpriteBatch.Begin(...) and its Draw method and several options in the GraphicsDevice class, but I'm not recognizing anything capable of this. I'm still pretty new to XNA so I may just not have recognized the terminology to do this.

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• Circle-Line Collision Detection Problem

  - by jazzdawg

  I am currently developing a breakout clone and I have hit a roadblock in getting collision detection between a ball (circle) and a brick (convex polygon) working correctly. I am using a Circle-Line collision detection test where each line represents and edge on the convex polygon brick. For the majority of the time the Circle-Line test works properly and the points of collision are resolved correctly. Collision detection working correctly. However, occasionally my collision detection code returns false due to a negative discriminant when the ball is actually intersecting the brick. Collision detection failing. I am aware of the inefficiency with this method and I am using axis aligned bounding boxes to cut down on the number of bricks tested. My main concern is if there are any mathematical bugs in my code below. /* * from and to are points at the start and end of the convex polygons edge. * This function is called for every edge in the convex polygon until a * collision is detected. */ bool circleLineCollision(Vec2f from, Vec2f to) { Vec2f lFrom, lTo, lLine; Vec2f line, normal; Vec2f intersectPt1, intersectPt2; float a, b, c, disc, sqrt_disc, u, v, nn, vn; bool one = false, two = false; // set line vectors lFrom = from - ball.circle.centre; // localised lTo = to - ball.circle.centre; // localised lLine = lFrom - lTo; // localised line = from - to; // calculate a, b & c values a = lLine.dot(lLine); b = 2 * (lLine.dot(lFrom)); c = (lFrom.dot(lFrom)) - (ball.circle.radius * ball.circle.radius); // discriminant disc = (b * b) - (4 * a * c); if (disc < 0.0f) { // no intersections return false; } else if (disc == 0.0f) { // one intersection u = -b / (2 * a); intersectPt1 = from + (lLine.scale(u)); one = pointOnLine(intersectPt1, from, to); if (!one) return false; return true; } else { // two intersections sqrt_disc = sqrt(disc); u = (-b + sqrt_disc) / (2 * a); v = (-b - sqrt_disc) / (2 * a); intersectPt1 = from + (lLine.scale(u)); intersectPt2 = from + (lLine.scale(v)); one = pointOnLine(intersectPt1, from, to); two = pointOnLine(intersectPt2, from, to); if (!one && !two) return false; return true; } } bool pointOnLine(Vec2f p, Vec2f from, Vec2f to) { if (p.x >= min(from.x, to.x) && p.x <= max(from.x, to.x) && p.y >= min(from.y, to.y) && p.y <= max(from.y, to.y)) return true; return false; }

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• Adding 'swerve' to a direction

  - by Skoder

  Hey. I'm not much of a maths expert, so this is probably quite straight forward. I was playing a soccer flash game where you take free kicks. You provide Power, Swerve and Direction. I'm reading up on vectors and such so I can use the direction and power information to shoot the ball with the correct velocity. What I don't understand is how the 'Swerve' information is used. What formula connects the Swerve information with the Direction and Power? (This is all in 2D) Thanks for any advice.

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• Scaling Sound Effects and Physics with Framerate

  - by Thomas Bradsworth

  (I'm using XNA and C#) Currently, my game (a shooter) runs flawlessly with 60 FPS (which I developed around). However, if the framerate is changed, there are two major problems: Gunshot sound effects are slower Jumping gets messed up Here's how I play gunshot sounds: update(gametime) { if(leftMouseButton.down) { enqueueBulletForSend(); playGunShot(); } } Now, obviously, the frequency of playGunShot depends on the framerate. I can easily fix the issue if the FPS is higher than 60 FPS by capping the shooting rate of the gun, but what if the FPS is less than 60? At first I thought to just loop and play more gunshots per frame, but I found that this can cause audio clipping or make the bullets fire in "clumps." Now for the second issue: Here's how jumping works in my game: if(jumpKey.Down && canJump) { velocity.Y += 0.224f; } // ... (other code) ... if(!onGround) velocity.Y += GRAVITY_ACCELERATION * elapsedSeconds; position += velocity; The issue here is that at < 60 FPS, the "intermediate" velocity is lost and therefore the character jumps lower. At 60 FPS, the game adds more "intermediate" velocities, and therefore the character jumps higher. For example, at 60 FPS, the following occurs: Velocity increased to 0.224 Not on ground, so velocity decreased by X Position increased by (0.224 - X) <-- this is the "intermediate" velocity At 30 FPS, the following occurs: Velocity increased to 0.224 Not on ground, so velocity decreased by 2X Position increased by (0.224 - 2X) <-- the "intermediate" velocity was lost All help is appreciated!

