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• Collisions between moving ball and polygons

  - by miguelSantirso

  I know this is a very typical problem and that there area a lot of similar questions, but I have been looking for a while and I have not found anything that fits what I want. I am developing a 2D game in which I need to perform collisions between a ball and simple polygons. The polygons are defined as an array of vertices. I have implemented the collisions with the bounding boxes of the polygons (that was easy) and I need to refine that collision in the cases where the ball collides with the bounding box. The ball can move quite fast and the polygons are not too big so I need to perform continuous collisions. I am looking for a method that allows me to detect if the ball collides with a polygon and, at the same time, calculate the new direction for the ball after bouncing in the polygon. (I am using XNA, in case that helps)

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• How can I simulate objects floating on water without a physics engine?

  - by user1075940

  In my game the water movement is done in a shader using Gerstner equations. The water movement looks realistic enough for a school project but I encounter serious problem when I wanted to do sailing on waves (similar to this). I managed to do collision with land by calculating quad's vertices and normals beneath ship, however same method can not be applied to water because XZ are displaced and Y is calculated in a shader :( How to approach this problem ? Is it possible to retrieve transformed grid from shader? Unfortunately no external physics libraries can be used.

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• What is the best type of c# timer to use with an Unity game that uses many timers simultaneously?

  - by Kyle Seidlitz

  I am developing a stand-alone 3d game in Unity that will have anywhere from 1 to 200 timers running simultaneously. For this game timer durations will range from 5 minutes to 4 days. There will not be any countdown displays or any UI for the timers. An object will be selected, a menu choice will then be selected, and the timer will start. Several events will occur at different intervals during the duration of the timer. The events will be confined to changing the material of the selected object, and calling a 1 second sound effect like a chime or a bell. If the user wants to save or end the game before all the timers are done, the start of the still running timers is to be saved to an XML file such that when the game is started again, any still running timers will have a calculation done to see if the timer is then done, where the game will change the materials appropriately. I am still trying to figure out what type of timer to use, and see also if there are any suggestions for saving and calculating times over several days. What class(es) of timers should I use? Are there any special issues I should look out for in terms of performance?

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• 2d shapes in XNA 4.0?

  - by Lautaro

  Having some experience of XNA but none of 3D programming. I have an idea i want to realize but i have not decided to do it in 3d or 2d. Im not sure which one will be best in XNA. I want to have a shape like a blob that can reshape depending on input. The morphing does not need to be very advanced. It could be a circle (2d) or globe (3d) that just has one point that moves slightly in a random direction. In ASP.NET i have made this through the 2d Draw classes where i can make lines, circles, squares etc and then modify the points that makes them up. But it seems to me that XNA does not have classes for making 2d shapes (can i get this confirmed?). If it had, then this would be the quickest solution for me.

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• Multi Pass Blend

  - by Kirk Patrick

  I am seeking the simplest working example of a two pass HLSL pixel shader. It can do anything really, but the main idea is to perform "ping ponging" to take the output of the first pass and then send it for the second pass. In my example I want to draw to the R channel and then draw to the G channel and produce a simple Venn Diagram in the shader, but need to detect overlap. I can currently detect one or the other but not overlap. There are a red and green circle overlapping, and I want to put a dynamic texture map in the overlap region. I can currently put it in either or. Below is how it looks in the shader. -------------------------------- Texture2D shaderTexture; SamplerState SampleType; ////////////// // TYPEDEFS // ////////////// struct PixelInputType { float4 position : SV_POSITION; float2 tex0 : TEXCOORD0; float2 tex1 : TEXCOORD1; float4 color : COLOR; }; //////////////////////////////////////////////////////////////////////////////// // Pixel Shader //////////////////////////////////////////////////////////////////////////////// float4 main(PixelInputType input) : SV_TARGET { float4 textureColor0; float4 textureColor1; // Sample the pixel color from the texture using the sampler at this texture coordinate location. textureColor0 = shaderTexture.Sample(SampleType, input.tex0); textureColor1 = shaderTexture.Sample(SampleType, input.tex1); if (input.color[0]==1.0f && input.color[1]==1.0f) // Requires multi-pass textureColor0 = textureColor1; return textureColor0; } Here is the calling code (that needs to be modified) m_d3dContext->IASetVertexBuffers(0, 2, vbs, strides, offsets); m_d3dContext->IASetIndexBuffer(m_indexBuffer.Get(), DXGI_FORMAT_R32_UINT,0); m_d3dContext->IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST); m_d3dContext->IASetInputLayout(m_inputLayout.Get()); m_d3dContext->VSSetShader(m_vertexShader.Get(), nullptr, 0); m_d3dContext->VSSetConstantBuffers(0, 1, m_constantBuffer.GetAddressOf()); m_d3dContext->PSSetShader(m_pixelShader.Get(), nullptr, 0); m_d3dContext->PSSetShaderResources(0, 1, m_SRV.GetAddressOf()); m_d3dContext->PSSetSamplers(0, 1, m_QuadsTexSamplerState.GetAddressOf());

