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• How to calculate continuous motion with angular velocity in 2d

  - by Rulk

  I'm really new with physics. Maybe someone would be able to help me to solve the next problem: I need to calculate position of an agent on the plane(2D) in next time step where time step is large(20+ seconds) What I know about agent's motion: Initial Position Direction(normalised vector) Velocity(linear function from time ) - object always moves along it's direction Angular Velocity(linear function from time) Optional: External force direction External force (linear function from time) Running discreet simulation with t-0 is not an option.

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• OpenGL doesn't draw (3.3+) [on hold]

  - by Dhiego Magalhães

  Brief: I've been following this tutorial about OpenGL for 2 days, and I still can't have a triangle drawn, so I'm asking for help here. The tutorial is turned to OpenGL version 3.3 programing, using vertex arrays, buffers, etc. The libraries are: GLFW3 and GLEW, and I setted them by myself. The screen keeps black all the time. Full code: link here (It's just like a Hello World opengl program) Further Details: I get no errors at all. I downloaded a software to test my video card, and it supports OpenGL 4.1+ Standard OpenGL code for drawing (from earlier version) such as this one works normally. I'm using Microsoft Visual Studio 10.0 I presume all the OpenGL implementation was dune right: I added Additional Dependences to the linker as glew32.lib, opengl32.lib, glfw3.lib. The glew.dll was placed at SysWOW64 - because I'm running window 64bits, and glew is 32. Notes: I've been working hard to find out what this is, but I can't find. I would appreciate if anyone could test this code for me, so I can know if I implemented something wrong, and that its not my code.

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• I get GL_INVALID_VALUE after calling glTexSubImage2D

  - by user892644

  I am trying to figure out why my texture allocation does not work. Here is the code: glTexStorage2D(GL_TEXTURE_2D, 2, GL_RGBA8, 2048, 2048); glTexSubImage2D(GL_TEXTURE_2D, 0, 0, 0, 2048, 2048, GL_RGB, GL_UNSIGNED_SHORT_5_6_5_REV, &BitMap[0]); glTexSubImage2D returns GL_INVALID_VALUE but the maximum texture allowed is 16384x16384 on my card. The source of the image is 16bit (Red 5, Green 6, Blue 5).

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• Memory allocation strategy for the vertex buffers (DirectX 10/11)

  - by Alex

  I have the following question. I write CAD system. So I have a 3D scene and there are many different objects (walls, doors, windows and so on). User can add or delete some objects. The question is: how can I organise the keeping of vertices for all my objects. I can create vertex buffer for every object. But I think drawing/switching from one buffer to another would have performance penalty. Another way - I can create several big buffers for every object type. But I don't understand how to update such buffers. It is too big to update whole buffer (for example buffer for all walls). What I need to do if I want to delete the object from the middle of the buffer? Actually I have the similar question: http://stackoverflow.com/questions/5515700/how-to-properly-update-vertex-buffers-in-directx-10 Most examples I've found work with very static models. Therefore, they tend to create a single vertex buffer with their list of points, and then are just manipulated by matrix transformations. I, on the other hand, will be updating the scene very often.

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• Corona sdk events dispatched with dispatchEvent() are handled directly upon call. Why so?

  - by Amoxus

  I noticed to my surprise that an event created with dispatchEvent(event) gets handled directly when called, and not together with other events at a specific phase of the frame loop. Two main reasons of having an event system are: so that you can call code B from code A, but still want to prioritize code A. to make sure there are no freaky loopedy loops where code A calls code B calls code A ... I wonder what Ansca's rationale behind having events being handled directly this way is. And does Corona handle loopedy loops and other such pitfalls gracefully? The following code demonstrates dispatchEvent(): T= {} Z = display.newRect(100,100,100,100) function T.doSomething() print("T.doSomething: begun") local event = { name="myEventType", target=T } Z:dispatchEvent( event ) print("T.doSomething: ended") end function Z.sayHello(event) print("Z.sayHello: begun and ended") end Z:addEventListener("myEventType", Z.sayHello) print("Main: begun") T.doSomething() print("Main: ended") However Ansca claims the contrary at http://developer.coronalabs.com/reference/index/objectdispatchevent Can anyone clear this up a little? ( Using Corona simulator V 2012.840 )

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• Having the same texture data in different ID3D11Texture2D

