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• Collision and Graphics integration

  - by Shlomi Atia

  I'm a little confused about the integration between collision and graphics. They both need to share the same position in the world. The most obvious choice is the center of the entity, which is good for bounding volumes and fixed sized sprites. However, for characters with variable height size sprites like this: http://gamemedia.wcgame.ru/data/2011-07-17/game-sprite-sheet.jpg This is no longer good. The character won't align to the ground if I'll draw it from the center. I can just make the sprites the same height, but it will be a waste of memory (the largest sprite is 4 times larger then the smallest one). Even then, this is not an option at all with skeletal sprites like this one: http://user-generated-content.java-gaming.org/img-vault/212a171fc1ebb27ab77608fb9b2dd9bd9205361ce6300b21a7f8d06d025fbbd8.png It seems that the graphics need to be drawn from the ground for characters, but not for other images such as scenery and obstacles. The only solution I could think of was having another position called draw-position, which is the entity center for images, and is the the bottom of the collision volume for characters. Then when I draw relative to that position, it should work properly. I haven't found any references for something like that, so I'm kinda insecure about it. Does anyone knows of a better approach for this problem? Thanks

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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 change LOD in geometry?

  - by ChaosDev

  Im looking for simple algorithm of LOD, for change geometry vertexes and decrease frame time. Im created octree, but now I want model or terrain vertex modify algorithm,not for increase(looking on tessellation later) but for decrease. I want something like this Questions: Is same algorithm can apply either to model and terrain correctly? Indexes need to be modified ? I must use octree or simple check distance between camera and object for desired effect ? New value of indexcount for DrawIndexed function needed ? Code: //m_LOD == 10 in the beginning //m_RawVerts - array of 3d Vector filled with values from vertex buffer. void DecreaseLOD() { m_LOD--; if(m_LOD<1)m_LOD=1; RebuildGeometry(); } void IncreaseLOD() { m_LOD++; if(m_LOD>10)m_LOD=10; RebuildGeometry(); } void RebuildGeometry() { void* vertexRawData = new byte[m_VertexBufferSize]; void* indexRawData = new DWORD[m_IndexCount]; auto context = mp_D3D->mp_Context; D3D11_MAPPED_SUBRESOURCE data; ZeroMemory(&data,sizeof(D3D11_MAPPED_SUBRESOURCE)); context->Map(mp_VertexBuffer->mp_buffer,0,D3D11_MAP_READ,0,&data); memcpy(vertexRawData,data.pData,m_VertexBufferSize); context->Unmap(mp_VertexBuffer->mp_buffer,0); context->Map(mp_IndexBuffer->mp_buffer,0,D3D11_MAP_READ,0,&data); memcpy(indexRawData,data.pData,m_IndexBufferSize); context->Unmap(mp_IndexBuffer->mp_buffer,0); DWORD* dwI = (DWORD*)indexRawData; int sz = (m_VertexStride/sizeof(float));//size of vertex element //algorithm must be here. std::vector<Vector3d> vertices; int i = 0; for(int j = 0; j < m_VertexCount; j++) { float x1 = (((float*)vertexRawData)[0+i]); float y1 = (((float*)vertexRawData)[1+i]); float z1 = (((float*)vertexRawData)[2+i]); Vector3d lv = Vector3d(x1,y1,z1); //my useless attempts if(j+m_LOD+1<m_RawVerts.size()) { float v1 = VECTORHELPER::Distance(m_RawVerts[dwI[j]],m_RawVerts[dwI[j+m_LOD]]); float v2 = VECTORHELPER::Distance(m_RawVerts[dwI[j]],m_RawVerts[dwI[j+m_LOD+1]]); if(v1>v2) lv = m_RawVerts[dwI[j+1]]; else if(v2<v1) lv = m_RawVerts[dwI[j+2]]; } (((float*)vertexRawData)[0+i]) = lv.x; (((float*)vertexRawData)[1+i]) = lv.y; (((float*)vertexRawData)[2+i]) = lv.z; i+=sz;//pass others vertex format values without change } for(int j = 0; j < m_IndexCount; j++) { //indices ? } //set vertexes to device UpdateVertexes(vertexRawData,mp_VertexBuffer->getSize()); delete[] vertexRawData; delete[] indexRawData; }