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• Rendering different materials in a voxel terrain

  - by MaelmDev

  Each voxel datapoint in my terrain model is made up of two properties: density and material type. Each is stored as an unsigned integer value (but the density is interpreted as a decimal value between 0 and 1). My current idea for rendering these different materials on the terrain mesh is to store eleven extra attributes in each vertex: six material values corresponding to the materials of the voxels that the vertices lie between, three decimal values that correspond to the interpolation each vertex has between each voxel, and two decimal values that are used to determine where the fragment lies on the triangle. The material and interpolation attributes are the exact same for each vertex in the triangle. The fragment shader samples each texture that corresponds to each material and then uses the aforementioned couple of decimal values to interpolate between these samples and obtain the final textured color of the fragment. It should work fine, but it seems like a big memory hog. I won't be able to reuse vertices in the mesh with indexing, and each vertex will have a lot of data associated with it. It also seems pretty slow. What are some ways to improve or replace this technique for drawing materials on a voxel terrain mesh?

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• Implmenting RLE into a tilemap or how to create a large 3D array?

  - by Smallbro

  Currently I've been using a 3D array for my tiles in a 2D world but the 3D side comes in when moving down into caves and whatnot. Now this is not memory efficient and I switched over to a 2D array and can now have much larger maps. The only issue I'm having now is that it seems that my tiles cannot occupy the same space as a tile on the same z level. My current structure means that each block has its own z variable. This is what it used to look like: map.blockData[x][y][z] = new Block(); however now it works like this map.blockData[x][y] = new Block(z); I'm not sure why but if I decide to use the same space on say the floor below it wont allow me to. Does anyone have any ideas on how I can add a z-axis to my 2D array? I'm using java but I reckon the concept carries across different languages. Edit: As Will posted, RLE sounds like the best method for achieving a fast 3D array. However I'm struggling to understand how I would even start to implement it? Would I create a 4D array the 4th being something which controls how many to skip? Or would the x-axis simply change altogether and have large gaps in between - for example [5][y][z] would skip 5 tiles? Is there something really obvious here which I am missing? The number of z levels I'm trying to have is around 66, it would be preferably that I can have up to or more than 1000 in x and y.

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• Collision Resolution

  - by CiscoIPPhone

  I know quite well how to check for collisions, but I don't know how to handle the collision in a good way. Simplified, if two objects collide I use some calculations to change the velocity direction. If I don't move the two objects they will still overlap and if the velocity is not big enough they will still collide after next update. This can cause objects to get stuck in each other. But what if I try to move the two objects so they do not overlap. This sounds like a good idea but I have realised that if there is more than two objects this becomes very complicated. What if I move the two objects and one of them collides with other objects so I have to move them too and they may collide with walls etc. I have a top down 2D game in mind but I don't think that has much to do with it. How are collisions usually handled? This question is asked on behalf of Wooh

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• how to do partial updates in OpenGL?

  - by Will

  It is general wisdom that you redraw the entire viewport on each frame. I would like to use partial updates; what are the various ways can do that, and what are their pros, cons and relative performance? (Using textures, FBOs, the accumulator buffer, any kind of scissors that can affect swapbuffers etc?) A scenario: a scene with a fair few thousand visible trees; although the textures are mipmapped and they are drawn via VBOs roughly front-to-back with so on, its still a lot of polys. Would streaming a single screen-sized texture be better than throwing them at the screen every frame? You'd have to redraw and recapture them only on camera movement or as often as your wind model updates or whatever, which need not be every frame.