  - by bdmnd

  Sorry if this has been answered elsewhere - I'm rather new to DX. My question concerns conservation of resources - specifically textures in VRAM. I assume that upon returning from a call to CreateTexture2D, a copy of any textures data supplied has been copied elsewhere, likely VRAM. Does DX11 have any facility for having multiple ID3D11Texture2D objects which point to the same data? This might at first seem silly, but imagine a ID3D11Texture2D which is an array of textures. In one material, an artist has chosen to blend three identically sized maps, saved on disk as A.dds, B.dds, and C.dds. Then imagine they have another material which also uses three maps, but this time A.dds, B.dds, and D.dds. The shader code knows the diffuse texture is a texture array, and also has the number of layers baked (three in each case). I would essentially like to set up just two ID3D11Texture2D objects, one for each material, but I don't want to waste VRAM for two identical copies of A.dds and B.dds. I could use explicit texture arrays, of course, but this reduces the number of resources available to the shader and can complicate code somewhat more than would otherwise be needed.

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• D3DXMatrixDecompose gives different quaternion than D3DXQuaternionRotationMatrix

  - by Fraser

  In trying to solve this problem, I tracked down the problem to the conversion of the rotation matrix to quaternion. In particular, consider the following matrix: -0.02099178 0.9997436 -0.008475631 0 0.995325 0.02009799 -0.09446743 0 0.09427284 0.01041905 0.9954919 0 0 0 0 1 SlimDX.Quaternion.RotationMatrix (which calls D3DXQuaternionRotationMatrix gives a different answer than SlimDX.Matrix.Decompose (which uses D3DXMatrixDecompose). The answers they give (after being normalized) are: X Y Z W Quaternion.RotationMatrix -0.05244324 0.05137424 0.002209336 0.9972991 Matrix.Decompose 0.6989997 0.7135442 -0.03674842 -0.03006023 Which are totally different (note the signs of X, Z, and W are different). Note that these aren't q/-q (two quaternions that represent the same rotation); they face completely different directions. I've noticed that with matrices for rotations very close to that one (successive frames in the animation) that the Matrix.Decompose version gives a solution that flips around wildly and occasionally goes into the desired position, while the Quaternion.RotationMatrix version gives solutions that are stable but go in the wrong direction. This is only for the right arm in my animation -- for the left arm, both functions give the correct solution, which is the same quaternion within error tolerances. This makes me think that there's some sort of numeric instability or weird stuff with signs going on. I tried implementing this and then this, but both gave me a completely incorrect solution (even for the matricies where the SlimDX ones were working correctly) -- maybe the rows and columns are flipped?

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• Implementing Camera Zoom in a 2D Engine

  - by Luke

  I'm currently trying to implement camera scaling/zoom in my 2D Engine. Normally I calculate the Sprite's drawing size and position similar to this pseudo code: render() { var x = sprite.x; var y = sprite.y; var sizeX = sprite.width * sprite.scaleX; // width of the sprite on the screen var sizeY = sprite.height * sprite.scaleY; // height of the sprite on the screen } To implement the scaling i changed the code to this: class Camera { var scaleX; var scaleY; var zoom; var finalScaleX; // = scaleX * zoom var finalScaleY; // = scaleY * zoom } render() { var x = sprite.x * Camera.finalScaleX; var y = sprite.y * Camera.finalScaleY; var sizeX = sprite.width * sprite.scaleX * Camera.finalScaleX; var sizeY = sprite.height * sprite.scaleY * Camera.finalScaleY; } The problem is that when the zoom is smaller than 1.0 all sprites are moved toward the top-left corner of the screen. This is expected when looking at the code but i want the camera to zoom on the center of the screen. Any tips on how to do that are welcome. :)

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• My Sprite comes out the screen

  - by IlNero

  If i an action moves the sprite,how can i keep the CCSprite on the screen???? this is my code: [enemy runAction:[CCSequence actions:[CCMoveBy actionWithDuration:2.0 position:ccp(-winSize.width*0.4, 0)], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(winSize.width*0.2, -winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(winSize.width*0.2, -winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(winSize.width*0.2, -winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(winSize.width*0.2, -winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(winSize.width*0.2, -winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(-winSize.width*0.3,winSize.width*0.3), randomValueBetween(winSize.height*0.3, -winSize.height*0.3))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(-winSize.width*0.2,winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(-winSize.width*0.3,winSize.width*0.3), randomValueBetween(winSize.height*0.3, -winSize.height*0.3))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(-winSize.width*0.2,winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(-winSize.width*0.3,winSize.width*0.3), randomValueBetween(winSize.height*0.3, -winSize.height*0.3))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:randomValueBetween(1.0, 0.3) position:ccp(randomValueBetween(-winSize.width*0.2,winSize.width*0.2), randomValueBetween(winSize.height*0.2, -winSize.height*0.2))], [CCDelayTime actionWithDuration:0.5], [CCMoveBy actionWithDuration:2.0 position:ccp(-winSize.width*1.5, 0)], [CCCallFuncN actionWithTarget:self selector:@selector(invisNode:)], nil]]; but whit this code the sprite sometimes comes out the screen, i need the sprite moves randomly in the screen without comes out..

