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• Class Design - Space Simulator

  - by Peteyslatts

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

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• 2D SAT Collision Detection not working when using certain polygons (With example)

  - by sFuller

  My SAT algorithm falsely reports that collision is occurring when using certain polygons. I believe this happens when using a polygon that does not contain a right angle. Here is a simple diagram of what is going wrong: Here is the problematic code: std::vector<vec2> axesB = polygonB->GetAxes(); //loop over axes B for(int i = 0; i < axesB.size(); i++) { float minA,minB,maxA,maxB; polygonA->Project(axesB[i],&minA,&maxA); polygonB->Project(axesB[i],&minB,&maxB); float intervalDistance = polygonA->GetIntervalDistance(minA, maxA, minB, maxB); if(intervalDistance >= 0) return false; //Collision not occurring } This function retrieves axes from the polygon: std::vector<vec2> Polygon::GetAxes() { std::vector<vec2> axes; for(int i = 0; i < verts.size(); i++) { vec2 a = verts[i]; vec2 b = verts[(i+1)%verts.size()]; vec2 edge = b-a; axes.push_back(vec2(-edge.y,edge.x).GetNormailzed()); } return axes; } This function returns the normalized vector: vec2 vec2::GetNormailzed() { float mag = sqrt( x*x + y*y ); return *this/mag; } This function projects a polygon onto an axis: void Polygon::Project(vec2* axis, float* min, float* max) { float d = axis->DotProduct(&verts[0]); float _min = d; float _max = d; for(int i = 1; i < verts.size(); i++) { d = axis->DotProduct(&verts[i]); _min = std::min(_min,d); _max = std::max(_max,d); } *min = _min; *max = _max; } This function returns the dot product of the vector with another vector. float vec2::DotProduct(vec2* other) { return (x*other->x + y*other->y); } Could anyone give me a pointer in the right direction to what could be causing this bug? Edit: I forgot this function, which gives me the interval distance: float Polygon::GetIntervalDistance(float minA, float maxA, float minB, float maxB) { float intervalDistance; if (minA < minB) { intervalDistance = minB - maxA; } else { intervalDistance = minA - maxB; } return intervalDistance; //A positive value indicates this axis can be separated. } Edit 2: I have recreated the problem in HTML5/Javascript: Demo

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• Arcball Problems with UDK

  - by opdude

  I'm trying to re-create an arcball example from a Nehe, where an object can be rotated in a more realistic way while floating in the air (in my game the object is attached to the player at a distance like for example the Physics Gun) however I'm having trouble getting this to work with UDK. I have created an LGArcBall which follows the example from Nehe and I've compared outputs from this with the example code. I think where my problem lies is what I do to the Quaternion that is returned from the LGArcBall. Currently I am taking the returned Quaternion converting it to a rotation matrix. Getting the product of the last rotation (set when the object is first clicked) and then returning that into a Rotator and setting that to the objects rotation. If you could point me in the right direction that would be great, my code can be found below. class LGArcBall extends Object; var Quat StartRotation; var Vector StartVector; var float AdjustWidth, AdjustHeight, Epsilon; function SetBounds(float NewWidth, float NewHeight) { AdjustWidth = 1.0f / ((NewWidth - 1.0f) * 0.5f); AdjustHeight = 1.0f / ((NewHeight - 1.0f) * 0.5f); } function StartDrag(Vector2D startPoint, Quat rotation) { StartVector = MapToSphere(startPoint); } function Quat Update(Vector2D currentPoint) { local Vector currentVector, perp; local Quat newRot; //Map the new point to the sphere currentVector = MapToSphere(currentPoint); //Compute the vector perpendicular to the start and current perp = startVector cross currentVector; //Make sure our length is larger than Epsilon if (VSize(perp) > Epsilon) { //Return the perpendicular vector as the transform newRot.X = perp.X; newRot.Y = perp.Y; newRot.Z = perp.Z; //In the quaternion values, w is cosine (theta / 2), where //theta is the rotation angle newRot.W = startVector dot currentVector; } else { //The two vectors coincide, so return an identity transform newRot.X = 0.0f; newRot.Y = 0.0f; newRot.Z = 0.0f; newRot.W = 0.0f; } return newRot; } function Vector MapToSphere(Vector2D point) { local float x, y, length, norm; local Vector result; //Transform the mouse coords to [-1..1] //and inverse the Y coord x = (point.X * AdjustWidth) - 1.0f; y = 1.0f - (point.Y * AdjustHeight); length = (x * x) + (y * y); //If the point is mapped outside of the sphere //( length > radius squared) if (length > 1.0f) { norm = 1.0f / Sqrt(length); //Return the "normalized" vector, a point on the sphere result.X = x * norm; result.Y = y * norm; result.Z = 0.0f; } else //It's inside of the sphere { //Return a vector to the point mapped inside the sphere //sqrt(radius squared - length) result.X = x; result.Y = y; result.Z = Sqrt(1.0f - length); } return result; } DefaultProperties { Epsilon = 0.000001f } I'm then attempting to rotate that object when the mouse is dragged, with the following update code in my PlayerController. //Get Mouse Position MousePosition.X = LGMouseInterfacePlayerInput(PlayerInput).MousePosition.X; MousePosition.Y = LGMouseInterfacePlayerInput(PlayerInput).MousePosition.Y; newQuat = ArcBall.Update(MousePosition); rotMatrix = MakeRotationMatrix(QuatToRotator(newQuat)); rotMatrix = rotMatrix * LastRot; LGMoveableActor(movingPawn.CurrentUseableObject).SetPhysics(EPhysics.PHYS_Rotating); LGMoveableActor(movingPawn.CurrentUseableObject).SetRotation(MatrixGetRotator(rotMatrix));