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• Are there any preexisting maps for a Minecraft-like level I could use in my engine?

  - by Rishav Sharan

  I am working on a tiny cube-based engine like Minecraft. I was wondering if there is a way for me to get large blocky terrain in a text format that I can use for rendering on my engine? I don't want to start on procedural generation now, I just want a resource where I can get the coord list for a pretty looking terrain. Alternatively, is it possible for me to parse the Minecraft world files and use that data to generate terrain/buildings in my code?

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• Split vector vs matrix notation for transformation

  - by seahorse

  Some rendering engines like Ogre prefer to use a individual vector based notation for transformations like the following Split vector notation: Net Transformation is represented by Scale vector = sx, sy, sz Transformation vector = tx, ty, tz Rotation Quaternion Vector = w,x,y,z Matrix notation: There are other engines which simply use a net combined transformation matrix. What are the advantages of the first notation over the second? Also for animation interpolation does it work in the first notation that we interpolate across the individual components and use the interpolated parts to get the net transformation? Is this another advantage?

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• Texturize a shape of multiple triangles in 2D

  - by Deukalion

  This is an example of a shape consisting of multiple points, triangles and eventually a shape: Red Dots = Vector3 (X, Y, Z) or Vector2 (X, Y) If I have a Texture of a certain size, how do I texturize this area in the best way so that the texture inside the shape matches the shape and does not overlap anywhere? Perhaps also with a chance to scale the texture in case it's too small or to big for the shape, but still so that it gets rendered correctly. Do I treat the shape as a rectangle? Figure out it's 4 corners? Or do I calculate the distance between Center - (Texture Width / 2) and Point (to see how "many" times the texture can fit between on that axis to estimate at what Coordinates the Texture should be at that certain point? I've looked at Texture Mapping but haven't found any concrete examples that it explains it well, it's also confusing with 0.0-1.0 values for Texture Coordinates.

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• How to Make Objects Fall Faster in a Physics Simulation

  - by David Dimalanta

  I used the collision physics (i.e. Box2d, Physics Body Editor) and implemented onto the java code. I'm trying to make the fall speed higher according to the examples: It falls slower if light object (i.e. feather). It falls faster depending on the object (i.e. pebble, rock, car). I decided to double its falling speed for more excitement. I tried adding the mass but the speed of falling is constant instead of gaining more speed. check my code that something I put under input processor's touchUp() return method under same roof of the class that implements InputProcessor and Screen: @Override public boolean touchUp(int screenX, int screenY, int pointer, int button) { // TODO Touch Up Event if(is_Next_Fruit_Touched) { BodyEditorLoader Fruit_Loader = new BodyEditorLoader(Gdx.files.internal("Shape_Physics/Fruity Physics.json")); Fruit_BD.type = BodyType.DynamicBody; Fruit_BD.position.set(x, y); FixtureDef Fruit_FD = new FixtureDef(); // --> Allows you to make the object's physics. Fruit_FD.density = 1.0f; Fruit_FD.friction = 0.7f; Fruit_FD.restitution = 0.2f; MassData mass = new MassData(); mass.mass = 5f; Fruit_Body[n] = world.createBody(Fruit_BD); Fruit_Body[n].setActive(true); // --> Let your dragon fall. Fruit_Body[n].setMassData(mass); Fruit_Body[n].setGravityScale(1.0f); System.out.println("Eggs... " + n); Fruit_Loader.attachFixture(Fruit_Body[n], Body, Fruit_FD, Fruit_IMG.getWidth()); Fruit_Origin = Fruit_Loader.getOrigin(Body, Fruit_IMG.getWidth()).cpy(); is_Next_Fruit_Touched = false; up = y; Gdx.app.log("Initial Y-coordinate", "Y at " + up); //Once it's touched, the next fruit will set to drag. if(n < 50) { n++; }else{ System.exit(0); } } return true; } And take note, at show() method , the view size from the camera is at 720x1280: camera_1 = new OrthographicCamera(); camera_1.viewportHeight = 1280; camera_1.viewportWidth = 720; camera_1.position.set(camera_1.viewportWidth * 0.5f, camera_1.viewportHeight * 0.5f, 0f); camera_1.update(); I know it's a good idea to add weight to make the falling object falls faster once I released the finger from the touchUp() after I picked the object from the upper right of the screen but the speed remains either constant or slow. How can I solve this? Can you help?

