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  • Collision within a poly

    - by G1i1ch
    For an html5 engine I'm making, for speed I'm using a path poly. I'm having trouble trying to find ways to get collision with the walls of the poly. To make it simple I just have a vector for the object and an array of vectors for the poly. I'm using Cartesian vectors and they're 2d. Say poly = [[550,0],[169,523],[-444,323],[-444,-323],[169,-523]], it's just a pentagon I generated. The object that will collide is object, object.pos is it's position and object.vel is it's velocity. They're both 2d vectors too. I've had some success to get it to find a collision, but it's just black box code I ripped from a c++ example. It's very obscure inside and all it does though is return true/false and doesn't return what vertices are collided or collision point, I'd really like to be able to understand this and make my own so I can have more meaningful collision. I'll tackle that later though. Again the question is just how does one find a collision to walls of a poly given you know the poly vertices and the object's position + velocity? If more info is needed please let me know. And if all anyone can do is point me to the right direction that's great.

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  • How can I get textures on edge of walls like in Super Metroid and Aquaria?

    - by meds
    Games like Super Metroid and Aquaria present the terrain with the other facing parts having rocks and stuff while deeper behind them (i.e. underground) there's different detail or just black. I would like to do something similar using polygons. Terrain is created in my current level as a set of overlapping square boxes. I'm not sure if this rendering method will work such a system for creating terrain but if anyone has ideas I'd love to hear them. Otherwise I'd like to know how I should re-write the terrain rendering system so it actually works to draw terrain in this manner...

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  • I need help with 2D collision response (of stacking rotating polygons, with friction and gravity, for a game)

    - by Register Sole
    Hi I am looking for suggestions on how to write a collision response for game programming purpose (so not a scientific simulation). I am dealing with 2D polygons that are rotating, and I want them to be able to stack. I also want friction and gravity. I have a detection mechanism that returns the separating axis, how long the polygons are overlapping, and up to 2 points of contact. For the response, I am currently using an impulse-based response, which main idea is: find the separating axis, length of overlap, and the point of contact (if there are two, pick a random point between to simulate averaged force. i believe there are better ways than this) separate the object (modifying their positions, taking into account of their masses. i do not separate them completely though, to keep track that they are colliding to reduce jitter) calculate normal force based on the coefficient of restitution as if there is no friction. calculate friction, as if there is no normal force. I also assume that the direction of the friction is the same throughout the collision. apply the two forces (which result in a rather inaccurate result, since each force is calculated as if the other is not present. for non-rotating bodies though, this method is exact) I am aware that this method requires the coefficient of friction to be sufficiently small due to the assumption that the direction of friction stays the same in a collision. Also, the result is visually satisfying if gravity is not present. However, when there is gravity, objects on ground jitter and drift (even with zero coefficient of restitution)! It also happens for stacking objects. Larger coefficient of restitution and gravity increase the jittering. I hope you can help me with this. Some things i would like to know more about is how to handle collision with two point of contacts (how to end up having an object sitting still on the ground?), how to reduce, and prevent if possible, jitter and drift (do people use the most accurate method possible, or is there a trick to overcome this?), and how to handle multiple objects collision (for example, in the case of stacking objects, how do I check collisions between all of them and keep them all stable at every frame so they don't jitter?). A total reformulation of my algorithm is also welcomed, as long as it works. Another thing to note is that I am not making a Physics game, so I only need a visually satisfying response (though a realistic response is preferable, if it is not performance-heavy). But surely jittering and drifting objects on flat ground are not at all acceptable. In addition, I am a Physics student, so feel free to talk about impulse and whatever needed. Finally, I'm sorry for the long post. I tried to be as concise as I can. Thank you for reading it! EDIT It seems what I didn't manage to come up all this time is to separate resting contact as a class of its own and how to solve them. Currently reading the paper suggested by Jedediah. More suggestions on the topic are welcome :) CASE CLOSED After reading various papers referenced in the paper, successfully implemented simultaneous impulse method (referring to the original paper by Erin Catto, [Catt05]). Thanks maaaan!! The paper is wonderful. The current system is visibly much better than the previous. Still haven't separated resting contact as a class of its own though, which brings me to my next question. Love you all! Haha (sorry, I'm just so happy thanks to you).