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• Rendering scaled-down card images

  - by user1065145

  I have high-quality SVG card images, but they drastically lose their quality when I downsize them. I have tried two ways of rendering cards (using Inkscape and Imagemagics): 1) Render SVG to high-res PNG and resize it then: inkscape -D --export-png=QS1024.png --export-width=1024 QS.svg convert QS1024.png -filter Lanczos -sampling-factor 1x1 -resize 71x QS71.png 2) Render SVG to image of proper size at once: inkscape -D --export-png=QS71.png --export-width=71 QS.svg Both approaches generate blurry card images, which looks even worse than old Windows cards. What are the best way to generate smaller card images from SVG sources and not to loose their quality a lot? UPDATE: I am using Inkscape to render SVG - PNG and ImageMagick then to downsize PNG. I've tried using convert -resize with couple of filters (Lanczos/Mitchell/etc), but result was pretty much the same. Original: 71x raster:

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• What functionality should I use in OpenGL 2.0?

  - by Jeffrey

  Considering OpenGL 2.1, we all know that glBegin and glEnd are the devil. Should I use only VBO to render 3d primitives (I can't find VAO in that version, weren't there already?)? Should I still use the matrix stack (why not?)? Should I still use glFrustum? Can I take advantage of shaders in GLSL 1.20? Where can I find a tutorial for VBO in OpenGL 2.1 and the "correct" way of programming in it? Also how am I supposed to animate something. Like a cube moving around an object or a player moving in the scene (static vbo data + shader?)? Note: Take your time to answer this question, I'll accept an answer tomorrow.

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• Projective texture and deferred lighting

