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Search found 93 results on 4 pages for 'convex hull'.

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• Polygon triangulation

  - by Saurabh

  Hey, I am working on nesting of sheet metal parts and am implementing Minkowski Sums to find No Fit Polygons for nesting. The problem is I can give only convex sets as input to the code which calculates Minkowski sums for me. Hence I need to break a concave polygon, with holes into Convex sets. I am open to triangulation also, but I am looking for a working code on VC++ (6.0). I am slightly running short on time as my whole code is ready and just waiting for input in the form of convex sets. I would really appreciate if somebody with prior experience can help me in this. I have gone through other posts but did not find anything matching to this. I am a student of mechanical engineering and really dun have much idea about computer languages. All I can handle is compiling a code on VC++ and incorporate it with my existing code. Looking forward to responses!! Thanks Warm regards Saurabh India

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• winrar command line folder stucture

  - by Lee Hull

  I am trying to zip up a folder.. Example: C:\Test*.* C:\Test\bin*.* I want to be able to zip up the Test folder with bin subfolder, however, I need the Test folder contents in the zip root. I am trying to do this using the WinRar command line (rar.exe) I've tried using rar.exe a "C:\File.zip" -ep "C:\Test" but it puts all the folder contents in root... Tried rar.exe a "C:\File.zip" -ep "C:\Test*.*" "C:\Test\bin" same thing.. any ideas?

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• Algorithm to merge adjacent rectangles into polygon

  - by Glitch

  I guess that my problem is related to "convex hull", but no the same. All shapes in the drawing are rectangles with same width and height. Many are adjacent to each other. I want to combine those adjacent rectangles into polygons. Unlike "convex hull", the resuled polygons could be "hollow" inside. Is there any open source algorithm available?

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• Single Table Per Class Hierarchy with an abstract superclass using Hibernate Annotations

  - by Andy Hull

  I have a simple class hierarchy, similar to the following: @Entity @Table(name="animal") @Inheritance(strategy=InheritanceType.SINGLE_TABLE) @DiscriminatorColumn(name="animal_type", discriminatorType=DiscriminatorType.STRING) public abstract class Animal { } @Entity @DiscriminatorValue("cat") public class Cat extends Animal { } @Entity @DiscriminatorValue("dog") public class Dog extends Animal { } When I query "from Animal" I get this exception: "org.hibernate.InstantiationException: Cannot instantiate abstract class or interface: Animal" If I make Animal concrete, and add a dummy discriminator... such as @DiscriminatorValue("animal")... my query returns my cats and dogs as instances of Animals. I remember this being trivial with HBM based mappings but I think I'm missing something when using annotations. Can anyone help? Thanks!

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• Proper way to copy a readonly NSMutableArray

  - by Jon Hull

  I have an object with a readonly property that I am trying to implement NSCopying for. It has a mutableArray called "subConditions" (which holds "SubCondition" objects). I have made it readonly because I want callers to be able to change the data in the array, but not the array itself. This worked really well until it was time to write the -copyWithZone: method. After fumbling around a bit, I managed to get something that seems to work. I am not sure if it is the best practice though. Here is a simplified version of my -copyWithZone: method: -(id)copyWithZone:(NSZone*)zone { Condition *copy = [[[self class]allocWithZone:zone]init]; NSArray *copiedArray = [[NSArray alloc]initWithArray:self.subConditions copyItems:YES]; [copy.subConditions setArray:copiedArray]; [copiedArray release]; return copy; } Is this the correct/best way to copy a readonly mutableArray?

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• ANTLR lexing getting confused over '...' and floats

  - by Andy Hull

  I think the ANTLR lexer is treating my attempt at a range expression "1...3" as a float. The expression "x={1..3}" is coming out of the lexer as "x={.3}" when I used the following token definitions: FLOAT : ('0'..'9')+ ('.' '0'..'9'+)? EXPONENT? | ('.' '0'..'9')+ EXPONENT? ; AUTO : '...'; When I change FLOAT to just check for integers, as so: FLOAT : ('0'..'9')+; then the expression "x={1...3}" is tokenized correctly. Can anyone help me to fix this? Thanks!