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  • How do I convert a partially transparent image into polygons?

    - by user82779
    I'm using GLEE2D, a level editor allowing me to import images, scale them, rotate them, and position them onto layers and export the data into XML format. However, it does not tell me objects' boundaries. I can calculate them, but only given the original image's polygons. How do I get polygons of objects in a transparent image? An example object (I outlined it): How would I turn the object, knowing the scaled size of the image, into polygons? Is there an algorithm for this? I'll use OpenGL to draw them.

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  • MySql Geospatial bug..?

    - by ShaChris23
    This question is for Mysql geospatial-extension experts. The following query doesn't the result that I'm expecting: create database test_db; use test_db; create table test_table (g polygon not null); insert into test_table (g) values (geomfromtext('Polygon((0 5,5 10,7 8,2 3,0 5))')); insert into test_table (g) values (geomfromtext('Polygon((2 3,7 8,9 6,4 1,2 3))')); select X(PointN(ExteriorRing(g),1)), Y(PointN(ExteriorRing(g),1)), X(PointN(ExteriorRing(g),2)), Y(PointN(ExteriorRing(g),2)), X(PointN(ExteriorRing(g),3)), Y(PointN(ExteriorRing(g),3)), X(PointN(ExteriorRing(g),4)), Y(PointN(ExteriorRing(g),4)) from test_table where MBRContains(g,GeomFromText('Point(3 6)')); Basically we are creating 2 Polygons, and we are trying to use MBRContains to determine whether a Point is within either of the two polygons. Surprisingly, it returns both polygons! Point 3,6 should only exist in the first inserted polygon. Note that both polygons are tilted (once you draw the polygons on a piece of paper, you will see) How come MySql returns both polygons? I'm using MySql Community Edition 5.1.

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  • Drawing and filling different polygons at the same time in MATLAB

    - by Hossein
    Hi,I have the code below. It load a CSV file into memory. This file contains the coordinates for different polygons.Each row of this file has X,Y coordinates and a string which tells that to which polygon this datapoint belongs. for example a polygone named "Poly1" with 100 data points has 100 rows in this file like : Poly1,X1,Y1 Poly1,X2,Y2 ... Poly1,X100,Y100 Poly2,X1,Y1 ..... The index.csv file has the number of datapoint(number of rows) for each polygon in file Polygons.csv. These details are not important. The thing is: I can successfully extract the datapoints for each polygon using the code below. However, When I plot the lines of different polygons are connected to each other and the plot looks crappy. I need the polygons to be separated(they are connected and overlapping the some areas though). I thought by using "fill" I can actually see them better. But "fill" just filles every polygon that it can find and that is not desirable. I only want to fill inside the polygons. Can someone help me? I can also send you my datapoint if necessary, they are less than 200Kb. Thanks [coordinates,routeNames,polygonData] = xlsread('Polygons.csv'); index = dlmread('Index.csv'); firstPointer = 0 lastPointer = index(1) for Counter=2:size(index) firstPointer = firstPointer + index(Counter) + 1 hold on plot(coordinates(firstPointer:lastPointer,2),coordinates(firstPointer:lastPointer,1),'r-') lastPointer = lastPointer + index(Counter) end

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  • GoogleMaps API draw polygon over a complete town

    - by Frank
    Hello SOers, I'm wondering if it's actually possible to draw a polygon over a complete town with the GoogleMaps API V3 or the V2? If so could you please give an example on how to do it (choose your favorite town :)). I've some difficulties understanding this API. Thanks.