  - by Vodácek

  In my previous question, I asked whether it is possible to do projective texturing with deferred lighting. Now (more than half a year later) I have a problem with my implementation of the same thing. I am trying to apply this technique in light pass. (my projector doesn't affect albedo). I have this projector View a Projection matrix: Matrix projection = Matrix.CreateOrthographicOffCenter(-halfWidth * Scale, halfWidth * Scale, -halfHeight * Scale, halfHeight * Scale, 1, 100000); Matrix view = Matrix.CreateLookAt(Position, Target, Vector3.Up); Where halfWidth and halfHeight is are half of the texture's width and height, Position is the Projector's position and target is the projector's target. This seems to be ok. I am drawing full screen quad with this shader: float4x4 InvViewProjection; texture2D DepthTexture; texture2D NormalTexture; texture2D ProjectorTexture; float4x4 ProjectorViewProjection; sampler2D depthSampler = sampler_state { texture = <DepthTexture>; minfilter = point; magfilter = point; mipfilter = point; }; sampler2D normalSampler = sampler_state { texture = <NormalTexture>; minfilter = point; magfilter = point; mipfilter = point; }; sampler2D projectorSampler = sampler_state { texture = <ProjectorTexture>; AddressU = Clamp; AddressV = Clamp; }; float viewportWidth; float viewportHeight; // Calculate the 2D screen position of a 3D position float2 postProjToScreen(float4 position) { float2 screenPos = position.xy / position.w; return 0.5f * (float2(screenPos.x, -screenPos.y) + 1); } // Calculate the size of one half of a pixel, to convert // between texels and pixels float2 halfPixel() { return 0.5f / float2(viewportWidth, viewportHeight); } struct VertexShaderInput { float4 Position : POSITION0; }; struct VertexShaderOutput { float4 Position :POSITION0; float4 PositionCopy : TEXCOORD1; }; VertexShaderOutput VertexShaderFunction(VertexShaderInput input) { VertexShaderOutput output; output.Position = input.Position; output.PositionCopy=output.Position; return output; } float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 { float2 texCoord =postProjToScreen(input.PositionCopy) + halfPixel(); // Extract the depth for this pixel from the depth map float4 depth = tex2D(depthSampler, texCoord); //return float4(depth.r,0,0,1); // Recreate the position with the UV coordinates and depth value float4 position; position.x = texCoord.x * 2 - 1; position.y = (1 - texCoord.y) * 2 - 1; position.z = depth.r; position.w = 1.0f; // Transform position from screen space to world space position = mul(position, InvViewProjection); position.xyz /= position.w; //compute projection float3 projection=tex2D(projectorSampler,postProjToScreen(mul(position,ProjectorViewProjection)) + halfPixel()); return float4(projection,1); } In first part of pixel shader is recovered position from G-buffer (this code I am using in other shaders without any problem) and then is tranformed to projector viewprojection space. Problem is that projection doesn't appear. Here is an image of my situation: The green lines are the rendered projector frustum. Where is my mistake hidden? I am using XNA 4. Thanks for advice and sorry for my English. EDIT: Shader above is working but projection was too small. When I changed the Scale property to a large value (e.g. 100), the projection appears. But when the camera moves toward the projection, the projection expands, as can bee seen on this YouTube video.

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• How does this snippet of code create a ray direction vector?

  - by Isaac Waller

  In the Minecraft source code, this code is used to create a direction vector for a ray from pitch and yaw:' float f1 = MathHelper.cos(-rotationYaw * 0.01745329F - 3.141593F); float f3 = MathHelper.sin(-rotationYaw * 0.01745329F - 3.141593F); float f5 = -MathHelper.cos(-rotationPitch * 0.01745329F); float f7 = MathHelper.sin(-rotationPitch * 0.01745329F); return Vec3D.createVector(f3 * f5, f7, f1 * f5); I was wondering how it worked, and what is the constant 0.01745329F?

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• Cocos2d update leaking memory

  - by Andrey Chernukha

  I have a weird issue - my app is leaking memory on device only, not on a simulator. It is leaking if i schedule update method anywhere, on any scene. It is leaking despite update method is empty, there's nothing inside it except NSLog. How can it be? I have even scheduled update on the very first scene where it seems there's nothing to leak, and scheduled another empty and it's leaking or not leaking but allocating something, the result is the same - the volume of the memory consumed is increasing and my app is crashing soon. I can detect the leakage via using Instruments-Memory-Activity Monitor or with help of following function: void report_memory(void) { struct task_basic_info info; mach_msg_type_number_t size = sizeof(info); kern_return_t kerr = task_info(mach_task_self(), TASK_BASIC_INFO, (task_info_t)&info, &size); if( kerr == KERN_SUCCESS ) { NSLog(@"Memory in use (in bytes): %u", info.resident_size); } else { NSLog(@"Error with task_info(): %s", mach_error_string(kerr)); } } Can anyone explain me what's going on?

