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Search found 36 results on 2 pages for 'concave'.

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• Convex Hull for Concave Objects

  - by Lighthink

  I want to implement GJK and I want it to handle concave shapes too (almost all my shapes are concave). I've thought of decomposing the concave shape into convex shapes and then building a hierarchical tree out of convex shapes, but I do not know how to do it. Nothing I could find on the Internet about it wasn't satisfying my needs, so maybe someone can point me in the right direction or give a full explanation.

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• Breaking a concave polygon into convex ones.

  - by Bart van Heukelom

  I'm using a game physics library (Box2D) which only supports convex polygon shapes. However, I'd like the level builder to be able to just specify concave polygons without having to worry about that. So, how can I automatically break apart a concave polygon into convex ones (or even all triangles). Speed would be cool, but ease of implementation is more important. The breaking apart will only be done on game initialization. (My language is Flash/ActionScript 3, but that shouldn't matter)

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• Given a large set of vertices in a non-convex polygon, how can i find the edges?

  - by tommy chheng

  I have a set of vertices(called A) and I want to find all the border vertices such that this border vertices set is an outline of the shape. Many of the vertices in A are redundant because they are inside the shape, I want to get rid of these vertices. My question is similar to http://stackoverflow.com/questions/477867/best-algorithm-to-find-the-edges-polygon-of-vertices but i need it to work for a non-convex polygon case.

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• Drawing particles as a smooth blob

  - by Nömmik

  I'm new to game/graphics development and I'm playing around with particles (in 2D). I want to draw particles close to each other as a blob, just as liquid/water. I do not want to draw big circles overlapping as the blob won't be smooth (and too big). I don't really know physics but I assume what I want is something looking similar to surface tension. I haven't been able to find anything on stackexchange or on Google (maybe I do not know the correct keywords?). So far I have found two possible solutions, but I am unable to find any concrete information about algorithms. One of them is to calculate the concave hull of particles I consider being a blob. I can calculate the blob by creating an equivalence class (on the relation "close to each other"). Strangely enough I haven't been able to find any algorithm explaining how to calculate the concave hull. Many posts (and among stackexchange) links to libraries or commercial products that do this (I need libraries to work in C#), but never any algorithm. Also this solution might have a problem with a circle of particles, which would not detect the empty space in the middle. While researching concave hull I stumbled upon something called alpha shapes. Which seems to be exactly what I want to do, however just as with concave hull I haven't found any source explaining how they actually work. I have found some presentation materials but not enough to go on. It's like a big secret everyone knows except me :-/ After calculating the concave hull or alpha shape I want to make it a Bézier curve to make it smooth and nice. Although I do find my approach a bit too complex, maybe I am trying to solve this the wrong way? If you can either suggest any other solution to my problem, or explain the pieces I am missing I would be very happy and grateful :-) Thanks.

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• Distance from a point to a polygon

  - by clwen

  I am trying to determine the distance from a point to a polygon in 2D space. The point can be inside or outside the polygon; The polygon can be convex or concave. If the point is within the polygon or outside the polygon with a distance smaller than a user-defined constant d, the procedure should return True; False otherwise. I have found a similar question: Distance from a point to a polyhedron or to a polygon. However, the space is 2D in my case and the polygon can be concave, so it's somehow different from that one. I suppose there should be a method simpler than offsetting the polygon by d and determining it's inside or outside the polygon. Any algorithm, code, or hints for me to google around would be appreciated.

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• Add 2 titles styles in Nivo Lightbox Jquery

  - by user2984054

  I need to add 2 different titles to customize each one of them in the Nivo Lightbox Example: http://prntscr.com/23o766 But it's look like is not possible, is there a way to put 2 titles on 1 image? Or anyway to resolve this? also, I would love to be able to use the title as a link, but there are a lot of limitations. thanks. Code: <a class="image image-full" data-lightbox-gallery="gallery1" href="nivo-lightbox/img/b/grey_antique_q_white_mortar_concave_finish_technique_view_b.jpg" title="Grey Antique Q White Mortar Concave Finish Technique View B"> <img id="sample_board_image" src="nivo-lightbox/img/s/grey_antique_q_white_mortar_concave_finish_technique_view_b.jpg" alt="Grey Antique Q White Mortar Concave Finish Technique View B"></img> </a> There's must be a way to add more than 1 style in the title or any other way to add that text in the overlay in the Lightbox. I actually already tried the insertion of another html on the nivo lightbox, but it gives me a lot of trouble, the content is not showing properly, is there a way the content fits on the lightbox? http://prntscr.com/23qm97

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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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• Drawing an outline around an arbitrary group of hexagons

  - by Perky

  Is there an algorithm for drawing an outline around around an arbitrary group of hexagons? The polygon outline drawn may be concave. See the images below, the green line is what I am trying to achieve. The hexagons are stored as vertices and drawn as polygons. Edit: I've uploaded images that should explain more. I want to favour convex hulls because it's conveys an area of control more quickly. Each hexagon is stored in a multidimensional array so they all have x and y coordinates, I can easily find adjacent hexagons and the opposite vertex, i.e. adjacentHexagon = getAdjacentHexagon( someHexagon, NORTHWEST ) if there isn't a hexagon immediately adjacent it will continue to search in that direction until it finds one or hits the map edges.