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• Zooming in isometric engine using XNA

  - by Yheeky

  I´m currently working on an isometric game engine and right now I´m looking for help concerning my zoom function. On my tilemap there are several objects, some of them are selectable. When a house (texture size 128 x 256) is placed on the map I create an array containing all pixels (= 32768 pixels). Therefore each pixel has an alpha value I check if the value is bigger than 200 so it seems to be a pixel which belongs to the building. So if the mouse cursor is on this pixel the building will be selected - PixelCollision. Now I´ve already implemented my zooming function which works quite well. I use a scale variable which will change my calculation on drawing all map items. What I´m looking for right now is a precise way to find out if a zoomed out/in house is selected. My formula works for values like 0,5 (zoomed out) or 2 (zoomed in) but not for in between. Here is the code I use for the pixel index: var pixelIndex = (int)(((yPos / (Scale * Scale)) * width) + (xPos / Scale) + 1); Example: Let´s assume my mouse is over pixel coordinate 38/222 on the original house texture. Using the code above we get the following pixel index. var pixelIndex = ((222 / (1 * 1)) * 128) + (38 / 1) + 1; = (222 * 128) + 39 = 28416 + 39 = 28455 If we now zoom out to scale 0,5, the texture size will change to 64 x 128 and the amount of pixels will decrease from 32768 to 8192. Of course also our mouse point changes by the scale to 19/111. The formula makes it easy to calculate the original pixelIndex using our new coordinates: var pixelIndex = ((111 / (0.5 * 0.5)) * 64) + (19 / 0.5) + 1; = (444 * 64) + 39 = 28416 + 39 = 28455 But now comes the problem. If I zoom out just to scale 0.75 it does not work any more. The pixel amount changes from 32768 to 18432 pixels since texture size is 96 x 192. Mouse point is transformed to point 28/166. The formula gives me a wrong pixelIndex. var pixelIndex = ((166 / (0.75 * 0.75)) * 96) + (28 / 0.75) + 1; = (295.11 * 96) + 38.33 = 28330.66 + 38.33 = 28369 Does anyone have a clue what´s wrong in my code? Must be the first part (28330.66) which causes the calculation problem. Thanks! Yheeky

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• Blending transition in cocos2d

  - by fiddler

  In my cocos2d-iphone game, I have 2 backgrounds (CCnodes), each containing a quite complex hierarchy of sprites. I would like to make a smooth transition between them: initially, only the first background is visible at the end, only the second one is visible Is there a good way to set the opacity of a full hierarchy of sprites ? I tried to recursively set the opacity of all the contained sprites. It kinda works except that: i guess it's not very efficient i would like the opacity of overlapping sprites to be 'merged' (as if the background was one single big sprite)

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• How would you code an AI engine to allow communication in any programming language?

  - by Tokyo Dan

  I developed a two-player iPhone board game. Computer players (AI) can either be local (in the game code) or remote running on a server. In the 2nd case, both client and server code are coded in Lua. On the server the actual AI code is separate from the TCP socket code and coroutine code (which spawns a separate instance of AI for each connecting client). I want to be able to further isolate the AI code so that that part can be a module coded by anyone in their language of choice. How can I do this? What tecniques/technology would enable communication between the Lua TCP socket/coroutine code and the AI module?