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• UIScrollView eating touches from its parent

  - by Jon Hull

  I have nested scrollViews (or rather a subclass of UIScrollView inside of an actual scrollview). I set the size of the inner view to its contentSize and set scrollEnabled = NO, because I only want the outside view scrolling. But the innerView occasionally eats touches and keeps the outerView from scrolling when it should. Is there something else I need to set to keep it from stealing the scrolling touches, but still allowing user interaction (e.g. editing a textView)?

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• Box 2d basic questions

  - by philipp

  I am a bit new to box2d and I am developing an game with type and letters. I am using an svg font and generate the box2d bodies direct from the glyphs path definition, using the convex hull of them. I also have an decomposition routine the decomposes this hull if necessary. All this it is more or less working, except that I got some strange errors which definitely are caused by the scale factors. The problem is caused by two factors: first: the world scale of box2d, second: the the precision of curve-approximation of the glyph vectors. So through scaling down the input vertices for box2d, it happens that they become equal caused by numerical precision, what causes errors in box2d. Through scaling the my glyphs a bit up, this goes away. I also goes away if I chose a different world scale factor, but this slows down the whole animation quite much! So if my view port is about 990px * 600px and i want to animate Glyphs in box2d which should have a size from about 50px * 50px up to 300px * 300px, which scale factor of the b2world should i choose? How small should the smallest distance from on vertex to another be, while approximating the glyph vectors? Thanks for help greetings philipp EDIT:: I continued reading the docs of box2d and after rethinking of the units system, which is designed to handle object from 0.1 up to 10 meters, I calculated a scale factor of 75. So Objects 600px width will are 8 meters wide in box2d and even small objects of about 20px width will become 0.26 meters width in box2d. I will go on trying with this values, but if there is somebody out there who could give me a clever advice i would be happy!

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• What would be a good filter to create 'magnetic deformers' from a depth map?

  - by sebf

  In my project, I am creating a system for deforming a highly detailed mesh (clothing) so that it 'fits' a convex mesh. To do this I use depth maps of the item and the 'hull' to determine at what point in world space the deviation occurs and the extent. Simply transforming all occluded vertices to the depths as defined by the 'hull' is fairly effective, and has good performance, but it suffers the problem of not preserving the features of the mesh and requires extensive culling to avoid false-positives. I would like instead to generate from the depth deviation map a set of simple 'deformers' which will 'push'* all vertices of the deformed mesh outwards (in world space). This way, all features of the mesh are preserved and there is no need to have complex heuristics to cull inappropriate vertices. I am not sure how to go about generating this deformer set however. I am imagining something like an algorithm that attempts to match a spherical surface to each patch of contiguous deviations within a certain range, but do not know where to start doing this. Can anyone suggest a suitable filter or algorithm for generating deformers? Or to put it another way 'compressing' a depth map? (*Push because its fitting to a convex 'bulgy' humanoid so transforms are likely to be 'spherical' from the POV of the surface.)

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• Which linear programming package should I use for high numbers of constraints and "warm starts"

  - by davidsd

  I have a "continuous" linear programming problem that involves maximizing a linear function over a curved convex space. In typical LP problems, the convex space is a polytope, but in this case the convex space is piecewise curved -- that is, it has faces, edges, and vertices, but the edges aren't straight and the faces aren't flat. Instead of being specified by a finite number of linear inequalities, I have a continuously infinite number. I'm currently dealing with this by approximating the surface by a polytope, which means discretizing the continuously infinite constraints into a very large finite number of constraints. I'm also in the situation where I'd like to know how the answer changes under small perturbations to the underlying problem. Thus, I'd like to be able to supply an initial condition to the solver based on a nearby solution. I believe this capability is called a "warm start." Can someone help me distinguish between the various LP packages out there? I'm not so concerned with user-friendliness as speed (for large numbers of constraints), high-precision arithmetic, and warm starts. Thanks!