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• Why the clip space in OpenGL has 4 dimensions?

  - by user827992

  I will use this as a generic reference, but the more i browser online docs and books, the less i understand about this. const float vertexPositions[] = { 0.75f, 0.75f, 0.0f, 1.0f, 0.75f, -0.75f, 0.0f, 1.0f, -0.75f, -0.75f, 0.0f, 1.0f, }; in this online book there is an example about how to draw the first and classic hello world for OpenGL about making a triangle. The vertex structure for the triangle is declared as stated in the code above. The book, as all the other sources about this, stress the point that the Clip Space is a 4D structure that is used to basically decide what will be rasterized and rendered to the screen. Here I have my questions: i can't imagine something in 4D, i don't think that a human can do that, what is a 4D for this Clip space ? the most human-readable doc that i have read speaks about a camera, which is just an abstraction over the clipping concept, and i get that, the problem is, why not using the concept of a camera in the first place which is a more familiar 3D structure? The only problem with the concept of a camera is that you need to define the prospective in other way and so you basically have to add another statement about what kind of camera you wish to have. How i'm supposed to read this 0.75f, 0.75f, 0.0f, 1.0f ? All i get is that they are all float values and i get the meaning of the first 3 values, what does it mean the last one?

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• Logic / Render phases with a single thread

  - by DevilWithin

  The question I have may generate different opinions from different developers, but I'd still like to have an answer on this. Its all about the updating and rendering steps of the game loop, and their use under multi and single threaded environments. Currently, there is one thread running, which takes care of sequentially executing events , logic and rendering. Sometimes, the logic part may wish to change the game state to something else, and in between do some loading of files. The result is that the game hangs completely while loading, and then proceeds to normal rendering of the new state. To go around this, i could make another thread, do the loading there while the main thread renders a smooth loading animation, and then proceed normally. The real question is about if i don't create another thread. I could refresh the screen from the logic thread, and provide some basic loading screen, which could be not so smoothly updated while the files load. In fact, this approach is not loved by a lot of developers, as it scrambles render code in the logic step, which may cause problems of different sorts.. Hope its clear!

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• Writing a Master's Thesis on evaluating visual scripting systems

  - by user1107412

  I am thinking to write my Master's thesis around theorizing, and then implementing a PlayMaker or Kismet-like (building game logic by visually arranging FSMs) tool in Unity. The only thing I am still concerned about is the actual research question that I should pose. I was kinda hoping that the more experienced game designers out there might know. Update: What about reducing the use of visual programming to graphically designing FSM-Action-Transition flows, which can then be attached to game entities (very much like http://playmaker.com does it)?

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• Incorrect results for frustum cull

  - by DeadMG

  Previously, I had a problem with my frustum culling producing too optimistic results- that is, including many objects that were not in the view volume. Now I have refactored that code and produced a cull that should be accurate to the actual frustum, instead of an axis-aligned box approximation. The problem is that now it never returns anything to be in the view volume. As the mathematical support library I'm using does not provide plane support functions, I had to code much of this functionality myself, and I'm not really the mathematical type, so it's likely that I've made some silly error somewhere. As follows is the relevant code: class Plane { public: Plane() { r0 = Math::Vector(0,0,0); normal = Math::Vector(0,1,0); } Plane(Math::Vector p1, Math::Vector p2, Math::Vector p3) { r0 = p1; normal = Math::Cross((p2 - p1), (p3 - p1)); } Math::Vector r0; Math::Vector normal; }; This class represents one plane as a point and a normal vector. class Frustum { public: Frustum( const std::array<Math::Vector, 8>& points ) { planes[0] = Plane(points[0], points[1], points[2]); planes[1] = Plane(points[4], points[5], points[6]); planes[2] = Plane(points[0], points[1], points[4]); planes[3] = Plane(points[2], points[3], points[6]); planes[4] = Plane(points[0], points[2], points[4]); planes[5] = Plane(points[1], points[3], points[5]); } Plane planes[6]; }; The points are passed in order where (the inverse of) each bit of the index of each point indicates whether it's the left, top, and back of the frustum, respectively. As such, I just picked any three points where they all shared one bit in common to define the planes. My intersection test is as follows (based on this): bool Intersects(Math::AABB lhs, const Frustum& rhs) const { for(int i = 0; i < 6; i++) { Math::Vector pvertex = lhs.TopRightFurthest; Math::Vector nvertex = lhs.BottomLeftClosest; if (rhs.planes[i].normal.x <= -0.0f) { std::swap(pvertex.x, nvertex.x); } if (rhs.planes[i].normal.y <= -0.0f) { std::swap(pvertex.y, nvertex.y); } if (rhs.planes[i].normal.z <= -0.0f) { std::swap(pvertex.z, nvertex.z); } if (Math::Dot(rhs.planes[i].r0, nvertex) < 0.0f) { return false; } } return true; } Also of note is that because I'm using a left-handed co-ordinate system, I wrote my Cross function to return the negative of the formula given on Wikipedia. Any suggestions as to where I've made a mistake?