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• SFML 2.0 Too Many Variables in Class Preventing Draw To Screen

  - by Josh

  This is a very strange phenomenon to me. I have a class definition for a game, but when I add another variable to the class, the draw method does not print everything to the screen. It will be easier understood showing the code and output. Code for good draw output: class board { protected: RectangleShape rect; int top, left; int i, j; int rowSelect, columnSelect; CircleShape circleArr[4][10]; CircleShape codeArr[4]; CircleShape keyArr[4][10]; //int pegPresent[4]; public: board(void); void draw(RenderWindow& Window); int mouseOver(RenderWindow& Window); void placePeg(RenderWindow& Window, int pegSelect); }; Screen: Code for missing draw: class board { protected: RectangleShape rect; int top, left; int i, j; int rowSelect, columnSelect; CircleShape circleArr[4][10]; CircleShape codeArr[4]; CircleShape keyArr[4][10]; int pegPresent[4]; public: board(void); void draw(RenderWindow& Window); int mouseOver(RenderWindow& Window); void placePeg(RenderWindow& Window, int pegSelect); }; Screen: As you can see, all I do is un-comment the protected array and most of the pegs are gone from the right hand side. I have checked and made sure that I didn't accidentally created a variable with that name already. I haven't used it anywhere. Why does it not draw the remaining pegs as it should? My only thought is that maybe I am declaring too many variables for the class, but that doesn't really make sense to me. Any thoughts and help is greatly appreciated.

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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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• How to do a multishot in xna?

  - by DeVonte

  I am trying to simulate a gun in which shoots multiple bullets at the same time(similar to a spread out shot). I am thinking I have to create another bullet array then do the same as I have below but in a different direction. Here is what I have so far: foreach (GameObject bullet in bullets) { // Find a bullet that isn't alive if (!bullet.alive) { //And set it to alive bullet.alive = true; if (flip == SpriteEffects.FlipHorizontally) //Facing right { float armCos = (float)Math.Cos(arm.rotation - MathHelper.PiOver2); float armSin = (float)Math.Sin(arm.rotation - MathHelper.PiOver2); // Set the initial position of our bullets at the end of our gun arm // 42 is obtained by taking the width of the Arm_Gun texture / 2 // and subtracting the width of the Bullet texture / 2. ((96/2)=(12/2)) bullet.position = new Vector2( arm.position.X + 42 * armCos, arm.position.Y + 42 * armSin); // And give it a velocity of the direction we're aiming. // Increae/decrease speed by changeing 15.0f bullet.Velocity = new Vector2( (float)Math.Cos(arm.rotation - MathHelper.PiOver4 + MathHelper.Pi + MathHelper.PiOver2), (float)Math.Sin(arm.rotation - MathHelper.PiOver4 + MathHelper.Pi + MathHelper.PiOver2)) * 15.0f; } else //Facing left { float armCos = (float)Math.Cos(arm.rotation + MathHelper.PiOver2); float armSin = (float)Math.Sin(arm.rotation + MathHelper.PiOver2); //Set the initial position of our bullet at the end of our gun arm //42 is obtained be taking the width of the Arm_Gun texture / 2 //and subtracting the width of the Bullet texture / 2. ((96/2)-(12/2)) bullet.position = new Vector2( arm.position.X - 42 * armCos, arm.position.Y - 42 * armSin); //And give it a velocity of the direction we're aiming. //Increase/decrease speed by changing 15.0f bullet.Velocity = new Vector2( -armCos, -armSin) * 15.0f; } return; }// End if }// End foreach

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• Parenting Opengl with Groups in LibGDX