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• Continuous Physics Engine's Collision Detection Techniques

  - by Griffin

  I'm working on a purely continuous physics engine, and I need to choose algorithms for broad and narrow phase collision detection. "Purely continuous" means I never do intersection tests, but instead want to find ways to catch every collision before it happens, and put each into "planned collisions" stack that is ordered by TOI. Broad Phase The only continuous broad-phase method I can think of is encasing each body in a circle and testing if each circle will ever overlap another. This seems horribly inefficient however, and lacks any culling. I have no idea what continuous analogs might exist for today's discrete collision culling methods such as quad-trees either. How might I go about preventing inappropriate and pointless broad test's such as a discrete engine does? Narrow Phase I've managed to adapt the narrow SAT to a continuous check rather than discrete, but I'm sure there's other better algorithms out there in papers or sites you guys might have come across. What various fast or accurate algorithm's do you suggest I use and what are the advantages / disatvantages of each? Final Note: I say techniques and not algorithms because I have not yet decided on how I will store different polygons which might be concave, convex, round, or even have holes. I plan to make a decision on this based on what the algorithm requires (for instance if I choose an algorithm that breaks down a polygon into triangles or convex shapes I will simply store the polygon data in this form).

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• How does a segment based rendering engine work?

  - by Calmarius

  As far as I know Descent was one of the first games that featured a fully 3D environment, and it used a segment based rendering engine. Its levels are built from cubic segments (these cubes may be deformed as long as it remains convex and sides remain roughly flat). These cubes are connected by their sides. The connected sides are traversable (maybe doors or grids can be placed on these sides), while the unconnected sides are not traversable walls. So the game is played inside of this complex. Descent was software rendered and it had to be very fast, to be playable on those 10-100MHz processors of that age. Some latter levels of the game are huge and contain thousands of segments, but these levels are still rendered reasonably fast. So I think they tried to minimize the amount of cubes rendered somehow. How to choose which cubes to render for a given location? As far as I know they used a kind of portal rendering, but I couldn't find what was the technique used in this particular kind of engine. I think the fact that the levels are built from convex quadrilateral hexahedrons can be exploited.

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• What kind of physics to choose for our arcade 3D MMO?

  - by Nick

  We're creating an action MMO using Three.js (WebGL) with an arcadish feel, and implementing physics for it has been a pain in the butt. Our game has a terrain where the character will walk on, and in the future 3D objects (a house, a tree, etc) that will have collisions. In terms of complexity, the physics engine should be like World of Warcraft. We don't need friction, bouncing behaviour or anything more complex like joints, etc. Just gravity. I have managed to implement terrain physics so far by casting a ray downwards, but it does not take into account possible 3D objects. Note that these 3D objects need to have convex collisions, so our artists create a 3D house and the player can walk inside but can't walk through the walls. How do I implement proper collision detection with 3D objects like in World of Warcraft? Do I need an advanced physics engine? I read about Physijs which looks cool, but I fear that it may be overkill to implement that for our game. Also, how does WoW do it? Do they have a separate raycasting system for the terrain? Or do they treat the terrain like any other convex mesh? A screenshot of our game so far:

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• How does a segment-based rendering engine (as in Descent) work?

  - by Calmarius

  As far as I know Descent was one of the first games that featured a fully 3D environment, and it used a segment based rendering engine. Its levels are built from cubic segments (these cubes may be deformed as long as it remains convex and sides remain roughly flat). These cubes are connected by their sides. The connected sides are traversable (maybe doors or grids can be placed on these sides), while the unconnected sides are not traversable walls. So the game is played inside of this complex. Descent was software rendered and it had to be very fast, to be playable on those 10-100MHz processors of that age. Some latter levels of the game are huge and contain thousands of segments, but these levels are still rendered reasonably fast. So I think they tried to minimize the amount of cubes rendered somehow. How to choose which cubes to render for a given location? As far as I know they used a kind of portal rendering, but I couldn't find what was the technique used in this particular kind of engine. I think the fact that the levels are built from convex quadrilateral hexahedrons can be exploited.

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• MySQL Exotic Storage Engines

  MySQL has an interesting architecture that allows you to plug in different modules to handle storage. What that means is that it's quite flexible, offering an interesting array of different storage engines with different features, strengths, and tradeoffs. Sean Hull presents some of the newest and more exotic storage engines, and even some that are still in development.

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• MySQL Exotic Storage Engines

  MySQL has an interesting architecture that allows you to plug in different modules to handle storage. What that means is that it's quite flexible, offering an interesting array of different storage engines with different features, strengths, and tradeoffs. Sean Hull presents some of the newest and more exotic storage engines, and even some that are still in development.