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• scaling point sprites with distance

  - by Will

  How can you scale a point sprite by its distance from the camera? GLSL fragment shader: gl_PointSize = size / gl_Position.w; seems along the right tracks; for any given scene all sprites seem nicely scaled by distance. Is this correct? How do you compute the proper scaling for my vertex attribute size? I want each sprite to be scaled by the modelview matrix. I had played with arbitrary values and it seems that size is the radius in pixels at the camera, and is not in modelview scale. I've also tried: gl_Position = pMatrix * mvMatrix * vec4(vertex,1.0); vec4 v2 = pMatrix * mvMatrix * vec4(vertex.x,vertex.y+0.5*size,vertex.z,1.0); gl_PointSize = length(gl_Position.xyz-v2.xyz) * gl_Position.w; But this makes the sprites be bigger in the distance, rather than smaller:

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• How to move an object using X and Y coordinates in JavaScript

  - by Geroy290

  I am making a 2d game with JavaScript and HTML5 and am trying to move an image that I have drawn with JavaScript like so: //canvas var c = document.getElementById("gameCanvas"); var ctx = c.getContext("2d"); //baseball var baseball = new Image(); baseball.onload = function() { ctx.drawImage(baseball, 400, 425); }; baseball.src = "baseball2.png"; I'm not sure how I would move it though, I have seen many people seem to just type something like ballX and ballY but I don't understand where the actual x and y definition comes from. Here is my code so far: http://jsfiddle.net/xRfua/ I have a different image source but it is a local source so I couldn't include it. Thanks in a dvance for any help!

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• Multithreading for a mixed-genre game in Python?

  - by arrogantc

  So here's the situation. I'm making a game that mixes two genres; arcade shooter and puzzler. They don't intertwine TOO much; all the interaction that really goes on is that every time an enemy is destroyed, a block is created. The blocks aren't even a part of the main collision detection system; they have their own more suited to their needs. What I want to ask is this; might it be a good idea to have the arcade shooter portion run on one thread, and the puzzle game portion run on another?

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• Character Jump Control

  - by Abdullah Sorathia

  I would like to know how can I control the jump movement of a character in Unity3D. Basically I am trying to program the jump in such a way that while a jump is in progress the character is allowed to move either left or right in mid-air when the corresponding keys are pressed. With my script the character will correctly move to the left when, for example, the left key is pressed, but when the right key is pressed afterwards, the character moves to the right before the movement to the left is completed. Following is the script: void Update () { if(touchingPlatform && Input.GetButtonDown("Jump")){ rigidbody.AddForce(jumpVelocity, ForceMode.VelocityChange); touchingPlatform = false; isJump=true; } //left & right movement Vector3 moveDir = Vector3.zero; if(Input.GetKey ("right")||Input.GetKey ("left")){ moveDir.x = Input.GetAxis("Horizontal"); // get result of AD keys in X if(ShipCurrentSpeed==0) { transform.position += moveDir * 3f * Time.deltaTime; }else if(ShipCurrentSpeed<=15) { transform.position += moveDir * ShipCurrentSpeed * 2f * Time.deltaTime; }else { transform.position += moveDir * 30f * Time.deltaTime; } }

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• Where can I find affordable legal advice for game software related inquiries?

  - by Steven Lu

  I am working on simulation middleware which is applicable for game engine implementations. What I would like to do is to make it freely available for use for all non-commercial purposes, while at the same time imposing some percentage of royalty on revenue (above a certain threshold) that is derived from my work. Something very similar to Epic's UDK licensing model. To facilitate the use of my software, I plan to offer binaries (static libs) for several platforms, as well as obfuscated source code which I will freely distribute, in addition to documentation of the API. I simply want to impose the restriction that if you try to make money from it, I get a cut eventually. I'm wondering if there are online forums and such where I am likely to find people who are willing to assist me in terms of learning what sort of things I have to do to get things down on the right kinds of documents. So far a site like this seems to be the most promising.