  - by Rudy_TM

  I am trying to make an object child of a Group, but this object has a draw method that calls opengl to draw in the screen. Its class its this public class OpenGLSquare extends Actor { private static final ImmediateModeRenderer renderer = new ImmediateModeRenderer10(); private static Matrix4 matrix = null; private static Vector2 temp = new Vector2(); public static void setMatrix4(Matrix4 mat) { matrix = mat; } @Override public void draw(SpriteBatch batch, float arg1) { // TODO Auto-generated method stub renderer.begin(matrix, GL10.GL_TRIANGLES); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x0, y0, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x0, y1, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x1, y1, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x1, y1, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x1, y0, 0f); renderer.color(color.r, color.g, color.b, color.a); renderer.vertex(x0, y0, 0f); renderer.end(); } } In my screen class I have this, i call it in the constructor MyGroupClass spriteLab = new MyGroupClass(spriteSheetLab); OpenGLSquare square = new OpenGLSquare(); square.setX0(100); square.setY0(200); square.setX1(400); square.setY1(280); square.color.set(Color.BLUE); square.setSize(); //spriteLab.addActorAt(0, clock); spriteLab.addActor(square); stage.addActor(spriteLab); And the render in the screen I have @Override public void render(float arg0) { this.gl.glClear(GL10.GL_COLOR_BUFFER_BIT |GL10.GL_DEPTH_BUFFER_BIT); stage.draw(); stage.act(Gdx.graphics.getDeltaTime()); } The problem its that when i use opengl with parent, it resets all the other chldren to position 0,0 and the opengl renderer paints the square in the exact position of the screen and not relative to the parent. I tried using batch.enableBlending() and batch.disableBlending() that fixes the position problem of the other children, but not the relative position of the opengl drawing and it also puts alpha to the glDrawing. What am i doing wrong?:/

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• What should I worry about when changing OpenGL origin to upper left of screen?

  - by derivative

  For self education, I'm writing a 2D platformer engine in C++ using SDL / OpenGL. I initially began with pure SDL using the tutorials on sdltutorials.com and lazyfoo.net, but I'm now rendering in an OpenGL context (specifically immediate mode but I'm learning about VAOs/VBOs) and using SDL for interface, audio, etc. SDL uses a coordinate system with the origin in the upper left of the screen and the positive y-axis pointing down. It's easy to set up my orthographic projection in OpenGL to mirror this. I know that texture coordinates are a right-hand system with values from 0 to 1 -- flipping the texture vertically before rendering (well, flip the file before loading) yields textures that render correctly... which is fine if I'm drawing the entire texture, but ultimately I'll be using tilesets and can imagine problems. What should I be concerned about in terms of rendering when I do this? If anybody has any advice or they've done this themselves and can point out future pitfalls, that would be great, but really any thoughts would be appreciated.

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• Bullet Physics - Casting a ray straight down from a rigid body (first person camera)

  - by Hydrocity

  I've implemented a first person camera using Bullet--it's a rigid body with a capsule shape. I've only been using Bullet for a few days and physics engines are new to me. I use btRigidBody::setLinearVelocity() to move it and it collides perfectly with the world. The only problem is the Y-value moves freely, which I temporarily solved by setting the Y-value of the translation vector to zero before the body is moved. This works for all cases except when falling from a height. When the body drops off a tall object, you can still glide around since the translate vector's Y-value is being set to zero, until you stop moving and fall to the ground (the velocity is only set when moving). So to solve this I would like to try casting a ray down from the body to determine the Y-value of the world, and checking the difference between that value and the Y-value of the camera body, and disable or slow down movement if the difference is large enough. I'm a bit stuck on simply casting a ray and determining the Y-value of the world where it struck. I've implemented this callback: struct AllRayResultCallback : public btCollisionWorld::RayResultCallback{ AllRayResultCallback(const btVector3& rayFromWorld, const btVector3& rayToWorld) : m_rayFromWorld(rayFromWorld), m_rayToWorld(rayToWorld), m_closestHitFraction(1.0){} btVector3 m_rayFromWorld; btVector3 m_rayToWorld; btVector3 m_hitNormalWorld; btVector3 m_hitPointWorld; float m_closestHitFraction; virtual btScalar addSingleResult(btCollisionWorld::LocalRayResult& rayResult, bool normalInWorldSpace) { if(rayResult.m_hitFraction < m_closestHitFraction) m_closestHitFraction = rayResult.m_hitFraction; m_collisionObject = rayResult.m_collisionObject; if(normalInWorldSpace){ m_hitNormalWorld = rayResult.m_hitNormalLocal; } else{ m_hitNormalWorld = m_collisionObject->getWorldTransform().getBasis() * rayResult.m_hitNormalLocal; } m_hitPointWorld.setInterpolate3(m_rayFromWorld, m_rayToWorld, m_closestHitFraction); return 1.0f; } }; And in the movement function, I have this code: btVector3 from(pos.x, pos.y + 1000, pos.z); // pos is the camera's rigid body position btVector3 to(pos.x, 0, pos.z); // not sure if 0 is correct for Y AllRayResultCallback callback(from, to); Base::getSingletonPtr()->m_btWorld->rayTest(from, to, callback); So I have the callback.m_hitPointWorld vector, which seems to just show the position of the camera each frame. I've searched Google for examples of casting rays, as well as the Bullet documentation, and it's been hard to just find an example. An example is really all I need. Or perhaps there is some method in Bullet to keep the rigid body on the ground? I'm using Ogre3D as a rendering engine, and casting a ray down is quite straightforward with that, however I want to keep all the ray casting within Bullet for simplicity. Could anyone point me in the right direction? Thanks.