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• Five Query Optimizations in MySQL

  Query optimization is an often overlooked part of applications. Sean Hull encourages at least some attention to query optimization up front and helps you identify some of the more common optimizations you may run across.

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• DRBD and MySQL - Virtualbox Setup

  DRBD is a Linux project that provides a real-time distributed filesystem. Sean Hull demonstrates how to use Sun's virtualbox software to create a pair of VMs, then configure those VMs with DRBD, and finally install and test MySQL running on volumes sitting on DRBD.

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• DRBD and MySQL - Virtualbox Setup

  DRBD is a Linux project that provides a real-time distributed filesystem. Sean Hull demonstrates how to use Sun's virtualbox software to create a pair of VMs, then configure those VMs with DRBD, and finally install and test MySQL running on volumes sitting on DRBD.

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• MySQL: Five Dials to Set

  In this article, Sean Hull looks at the first five out of ten dials that you can turn to get an initial MySQL vanilla install working for your specific application requirements.

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• Largest triangle from a set of points

  - by Faken

  I have a set of random points from which i want to find the largest triangle by area who's verticies are each on one of those points. So far I have figured out that the largest triangle's verticies will only lie on the outside points of the cloud of points (or the convex hull) so i have programmed a function to do just that (using Graham scan in nlogn time). However that's where I'm stuck. The only way I can figure out how to find the largest triangle from these points is to use brute force at n^3 time which is still acceptable in an average case as the convex hull algorithm usually kicks out the vast majority of points. However in a worst case scenario where points are on a circle, this method would fail miserably. Dose anyone know an algorithm to do this more efficiently? Note: I know that CGAL has this algorithm there but they do not go into any details on how its done. I don't want to use libraries, i want to learn this and program it myself (and also allow me to tweak it to exactly the way i want it to operate, just like the graham scan in which other implementations pick up collinear points that i don't want).

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• How can I make an object's hitbox rotate with its texture?

  - by Matthew Optional Meehan

  In XNA, when you have a rectangular sprite that doesnt rotate, it's easy to get its four corners to make a hitbox. However, when you do a rotation, the points get moved and I assume there is some kind of math that I can use to aquire them. I am using the four points to draw a rectangle that visually represents the hitboxes. I have seen some per-pixel collision examples, but I can forsee they would be hard to draw a box/'convex hull' around. I have also seen physics like farseer but I'm not sure if there is a quick tutorial to do what I want.

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• what is the easiest way to make a hitbox that rotates with it's texture

  - by Matthew Optional Meehan

  In xna when you have a sprite that doesnt rotate it's very easy to get the four corner of a sprite to make a hitbox, but when you do a rotation the points get moved and I assume there is some kind of math that I can use to aquire them. I am using the four points to draw a rectangle that visually represents the hitboxes. I have seen some per-pixel collission examples but I can forsee they would be hard to draw a box/'convex hull' around. I have also seen physics like farseer but I'm not sure if there is a quick tutorial to do what I want. What do you guys think is the best approach becuase I am looking to complete this work by the end of the week.

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• What is the minimum of shader I need to use to run basic calculation on GPU?

  - by Jinxi

  I read, that the Hull Shader, Domain Shader, Geometry Shader and Pixel Shader can be used optional. So, is the Vertex Shader optional too? If no: What does a basic Vertex Shader look like? Just like a simple pass through? Is the Vertex Shader necessary to tell what kind of datastructure (Van Stripes or Meshes) are used? What can I do, with just the vertex shader? Are the fixed functions working without any help of programming a programmable stage?

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• Implementing 2D CSG (for collision shapes)?

  - by bluescrn

  Are there any simple (or well documented) algorithms for basic CSG operations on 2D polygons? I'm looking for a way to 'add' a number of overlapping 2D collision shapes. These may be convex or concave, but will be closed shapes, defined as a set of line segments, with no self-intersections. The use of this would be to construct a clean set of collision edges, for use with a 2D physics engine, from a scene consisting of many arbitrarily placed (and frequently overlapping) objects, each with their own collision shape. To begin with, I only need to 'add' shapes, but the ability to 'subtract', to create holes, may also be useful.

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