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• Continuous Collision Detection Techniques

  - by Griffin

  I know there are quite a few continuous collision detection algorithms out there , but I can't find a list or summary of different 2D techniques; only tutorials on specific algorithms. What techniques are out there for calculating when different 2D bodies will collide and what are the advantages / disadvantages of each? I say techniques and not algorithms because I have not yet decided on how I will store different polygons which might be concave or even have holes. I plan to make a decision on this based on what the algorithm requires (for instance if an algorithm breaks down a polygon into triangles or convex shapes I will simply store the polygon data in this form).

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• Outline Shader Effect for Orthogonal Geometry in XNA

  - by Griffin

  I just recently started learning the art of shading, but I can't give an outline width to 2D, concave geometry when restrained to a single vertex/pixel shader technique (thanks to XNA). the shape I need to give an outline to has smooth, per-vertex coloring, as well as opacity. The outline, which has smooth, per-vertex coloring, variable width, and opacity cannot interfere with the original shape's colors. A pixel depth border detection algorithm won't work because pixel depth isn't a 3.0 semantic. expanding geometry / redrawing won't work because it interferes with the original shape's colors. I'm wondering if I can do something with the stencil/depth buffer outside of the shader functions since I have access to that through the graphics device. But I don't believe I'm able to manipulate actual values. How might I do this?

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• Drawing Shape in DebugView (Farseer)

  - by keyvan kazemi

  As the title says, I need to draw a shape/polygon in Farseer using debugview. I have this piece of code which converts a Texture to polygon: //load texture that will represent the tray trayTexture = Content.Load<Texture2D>("tray"); //Create an array to hold the data from the texture uint[] data = new uint[trayTexture.Width * trayTexture.Height]; //Transfer the texture data to the array trayTexture.GetData(data); //Find the vertices that makes up the outline of the shape in the texture Vertices verts = PolygonTools.CreatePolygon(data, trayTexture.Width, false); //Since it is a concave polygon, we need to partition it into several smaller convex polygons _list = BayazitDecomposer.ConvexPartition(verts); Vector2 vertScale = new Vector2(ConvertUnits.ToSimUnits(1)); foreach (Vertices verti in _list) { verti.Scale(ref vertScale); } tray = BodyFactory.CreateCompoundPolygon(MyWorld, _list, 10); Now in DebugView I guess I have to use "DrawShape" method which requires: DrawShape(Fixture fixture, Transform xf, Color color) My question is how can I get the variables needed for this method, namely Fixture and Transform?

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• matrix to transform unit cube to space defined by 8 arbitrary points

  - by aadster

  I asked a question relating to similar to this already, but I think this is a clearer objective of what Im trying to achieve.. or whether its possible at all! Im trying to find a transformation (matrix ideally) which would transform the 8 points of a 3d unit cube to 8 arbitrary points in space. The 8 target points have no known structure. e.g: My gut feeling is that a matrix is unable to provide this xform since the cube faces vertices can be concave.. but are there any other methods of transformation? Thanks!

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• OpenGL 3 equivalent of GLUTesselator?

  - by user146780

  I was wondering, since things like display lists are now deprecated, I'm thinking the GLU polygon tesselator is probably also deprecated. What is the new and correct way of creating concave or complex polygons and complying with the new GL 3 standard? Thanks.

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• OpenGL 3 equivillant of GLUTesselator?

  - by user146780

  I was wondering, since things like display lists are now deprecated, I'm thinking the GLU polygon tesselator is probably also deprecated. What is the new and correct way of creating concave or complex polygons and complying with the new GL 3 standard? Thanks.

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• Arrange points in sequence.

  - by Himadri

  I have some points in 3D which are in a single plane. I want to arrange them in clock wise or counter clockwise order. The points can create a concave or convex polygon in a single plane. Can any body give any suggestions?

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• Cuboid inside generic polyhedron

  - by DOFHandler

  I am searching for an efficient algorithm to find if a cuboid is completely inside or completely outside or (not-inside and not-outside) a generic (concave or convex) polyhedron. The polyhedron is defined by a list of 3D points and a list of facets. Each facet is defined by the subset of the contour points ordinated such as the right-hand normal points outward the solid. Any suggestion? Thank you

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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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• 3D physics engine for accurate collision handling on desktop/laptop computers (non-console)

  - by Georges Oates Larsen

  What are your suggestions for a physics engine that satisfies the following criteria? Capable of calculating collisions between multiple concave mesh-based colliders Handles many collisions going on at once (for instance one mesh being wedged between two others, which themselves may be wedged between two meshes) Does not allow for collider passthrough, even at high speeds. For instance, if I am applying force to a programmatically hinged object that makes it spin, I do not want it to pass through another rigidbody that it collides with while spinning. I have this problem using PhysX As implied before, reacts well to hinged objects, preferably has its own implementation of a hinge, but I am willing to program my own. The important part is that it has some sort of interface that guarantees accurate collision tracking even when dealing with these things Platform independent -- runs on mac as well as PC, also not tied down to specific graphics cards I think that's the best way to explain what I am looking for. Basically, I need SUPER reliable collisions. Something that can't be accomplished with a simple ray casting approach that sends a ray from the last position of the object to the current position (as this object may be potentially large and colliding with small objects via rotation) Bonus points for also including an OPEN SOURCE engine.