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• Detecting walls or floors in pygame

  - by Serial

  I am trying to make bullets bounce of walls, but I can't figure out how to correctly do the collision detection. What I am currently doing is iterating through all the solid blocks and if the bullet hits the bottom, top or sides, its vector is adjusted accordingly. However, sometimes when I shoot, the bullet doesn't bounce, I think it's when I shoot at a border between two blocks. Here is the update method for my Bullet class: def update(self, dt): if self.can_bounce: #if the bullet hasnt bounced find its vector using the mousclick pos and player pos speed = -10. range = 200 distance = [self.mouse_x - self.player[0], self.mouse_y - self.player[1]] norm = math.sqrt(distance[0] ** 2 + distance[1] ** 2) direction = [distance[0] / norm, distance[1 ] / norm] bullet_vector = [direction[0] * speed, direction[1] * speed] self.dx = bullet_vector[0] self.dy = bullet_vector[1] #check each block for collision for block in self.game.solid_blocks: last = self.rect.copy() if self.rect.colliderect(block): topcheck = self.rect.top < block.rect.bottom and self.rect.top > block.rect.top bottomcheck = self.rect.bottom > block.rect.top and self.rect.bottom < block.rect.bottom rightcheck = self.rect.right > block.rect.left and self.rect.right < block.rect.right leftcheck = self.rect.left < block.rect.right and self.rect.left > block.rect.left each test tests if it hit the top bottom left or right side of the block its colliding with if self.can_bounce: if topcheck: self.rect = last self.dy *= -1 self.can_bounce = False print "top" if bottomcheck: self.rect = last self.dy *= -1 #Bottom check self.can_bounce = False print "bottom" if rightcheck: self.rect = last self.dx *= -1 #right check self.can_bounce = False print "right" if leftcheck: self.rect = last self.dx *= -1 #left check self.can_bounce = False print "left" else: # if it has already bounced and colliding again kill it self.kill() for enemy in self.game.enemies_list: if self.rect.colliderect(enemy): self.kill() #update position self.rect.x -= self.dx self.rect.y -= self.dy This definitely isn't the best way to do it but I can't think of another way. If anyone has done this or can help that would be awesome!

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• Projectiles in tile mapped turn-based tactics game?

  - by Petteri Hietavirta

  I am planning to make a Laser Squad clone and I think I have most of the aspects covered. But the major headache is the projectiles shot/thrown. The easy way would be to figure out the probability of hit and just mark miss/hit. But I want to be able to have the projectile to hit something eventually (collateral damage!). Currently everything is flat 2D tile map and there would be full (wall, door) and half height (desk, chair, window) obstacles. My idea is to draw an imaginary line from the shooter to the target and add some horizontal&vertical error based on the player skills. Then I would trace the modified path until it hits something. This is basically what the original Laser Squad seems to do. Can you recommend any algorithms or other approaches for this?