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• What is the most efficient way to add and removed Slick2D sprites?

  - by kirchhoff

  I'm making a game in Java with Slick2D and I want to create planes which shoots: int maxBullets = 40; static int bullet = 0; Missile missile[] = new Missile[maxBullets]; I want to create/move my missiles in the most efficient way, I would appreciate your advise: public void shoot() throws SlickException{ if(bullet<maxBullets){ if(missile[bullet] != null){ missile[bullet].resetLocation(plane.getCentreX(), plane.getCentreY(), plane.image.getRotation()); }else{ missile[bullet] = new Missile("resources/missile.png", plane.getCentreX(), plane.getCentreY(), plane.image.getRotation()); } }else{ bullet = 0; missile[bullet].resetLocation(plane.getCentreX(), plane.getCentreY(), plane.image.getRotation()); } bullet++; } I created the method resetLocation in my Missile class in order to avoid loading again the resource. Is it correct? In the update method I've got this to move all the missiles: if(bullet > 0 && bullet < maxBullets){ float hyp = 0.4f * delta; if(bullet == 1){ missile[0].move(hyp); }else{ for(int x = 0; x<bullet; x++){ missile[x].move(hyp); } } }

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• What are the common character animation techniques used in tile based hack&slash games?

  - by Gorky

  I wonder what kind of animation techniques are used for creature and character animation in modern hack&slash type tile based games? Keyframing for different actions may be one option. Skeletal framing may be another. But how about the physics? Or do they use a totally hybrid system of inverse kinematics supported with a skeleton,physics and mixed with interpolated keyframing for more realistic animations? If so, how and for what reasons? I can think of many different solutions for the issues below but I wonder what's used and best suited for issues like: Walking or moving on an uneven terrain Combat interaction, combat physics and collisions Attaching rigid items to character and their iteractions ih physics world Soft body dynamics like hair, vegetation, clothes and fabric in line with animations and iteractions.

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• Finding the endpoint of a named bone in Irrlicht

  - by Boreal

  I'm making a tank game that will have multiple tanks. I want to be able to define the weapon placements using bones that I can add right inside the modelling program (Blender to be exact). All tanks will have a bone called Body and a bone called Turret, and then names like Cannon0 and PickupGun for where the shots will be fired from that are attached to the Turret bone. Is there some way to find the absolute end position of a bone that I choose by name?

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• Lighting with VBO

  - by nkint

  I'm using a Java JOGL wrapper called processing.org. I have coded some enviroment on it and I'm quite proud of it even if it has some ready stuffs that I didn't know anything about it (==LIGHTS). Then, for some geometry, I've decided to use a VBO. I had to pass in the hard way and recode all lights. But I can't achieve the same result. This is the original light system: And this with VBO: With this code: Vec3D l; gl.glEnable(GL.GL_LIGHTING); gl.glEnable(GL.GL_LIGHT0); gl.glEnable(GL.GL_COLOR_MATERIAL); gl.glMaterialfv(GL.GL_FRONT_AND_BACK, GL.GL_AMBIENT, new float[]{0.8f,0f,0f}, 0); l = new Vec3D(0,0,-10); gl.glColor3f(0.8f,0f,0f); gl.glLightfv(GL.GL_LIGHT0, GL.GL_POSITION, new float[] { l.x, l.y, l.z, 0 }, 0); gl.glLightfv(GL.GL_LIGHT0, GL.GL_SPOT_DIRECTION, new float[] { 1, 1, 1, 1 }, 0); I can't achive the same light, the same color material, and the same wireframe stuffs. If needed I can also post the code I use for VBO, but it is quite standard vertex array grabbed on the net that uses glDrawArrays