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  • OpenGL Polygon Stipple Not Working On Different Machine

    - by FranticPedantic
    I have a situation where I am trying to draw a semi-transparent rectangle over a background that is not using openGL and so I can not use blending. I decided to use polygon stippling for a 'screen door transparency' effect as recommended by some. It works fine on my machine and some others, but on some machines with slightly old Intel graphics cards it's failing to render the rectangle at all. If I turn off polygon stipple, it renders fine (but without the stipple). I have compared many of the state variables that I thought might affect it (see code) between machines and they are all the same, and I get no errors. static const GLubyte stipplePatternChkr[128]; //definition omitted for clarity //but works on my machine // stipple the box glPolygonMode(GL_FRONT_AND_BACK, GL_FILL); glColor4ubv(Color(COLORREF_PADGRAY)); glEnable(GL_POLYGON_STIPPLE); glPolygonStipple(stipplePatternChkr); CRect rcStipple(dim); rcStipple.DeflateRect(padding - 1, padding - 1); glBegin(GL_QUADS); glVertex2i(rcStipple.left, rcStipple.bottom); glVertex2i(rcStipple.right, rcStipple.bottom); glVertex2i(rcStipple.right, rcStipple.top); glVertex2i(rcStipple.left, rcStipple.top); glEnd(); glDisable(GL_POLYGON_STIPPLE); int err = glGetError(); if (err != GL_NO_ERROR) { TRACE("glError(%s: %s)\n", s, gluErrorString(err)); } float x; glGetFloatv(GL_UNPACK_ALIGNMENT, &x); TRACE("unpack alignment %f\n", x); glGetFloatv(GL_UNPACK_IMAGE_HEIGHT, &x); TRACE("unpack height %f\n", x); glGetFloatv(GL_UNPACK_LSB_FIRST, &x); TRACE("unpack lsb %f\n", x); glGetFloatv(GL_UNPACK_ROW_LENGTH, &x); TRACE("unpack length %f\n", x); glGetFloatv(GL_UNPACK_SKIP_PIXELS, &x); TRACE("upnack skip %f\n", x); glGetFloatv(GL_UNPACK_SWAP_BYTES, &x); TRACE("upnack swap %f\n", x);

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  • Generate 2D cross-section polygon from 3D mesh

    - by nornagon
    I'm writing a game which uses 3D models to draw a scene (top-down orthographic projection), but a 2D physics engine to calculate response to collisions, etc. I have a few 3D assets for which I'd like to be able to automatically generate a hitbox by 'slicing' the 3D mesh with the X-Y plane and creating a polygon from the resultant edges. Google is failing me on this one (and not much helpful material on SO either). Suggestions?

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  • Merge overlapping triangles into a polygon

    - by nornagon
    I've got a bunch of overlapping triangles from a 3D model projected into a 2D plane. I need to merge each island of touching triangles into a closed, non-convex polygon. The resultant polygons shouldn't have any holes in them (since the source data doesn't). Many of the source triangles share (floating point identical) edges with other triangles in the source data. What's the easiest way to do this? Performance isn't particularly important, since this will be done at design time.

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  • Polygon packing 2D

    - by Ilnur
    Hi! I have problem of packing 2 arbitrary polygons. I.e. we have 2 arbitrary polygons. We are to find such placement of this polygons (we could make rotations and movements), when rectangle, which circumscribes this polygons has minimal area. I know, that this is a NP-complete problem. I want to choose an efficient algorithm for solving this problem. I' looking for No-Fit-Polygon approach. But I could't find anywhere the simple and clear algorithm for finding the NFP of two arbitrary polygons.

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  • Polygon area calculation using Latitude and Longitude generated from Cartesian space and a world fil

    - by Heath
    Given a series of GPS coordinate pairs, I need to calculate the area of a polygon (n-gon). This is relatively small (not larger than 50,000 sqft). The geocodes are created by applying an affine transform with data from a world file. I have tried to use a two step approach by doing converting the geocodes to cartesian coordinates: double xPos = (lon-lonAnchor)*( Math.toRadians( 6378137 ) )*Math.cos( latAnchor ); double yPos = (lat-latAnchor)*( Math.toRadians( 6378137 ) ); then I use a cross product calculation to determine the area. The issue is that the results are a bit off in accuracy (around 1%). Is there anything I can look into to improve this? Thanks.