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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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• (Abstract) Game engine design

  - by lukeluke

  I am writing a simple 2D game (for mobile platforms) for the first time. From an abstract point of view, i have the main player controlled by the human, the enemies, elments that will interact with the main player, other living elements that will be controlled by a simple AI (both enemies and non-enemies). The human player will be totally controlled by the player, the other actors will be controlled by AI. So i have a class CActor and a class CActorLogic to start with. I would define a CActor subclass CHero (the main player controlled with some input device). This class will probably implement some type of listener, in order to capture input events. The other players controlled by the AI will be probably a specific subclass of CActor (a subclass per-type, obviously). This seems to be reasonable. The CActor class should have a reference to a method of CActorLogic, that we will call something like CActorLogic::Advance() or similar. Actors should have a visual representation. I would introduce a CActorRepresentation class, with a method like Render() that will draw the actor (that is, the right frame of the right animation). Where to change the animation? Well, the actor logic method Advance() should take care of checking collisions and other things. I would like to discuss the design of a game engine (actors, entities, objects, messages, input handling, visualization of object states (that is, rendering, sound output and so on)) but not from a low level point of view, but from an high level point of view, like i have described above. My question is: is there any book/on line resource that will help me organize things (using an object oriented approach)? Thanks

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• How to send multiple MVP matrices to a vertex shader in OpenGL ES 2.0

  - by Carbon Crystal

  I'm working my way through optimizing the rendering of sprites in a 2D game using OpenGL ES and I've hit the limit of my knowledge when it comes to GLSL and vertex shaders. I have two large float buffers containing my vertex coordinates and texture coordinates (eventually this will be one buffer) for multiple sprites in order to perform a single glDrawArrays call. This works but I've hit a snag when it comes to passing the transformation matrix into the vertex shader. My shader code is: uniform mat4 u_MVPMatrix; attribute vec4 a_Position; attribute vec2 a_TexCoordinate; varying vec2 v_TexCoordinate; void main() { v_TexCoordinate = a_TexCoordinate; gl_Position = u_MVPMatrix * a_Position; } In Java (Android) I am using a FloatBuffer to store the vertex/texture data and this is provided to the shader like so: mGlEs20.glVertexAttribPointer(mVertexHandle, Globals.GL_POSITION_VERTEX_COUNT, GLES20.GL_FLOAT, false, 0, mVertexCoordinates); mGlEs20.glVertexAttribPointer(mTextureCoordinateHandle, Globals.GL_TEXTURE_VERTEX_COUNT, GLES20.GL_FLOAT, false, 0, mTextureCoordinates); (The Globals.GL_POSITION_VERTEX_COUNT etc are just integers with the value of 2 right now) And I'm passing the MVP (Model/View/Projection) matrix buffer like this: GLES20.glUniformMatrix4fv(mMVPMatrixHandle, 1, false, mModelCoordinates); (mModelCoordinates is a FloatBuffer containing 16-float sequences representing the MVP matrix for each sprite) This renders my scene but all the sprites share the same transformation, so it's obviously only picking the first 16 elements from the buffer which makes sense since I am passing in "1" as the second parameter. The documentation for this method says: "This should be 1 if the targeted uniform variable is not an array of matrices, and 1 or more if it is an array of matrices." So I tried modifying the shader with a fixed size array large enough to accomodate most of my scenarios: uniform mat4 u_MVPMatrix[1000]; But this lead to an error in the shader: cannot convert from 'uniform array of 4X4 matrix of float' to 'Position 4-component vector of float' This just seems wrong anyway as it's not clear to me how the shader would know when to transition to the next matrix anyway. Anyone have an idea how I can get my shader to pick up a different MVP matrix (i.e. the NEXT 16 floats) from my MVP buffer for every 4 vertices it encounters? (I am using GL_TRIANGLE_STRIP so each sprite has 4 vertices). Thanks!

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• 2-d lighting day/night cycle

  - by Richard

  Off the back of this post in which I asked two questions and received one answer, which I accepted as a valid answer. I have decided to re-ask the outstanding question. I have implemented light points with shadow casting as shown here but I would like an overall map light with no point/light source. The map setup is a top-down 2-d 50X50 pixel grid. How would I go about implementing a day/night cycle lighting across a map?