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• Can I animate render targets or the swap chain?

  - by Eric F.

  I want to animate some synthetic video bits to fullscreen w/o tearing. Can I set up D3D 9/10/11 in exclusive mode, and have it present a series of buffers that I'm writing to? I know how to copy system memory bits into a texture, then draw that texture as a fullscreen quad, but it seems like overkill. Why should I use the triangle rasterizer when I want to do something so simple? All I want to do is set up a long (4-8 buffer) swapchain and set the bits of the back buffer that is about to be displayed. Or, I want to allocate 4-8 RenderTargets, and on each frame, copy the bits from system memory to the RenderTarget, then set it as the next thing to display. I've never seen or heard about anybody doing this, but it seems so dead simple!

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• what's wrong with this Lua code (creating text inside listener in Corona)

  - by Greg

  If you double/triple click on the myObject here the text does NOT disappear. Why is this not working when there are multiple events being fired? That is, are there actually multiple "text" objects, with some existing but no longer having a reference to them held by the local "myText" variable? Do I have to manually removeSelf() on the local "myText" field before assigning it another "display.newText(...)"? display.setStatusBar( display.HiddenStatusBar ) local myText local function hideMyText(event) print ("hideMyText") myText.isVisible = false end local function showTextListener(event) if event.phase == "began" then print("showTextListener") myText = display.newText("Hello World!", 0, 0, native.systemFont, 30) timer.performWithDelay(1000, hideMyText, 1 ) end end -- Display object to press to show text local myObject = display.newImage( "inventory_button.png", display.contentWidth/2, display.contentHeight/2) myObject:addEventListener("touch", showTextListener) Question 2 - Also why is it the case that if I add a line BEFORE "myText = ..." of: a) "if myText then myText:removeSelf() end" = THIS FIXES THINGS, whereas b) "if myText then myText=nil end" = DOES NOT FIX THINGS Interested in hearing how Lua works here re the answer...

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• A Star Path finding endless loop

  - by PoeHaH

  I have implemented A* algorithm. Sometimes it works, sometimes it doesn't, and it goes through an endless loop. After days of debugging and googling, I hope you can come to the rescue. This is my code: The algorythm: public ArrayList<Coordinate> findClosestPathTo(Coordinate start, Coordinate goal) { ArrayList<Coordinate> closed = new ArrayList<Coordinate>(); ArrayList<Coordinate> open = new ArrayList<Coordinate>(); ArrayList<Coordinate> travelpath = new ArrayList<Coordinate>(); open.add(start); while(open.size()>0) { Coordinate current = searchCoordinateWithLowestF(open); if(current.equals(goal)) { return travelpath; } travelpath.add(current); open.remove(current); closed.add(current); ArrayList<Coordinate> neighbors = current.calculateCoordAdjacencies(true, rowbound, colbound); for(Coordinate n:neighbors) { if(closed.contains(n) || map.isWalkeable(n)) { continue; } int gScore = current.getGvalue() + 1; boolean gScoreIsBest = false; if(!open.contains(n)) { gScoreIsBest = true; n.setHvalue(manhattanHeuristic(n,goal)); open.add(n); } else { if(gScore<n.getGvalue()) { gScoreIsBest = true; } } if(gScoreIsBest) { n.setGvalue(gScore); n.setFvalue(n.getGvalue()+n.getHvalue()); } } } return null; } What I have found out is that it always fails whenever there's an obstacle in the path. If I'm running it on 'open terrain', it seems to work. It seems to be affected by this part: || map.isWalkeable(n) Though, the isWalkeable function seems to work fine. If additional code is needed, I will provide it. Your help is greatly appreciated, Thanks :)

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• how can i get rotation vector from matrix4x4 in xna?