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• Drawing a texture line between two vectors in XNA WP7

  - by Krav

  I want to create a simple graph maker in WP7. The goal is to draw a texture line between two vectors what the user defines with touch. I already made the rotation, and it is working, but not correctly, because it doesn't calculate the line's texture height, and because of that, there are too many overlapping textures. So it does draw the line, but too many of them. How could I calculate it correctly? Here is the code: public void DrawLine(Vector2 st,Vector2 dest,NodeUnit EdgeParent,NodeUnit EdgeChild) { float d = Vector2.Distance(st, dest); float rotate = (float)(Math.Atan2(st.Y - dest.Y, st.X - dest.X)); direction = new Vector2(((dest.X - st.X) / (float)d), (dest.Y - st.Y) / (float)d); Vector2 _pos = st; World.TheHive.Add(new LineHiveMind(linetexture, _pos, rotate, EdgeParent, EdgeChild,new List<LineUnit>())); for (int i = 0; i < d; i++) { World.TheHive.Last()._lines.Add(new LineUnit(linetexture, _pos, rotate, EdgeParent, EdgeChild)); _pos += direction; } } d is for the Distance of the st (Starting node) and dest (Destination node) rotate is for rotation direction calculates the direction between the starting and the destination node _pos is for starting position changing Thanks for any suggestions/help!

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• Detailed Modern Opengl Tutorial?

  - by Kogesho

  I am asking for a specific modern opengl tutorial. I need a tutorial that does not skip to explain any lines of code. It should also include different independent objects moving/rotating (most tutorials use only one object), as well as imported 3d objects and collision detection for them. It should also avoid stuff that won't be used. Arcysnthesis for example gives a new concept, and after teaching it, in the next tutorial, it explains how bad it is for performance and introduces another method. Do you know any?

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• System hangs at glReadPixel call with GL_TEXTURE_2D_ARRAY for texturing

  - by Roshan

  I am calling glReadPixel after glDrawArray call. I am rendering a geometry with 3D texture on it as a target GL_TEXTURE_2D_ARRAY. My systems hangs at glreadpixel call. When i use target as GL_TEXTURE_3D the issue does not occurs and it correctly reads the framebuffer contents. glReadPixels(0, 0, GetViewportWidth(), GetViewportHeight(), GL_RGBA, GL_UNSIGNED_BYTE, (GLvoid *)rendered_pixels); I am using SNORM textures with GL_byte data in glTeximage3D call and I am not calling glPixelStorei, is it because of this? What should be the parameter for pixelstore call?

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• Problems loading Hilva tutorials

  - by Beska

  I'm a newcomer to XNA, and I'm evaluating some libraries. The Hilva Graphics Engine looks interesting, and I'm trying to run their tutorials. However, all of them give me errors. For example, if I download the ParallaxMappingSample demo, and try to build it, I get Error 1 Error loading pipeline assembly "C:\Users\Me\Desktop\ParallaxMappingSample\Hilva.Content.dll". ParallaxMappingSample I get similar errors for all of the samples. Unfortunately, this error isn't very enlightening. I can see the Hilva.Content.dll in the appropriate directory. I tried removing and readding the reference from the content project, but I get the same error. I'm not sure it's relevant, but I'm on Windows 7, I'm using Microsoft Visual Studio 2010, and XNA 4.0. Is there an easy (or difficult) solution? EDIT: If you happen to try this, even if you don't have a solution, let me know about it in a comment. Whether it works for you, or if you get the same problem...either result would be something that might let me know if it's just a problem with the tutorial, or if it's on my end.

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• how to use string::find to look for a word rather each character seperately

  - by RubyKing

  Hello how would I look through a string for a word rather then each character in that word. I have my code here and it always seems to find everything that is .obj even if its o or b or j or "." is there anyway to get passed this here is my code? I checked the docuementation here link but nothing returned any results I craved so hard string &str = *it; if(it->find(".obj")) { cout << "Found .Obj" << endl; } I also tried to use string::compare but that failed :(

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• Who should respond to collision: Unit or projectile?