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• Draw contour around object in Opengl

  - by Maciekp

  I need to draw contour around 2d objects in 3d space. I tried drawing lines around object(+points to fill the gap), but due to line width, some part of it(~50%) was covering object. I tried to use stencil buffer, to eliminate this problem, but I got sth like this(contour is green): http://goo.gl/OI5uc (sorry I can't post images, due to my reputation) You can see(where arrow points), that some parts of line are behind object, and some are above. This changes when I move camera, but always there is some part, that is covering it. Here is code, that I use for drawing object: glColorMask(1,1,1,1); std::list<CObjectOnScene*>::iterator objIter=ptr->objects.begin(),objEnd=ptr->objects.end(); int countStencilBit=1; while(objIter!=objEnd) { glColorMask(1,1,1,1); glStencilFunc(GL_ALWAYS,countStencilBit,countStencilBit); glStencilOp(GL_REPLACE,GL_KEEP,GL_REPLACE ); (*objIter)->DrawYourVertices(); glStencilFunc(GL_NOTEQUAL,countStencilBit,countStencilBit); glStencilOp(GL_KEEP,GL_KEEP,GL_REPLACE); (*objIter)->DrawYourBorder(); ++objIter; ++countStencilBit; } I've tried different settings of stencil buffer, but always I was getting sth like that. Here is question: 1.Am I setting stencil buffer wrong? 2. Are there any other simple ways to create contour on such objects? Thanks in advance. EDIT: 1. I don't have normals of objects. 2. Object can be concave. 3. I can't use shaders(see below why).

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• Finding the centeroid of a polygon?

  - by user146780

  I have tried: for each vertex, add to total, divide by number of verities to get center. I'v also tried: Find the topmost, bottommost - get midpoint... find leftmost, rightmost, find midpoint. Both of these did not return the perfect center because I'm relying on the center to scale a polygon. I want to scale my polygons so I may put a border around them. What is the best way to find the centroid of a polygon given that the polygon may be concave, convex and have many many sides of various lengths. Thanks

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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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• Chipmunk Physics or Box2D for C++ 2D GameEngine ?

  - by Mr.Gando

  Hello, I'm developing what it's turning into a "cross-platform" 2D Game Engine, my initial platform target is iPhone OS, but could move on to Android or even some console like the PSP, or Nintendo DS, I want to keep my options open. My engine is developed in C++, and have been reading a lot about Box2D and Chipmunk but still I can't decide which one to use as my Physics Middleware. Chipmunk appears to have been made to be embedded easily, and Box2D seems to be widely used. Chipmunk is C , and Box2D is C++, but I've heard the API's of Box2D are much worse than chipmunk's API's. For now I will be using the engine shape creation and collision detection features for irregular polygons (not concave). I value: 1) Good API's 2) Easy to integrate. 3) Portability. And of course if you notice anything else, I would love to hear it. Which one do you think that would fit my needs better ?

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• textures and vertex arrays with OpenGL?

  - by user146780

  Basically what I'd like to do is make textured NGONS. I also want to use a tesselator (GLU) to make concave and multicontour objects. I was wondering how the texture comes into play though. I think that the tesselator will return verticies so I will add these to my array, that's fine. But my vertex array will contain more than one polygon object so then how can I tell it when to bind the texture like in immediate mode? Right now I feel stuck with one call to bind. How can this be done? Thanks

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• Gradients and memory

  - by user146780

  I'm creating a drawing application with OpenGL. I'v created an algorithm that generates gradient textures. I then map these to my polygons and this works quite well. What I realized is how much memory this requires. Creating 1000 gradients takes about 800MB and that's way too much. Is there an alternative to textures, or a way to compress them, or another way to map gradients to polygons that doesn't use up as much memory? Thanks My polygons are concave, I use GLUTesselator, and they are multicolored and point to point

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• Finding the centroid of a polygon?

  - by user146780

  I have tried: for each vertex, add to total, divide by number of verities to get center. I'v also tried: Find the topmost, bottommost - get midpoint... find leftmost, rightmost, find midpoint. Both of these did not return the perfect center because I'm relying on the center to scale a polygon. I want to scale my polygons so I may put a border around them. What is the best way to find the centroid of a polygon given that the polygon may be concave, convex and have many many sides of various lengths. Thanks

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