  - by mr.Smyle

  i want to get rotation vector from matrix to realize some parent-children system for models. Matrix bonePos = link.Bone.Transform * World; Matrix m = Matrix.CreateTranslation(link.Offset) * Matrix.CreateScale(link.gameObj.Scale.X, link.gameObj.Scale.Y, link.gameObj.Scale.Z) * Matrix.CreateFromYawPitchRoll(MathHelper.ToRadians(link.gameObj.Rotation.Y), MathHelper.ToRadians(link.gameObj.Rotation.X), MathHelper.ToRadians(link.gameObj.Rotation.Z)) //need rotation vector from bone matrix here (now it's global model rotation vector) * Matrix.CreateFromYawPitchRoll(MathHelper.ToRadians(Rotation.Y), MathHelper.ToRadians(Rotation.X), MathHelper.ToRadians(Rotation.Z)) * Matrix.CreateTranslation(bonePos.Translation); link.gameObj.World = m; where : link - struct with children model settings, like position, rotation etc. And link.Bone - Parent Bone

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• Isometric algorithm [fixed]

  - by David

  so i've been toying with isometric and i just cant get the tiles to be in the right order. im probably missing something obvious and i just cant see it... but even at the risk of looking stupid, heres my code. for (int i = 0; i < Tile.MapSize; i++) { for (int j = 0; j < Tile.MapSize; j++) { spriteBatch.Draw( Tile.TileSetTexture, new Rectangle( (-j * Tile.TileWidth / 2) + (i * Tile.TileWidth / 2), (i * (Tile.TileHeight - 9) / 2) - (-j * (Tile.TileHeight - 9) / 2), Tile.TileWidth, Tile.TileHeight), Tile.GetSourceRectangle(tileID), Color.White, 0.0f, new Vector2(-350, -60), SpriteEffects.None, 1.0f); } } and heres what i end up with delicious messed up map yep, bit of an issue. so if anyone could help, i'd appreciate it. edit* works now <_<

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• Isometric layer moving inside map

  - by gronzzz

  i'm created isometric map and now trying to limit layer moving. Main idea, that i have left bottom, right bottom, left top, right top points, that camera can not move outside, so player will not see map out of bounds. But i can not understand algorithm of how to do that. It's my layer scale/moving code. - (void)touchBegan:(UITouch *)touch withEvent:(UIEvent *)event { _isTouchBegin = YES; } - (void)touchMoved:(UITouch *)touch withEvent:(UIEvent *)event { NSArray *allTouches = [[event allTouches] allObjects]; UITouch *touchOne = [allTouches objectAtIndex:0]; CGPoint touchLocationOne = [touchOne locationInView: [touchOne view]]; CGPoint previousLocationOne = [touchOne previousLocationInView: [touchOne view]]; // Scaling if ([allTouches count] == 2) { _isDragging = NO; UITouch *touchTwo = [allTouches objectAtIndex:1]; CGPoint touchLocationTwo = [touchTwo locationInView: [touchTwo view]]; CGPoint previousLocationTwo = [touchTwo previousLocationInView: [touchTwo view]]; CGFloat currentDistance = sqrt( pow(touchLocationOne.x - touchLocationTwo.x, 2.0f) + pow(touchLocationOne.y - touchLocationTwo.y, 2.0f)); CGFloat previousDistance = sqrt( pow(previousLocationOne.x - previousLocationTwo.x, 2.0f) + pow(previousLocationOne.y - previousLocationTwo.y, 2.0f)); CGFloat distanceDelta = currentDistance - previousDistance; CGPoint pinchCenter = ccpMidpoint(touchLocationOne, touchLocationTwo); pinchCenter = [self convertToNodeSpace:pinchCenter]; CGFloat predictionScale = self.scale + (distanceDelta * PINCH_ZOOM_MULTIPLIER); if([self predictionScaleInBounds:predictionScale]) { [self scale:predictionScale scaleCenter:pinchCenter]; } } else { // Dragging _isDragging = YES; CGPoint previous = [[CCDirector sharedDirector] convertToGL:previousLocationOne]; CGPoint current = [[CCDirector sharedDirector] convertToGL:touchLocationOne]; CGPoint delta = ccpSub(current, previous); self.position = ccpAdd(self.position, delta); } } - (void)touchEnded:(UITouch *)touch withEvent:(UIEvent *)event { _isDragging = NO; _isTouchBegin = NO; // Check if i need to bounce _touchLoc = [touch locationInNode:self]; } #pragma mark - Update - (void)update:(CCTime)delta { CGPoint position = self.position; float scale = self.scale; static float friction = 0.92f; //0.96f; if(_isDragging && !_isScaleBounce) { _velocity = ccp((position.x - _lastPos.x)/2, (position.y - _lastPos.y)/2); _lastPos = position; } else { _velocity = ccp(_velocity.x * friction, _velocity.y *friction); position = ccpAdd(position, _velocity); self.position = position; } if (_isScaleBounce && !_isTouchBegin) { float min = fabsf(self.scale - MIN_SCALE); float max = fabsf(self.scale - MAX_SCALE); int dif = max > min ? 1 : -1; if ((scale > MAX_SCALE - SCALE_BOUNCE_AREA) || (scale < MIN_SCALE + SCALE_BOUNCE_AREA)) { CGFloat newSscale = scale + dif * (delta * friction); [self scale:newSscale scaleCenter:_touchLoc]; } else { _isScaleBounce = NO; } } }