  - by aleguna

  In an RTS if a projectile hits a unit. Who should handle the collision? If projectile handles the collision, it must be aware of all possible types of units, to know what damage to inflict. For example a bullet will likely kill a human, but it will do nothing to a tank. The same goes if unit handles a collision. So either way one of them should be aware of all possible types of the other. Of course the 'true' way would be to do full physics simulation, but that's not an option for an RTS with 1000s of units and projectiles... So what are the common practicies in this regards?

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• point to rectangle distance

  - by john smith

  I have a 2D rectangle with x, y position and it's height and width and a randomly positioned point nearby it. Is there a way to check if this point might collide with the rectangle if closer than a certain distance? like imagine an invisible radius outside of that point colliding with said rectangle. I have problems with this simply because it is not a square, it would be so much easier this way! Any help? Thanks in advance.

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• Drawing flaming letters in 3d on OpenGL ES 2.0

  - by Chiquis

  I am a bit confused about how to achieve this. What i want is to "draw with flames". I have achieved this with textures successfully, but now my concern is about doing this with particles to achieve the flaming effect. Am I supposed to have a Path in where i should add many particle emitters along the path that will "be emitting flames"? I understand the concept for 2d, but for 3d are the particles (that are quads) always supposed to be facing the user? Edit: Something else im worried about is the performance hit that will occur by having that many particle emitters, because there can be many letters and drawings at the same time. And each of these elements will have many particle emitters.

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• In 3D camera math, calculate what Z depth is pixel unity for a given FOV

  - by badweasel

  I am working in iOS and OpenGL ES 2.0. Through trial and error I've figured out a frustum to where at a specific z depth pixels drawn are 1 to 1 with my source textures. So 1 pixel in my texture is 1 pixel on the screen. For 2d games this is good. Of course it means that I also factor in things like the size of the quad and the size of the texture. For example if my sprite is a quad 32x32 pixels. The quad size is 3.2 units wide and tall. And the texcoords are 32 / the size of the texture wide and tall. Then the frustum is: matrixFrustum(-(float)backingWidth/frustumScale,(float)backingWidth/frustumScale, -(float)backingHeight/frustumScale, (float)backingHeight/frustumScale, 40, 1000, mProjection); Where frustumScale is 800 for a retina screen. Then at a distance of 800 from camera the sprite is pixel for pixel the same as photoshop. For 3d games sometimes I still want to be able to do this. But depending on the scene I sometimes need the FOV to be different things. I'm looking for a way to figure out what Z depth will achieve this same pixel unity for a given FOV. For this my mProjection is set using: matrixPerspective(cameraFOV, near, far, (float)backingWidth / (float)backingHeight, mProjection); With testing I found that at an FOV of 45.0 a Z of 38.5 is very close to pixel unity. And at an FOV of 30.0 a Z of 59.5 is about right. But how can I calculate a value that is spot on? Here's my matrixPerspecitve code: void matrixPerspective(float angle, float near, float far, float aspect, mat4 m) { //float size = near * tanf(angle / 360.0 * M_PI); float size = near * tanf(degreesToRadians(angle) / 2.0); float left = -size, right = size, bottom = -size / aspect, top = size / aspect; // Unused values in perspective formula. m[1] = m[2] = m[3] = m[4] = 0; m[6] = m[7] = m[12] = m[13] = m[15] = 0; // Perspective formula. m[0] = 2 * near / (right - left); m[5] = 2 * near / (top - bottom); m[8] = (right + left) / (right - left); m[9] = (top + bottom) / (top - bottom); m[10] = -(far + near) / (far - near); m[11] = -1; m[14] = -(2 * far * near) / (far - near); } And my mView is set using: lookAtMatrix(cameraPos, camLookAt, camUpVector, mView); * UPDATE * I'm going to leave this here in case anyone has a different solution, can explain how they do it, or why this works. This is what I figured out. In my system I use a 10th scale unit to pixels on non-retina displays and a 20th scale on retina displays. The iPhone is 640 pixels wide on retina and 320 pixels wide on non-retina (obsolete). So if I want something to be the full screen width I divide by 20 to get the OpenGL unit width. Then divide that by 2 to get the left and right unit position. Something 32 units wide centered on the screen goes from -16 to +16. Believe it or not I have an excel spreadsheet do all this math for me and output all the vertex data for my sprite sheet. It's an arbitrary thing I made up to do .1 units = 1 non-retina pixel or 2 retina pixels. I could have made it .01 units = 2 pixels and someday I might switch to that. But for now it's the other. So the width of the screen in units is 32.0, and that means the left most pixel is at -16.0 and the right most is at 16.0. After messing a bit I figured out that if I take the [0] value of an identity modelViewProjection matrix and multiply it by 16 I get the depth required to get 1:1 pixels. I don't know why. I don't know if the 16 is related to the screen size or just a lucky guess. But I did a test where I placed a sprite at that calculated depth and varied the FOV through all the valid values and the object stays steady on screen with 1:1 pixels. So now I'm just calculating the unityDepth that way. If someone gives me a better answer I'll checkmark it.

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• ERROR #342: DEVICE_SHADER_LINKAGE_SEMANTICNAME_NOT_FOUND

  - by Telanor

  I've stared at this for at least half an hour now and I cannot figure out what directx is complaining about. I know this error normally means you put float3 instead of a float4 or something like that, but I've checked over and over and as far as I can tell, everything matches. This is the full error message: D3D11: ERROR: ID3D11DeviceContext::DrawIndexed: Input Assembler - Vertex Shader linkage error: Signatures between stages are incompatible. The input stage requires Semantic/Index (COLOR,0) as input, but it is not provided by the output stage. [ EXECUTION ERROR #342: DEVICE_SHADER_LINKAGE_SEMANTICNAME_NOT_FOUND ] This is the vertex shader's input signature as seen in PIX: // Input signature: // // Name Index Mask Register SysValue Format Used // -------------------- ----- ------ -------- -------- ------ ------ // POSITION 0 xyz 0 NONE float xyz // NORMAL 0 xyz 1 NONE float // COLOR 0 xyzw 2 NONE float The HLSL structure looks like this: struct VertexShaderInput { float3 Position : POSITION0; float3 Normal : NORMAL0; float4 Color: COLOR0; }; The input layout, from PIX, is: The C# structure holding the data looks like this: [StructLayout(LayoutKind.Sequential)] public struct PositionColored { public static int SizeInBytes = Marshal.SizeOf(typeof(PositionColored)); public static InputElement[] InputElements = new[] { new InputElement("POSITION", 0, Format.R32G32B32_Float, 0), new InputElement("NORMAL", 0, Format.R32G32B32_Float, 0), new InputElement("COLOR", 0, Format.R32G32B32A32_Float, 0) }; Vector3 position; Vector3 normal; Vector4 color; #region Properties ... #endregion public PositionColored(Vector3 position, Vector3 normal, Vector4 color) { this.position = position; this.normal = normal; this.color = color; } public override string ToString() { StringBuilder sb = new StringBuilder(base.ToString()); sb.Append(" Position="); sb.Append(position); sb.Append(" Color="); sb.Append(Color); return sb.ToString(); } } SizeInBytes comes out to 40, which is correct (4*3 + 4*3 + 4*4 = 40). Can anyone find where the mistake is?

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• How to obtain window handle in SDL 2.0.3

  - by Diorthotis

  I need to obtain the handle of the window for SDL 2.0.3. I got the suggestion to use info.window after initializing SDL and filling the info variable with data by calling SDL_GetWindowWMInfo(); included in the header file SDL_syswm.h. My compiler (visual studio 2008 professional edition) gives the following error: 226) : error C2039: 'window' : is not a member of 'SDL_SysWMinfo' 1 include\sdl_syswm.h(173) : see declaration of 'SDL_SysWMinfo' Any help appreciated. Thanks. Nevermind, I needed to use "info.info.win.window". That seems a bit redundant, but whateves.

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• Text on a model

  - by alecnash

  I am trying to put some text on a Model and I want it to be dynamic. Did some research and came up with drawing the text on the texture and then set it on the model. I use something like this: public static Texture2D SpriteFontTextToTexture(SpriteFont font, string text, Color backgroundColor, Color textColor) { Size = font.MeasureString(text); RenderTarget2D renderTarget = new RenderTarget2D(GraphicsDevice, (int)Size.X, (int)Size.Y); GraphicsDevice.SetRenderTarget(renderTarget); GraphicsDevice.Clear(Color.Transparent); Spritbatch.Begin(); //have to redo the ColorTexture Spritbatch.Draw(ColorTexture.Create(GraphicsDevice, 1024, 1024, backgroundColor), Vector2.Zero, Color.White); Spritbatch.DrawString(font, text, Vector2.Zero, textColor); Spritbatch.End(); GraphicsDevice.SetRenderTarget(null); return renderTarget; } When I was working with primitives and not models everything worked fine because I set the texture exactly where I wanted but with the model (RoundedRect 3D button). It now looks like that: Is there a way to have the text centered only on one side?

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• Cocos2d Box2d contact listener call different method in collided object

  - by roma86

  I have the building object, wen it hit with other, i want to call some method inside it. Building.mm -(void)printTest { NSLog(@"printTest method work correctly"); } in my ContactListener i trying to call it so: ContactListener.mm #import "ContactListener.h" #import "Building.h" void ContactListener::BeginContact(b2Contact* contact) { b2Body* bodyA = contact->GetFixtureA()->GetBody(); b2Body* bodyB = contact->GetFixtureB()->GetBody(); Building *buildA = (Building *)bodyA->GetUserData(); Building *buildB = (Building *)bodyB->GetUserData(); if (buildB.tag == 1) { NSLog(@"tag == 1"); } if (buildA.tag == 2) { NSLog(@"tag == 2"); [buildA printTest]; } } NSLog(@"tag == 2"); work correctly, but [buildA printTest]; get error Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[CCSprite printTest]: unrecognized selector sent to instance 0x18595f0' Obviously I'm referring to the wrong object. How i can get different method and property in contacted objects from contactlistener class? Thanks.

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• Point line collision reaction

  - by user4523

  I am trying to program point line segment collision detection and reaction. I am doing this for fun and to learn. The point moves (it has a velocity, and can be controlled by the user), whilst the lines are strait and stationary. The lines are not axis aligned. Everything is in 2D. It is quite straight forward to work out if a collision has occurred. For each frame, the point moves from A to B. AB is a line, and if it crosses the line segment, a collision has occurred (or will occur) and I am able to work out the point of intersection (poi). The problem I am having is with the reaction. Ideally I would like the point to be prevented from moving across the line. In one frame, I can move the point back to the poi (or only alow it to move as far as the poi), and alter the velocity. The problem I am having with this approach (I think) is that, next frame the user may try to cross the line again. Although the point is on the poi, the point may not be exactly on the line. Since it is not axis aligned, I think there is always some subtle rounding issue (A float representation of a point on a line might be rounded to a point that is slightly on one side or the other). Because of this, next frame the path might not intersect the line (because it can start on the other side and move away from it) and the point is effectively allowed to cross the line. Firstly, does the analysis sound correct? Having accepted (maybe) that I cannot always exactly position the point on the line, I tried to move the point away from the line slightly (either along the normal to the line, or along the path vector). I then get a problem at edges. Attempting to fix one collision by moving the point away from the line (even slightly) can cause it to cross another line (one shape I am dealing with is a star, with sharp corners). This can mean that the solution to one collision inadvertently creates another collision, which is ignored. Again, does this sound correct? Anyway, whatever I try, I am having difficulty with edges, and the point is occasionally able to penetrate the polygons and cross lines, which is undesirable. Whilst I can find a lot of information about collision detection on the web (and on this site) I can find precious little information on collision reaction. Does any one know of any good point line collision reaction tutorials? Or is my approach too flawed/over complicated?

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• How to prevent "underwater sight" in games

  - by CPP_Person

  In many games where the player can go underwater, it seems like when you look where the top half of the screen is in the air, and the bottom half the screen is in the water, it's almost like the water doesn't exist and the player is... flying slowly with water sounds? Is there a logical way to solve this? An algorithm? Doesn't seem like any solution has come up yet since many games still have this. I don't want to make the same mistake.

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• What is the standard technique for shifting the frames of a sprite according to user input?

  - by virtual__

  From my own experience, I developed two techniques for changing the sprites of a character that's reacting to user input -- this in the context of a classic 2D platformer. The first one is to store all character's pixmaps in a list, putting the index of the currently used pixmap in an ordinary variable. This way, every time the player presses a key -- say the right arrow for moving the character forward -- the graphics engine sees what's the next pixmap to draw, draws it, and increments the index counter. That's a pretty common approach I believe, the problem is that in this case the animation's quality depends not only on the number of sprites available but also on how often your engine listens to user input. The second technique is to actually play an animation every key press event. For this you can use any sort of animation framework you want. It's only necessary to set the timer, the animation steps and to call the animation's play() method on your key press event handler. The problem with that approach is that is lacks responsiveness, since the character won't react to any input while the current animation is still being played. What I want to know is whether you are using one of these techniques -- or something similar -- in your games, or whether there's a standard method for animating sprites out there that's widely known by everybody but me.

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