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• Unexpected results for projection on to plane

  - by ravenspoint

  I want to use this projection matrix: GLfloat shadow[] = { -1,0,0,0, 1,0,-1,1, 0,0,-1,0, 0,0,0,-1 }; It should cast object shadows onto the y = 0 plane from a point light at 1,1,-1. I create a rectangle in the x = 0.5 plane glBegin( GL_QUADS ); glVertex3f( 0.5,0.2,-0.5); glVertex3f( 0.5,0.2,-1.5); glVertex3f( 0.5,0.5,-1.5); glVertex3f( 0.5,0.5,-0.5); glEnd(); Now if I manually multiply these vertices with the matrix, I get. glBegin( GL_QUADS ); glVertex3f( 0.375,0,-0.375); glVertex3f( 0.375,0,-1.625); glVertex3f( 0,0,-2); glVertex3f( 0,0,0); glEnd(); Which produces a reasonable display ( camera at 0,5,0 looking down y axis ) So rather than do the calculation manually, I should be able to use the opengl model transormation. I write this code: glMatrixMode (GL_MODELVIEW); GLfloat shadow[] = { -1,0,0,0, 1,0,-1,1, 0,0,-1,0, 0,0,0,-1 }; glLoadMatrixf( shadow ); glBegin( GL_QUADS ); glVertex3f( 0.5,0.2,-0.5); glVertex3f( 0.5,0.2,-1.5); glVertex3f( 0.5,0.5,-1.5); glVertex3f( 0.5,0.5,-0.5); glEnd(); But this produces a blank screen! What am I doing wrong? Is there some debug mode where I can print out the transformed vertices, so I can see where they are ending up? Note: People have suggested that using glMultMatrixf() might make a difference. It doesn't. Replacing glLoadMatrixf( shadow ); with glLoadIdentity(); glMultMatrixf( shadow ); gives the identical result ( of course! )

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• Overriding component behavior

  - by deft_code

  I was thinking of how to implement overriding of behaviors in a component based entity system. A concrete example, an entity has a heath component that can be damaged, healed, killed etc. The entity also has an armor component that limits the amount of damage a character receives. Has anyone implemented behaviors like this in a component based system before? How did you do it? If no one has ever done this before why do you think that is. Is there anything particularly wrong headed about overriding component behaviors? Below is rough sketch up of how I imagine it would work. Components in an entity are ordered. Those at the front get a chance to service an interface first. I don't detail how that is done, just assume it uses evil dynamic_casts (it doesn't but the end effect is the same without the need for RTTI). class IHealth { public: float get_health( void ) const = 0; void do_damage( float amount ) = 0; }; class Health : public Component, public IHealth { public: void do_damage( float amount ) { m_damage -= amount; } private: float m_health; }; class Armor : public Component, public IHealth { public: float get_health( void ) const { return next<IHealth>().get_health(); } void do_damage( float amount ) { next<IHealth>().do_damage( amount / 2 ); } }; entity.add( new Health( 100 ) ); entity.add( new Armor() ); assert( entity.get<IHealth>().get_health() == 100 ); entity.get<IHealth>().do_damage( 10 ); assert( entity.get<IHealth>().get_health() == 95 ); Is there anything particularly naive about the way I'm proposing to do this?

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• How do I create a third Person View using DXUTCamera in DX10?

  - by David

  I am creating a 3d flying game and using DXUTCamera for my view. I can get the camera to take on the characters position, But I would like to view my character in the 3rd person. Here is my code for first person view: //Put the camera on the object. D3DXVECTOR3 viewerPos; D3DXVECTOR3 lookAtThis; D3DXVECTOR3 up ( 5.0f, 1.0f, 0.0f ); D3DXVECTOR3 newUp; D3DXMATRIX matView; //Set the viewer's position to the position of the thing. viewerPos.x = character->x; viewerPos.y = character->y; viewerPos.z = character->z; // Create a new vector for the direction for the viewer to look character->setUpWorldMatrix(); D3DXVECTOR3 newDir, lookAtPoint; D3DXVec3TransformCoord(&newDir, &character->initVecDir, &character->matAllRotations); // set lookatpoint D3DXVec3Normalize(&lookAtPoint, &newDir); lookAtPoint.x += viewerPos.x; lookAtPoint.y += viewerPos.y; lookAtPoint.z += viewerPos.z; g_Camera.SetViewParams(&viewerPos, &lookAtPoint); So does anyone have an ideas how I can move the camera to the third person view? preferably timed so there is a smooth action in the camera movement. (I'm hoping I can just edit this code instead of bringing in another camera class)

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• How could you model "scent trails" in a game?