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• Pokemon Yellow wrap transitions

  - by Alex Koukoulas

  So I've been trying to make a pretty accurate clone of the good old Pokemon Yellow for quite some time now and one puzzling but nonetheless subtle mechanic has puzzled me. As you can see in the uploaded image there is a certain colour manipulation done in two stages after entering a wrap to another game location (such as stairs or entering a building). One easy (and sloppy) way of achieving this and the one I have been using so far is to make three copies of each image rendered on the screen all of them with their colours adjusted accordingly to match each stage of the transition. Of course after a while this becomes tremendously time consuming. So my question is does anyone know any better way of achieving this colour manipulation effect using java? Thanks in advance, Alex

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• forward motion car physics - gradual slow

  - by spartan2417

  Im having trouble creating realistic car movements in xna 4. Right now i have a car going forward and hitting a terminal velocity which is fine but when i release the up key i need to the car to slow down gradually and then come to a stop. Im pretty sure this is easy code but i cant seem to get it to work the code - update if (Keyboard.GetState().IsKeyDown(Keys.Up)) { double elapsedTime = gameTime.ElapsedGameTime.Milliseconds; CalcTotalForce(); Acceleration = Vector2.Divide(CalcTotalForce(), MASS); Velocity = Vector2.Add(Velocity, Vector2.Multiply(Acceleration, (float)(elapsedTime))); Position = Vector2.Add(Position, Vector2.Multiply(Velocity, (float)(elapsedTime))); } added functions public Vector2 CalcTraction() { //Traction force = vector direction * engine force return Vector2.Multiply(forwardDirection, ENGINE_FORCE); } public Vector2 CalcDrag() { //Drag force = constdrag * velocity * speed return Vector2.Multiply(Vector2.Multiply(Velocity, DRAG_CONST), Velocity.Y); } public Vector2 CalcRoll() { //roll force = const roll * velocity return Vector2.Multiply(Velocity, ROLL_CONST); } public Vector2 CalcTotalForce() { //total force = traction + (-drag) + (-rolling) return Vector2.Add(CalcTraction(), Vector2.Add(-CalcDrag(), -CalcRoll())); } anyone have any ideas?

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• std::vector::size with glDrawElements crashes?