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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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• 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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• Reacting to rectangle on rectangle collisions

  - by mcjohnalds45

  I don't know how to react to collisions between two axis aligned rectangles that have x, y, width and height values (x and y are from the centre of the box) to make them simply not overlap. I figured I'd just make them move away from each other depending on how far they intersect in the opposite direction (left, right, up or down) of where they collided. If I check for collisions only on the x axis or only on the y axis it works fine, but when checking for both collisions crazy stuff happens. This code executes when the first box collides with the second. It's in lua but feel free to answer in anything that isn't to too counter-intuitive. if box1.x < box2.x then box1.x = box1.x + box2.x - box1.x - (box1.width / 2) - (box2.width / 2) end if box1.x > box2.x then box1.x = box1.x - (box1.x - box2.x - (box1.width / 2) - (box2.width / 2)) end if box1.y < box2.y then box1.y = box1.y + box2.y - box1.y - (box1.height / 2) - (box2.height / 2) end if box1.y > box2.y then box1.y = box1.y - (box1.y - box2.y - (box1.height / 2) - (box2.height / 2)) end

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• Why do I get an exception when playing multiple sound instances?

  - by Boreal

  Right now, I'm adding a rudimentary sound engine to my game. So far, I am able to load in a WAV file and play it once, then free up the memory when I close the game. However, the game crashes with a nice ArgumentOutOfBoundsException when I try to play another sound instance. Specified argument was out of the range of valid values. Parameter name: readLength I'm following this tutorial pretty much exactly, but I still keep getting the aforementioned error. Here's my sound-related code. /// <summary> /// Manages all sound instances. /// </summary> public static class Audio { static XAudio2 device; static MasteringVoice master; static List<SoundInstance> instances; /// <summary> /// The XAudio2 device. /// </summary> internal static XAudio2 Device { get { return device; } } /// <summary> /// Initializes the audio device and master track. /// </summary> internal static void Initialize() { device = new XAudio2(); master = new MasteringVoice(device); instances = new List<SoundInstance>(); } /// <summary> /// Releases all XA2 resources. /// </summary> internal static void Shutdown() { foreach(SoundInstance i in instances) i.Dispose(); master.Dispose(); device.Dispose(); } /// <summary> /// Registers a sound instance with the system. /// </summary> /// <param name="instance">Sound instance</param> internal static void AddInstance(SoundInstance instance) { instances.Add(instance); } /// <summary> /// Disposes any sound instance that has stopped playing. /// </summary> internal static void Update() { List<SoundInstance> temp = new List<SoundInstance>(instances); foreach(SoundInstance i in temp) if(!i.Playing) { i.Dispose(); instances.Remove(i); } } } /// <summary> /// Loads sounds from various files. /// </summary> internal class SoundLoader { /// <summary> /// Loads a .wav sound file. /// </summary> /// <param name="format">The decoded format will be sent here</param> /// <param name="buffer">The data will be sent here</param> /// <param name="soundName">The path to the WAV file</param> internal static void LoadWAV(out WaveFormat format, out AudioBuffer buffer, string soundName) { WaveStream wave = new WaveStream(soundName); format = wave.Format; buffer = new AudioBuffer(); buffer.AudioData = wave; buffer.AudioBytes = (int)wave.Length; buffer.Flags = BufferFlags.EndOfStream; } } /// <summary> /// Manages the data for a single sound. /// </summary> public class Sound : IAsset { WaveFormat format; AudioBuffer buffer; /// <summary> /// Loads a sound from a file. /// </summary> /// <param name="soundName">The path to the sound file</param> /// <returns>Whether the sound loaded successfully</returns> public bool Load(string soundName) { if(soundName.EndsWith(".wav")) SoundLoader.LoadWAV(out format, out buffer, soundName); else return false; return true; } /// <summary> /// Plays the sound. /// </summary> public void Play() { Audio.AddInstance(new SoundInstance(format, buffer)); } /// <summary> /// Unloads the sound from memory. /// </summary> public void Unload() { buffer.Dispose(); } } /// <summary> /// Manages a single sound instance. /// </summary> public class SoundInstance { SourceVoice source; bool playing; /// <summary> /// Whether the sound is currently playing. /// </summary> public bool Playing { get { return playing; } } /// <summary> /// Starts a new instance of a sound. /// </summary> /// <param name="format">Format of the sound</param> /// <param name="buffer">Buffer holding sound data</param> internal SoundInstance(WaveFormat format, AudioBuffer buffer) { source = new SourceVoice(Audio.Device, format); source.BufferEnd += (s, e) => playing = false; source.Start(); source.SubmitSourceBuffer(buffer); // THIS IS WHERE THE EXCEPTION IS THROWN playing = true; } /// <summary> /// Releases memory used by the instance. /// </summary> internal void Dispose() { source.Dispose(); } } The exception occurs on line 156 when I am playing the sound: source.SubmitSourceBuffer(buffer);