  - by Sebastien Diot

  Say you want to create a 3D game, and have either players, or mobiles, be able to tract other entity by following their scent trails. Is there any known data-structure that matches this use case? If you have only few individuals going about, you can probably do something like a map of 3D coord to entity ID, but real scent works differently, because it fades over time, but slowly. And most of the time, you can only know approximately what went there, and approximately how many things of that type went there. And the approximation becomes worst with time, until it's gone. I imagine it's kind of like starting with an exact number, and slowly loosing the least significant digits, until you loose the most significant digit too. But that doesn't really help me, because entity IDs aren't normally encoded to contain the entity type, in addition to it's individual ID.

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• How can I create tiles that scale to multiple resolutions?

  - by Darestium

  I am trying to create a multiplayer version of the popular Flash game N in Java. However, I'm not sure how to create a tileset that will scale up. Are the tiles for N pre-drawn or are they defined with mathamatical formulas in code? I do see how they would scale up in Flash if they were pre-rendered. So if anyone has any ideas how I should go about creating the tileset, or how they are created in the game please let me know. You can check out the game here.

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• How to have operations with character/items in binary with concrete operations?

  - by Piperoman

  I have the next problem. A item can have a lot of states: NORMAL = 0000000 DRY = 0000001 HOT = 0000010 BURNING = 0000100 WET = 0001000 COLD = 0010000 FROZEN = 0100000 POISONED= 1000000 A item can have some states at same time but not all of them Is impossible to be dry and wet at same time. If you COLD a WET item, it turns into FROZEN. If you HOT a WET item, it turns into NORMAL A item can be BURNING and POISON Etc. I have tried to set binary flags to states, and use AND to combine different states, checking before if it is possible or not to do it, or change to another status. Does there exist a concrete approach to solve this problem efficiently without having an interminable switch that checks every state with every new state? It is relatively easy to check 2 different states, but if there exists a third state it is not trivial to do.

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• MiniMax not working properly(for checkers game)

  - by engineer

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

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• How can I save state from script in a multithreaded engine?

  - by Peter Ren

  We are building a multithreaded game engine and we've encountered some problems as described below. The engine have 3 threads in total: script, render, and audio. Each frame, we update these 3 threads simultaneously. As these threads updating themselves, they produce some tasks and put them into a public storage area. As all the threads finish their update, each thread go and copy the tasks for themselves one by one. After all the threads finish their task copying, we make the threads process those tasks and update these threads simultaneously as described before. So this is the general idea of the task schedule part of our engine. Ok, well, all the task schedule part work well, but here's the problem: For the simplest, I'll take Camera as an example: local oldPos = camera:getPosition() -- ( 0, 0, 0 ) camera:setPosition( 1, 1, 1 ) -- Won't work now, cuz the render thread will process the task at the beginning of the next frame local newPos = camera:getPosition() -- Still ( 0, 0, 0 ) So that's the problem: If you intend to change a property of an object in another thread, you have to wait until that thread process this property-changing message. As a result, what you get from the object is still the information in the last frame. So, is there a way to solve this problem? Or are we build the task schedule part in a wrong way? Thanks for your answers :)

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• glGetActiveAttrib on Android NDK