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  • google maps clicking inside a polygon

    - by amarsh-anand
    The following javascript snippet is supposed to do the following: As the user clicks on the map, initialize headMarker and draw a circle (polygon) around it As the user clicks inside the circle, initialize tailMarker and draw the path between these two markers 1 is happening as expected. But as the user clicks inside the circle, overlay is non-null while point is null in the function(overlay,point) . Can someone tell me a way out. GEvent.addListener(map, "click", function(overlay,point) { if (isCreateHeadPoint) { // add the head marker headMarker = new GMarker(point,{icon:redIcon,title:'0'}); map.addOverlay(headMarker); isCreateHeadPoint = false; // draw the circle drawMapCircle(point.lat(),point.lng(),1,'#cc0000',2,0.8,'#0',0.1); } else { // add the tail marker tailMarker = new GMarker(point,{icon:greenIcon,title:''}); map.addOverlay(tailMarker); isCreateHeadPoint = true; // load thes path from head to tail direction.load("from:" + headMarker.getPoint().lat()+ ", " + headMarker.getPoint().lng()+ " to:" + tailMarker.getPoint().lat() + "," + tailMarker.getPoint().lng(), {getPolyline:true}); } });

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  • Does this mySQL Stored Procedure Work?

    - by Laxmidi
    Hi, I got the following stored procedure from http://dev.mysql.com/doc/refman/5.1/en/functions-that-test-spatial-relationships-between-geometries.html Does this work? CREATE FUNCTION myWithin(p POINT, poly POLYGON) RETURNS INT(1) DETERMINISTIC BEGIN DECLARE n INT DEFAULT 0; DECLARE pX DECIMAL(9,6); DECLARE pY DECIMAL(9,6); DECLARE ls LINESTRING; DECLARE poly1 POINT; DECLARE poly1X DECIMAL(9,6); DECLARE poly1Y DECIMAL(9,6); DECLARE poly2 POINT; DECLARE poly2X DECIMAL(9,6); DECLARE poly2Y DECIMAL(9,6); DECLARE i INT DEFAULT 0; DECLARE result INT(1) DEFAULT 0; SET pX = X(p); SET pY = Y(p); SET ls = ExteriorRing(poly); SET poly2 = EndPoint(ls); SET poly2X = X(poly2); SET poly2Y = Y(poly2); SET n = NumPoints(ls); WHILE i<n DO SET poly1 = PointN(ls, (i+1)); SET poly1X = X(poly1); SET poly1Y = Y(poly1); IF ( ( ( ( poly1X <= pX ) && ( pX < poly2X ) ) || ( ( poly2X <= pX ) && ( pX < poly1X ) ) ) && ( pY > ( poly2Y - poly1Y ) * ( pX - poly1X ) / ( poly2X - poly1X ) + poly1Y ) ) THEN SET result = !result; END IF; SET poly2X = poly1X; SET poly2Y = poly1Y; SET i = i + 1; END WHILE; RETURN result; End; Usage: SET @point = PointFromText('POINT(5 5)') ; SET @polygon = PolyFromText('POLYGON((0 0,10 0,10 10,0 10))') ; SELECT myWithin(@point, @polygon) AS result ; I'm using phpMyAdmin and it blows up when using stored procedures. If this one works, then I'll try to figure out how to call it in php instead. Thanks, Laxmidi

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  • Clicking inside a polygon in Google Maps

    - by amarsh-anand
    The included JavaScript snippet is supposed to do the following: As the user clicks on the map, initialize headMarker and draw a circle (polygon) around it As the user clicks inside the circle, initialize tailMarker and draw the path between these two markers 1 is happening as expected. But as the user clicks inside the circle, in the function(overlay,point), overlay is non-null while point is null. Because of this, the code fails to initialize tailMarker. Can someone tell me a way out. GEvent.addListener(map, "click", function(overlay,point) { if (isCreateHeadPoint) { // add the head marker headMarker = new GMarker(point,{icon:redIcon,title:'0'}); map.addOverlay(headMarker); isCreateHeadPoint = false; // draw the circle drawMapCircle(point.lat(),point.lng(),1,'#cc0000',2,0.8,'#0',0.1); } else { // add the tail marker tailMarker = new GMarker(point,{icon:greenIcon,title:''}); map.addOverlay(tailMarker); isCreateHeadPoint = true; // load thes path from head to tail direction.load("from:" + headMarker.getPoint().lat()+ ", " + headMarker.getPoint().lng()+ " " + "to:" + tailMarker.getPoint().lat() + "," + tailMarker.getPoint().lng(), {getPolyline:true}); } });