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• Making AI jump on a spot effectively

  - by Pasquale Sada

  How to calculate, in 3D environment, the closest point, from which an AI character can jump onto a platform? Setup I have an initial velocity V(Vx,Vy,VZ) and a spot where the character stands still at S(Sx,Sy,Sz). What I'm trying to achieve is a successful 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 obstacles 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; Ended up using the lowest angle (20 degree) and checking for collision on the trajectory. If found any increase the angle. Here some code (to improve the code maybe must stop the check at the highest point of the curve): Vector3 BallisticVel(Vector3 target, float angle) { 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; } Vector3 TrajectoryPoint(Vector3 startingPosition, Vector3 startingVelocity, float n ) { float t = 1/60 ; // seconds per time step Vector3 stepVelocity = t * startingVelocity; // m/s Vector3 stepGravity = t * t * Physics.gravity; // m/s/s return startingPosition + n * stepVelocity + 0.5f * (n*n+n) * stepGravity; } bool CheckTrajectory(Vector3 startingPosition,Vector3 target, float angle_jump) { Debug.Log("checking"); if(angle_jump < 80f) { Debug.Log("if"); Vector3 startingVelocity = BallisticVel(target, angle_jump); for (int i = 0; i < 180; i++) { //Debug.Log(i); Vector3 trajectoryPosition = TrajectoryPoint( startingPosition, startingVelocity, i ); if(Physics.Raycast(trajectoryPosition,Vector3.forward,safeDistance)) { angle_jump += 10; break; // restart loop with the new angle } else continue; } return true; JumpVelocity = BallisticVel(target, angle_jump); } return false; }

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• How do I use D3DXVec3Unproject with D3D11?

  - by Miguel P

  I'm having a small issue with D3DXVec3Unproject. I'm currently using Direct3D 11 and not 10, and the signature for this function is: D3DXVECTOR3 *pOut, CONST D3DXVECTOR3 *pV, CONST D3D10_VIEWPORT *pViewport, CONST D3DXMATRIX *pProjection, CONST D3DXMATRIX *pView, CONST D3DXMATRIX *pWorld As you may have noticed, it requires a D3D10_VIEWPORT, and I'm using a Direct3D 11 viewport, D3D11_VIEWPORT. Do you have any ideas how I can use D3DXVec3Unproject with Direct3D 11?

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• Finding the shorter turning direction towards a target

  - by A.B.

  I'm trying to implement a type of movement where the object gradually faces the target. The problem I've run into is figuring out which turning direction is faster. The following code works until the object's orientation crosses the -PI or PI threshold, at which point it will start turning into the opposite direction void moveToPoint(sf::Vector2f destination) { if (destination == position) return; auto distance = distanceBetweenPoints(position, destination); auto direction = angleBetweenPoints(position, destination); /// Decides whether incrementing or decrementing orientation is faster /// the next line is the problem if (atan2(sin(direction - rotation), cos(direction - rotation)) > 0 ) { /// Increment rotation rotation += rotation_speed; } else { /// Decrement rotation rotation -= rotation_speed; } if (distance < movement_speed) { position = destination; } else { position.x = position.x + movement_speed*cos(rotation); position.y = position.y + movement_speed*sin(rotation); } updateGraphics(); } 'rotation' and 'rotation_speed' are implemented as custom data type for radians which cannot have values lower than -PI and greater than PI. Any excess or deficit "wraps around". For example, -3.2 becomes ~3.08.

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• How do I create a bounding frustrum from a view & projection matrix?