  - by user408952

  In my code-base I need to link the vertex declarations from a mesh to the attributes of a shader. To do this I retrieve all the attribute names after linking the shader. I use the following code (with some added debug info since it's not really working): int shaders[] = { m_ps, m_vs }; if(linkProgram(shaders, 2)) { ASSERT(glIsProgram(m_program) == GL_TRUE, "program is invalid"); int attrCount = 0; GL_CHECKED(glGetProgramiv(m_program, GL_ACTIVE_ATTRIBUTES, &attrCount)); int maxAttrLength = 0; GL_CHECKED(glGetProgramiv(m_program, GL_ACTIVE_ATTRIBUTE_MAX_LENGTH, &maxAttrLength)); LOG_INFO("shader", "got %d attributes for '%s' (%d) (maxlen: %d)", attrCount, name, m_program, maxAttrLength); m_attrs.reserve(attrCount); GLsizei attrLength = -1; GLint attrSize = -1; GLenum attrType = 0; char tmp[256]; for(int i = 0; i < attrCount; i++) { tmp[0] = 0; GL_CHECKED(glGetActiveAttrib(m_program, GLuint(i), sizeof(tmp), &attrLength, &attrSize, &attrType, tmp)); LOG_INFO("shader", "%d: %d %d '%s'", i, attrLength, attrSize, tmp); m_attrs.append(String(tmp, attrLength)); } } GL_CHECKED is a macro that calls the function and calls glGetError() to see if something went wrong. This code works perfectly on Windows 7 using ANGLE and gives this this output: info:shader: got 2 attributes for 'static/simplecolor.glsl' (3) (maxlen: 11) info:shader: 0: 7 1 'a_Color' info:shader: 1: 10 1 'a_Position' But on my Nexus 7 (1st gen) I get the following (the errors are the output from the GL_CHECKED macro): I/testgame:shader(30865): got 2 attributes for 'static/simplecolor.glsl' (3) (maxlen: 11) E/testgame:gl(30865): 'glGetActiveAttrib(m_program, GLuint(i), sizeof(tmp), &attrLength, &attrSize, &attrType, tmp)' failed: INVALID_VALUE [jni/src/../../../../src/Game/Asset/ShaderAsset.cpp:50] I/testgame:shader(30865): 0: -1 -1 '' E/testgame:gl(30865): 'glGetActiveAttrib(m_program, GLuint(i), sizeof(tmp), &attrLength, &attrSize, &attrType, tmp)' failed: INVALID_VALUE [jni/src/../../../../src/Game/Asset/ShaderAsset.cpp:50] I/testgame:shader(30865): 1: -1 -1 '' I.e. the call to glGetActiveAttrib gives me an INVALID_VALUE. The opengl docs says this about the possible errors: GL_INVALID_VALUE is generated if program is not a value generated by OpenGL. This is not the case, I added an ASSERT to make sure glIsProgram(m_program) == GL_TRUE, and it doesn't trigger. GL_INVALID_OPERATION is generated if program is not a program object. Different error. GL_INVALID_VALUE is generated if index is greater than or equal to the number of active attribute variables in program. i is 0 and 1, and the number of active attribute variables are 2, so this isn't the case. GL_INVALID_VALUE is generated if bufSize is less than 0. Well, it's not zero, it's 256. Does anyone have an idea what's causing this? Am I just lucky that it works in ANGLE, or is the nvidia tegra driver wrong?

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• Most efficient way to implement delta time

  - by Starkers

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

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• How to create an extensible rope in Box2D?

  - by Thomas

  Let's say I'm trying to create a ninja lowering himself down a rope, or pulling himself back up, all whilst he might be swinging from side to side or hit by objects. Basically like http://ninja.frozenfractal.com/ but with Box2D instead of hacky JavaScript. Ideally I would like to use a rope joint in Box2D that allows me to change the length after construction. The standard Box2D RopeJoint doesn't offer that functionality. I've considered a PulleyJoint, connecting the other end of the "pulley" to an invisible kinematic body that I can control to change the length, but PulleyJoint is more like a rod than a rope: it constrains maximum length, but unlike RopeJoint it constrains the minimum as well. Re-creating a RopeJoint every frame using a new length is rather inefficient, and I'm not even sure it would work properly in the simulation. I could create a "chain" of bodies connected by RotationJoints but that is also less efficient, and less robust. I also wouldn't be able to change the length arbitrarily, but only by adding and removing a whole number of links, and it's not obvious how I would connect the remainder without violating existing joints. This sounds like something that should be straightforward to do. Am I overlooking something?

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• Error in my Separating Axis Theorem collision code

  - by Holly

  The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; int x; int y; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } public void update(int xPos, int yPos){ x = xPos; y = yPos; } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(new Vect(vertices[0].x+x, vertices[0].y+y)); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(new Vect(vertices[i].x+x, vertices[i].y+y)); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if(y > other.x && other.y > x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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