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  • Combine Arbitrary number of polygons together

    - by Jakobud
    I have an arbitrary number of polygons (hexes in this case) that are arranged randomly, but they are all touching another hex. Each individual hex has 6 x,y vertices. The vertex's are known for all the hexes. Can anyone point me in the direction of an algorithm that will combine all the hexes into a single polygon? Essentially I'm just looking for a function that spits out an array of vertex locations that are ordered in a way that when drawing lines from one to the next, it forms the polygon. This is my method so far: Create array of all the vertices for all the hexes. Determine the number of times a vertex occurs in the array If vertex is in the array 3+ times, delete the vertices from the array. If vertex is in the array 2 times, delete one of them. The next step is tricky though. I'm using canvas to draw out these polygons, which essentially involves drawing a line from one vertex to the next. So the order of the vertices in the final array is important. It can't be sorted arbitrarily. Also, I'm not looking for a "convex hull" algorithm, as that would not draw the polygon correctly. Are there any functions out there that do something like this? Am I on the right track or is there a better more efficient way?

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  • overloaded stream insertion operator with a vector

    - by Julz
    hi, i'm trying to write an overloaded stream insertion operator for a class who's only member is a vector. i dont really know what i'm doing. (lets make that clear) it's a vector of "Points" which is a struct containing two doubles. i figure what i want is to insert user input (a bunch of doubles) into a stream that i then send to a modifier method? i keep working off other stream insertion examples such as... std::ostream& operator<< (std::ostream& o, Fred const& fred) { return o << fred.i_; } but when i try a similar..... istream & operator >> (istream &inStream, Polygon &vertStr) { inStream >> ws; inStream >> vertStr.vertices; return inStream; } i get an error "no match for operator etc etc. if i leave off the .vertices it compiles but i figure it's not right? (vertices is the name of my vector ) and even if it is right, i dont actually know what syntax to use in my driver to use it? also not %100 on what my modifier method needs to look like. here's my Polygon class //header #ifndef POLYGON_H #define POLYGON_H #include "Segment.h" #include <vector> class Polygon { friend std::istream & operator >> (std::istream &inStream, Polygon &vertStr); public: //Constructor Polygon(const Point &theVerts); //Default Constructor Polygon(); //Copy Constructor Polygon(const Polygon &polyCopy); //Accessor/Modifier methods inline std::vector<Point> getVector() const {return vertices;} //Return number of Vector elements inline int sizeOfVect() const {return (int) vertices.capacity();} //add Point elements to vector inline void setVertices(const Point &theVerts){vertices.push_back (theVerts);} private: std::vector<Point> vertices; }; #endif //Body using namespace std; #include "Polygon.h" // Constructor Polygon::Polygon(const Point &theVerts) { vertices.push_back (theVerts); } //Copy Constructor Polygon::Polygon(const Polygon &polyCopy) { vertices = polyCopy.vertices; } //Default Constructor Polygon::Polygon(){} istream & operator >> (istream &inStream, Polygon &vertStr) { inStream >> ws; inStream >> vertStr; return inStream; } any help greatly appreciated, sorry to be so vague, a lecturer has just kind of given us a brief example of stream insertion then left us on our own thanks. oh i realise there are probably many other problems that need fixing

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  • overloaded stream insetion operator with a vector