  - by Narf the Mouse

  Given a left-handed Projection matrix, a left-handed View matrix, a ViewProj matrix of View * Projection - How do I create a bounding Frustum comprised of near, far, left, right and top, bottom planes? The only example I could find on Google (Tutorial 16: Frustum Culling) seems to not work; for example, if the math is used as given, the near-plane's distance is a negative. This places the near-plane behind the camera...

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• Sorting objects before rendering

  - by dreta

  I'm trying to implement a scene graph and in all the articles i've come across there is talk about object sorting. So you'd sort your objects by "material" for example. Now untill i sat down and started implementing it, i kind of took this for granted, because it made sense. But now i'm wondering what does sorting actually change? In my engine, i have a manager for UBOs, i use those to store data that'll be shared between programs, at the moment that only involves time, camera and projection matrices and lights (i'm not worrying about managing which lights affect which objects ATM). Now for each model i have to change the model to world matrix uniform, no sorting is going to change that. So is the jump from changing this matrix to also setting a material for each object that bad? I vaguely remember reading somewhere that each time you change something in the pipeline, it has to get flushed and that can cause performance issues. But for each drawing call i'm setting up a model to world matrix anyway, so what sense does it make to ever be concerned about this? BTW is there any information about whether changing a uniform and calling glBufferSubData is more (or less) expensive.

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• Outline Shader Effect for Orthogonal Geometry in XNA

  - by Griffin

  I just recently started learning the art of shading, but I can't give an outline width to 2D, concave geometry when restrained to a single vertex/pixel shader technique (thanks to XNA). the shape I need to give an outline to has smooth, per-vertex coloring, as well as opacity. The outline, which has smooth, per-vertex coloring, variable width, and opacity cannot interfere with the original shape's colors. A pixel depth border detection algorithm won't work because pixel depth isn't a 3.0 semantic. expanding geometry / redrawing won't work because it interferes with the original shape's colors. I'm wondering if I can do something with the stencil/depth buffer outside of the shader functions since I have access to that through the graphics device. But I don't believe I'm able to manipulate actual values. How might I do this?

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• Interpolating between two networked states?

  - by Vaughan Hilts

  I have many entities on the client side that are simulated (their velocities are added to their positions on a per frame basis) and I let them dead reckon themselves. They send updates about where they were last seen and their velocity changes. This works great and other players see this work find. However, after a while these players begin to desync after some time. This is because of latency. I'd like to know how I can interpolate between states so they appear to be in the correct position. I know where the player was LAST seen and their current velocity but interpolating to the last seen state causes the player to actually move -backwards-. I could not use velocity at all for other clients and simply 'lerp' them towards the appropriate direction but I feel this would cause jaggy movement. What are the alternatives?

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• Checking whether a specific key was pressed in enchantJS

  - by MxyL

  I am using enchantJS and would like to use the letters and numbers as well as numpad on a keyboard to do different things (eg: hotkeys). From this page http://users.csc.calpoly.edu/~foaad/enchant/guide/playerInput.html By default, enchant.js provides input listeners for six buttons: UP, DOWN, LEFT, RIGHT, A, and B. By default, the directions are bound to the arrow keys. Any of the six buttons may also be bound to any key with an ASCII value. We’ll address that later. So enchant provides the ability to bind keys to different input such as up, down, left, right...but how can I simply check whether the D or X key was pressed, and if so, perform certain actions based on that event?

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• Which game logic should run when doing prediction for PNP state updates

  - by spaceOwl

  We are writing a multiplayer game, where each game client (player) is responsible for sending state updates regarding its "owned" objects to other players. Each message that arrives to other (remote) clients is processed as such: Figure out when the message was sent. Create a diff between NOW and that time. Run game specific logic to bring the received state to "current" time. I am wondering which sort of logic should execute as part of step #3 ? Our game is composed of a physical update (position, speed, acceleration, etc) and many other components that can update an object's state and occur regularly (locally). There's a trade off here - Getting the new state quickly or remaining "faithful" to the true state representation and executing the whole thing to predict the "true" state when receiving state updates from remote clients. Which one is recommended to be used? and why?

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