  - by NoobScratcher

  ( win32 / OpenGL 3.3 / GLSL 330 ) I decided after a long time of trying to do a graphical user interface using just opengl graphics to go back to a gui toolkit and so in the process have had to port alot of my code to win32. But I have a problem with my glDrawElement function. my program compiles and runs fine until it gets to glDrawElements then crashes.. which is rather annoying right. so I was trying to figure out why and I found out its std::vector::size member not returning the correct amount of faces in the unsigned interger vector eg, "vector<unsigned int>faces; " so when I use cout << faces.size() << endl; I got 68 elements???? instead of 24 as you can see here in this .obj file: # Blender v2.61 (sub 0) OBJ File: '' # www.blender.org v 1.000000 -1.000000 -1.000000 v 1.000000 -1.000000 1.000000 v -1.000000 -1.000000 1.000000 v -1.000000 -1.000000 -1.000000 v 1.000000 1.000000 -0.999999 v 0.999999 1.000000 1.000001 v -1.000000 1.000000 1.000000 v -1.000000 1.000000 -1.000000 s off f 1 2 3 4 f 5 8 7 6 f 1 5 6 2 f 2 6 7 3 <--- 24 Faces not 68? f 3 7 8 4 f 5 1 4 8 I'm using a parser I created to get the faces/vertexes in my .obj file: char modelbuffer [20000]; int MAX_BUFF = 20000; unsigned int face[3]; FILE * pfile; pfile = fopen(szFileName, "rw"); while(fgets(modelbuffer, MAX_BUFF, pfile) != NULL) { if('v') { Point p; sscanf(modelbuffer, "v %f %f %f", &p.x, &p.y, &p.z); points.push_back(p); cout << " p.x = " << p.x << " p.y = " << p.y << " p.z = " << p.x << endl; } if('f') { sscanf(modelbuffer, "f %d %d %d %d", &face[0], &face[1], &face[2], &face[3]); cout << "face[0] = " << face[0] << " face[1] = " << face[1] << " face[2] = " << face[2] << " face[3] = " << face[3] << "\n"; faces.push_back(face[0] - 1); faces.push_back(face[1] - 1); faces.push_back(face[2] - 1); faces.push_back(face[3] - 1); cout << face[0] - 1 << face[1] - 1 << face[2] - 1 << face[3] - 1 << endl; } } using this struct to store the x,y,z positions also this vector was used with Point: vector<Point>points; struct Point { float x, y, z; }; If someone could tell me why its not working and how to fix it that would be awesome I also provide a pastebin to the full source code if you want a closer look. http://pastebin.com/gznYLVw7

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• How important is a single-player mode in a 2-player game?

  - by Davy8

  So say you have a 2 player game, taking Chess as an example (except it's an original game with no ready-to-go AI available). Let's say there's also a social-aspect to the meta-game, so let's say it's a Chess game on Facebook where you can challenge your friends. How important is it to have a single-player mode, knowing that an AI will need to be created (I've done minimax AI for tic tac toe, but nothing too sophisticated)? Is it important enough that it should be in the initial launch of the game? Can it wait for a future iteration (knowing that being hosted on the web means the game can be updated at any time)?

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• Quaternion LookAt for camera

  - by Homar

  I am using the following code to rotate entities to look at points. glm::vec3 forwardVector = glm::normalize(point - position); float dot = glm::dot(glm::vec3(0.0f, 0.0f, 1.0f), forwardVector); float rotationAngle = (float)acos(dot); glm::vec3 rotationAxis = glm::normalize(glm::cross(glm::vec3(0.0f, 0.0f, 1.0f), forwardVector)); rotation = glm::normalize(glm::quat(rotationAxis * rotationAngle)); This works fine for my usual entities. However, when I use this on my Camera entity, I get a black screen. If I flip the subtraction in the first line, so that I take the forward vector to be the direction from the point to my camera's position, then my camera works but naturally my entities rotate to look in the opposite direction of the point. I compute the transformation matrix for the camera and then take the inverse to be the View Matrix, which I pass to my OpenGL shaders: glm::mat4 viewMatrix = glm::inverse( cameraTransform->GetTransformationMatrix() ); The orthographic projection matrix is created using glm::ortho. What's going wrong?

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• Target tracking with a small delay (actionscript 3.0)

  - by John Dodson

  I'm having trouble thinking of a good method to track my character with an enemy attack. Of course, I don't want the attack to track my character's current position; I want it to track where the character was about 1 second before (so you can move around and make the attack miss and loop around you sort of a thing). The general structure of my game uses a timer to update all of my events. I have a timer going off every 25 milliseconds that updates everything, including my player's position and the enemies position. Right now I just have the enemy attack directly targeting my character....which works fine except that it's impossible to escape =p. Let me know if I didn't supply enough details. My approach was going to basically be get my character's position from about 1 second ago, then have the enemy target that position, the only problem is I can't think of a good way to get my character's position from previous times. Thanks for the help!

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• Which purpose do armor points serve?

  - by Bane

  I have seen a mechanic which I call "armor points" in many games: Quake, Counter Strike, etc. Generally, while the player has these armor points, he takes less damage. However, they act in a similar fashion that health points do: you lose them by taking said damage. Why would you design such a feature? Is this just health 2.0, or am I missing something? To me, armor only makes sense in, for example, RPG games, where it is a constant that determines your resistance. But I don't see why would it need to be reduceable during combat.

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