    - by julz666
    hi, i'm trying to write an overloaded stream insertion operator for a class who's only member is a vector. i dont really know what i'm doing. (lets make that clear) it's a vector of "Points" which is a struct containing two doubles. i figure what i want is to insert user input (a bunch of doubles) into a stream that i then send to a modifier method? i keep working off other stream insertion examples such as... std::ostream& operator<< (std::ostream& o, Fred const& fred) { return o << fred.i_; } but when i try a similar..... istream & operator >> (istream &inStream, Polygon &vertStr) { inStream >> ws; inStream >> vertStr.vertices; return inStream; } i get an error "no match for operator etc etc. if i leave off the .vertices it compiles but i figure it's not right? (vertices is the name of my vector ) and even if it is right, i dont actually know what syntax to use in my driver to use it? also not %100 on what my modifier method needs to look like. here's my Polygon class //header #ifndef POLYGON_H #define POLYGON_H #include "Segment.h" #include <vector> class Polygon { friend std::istream & operator >> (std::istream &inStream, Polygon &vertStr); public: //Constructor Polygon(const Point &theVerts); //Default Constructor Polygon(); //Copy Constructor Polygon(const Polygon &polyCopy); //Accessor/Modifier methods inline std::vector<Point> getVector() const {return vertices;} //Return number of Vector elements inline int sizeOfVect() const {return (int) vertices.capacity();} //add Point elements to vector inline void setVertices(const Point &theVerts){vertices.push_back (theVerts);} private: std::vector<Point> vertices; }; #endif //Body using namespace std; #include "Polygon.h" // Constructor Polygon::Polygon(const Point &theVerts) { vertices.push_back (theVerts); } //Copy Constructor Polygon::Polygon(const Polygon &polyCopy) { vertices = polyCopy.vertices; } //Default Constructor Polygon::Polygon(){} istream & operator >> (istream &inStream, Polygon &vertStr) { inStream >> ws; inStream >> vertStr; return inStream; } any help greatly appreciated, sorry to be so vague, a lecturer has just kind of given us a brief example of stream insertion then left us on our own thanks. oh i realise there are probably many other problems that need fixing

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  • vector collision on polygon in 3d space detection/testing?

    - by LRFLEW
    In the 3d fps in java I'm working on, I need a bullet to be fired and to tell if it hit someone. All visual objects in the game are defined through OpenGL, so the object it can be colliding with can be any drawable polygon (although they will most likely be triangles and rectangles anyways). The bullet is not an object, but will be treated as a vector that instantaneously moves all the way across the map (like the snipper riffle in Halo). What's the best way to detect/test collisions with the polygon and the vector. I have access to OpenCL, however I have absolutely no experience with it. I am very early in the developmental stage, so if you think there's a better way of going about this, feel free to tell me (I barley have a player model to collide with anyways, so I'm flexible with it). Thanks

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  • how to cout a vector of structs (that's a class member, using extraction operator)

    - by Julz
    hi, i'm trying to simply cout the elements of a vector using an overloaded extraction operator. the vector contians Point, which is just a struct containing two doubles. the vector is a private member of a class called Polygon, so heres my Point.h #ifndef POINT_H #define POINT_H #include <iostream> #include <string> #include <sstream> struct Point { double x; double y; //constructor Point() { x = 0.0; y = 0.0; } friend std::istream& operator >>(std::istream& stream, Point &p) { stream >> std::ws; stream >> p.x; stream >> p.y; return stream; } friend std::ostream& operator << (std::ostream& stream, Point &p) { stream << p.x << p.y; return stream; } }; #endif my Polygon.h #ifndef POLYGON_H #define POLYGON_H #include "Segment.h" #include <vector> class Polygon { //insertion operator needs work friend std::istream & operator >> (std::istream &inStream, Polygon &vertStr); // extraction operator friend std::ostream & operator << (std::ostream &outStream, const Polygon &vertStr); public: //Constructor Polygon(const std::vector<Point> &theVerts); //Default Constructor Polygon(); //Copy Constructor Polygon(const Polygon &polyCopy); //Accessor/Modifier methods inline std::vector<Point> getVector() const {return vertices;} //Return number of Vector elements inline int sizeOfVect() const {return vertices.size();} //add Point elements to vector inline void setVertices(const Point &theVerts){vertices.push_back (theVerts);} private: std::vector<Point> vertices; }; and Polygon.cc using namespace std; #include "Polygon.h" // Constructor Polygon::Polygon(const vector<Point> &theVerts) { vertices = theVerts; } //Default Constructor Polygon::Polygon(){} istream & operator >> (istream &inStream, Polygon::Polygon &vertStr) { inStream >> ws; inStream >> vertStr; return inStream; } // extraction operator ostream & operator << (ostream &outStream, const Polygon::Polygon &vertStr) { outStream << vertStr.vertices << endl; return outStream; } i figure my Point insertion/extraction is right, i can insert and cout using it and i figure i should be able to just...... cout << myPoly[i] << endl; in my driver? (in a loop) or even... cout << myPoly[0] << endl; without a loop? i've tried all sorts of myPoly.at[i]; myPoly.vertices[i]; etc etc also tried all veriations in my extraction function outStream << vertStr.vertices[i] << endl; within loops, etc etc. when i just create a... vector<Point> myVect; in my driver i can just... cout << myVect.at(i) << endl; no problems. tried to find an answer for days, really lost and not through lack of trying!!! thanks in advance for any help. please excuse my lack of comments and formatting also there's bits and pieces missing but i really just need an answer to this problem thanks again

