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• Graph data structures and journal format for mini-IDE

  - by matec

  Background: I am writing a small/partial IDE. Code is internally converted/parsed into a graph data structure (for fast navigation, syntax-check etc). Functionality to undo/redo (also between sessions) and restoring from crash is implemented by writing to and reading from journal. The journal records modifications to the graph (not to the source). Question: I am hoping for advice on a decision on data-structures and journal format. For the graph I see two possible versions: g-a Graph edges are implemented in the way that one node stores references to other nodes via memory address g-b Every node has an ID. There is an ID-to-memory-address map. Graph uses IDs (instead of addresses) to connect nodes. Moving along an edge from one node to another each time requires lookup in ID-to-address map. And also for the journal: j-a There is a current node (like current working directory in a shell + file-system setting). The journal contains entries like "create new node and connect to current", "connect first child of current node" (relative IDs) j-b Journal uses absolute IDs, e.g. "delete edge 7 - 5", "delete node 5" I could e.g. combine g-a with j-a or combine g-b with j-b. In principle also g-b and j-a should be possible. [My first/original attempt was g-a and a version of j-b that uses addresses, but that turned out to cause severe restrictions: nodes cannot change their addresses (or journal would have to keep track of it), and using journal between two sessions is a mess (or even impossible)] I wonder if variant a or variant b or a combination would be a good idea, what advantages and disadvantages they would have and especially if some variant might be causing troubles later.

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• How do you track existing requirements over time?

  - by CaptainAwesomePants

  I'm a software engineer working on a complex, ongoing website. It has a lot of moving parts and a small team of UI designers and business folks adding new features and tweaking old ones. Over the last year or so, we've added hundreds of interesting little edge cases. Planning, implementing, and testing them is not a problem. The problem comes later, when we want to refactor or add another new feature. Nobody remembers half of the old features and edge cases from a year ago. When we want to add a new change, we notice that code does all sorts of things in there, and we're not entirely sure which things are intentional requirements and which are meaningless side effects. Did someone last year request that the login token was supposed to only be valid for 30 minutes, or did some programmers just pick a sensible default? Can we change it? Back when the product was first envisioned, we created some documentation describing how the site worked. Since then we created a few additional documents describing new features, but nobody ever goes back and updates those documents when new features are requested, so the only authoritative documentation is the code itself. But the code provides no justification, no reason for its actions: only the how, never the why. What do other long-running teams do to keep track of what the requirements were and why?

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• How to represent a graph with multiple edges allowed between nodes and edges that can selectively disappear

  - by Pops

  I'm trying to figure out what sort of data structure to use for modeling some hypothetical, idealized network usage. In my scenario, a number of users who are hostile to each other are all trying to form networks of computers where all potential connections are known. The computers that one user needs to connect may not be the same as the ones another user needs to connect, though; user 1 might need to connect computers A, B and D while user 2 might need to connect computers B, C and E. Image generated with the help of NCTM Graph Creator I think the core of this is going to be an undirected cyclic graph, with nodes representing computers and edges representing Ethernet cables. However, due to the nature of the scenario, there are a few uncommon features that rule out adjacency lists and adjacency matrices (at least, without non-trivial modifications): edges can become restricted-use; that is, if one user acquires a given network connection, no other user may use that connection in the example, the green user cannot possibly connect to computer A, but the red user has connected B to E despite not having a direct link between them in some cases, a given pair of nodes will be connected by more than one edge in the example, there are two independent cables running from D to E, so the green and blue users were both able to connect those machines directly; however, red can no longer make such a connection if two computers are connected by more than one cable, each user may own no more than one of those cables I'll need to do several operations on this graph, such as: determining whether any particular pair of computers is connected for a given user identifying the optimal path for a given user to connect target computers identifying the highest-latency computer connection for a given user (i.e. longest path without branching) My first thought was to simply create a collection of all of the edges, but that's terrible for searching. The best thing I can think to do now is to modify an adjacency list so that each item in the list contains not only the edge length but also its cost and current owner. Is this a sensible approach? Assuming space is not a concern, would it be reasonable to create multiple copies of the graph (one for each user) rather than a single graph?

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• How does the new google maps make buildings and cityscapes 3D?

  - by Aerovistae

  Anyone who's seen the new Google maps has no doubt taken note of the incredible amount of three-dimensional detail in select American cities such as Boston, New York, Chicago, and San Francisco. They've even modeled the trees, bridges and some of the boats in the harbor! Minor architectural details are present. It's crazy. Looking at it up close, I've found there's a rectangular area around each of those cities, and anything within them is 3Dified, but it cuts off hard and fast at the edge, even if it's in the middle of a building. The edge of the rectangle is where the 3D stops. This leads me to think it's being done algorithmically (which would make sense, given the scale of the project, how many trees and buildings and details there are), and yet I can't imagine how that's possible. How could an algorithm model all these things without extensive data on their shapes and contours? How could it model the individual wires of a bridge, or the statues in a park? It must be done by hand, and yet how could it be for so much detail! Does anyone have any insight on this?

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• What could cause a sudden stop in Box2D?

  - by alexanderpine

  I'm using Box2d for a game, and I have a bug that's driving me nuts. I've simplified the situation down to a square player sliding back and forth frictionlessly on top of a floor composed of a series of square tiles, driven by the left and right keys (which apply a horizontal force). Works great, sliding back and forth across the whole floor. