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• Converting 2D coordinates from multiple viewpoints into 3D coordinates

  - by Kirk Smith

  Here's the situation. I've got a set of 2D coordinates that specify a point on an image. These 2D coordinates relate to an event that happened in a 3D space (video game). I have 5 images with the same event point on it, so I have 5 sets of 2D coordinates for a single 3D coordinate. I've tried everything I can think to translate these 2D coordinates into 3D coordinates, but the math just escapes me. I have a good estimate of the coordinates from which each image was taken, they're not perfect but they're close. I tried simplifying this and opening up Cinema 4D, a 3D modeling application. I placed 5 cameras at the coordinates where the pictures were taken and lined up the pictures with the event points for each one and tried to find a link, but nothing was forthcoming. I know it's a math question, but like I said, I just can't get it. I took physics in high school 6 years ago, but we didn't deal with a whole lot of this sort of thing. Any help will be very much appreciated, I've been thinking on it for quite a while and I just can't come up with anything.

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• How do *you* track and document routine maintenance?

  - by Zak

  What software or system do you guys out on server fault use to remind you to do routine maintenance? How do you checklist and log the various items you are supposed to check? Do you have an internal process document? Do you have cron mail you every week with reminders to check system logs? Also, do you work on a team to do system maintenance, and if so, how do you coordinate who will do what maintenance? If you use a bug/issue tracking system to enter tasks, do you have a cron job enter recurring tasks?

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• Writing the correct value in the depth buffer when using ray-casting

  - by hidayat

  I am doing a ray-casting in a 3d texture until I hit a correct value. I am doing the ray-casting in a cube and the cube corners are already in world coordinates so I don't have to multiply the vertices with the modelviewmatrix to get the correct position. Vertex shader world_coordinate_ = gl_Vertex; Fragment shader vec3 direction = (world_coordinate_.xyz - cameraPosition_); direction = normalize(direction); for (float k = 0.0; k < steps; k += 1.0) { .... pos += direction*delta_step; float thisLum = texture3D(texture3_, pos).r; if(thisLum > surface_) ... } Everything works as expected, what I now want is to sample the correct value to the depth buffer. The value that is now written to the depth buffer is the cube coordinate. But I want the value of pos in the 3d texture to be written. So lets say the cube is placed 10 away from origin in -z and the size is 10*10*10. My solution that does not work correctly is this: pos *= 10; pos.z += 10; pos.z *= -1; vec4 depth_vec = gl_ProjectionMatrix * vec4(pos.xyz, 1.0); float depth = ((depth_vec.z / depth_vec.w) + 1.0) * 0.5; gl_FragDepth = depth;

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• How can I find the right UV coordinates for interpolating a bezier curve?

  - by ssb

  I'll let this picture do the talking. I'm trying to create a mesh from a bezier curve and then add a texture to it. The problem here is that the interpolation points along the curve do not increase linearly, so points farther from the control point (near the endpoints) stretch and those in the bend contract, causing the texture to be uneven across the curve, which can be problematic when using a pattern like stripes on a road. How can I determine how far along the curve the vertices actually are so I can give a proper UV coordinate? EDIT: Allow me to clarify that I'm not talking about the trapezoidal distortion of the roads. That I know is normal and I'm not concerned about. I've updated the image to show more clearly where my concerns are. Interpolating over the curve I get 10 segments, but each of these 10 segments is not spaced at an equal point along the curve, so I have to account for this in assigning UV data to vertices or else the road texture will stretch/shrink depending on how far apart vertices are at that particular part of the curve.

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• How can I better implement A star algorithm with a very large set of nodes?

  - by Stephen

  I'm making a game with nodejs in which many enemies must converge on the player as the player moves around a relatively open space (right now it is an open field with few obstacles, but eventually there may be some small buildings in the field with 1 or 2 rooms). It's a multiplayer game using websockets, so the server needs to keep track of enemies and players. I found this javascript A* library which I've modified to be used on the server as a nodejs module. The library utilizes a Binary Heap to track the nodes for the algorithm, so it should be pretty fast (and indeed, with a small grid, say 100x100 it is lightning fast). The problem is that my game is not really tile-based. As the player moves around the map, he is moving on a more or less 1-to-1 per-pixel coordinate system (the player can move in 8 directions, 1 or 2 pixels at a time). In preliminary tests, on an 800x600 field, the path-finding can take anywhere from 400 to 1000 ms. Multiply that by 10 enemies and the game starts to get pretty choppy. I have already set it up so that each enemy will only do a path-finding call once per second or even as slow as once every 2 seconds (they have to keep updating their path because the players can move freely). But even with this long interval, there are noticeable lag spikes or chops every couple of seconds as the enemies update their paths. I'm willing to approach the problem of path-finding differently, if there's another option. I'm assuming that the real problem is the enormous grid (800x600). It also occurs to me that maybe the large arrays are to blame, as I've read that V8 has trouble with large arrays.

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• Per-vertex animation with VBOs: VBO per character or VBO per animation?

  - by charstar

  Goal To leverage the richness of well vetted animation tools such as Blender to do the heavy lifting for a small but rich set of animations. I am aware of additive pose blending like that from Naughty Dog and similar techniques but I would prefer to expend a little RAM/VRAM to avoid implementing a thesis-ready pose solver. I would also like to avoid implementing a key-frame + interpolation curve solver (reinventing Blender vertex groups and IPOs), if possible. Scenario Meshes are animated using either skeletons (skinned animation) or some form of morph targets (i.e. per-vertex key frames). However, in either case, the animations are known in full at load-time, that is, there is no physics, IK solving, or any other form of in-game pose solving. The number of character actions (animations) will be limited but rich (hand-animated). There may be multiple characters using a each mesh and its animations simultaneously in-game (they will likely be at different frames of the same animation at the same time). Assume color and texture coordinate buffers are static. Current Considerations Much like a non-shader-powered pose solver, create a VBO for each character and copy vertex and normal data to each VBO on each frame (VBO in STREAMING). Create one VBO for each animation where each frame (interleaved vertex and normal data) is concatenated onto the VBO. Then each character simply has a buffer pointer offset based on its current animation frame (e.g. pointer offset = (numVertices+numNormals)*frameNumber). (VBO in STATIC) Known Trade-Offs In 1 above: Each VBO would be small but there would be many VBOs and therefore lots of buffer binding and vertex copying each frame. Both client and pipeline intensive. In 2 above: There would be few VBOs therefore insignificant buffer binding and no vertex data getting jammed down the pipe each frame, but each VBO would be quite large. Are there any pitfalls to number 2 (aside from finite memory)? I've found a lot of information on what you can do, but no real best practices. Are there other considerations or methods that I am missing?

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• Camera field of view: 3D projections & trigonometry

  - by Thomas O

  Okay, here goes. I have a camera at (Xc, Yc, Zc.) The Xc and Yc coordinates are latitude/longitude, and the Zc coordinate is an altitude in metres. I have a point at (Xp, Yp, Zp) and a field of view on the camera (Th1, Th2) - where Th1 is horizontal FOV and Th2 is vertical FOV. Given this information, I'd like to: test if the point is visible (i.e. in the camera's FOV) project the point as the camera would see it I've figured out already that the camera's horizontal view at any given distance is tan(Th1) * distance, but I don't know how to test if the point is visible. Accuracy is not critical. I would prefer a simple solution over a complicated solution, if it works well enough. The computations will be performed by a small microcontroller, which isn't very fast at things like trig functions. P.S. this is not homework, I'm doing this for some game development. It will be integrated with the real world, hence the latitude/longitude/altitude. It involves flying real RC planes through virtual hoops (or chasing virtual targets), so I have to project the positions of these hoops on a display.

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• Issue in understanding how to compare performance of classifier using ROC

  - by user1214586

  I am trying to demystify pattern recognition techniques and understood few of them. I am trying to design a classifier M. A gesture is classified based on the hamming distance between the sample time series y and the training time series x. The result of the classifier are probabilistic values. There are 3 classes/categories with labels A,B,C which classifies hand gestures where there are 100 samples for each class which are to be classified (single feature and data length=100). The data are different time series (x coordinate vs time). The training set is used to assign probabilities indicating which gesture has occured how many times. So,out of 10 training samples if gesture A appeared 6 times then probability that a gesture falls under category A is P(A)=0.6 similarly P(B)=0.3 and P(C)=0.1 Now, I am trying to compare the performance of this classifier with Bayes classifier, K-NN, Principal component analysis (PCA) and Neural Network. On what basis,parameter and method should I do it if I consider ROC or cross validate since the features for my classifier are the probabilistic values for the ROC plot hence what shall be the features for k-nn,bayes classification and PCA? Is there a code for it which will be useful. What should be the value of k is there are 3 classes of gestures? Please help. I am in a fix.

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• Can't use the hardware scissor any more, should I use the stencil buffer or manually clip sprites?

  - by Alex Ames

  I wrote a simple UI system for my game. There is a clip flag on my widgets that you can use to tell a widget to clip any children that try to draw outside their parent's box (for scrollboxes for example). The clip flag uses glScissor, which is fed an axis aligned rectangle. I just added arbitrary rotation and transformations to my widgets, so I can rotate or scale them however I want. Unfortunately, this breaks the scissor that I was using as now my clip rectangle might not be axis aligned. There are two ways I can think of to fix this: either by using the stencil buffer to define the drawable area, or by having a wrapper function around my sprite drawing function that will adjust the vertices and texture coords of the sprites being drawn based on the clipper on the top of a clipper stack. Of course, there may also be other options I can't think of (something fancy with shaders possibly?). I'm not sure which way to go at the moment. Changing the implementation of my scissor functions to use the stencil buffer probably requires the smallest change, but I'm not sure how much overhead that has compared to the coordinate adjusting or if the performance difference is even worth considering.

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• Does Unity have existing support for Timelines?

  - by Raven Dreamer

  I am planning the development of a game in Unity3D, and trying to come to terms with what the engine has already provided, and what I must code myself. The game itself is going to be a rhythm game, which means synching audio and graphical events so that they always play when they're supposed to. What I'm looking to avoid is a potential scenario of lag where either the audio or the graphics starts to progress faster than the other. When we discussed this type of coordinating system in my game design class back at university, my professor called this type of design a "Timeline" class. The idea being that you can instantiate one or more of these to progress at different rates, schedule things to happen in the future, and synch up periodic events. However, calling this a "Timeline" class seems to have been limited to my professor himself, as googling for whether a certain API features "Timeline" functionality has been a fruitless endeavor. Is there some more common name for this kind of functionality? Does Unity have any pre-existing methods to coordinate the scheduling of events like this, or is this the kind of thing that needs to be built onto the engine? And if it does, I'd appreciate being pointed towards some tutorials!

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• Xna Equivalent of Viewport.Unproject in a draw call as a matrix transformation

  - by Nick Crowther

  I am making a 2D sidescroller and I would like to draw my sprite to world space instead of client space so I do not have to lock it to the center of the screen and when the camera stops the sprite will walk off screen instead of being stuck at the center. In order to do this I wanted to make a transformation matrix that goes in my draw call. I have seen something like this: http://stackoverflow.com/questions/3570192/xna-viewport-projection-and-spritebatch I have seen Matrix.CreateOrthographic() used to go from Worldspace to client space but, how would I go about using it to go from clientspace to worldspace? I was going to try putting my returns from the viewport.unproject method I have into a scale matrix such as: blah = Matrix.CreateScale(unproject.X,unproject.Y,0); however, that doesn't seem to work correctly. Here is what I'm calling in my draw method(where X is the coordinate my camera should follow): Vector3 test = screentoworld(X, graphics); var clienttoworld = Matrix.CreateScale(test.X,test.Y, 0); animationPlayer.Draw(theSpriteBatch, new Vector2(X.X,X.Y),false,false,0,Color.White,new Vector2(1,1),clienttoworld); Here is my code in my unproject method: Vector3 screentoworld(Vector2 some, GraphicsDevice graphics): Vector2 Position =(some.X,some.Y); var project = Matrix.CreateOrthographic(5*graphicsdevice.Viewport.Width, graphicsdevice.Viewport.Height, 0, 1); var viewMatrix = Matrix.CreateLookAt( new Vector3(0, 0, -4.3f), new Vector3(X.X,X.Y,0), Vector3.Up); //I have also tried substituting (cam.Position.X,cam.Position.Y,0) in for the (0,0,-4.3f) Vector3 nearSource = new Vector3(Position, 0f); Vector3 nearPoint = graphicsdevice.Viewport.Unproject(nearSource, project, viewMatrix, Matrix.Identity); return nearPoint;

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• Blur gets displaced compared to original image

  - by user1294203

  I have implemented a SSAO and I'm using a blur step to smooth it out. The problem is that the blurred texture is slightly displaced compared to the original. I'm blurring using a 4x4 kernel since that was my noise kernel in SSAO. The following is the blurring shader: float result = 0.0; for(int i = 0; i < 4; i++){ for(int j = 0; j < 4; j++){ vec2 offset = vec2(TEXEL_SIZE.x * i, TEXEL_SIZE.y * j); result += texture(aoSampler, TexCoord + offset).r; } } out_AO = vec4(vec3(0.0), result * 0.0625); Where TEXEL_SIZE is one over my window resolution. I was thinking that this is was an error based on how OpenGL counts the Texel center, so I tried displacing the texture coordinate I was using by 0.5 * TEXEL_SIZE, but there was still a slight displacement. The texture input to my blur shader, has wrap parameters: glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP); glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP); When I tell the blur shader to just output the the value of the pixel, the result is not displaced, so it must have something to do with how neighboring pixels are sampled. Any thoughts?

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• Rendering Text with the HTML5 Canvas

  - by dwahlin

  In a previous post I walked through the fundamentals of rendering shapes such as squares and circles using the HTML5 Canvas API. In this post I’ll provide a simple example of rendering and rotating text. To render text you can use the fillText() or strokeText() functions which take the text to render as well as the x and y coordinates of where to render it. To rotate text you can use the transform functions available with the HTML5 Canvas such as save(), rotate(), and restore(). To run the live demos that follow click the Result tab in the blue bar of each demo.   Rendering Text This example provides a simple look at how text can be rendered using the HTML5 Canvas. It iterates through a loop, updates the text and font size dynamically, measures the width of the text using the measureText() function, and then calls fillText() to render the text with the desired font size to the screen.   Here’s what the code above renders:   Rotating Text This example shows how text can be rendered and even rotated by using transform functions built into the HTML5 Canvas. The code starts by rendering text the standard way using fillText(). It then saves the state of the canvas performs an x,y coordinate transform (moves to 100, 300 respectively) and then rotates the canvas –90 degrees using the rotate() function. After the text is rendered, the canvas is reverted back to it’s existing state (saved by calling the save() function) by calling the restore() function. An additional line of text is then rendered.   Here’s what the code above renders:   If you’re interested in learning more about the HTML5 Canvas and how it can be used in your Web or Windows 8 applications, check out my HTML5 Canvas Fundamentals course from Pluralsight.

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• What's the best algorithm for... [closed]

  - by Paska

  Hi programmers! Today come out a little problem. I have an array of coordinates (latitude and longitude) maded in this way: [0] = "45.01234,9.12345" [1] = "46.11111,9.12345" [2] = "47.22222,9.98765" [...] etc In a loop, convert these coordinates in meters (UTM northing / UTM easting) and after that i convert these coords in pixel (X / Y) on screen (the output device is an iphone) to draw a route line on a custom map. [0] = "512335.00000,502333.666666" [...] etc The returning pixel are passed to a method that draw a line on screen (simulating a route calculation). [0] = "20,30" [1] = "21,31" [2] = "25,40" [...] etc As coordinate (lat/lon) are too many, i need to truncate lat/lon array eliminating the values that doesn't fill in the map bound (the visible part of map on screen). Map bounds are 2 couple of coords lat/lon, upper left and lower right. Now, what is the best way to loop on this array (NOT SORTED) and check if a value is or not in bound and after remove the value that is outside? To return a clean array that contains only the coords visible on screen? Note: the coords array is a very big array. 4000/5000 couple of items. This is a method that should be looped every drag or zoom. Anyone have an idea to optimize search and controls in this array? many thanks, A

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• Z Order in 2D with orthographic projection and texture atlas

  - by Carbon Crystal

  I am working with a 2D game in OpenGL ES and have a question about z-order together with a texture atlas. I am using an orthographic projection because I want pixel-perfect rendering of 2D sprites, however from what I can determine the draw order is really the only thing that will determine which textures (sprites) appear above or below their neighbors. That is, the "z-index" is a function of the order in which the textures are drawn as opposed to the z coordinate on the vertex array being drawn. So.. I have a texture atlas to save binding multiple textures for each draw call but this immediately creates a problem if there is more than one atlas in play. If I need to draw textures from more than one atlas (typically the case if I have too many sprites to fit in a single atlas of a reasonable size), then I can't maintain a "draw order" across atlases unless I want to bind/unbind the atlas textures more than once.. which kinda defeats the purpose. Does anyone have any clues as to what the best approach is here? Currently I'm running under an assumption that I will have to declare different fixed "depths" (e.g foreground, background etc) in my 2D scene and assume that the z-order for sprites at a given depth is the same. Then I can have as many atlases as I need at each depth and simply draw the depths in order (along with their associated atlases) I'd love to hear what other people are doing.

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• Advantages and Disadvantages of the Waterfall Methodology

  In my personal opinion I believe the waterfall method is one of the worst methodologies to use when developing larger systems because it leaves is no room for mistakes. As the name implies the waterfall methodology does not allow  for projects to go back up stream to recover from design errors, missing and/or limited requirements. In addition, hidden bugs are not usually found until the testing phase. This can prove to be very costly and time consuming to the developer and the client. According to NCycles.com, the waterfall methodology structures a project into separate stages with defined deliverables from each phase. Define Design Code Test Implement Document and Maintain The advantages found by Ncycle.com to this methodology are: Ease in analyzing potential changes  Ability to coordinate larger teams, even if geographically distributed Can enable precise dollar budget Less total time required from Subject Matter Experts The disadvantages found by Ncycle.com to this methodology are: Lack of flexibility Hard to predict all needs in advance Intangible knowledge lost between hand-offs Lack of team cohesion Design flaws not discovered until the Testing phase References: NCycles.com  (2002). Retrieved from http://www.ncycles.com/e_whi_Methodologies.htmmethodology on April 17, 2009

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• Static "LoD" hack opinions

  - by David Lively

  I've been playing with implementing dynamic level of detail for rendering a very large mesh in XNA. It occurred to me that (duh) the whole point of this is to generate small triangles close to the camera, and larger ones far away. Given that, rather than constantly modifying or swapping index buffers based on a feature's rendered size or distance from the camera, it would be a lot easier (and potentially quite a bit faster), to render a single "fan" or flat wedge/frustum-shaped planar mesh that is tessellated into small triangles close to the near or small end of the frustum and larger ones at the far end, sort of like this (overhead view) (Pardon the gap in the middle - I drew one side and mirrored it) The triangle sizes are chosen so that all are approximately the same size when projected. Then, that mesh would be transformed to track the camera so that the Z axis (center vertical in this image) is always aligned with the view direction projected into the XZ plane. The vertex shader would then read terrain heights from a height texture and adjust the Y coordinate of the mesh to match a height field that defines the terrain. This eliminates the need for culling (since the mesh is generated to match the viewport dimensions) and the need to modify the index and/or vertex buffers when drawing the terrain. Obviously this doesn't address terrain with overhangs, etc, but that could be handled to a certain extent by including a second mesh that defines a sort of "ceiling" via a different texture. The other LoD schemes I've seen aren't particularly difficult to implement and, in some cases, are a lot more flexible, but this seemed like a decent quick-and-dirty way to handle height map-based terrain without getting into geometry manipulation. Has anyone tried this? Opinions?

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• CS3, Illustrator - Where Do X/Y Coordinates Measure from?

  - by nicorellius

  I have a project where there are several PDF files. I'm using Illustrator to make these. It seems the point/line of origin is inconsistent from image to image (file to file). Where is the point of origin, by default, in CS3 Illustrator? It would be nice if, while I was positioning images, I could just say, "OK, x coordinate is 5.5 inches in this document, so it is 5.5 in that one." But it seems this is not the case. Anyone know how Illustrator sets these parameters?

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• XNA calculate normals for linesegment

  - by Gerhman

  I am quite new to 3D graphical programming and thus far only understand that normal somehow define the direction in which a vertex faces and therefore the direction in which light is reflected. I have now idea how they are calculated though, only that they are defined by a Vector3. For a visualizer that I am creating I am importing a bunch of coordinate which represent layer upon layer of line segments. At the moment I am only using a vertex buffer and adding the start and end point of each line and then rendering a linelist. The thing is now that I need to calculate the normal for the vertices of these line segments so that I can get some realistic lighting. I have no idea how to calculate these normal but I know they all face sideways and not up or down. To calculate them all I have are the start and end positions of each line segment. The below image is a representation of what I think I need to do in the case of an example layer: The red arrows represent the normal that should be calculates, the blue text represent the coordinates of the vertices and the green numbers represent their indices. I would greatly appreciate it if someone could please explain to me how I should calculate these normal.

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• What is UVIndex and how do I use it on OpenGL?

  - by Delta

  I am a noob in OpenGL ES 2.0 (for WebGL) and I'm trying to draw a simple model I've made with a 3D tool and exported to .fbx format. I've been able to draw some models that only have: A vertex buffer, a index buffer for the vertices, a normal buffer and a texture coordinate buffer, but this model now has a "UVIndex" and I'm not sure where am I supposed to put this UVIndex. My code looks like this: GL.bindBuffer(GL.ARRAY_BUFFER, this.Model.House.VertexBuffer); GL.vertexAttribPointer(this.Shader.TextureAndLighting.Attribute["vPosition"],3,GL.FLOAT, false, 0, 0); GL.bindBuffer(GL.ARRAY_BUFFER, this.Model.House.NormalBuffer); GL.vertexAttribPointer(this.Shader.TextureAndLighting.Attribute["vNormal"], 3, GL.FLOAT, false, 0, 0); GL.bindBuffer(GL.ARRAY_BUFFER, this.Model.House.TexCoordBuffer); GL.vertexAttribPointer(this.Shader.TextureAndLighting.Attribute["TexCoord"], 2, GL.FLOAT, false, 0, 0); GL.bindBuffer(GL.ELEMENT_ARRAY_BUFFER, this.Model.House.IndexBuffer); GL.bindTexture(GL.TEXTURE_2D, this.Texture.HTex1); GL.activeTexture(GL.TEXTURE0); GL.drawElements(GL.TRIANGLES, this.Model.House.IndexBuffer.Length, GL.UNSIGNED_SHORT, 0); But my model renders totally incorrect and I think it has to do with the fact that I am ignoring this "UVIndex" in the .fbx file, since I've never drawn any model that uses this UVIndex I really have no clue on what to do with it. This is the json file containing the model's data: http://pastebin.com/raw.php?i=G294TVmz

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• How to manage preventive maintenance planning for external IT support?

  - by code-gijoe

  I am a bit puzzled by the way to handle server upgrade planning for software we maintain on remote sites. This is my case: I work for a software company that has many external clients. We are trying to be more Agile in our development so we plan to release small improvements every quarter and we wish to keep our clients informed of maintenance schedules. Instead of having angry clients that believe there ROI of our support plan is low, we want to be more proactive. Lets say we have 100 machines to take care of, is there some tool to assist me in planing the maintenance with clients? Right now I get a call from a client that is unhappy requesting we upgrade them, that is when we go into panic mode and start making calls. That is when I need to check my calendar, coordinate with the other guys, call a few times, change the date again and again until everyone is happy. Can this be done better?

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• Proportional speed movement between mouse and cube

  - by user1350772

  Hi i´m trying to move a cube with the freeglut mouse "glutMotionFunc(processMouseActiveMotion)" callback, my problem is that the movement is not proportional between the mouse speed movement and the cube movement. MouseButton function: #define MOVE_STEP 0.04 float g_x=0.0f; glutMouseFunc(MouseButton); glutMotionFunc(processMouseActiveMotion); void MouseButton(int button, int state, int x, int y){ if(button == GLUT_LEFT_BUTTON && state== GLUT_DOWN){ initial_x=x; } } When the left button gets clicked the x cordinate is stored in initial_x variable. void processMouseActiveMotion(int x,int y){ if(x>initial_x){ g_x-= MOVE_STEP; }else{ g_x+= MOVE_STEP; } initial_x=x; } When I move the mouse I look in which way it moves comparing the mouse new x coordinate with the initial_x variable, if xinitial_x the cube moves to the right, if not it moves to the left. Any idea how can i move the cube according to the mouse movement speed? Thanks EDIT 1 The idea is that when you click on any point of the screen and you drag to the left/right the cube moves proportionally of the mouse mouvement speed.

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• Explicitly pass context object versus injecting with IoC

  - by SonOfPirate

  I have a layered service application where the service layer delegates operations into the domain layer for execution. Many of these operations need to know the context under which they are operation. (The context included the identity of the current user, culture information, etc. received from the caller.) For example, I have an API method that returns a list of announcements. The list is based on the current user's role and each announcement is localized to their culture. The API is a thin-facade that delegates to an Application Service in my domain layer. The Application Service method obviously needs to know the context of the current request/operation as another call to the same API from another user should result in a different list. Within this method, we also have logging that uses some of the context information so we a clear understanding of the context when the operation was performed (this is especially useful if something goes wrong.) While this is a contrived example, in the real world, my Application Services will coordinate operations with many collaborative components, any number of them also needing the context information. My choice is to pass the context to the Application Service which would then pass it with any calls to collaborators or have the IoC container satisfy the dependency the Application Service and any collaborators have on the context. I am wondering if it is considered good/bad, best practices/code smell, etc. if I pass the context object as a parameter to the domain methods or if injecting the context via an IoC container is preferred. (EDIT: I should mention that the context object is instantiated per-request.)

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• OpenGL sprites and point size limitation

  - by Srdan

  I'm developing a simple particle system that should be able to perform on mobile devices (iOS, Andorid). My plan was to use GL_POINT_SPRITE/GL_PROGRAM_POINT_SIZE method because of it's efficiency (GL_POINTS are enough), but after some experimenting, I found myself in a trouble. Sprite size is limited (to usually 64 pixels). I'm calculating size using this formula gl_PointSize = in_point_size * some_factor / distance_to_camera to make particle sizes proportional to distance to camera. But at some point, when camera is close enough, problem with size limitation emerges and whole system starts looking unrealistic. Is there a way to avoid this problem? If no, what's alternative? I was thinking of manually generating billboard quad for each particle. Now, I have some questions about that approach. I guess minimum geometry data would be four vertices per particle and index array to make quads from these vertices (with GL_TRIANGLE_STRIP). Additionally, for each vertex I need a color and texture coordinate. I would put all that in an interleaved vertex array. But as you can see, there is much redundancy. All vertices of same particle share same color value, and four texture coordinates are same for all particles. Because of how glDrawArrays/Elements works, I see no way to optimise this. Do you know of a better approach on how to organise per-particle data? Should I use buffers or vertex arrays, or there is no difference because each time I have to update all particles' data. About particles simulation... Where to do it? On CPU or on a vertex processors? Something tells me that mobile's CPU would do it faster than it's vertex unit (at least today in 2012 :). So, any advice on how to make a simple and efficient particle system without particle size limitation, for mobile device, would be appreciated. (animation of camera passing through particles should be realistic)

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• backface culling error (in world space)

  - by acrilige

  I write simple software renderer. In my pipeline i have stage of backface culling. But looks like it has some error (see picture). I perform culling right after world transformation (is it correct?). (i can't insert picture in post coz i don't have enough points, so i just upload it (cube model): http://imageshack.us/photo/my-images/705/bcerror.png/) Vector3F view_dir(0.0f, 0.0f, 1.0f); std::vector<Triangle> to_remove; for (Triangle &t : m_triangles) { Vector4F e1 = t.v2 - t.v1; Vector4F e2 = t.v3 - t.v1; Vector3F normal( e1.y * e2.z - e1.z * e2.y, e1.z * e2.x - e1.x * e2.z, e1.x * e2.y - e1.y * e2.x ); normal.Normalize(); float dot = Dot(view_dir, normal); if (dot <= 0) to_remove.push_back(t); } for (Triangle& t : to_remove) m_triangles.erase(std::remove(m_triangles.begin(), m_triangles.end(), t), m_triangles.end()); Camera sits in origin and points in screen (RH). What is the reason? For better explanation i upload picture with cube rotation screenshots: http://imageshack.us/photo/my-images/842/bcmove.png/ UPDATED: The error occurs only when triangle has non-zero offset from origin UPDATED 2: If i process backface culling in clip space (after transforming all vertices with view and projection matrix), and just check z coordinate of triangle normal - it works perfect... Can i perform culing RIGHT BEFORE view/proj transforms? In this case looks like culling will not depends of projection and it's not right?.. UPDATED 3: I found answer and will post it in two hours - again coz of reputation lack.

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