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  • Multiple circles -> One Polygon?

    - by Josh
    Using Google Maps API v3, I was able to create multiple google.maps.Circle objects on my map. However, I now need to "connect" them somehow. I have the following map with multiple circles: I now need to get it to look something like this: I've looked all over the Internet for solutions, but to no avail. Any ideas?

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  • 2D polygon triangulation

    - by logank9
    The code below is my attempt at triangulation. It outputs the wrong angles (it read a square's angles as 90, 90. 90, 176) and draws the wrong shapes. What am I doing wrong? //use earclipping to generate a list of triangles to draw std::vector<vec> calcTriDraw(std::vector<vec> poly) { std::vector<double> polyAngles; //get angles for(unsigned int i = 0;i < poly.size();i++) { int p1 = i - 1; int p2 = i; int p3 = i + 1; if(p3 > int(poly.size())) p3 -= poly.size(); if(p1 < 0) p1 += poly.size(); //get the angle from 3 points double dx, dy; dx = poly[p2].x - poly[p1].x; dy = poly[p2].y - poly[p1].y; double a = atan2(dy,dx); dx = poly[p3].x - poly[p2].x; dy = poly[p3].y - poly[p2].y; double b = atan2(dy,dx); polyAngles.push_back((a-b)*180/PI); } std::vector<vec> triList; for(unsigned int i = 0;i < poly.size() && poly.size() > 2;i++) { int p1 = i - 1; int p2 = i; int p3 = i + 1; if(p3 > int(poly.size())) p3 -= poly.size(); if(p1 < 0) p1 += poly.size(); if(polyAngles[p2] >= 180) { continue; } else { triList.push_back(poly[p1]); triList.push_back(poly[p2]); triList.push_back(poly[p3]); poly.erase(poly.begin()+p2); std::vector<vec> add = calcTriDraw(poly); triList.insert(triList.end(), add.begin(), add.end()); break; } } return triList; }

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  • Generating a beveled edge for a 2D polygon

    - by Metaphile
    I'm trying to programmatically generate beveled edges for geometric polygons. For example, given an array of 4 vertices defining a square, I want to generate something like this. But computing the vertices of the inner shape is baffling me. Simply creating a copy of the original shape and then scaling it down will not produce the desired result most of the time. My algorithm so far involves analyzing adjacent edges (triples of vertices; e.g., the bottom-left, top-left, and top-right vertices of a square). From there, I need to find the angle between them, and then create a vertex somewhere along that angle, depending on how deep I want the bevel to be. And because I don't have much of a math background, that's where I'm stuck. How do I find that center angle? Or is there a much simpler way of attacking this problem?

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  • Most efficient way to draw circles for polygon outlines

    - by user146780
    I'm using OpenGL and was told I should draw circles at each vertex of my outline to get smoothness. I tried this and it works great. The problem is speed. It crippled my application to draw a circle at each vertex. I'm not sure how else to fix the anomaly of my outlines other than circles, but using display lists and trying with vertex array both were brutally slow. Thanks

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