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• How do I prevent my platformer's character from clipping on wall tiles?

  - by Jonathan Hobbs

  Currently, I have a platformer with tiles for terrain (graphics borrowed from Cave Story). The game is written from scratch using XNA, so I'm not using an existing engine or physics engine. The tile collisions are described pretty much exactly as described in this answer (with simple SAT for rectangles and circles), and everything works fine. Except when the player runs into a wall whilst falling/jumping. In that case, they'll catch on a tile and begin thinking they've hit a floor or ceiling that isn't actually there. The player is moving right and falling downwards. So after movement, collisions are checked - and first, it turns out the player character is colliding with the tile 3rd from the floor, and pushed upwards. Second, he's found to be colliding with the tile beside him, and pushed sideways - the end result being the player character thinks he's on the ground and isn't falling, and 'catches' on the tile for as long as he's running into it. I could solve this by defining the tiles from top to bottom instead, which makes him fall smoothly, but then the inverse case happens and he'll hit a ceiling that isn't there when jumping upwards against the wall. How should I approach resolving this, so that the player character can just fall along the wall as it should?

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• How can I mark a pixel in the stencil buffer?

  - by János Turánszki

  I never used the stencil buffer for anything until now, but I want to change this. I have an idea of how it should work: the gpu discards or keeps rasterized pixels before the pixel shader based on the stencil buffer value on the given position and some stencil operation. What I don't know is how would I mark a pixel in the stencil buffer with a specific value. For example I draw my scene and want to mark everything which is drawn with a specific material (this material could be looked up from a texture so ideally I should mark the pixel in the pixel shader), so that later when I do some post processing on my scene I would only do it on the marked pixels. I didn't find anything on the internet besides how to set up a stencil buffer and explaining the different stencil operations. I was expecting to find some System-Value semantics like SV_Depth to write to in the pixel shader (because the stencil buffer shares the same resource with the depth buffer in D3D11), but there is no such thing on MSDN. So how should I do this? If I am misunderstanding something please help me clear that up.

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• How do I create a camera?

  - by Morphex

  I am trying to create a generic camera class for a game engine, which works for different types of cameras (Orbital, GDoF, FPS), but I have no idea how to go about it. I have read about quaternions and matrices, but I do not understand how to implement it. Particularly, it seems you need "Up", "Forward" and "Right" vectors, a Quaternion for rotations, and View and Projection matrices. For example, an FPS camera only rotates around the World Y and the Right Axis of the camera; the 6DoF rotates always around its own axis, and the orbital is just translating for a set distance and making it look always at a fixed target point. The concepts are there; implementing this is not trivial for me. SharpDX seems to have has already Matrices and Quaternions implemented, but I don't know how to use them to create a camera. Can anyone point me on what am I missing, what I got wrong? I would really enjoy if you could give a tutorial, some piece of code, or just plain explanation of the concepts.

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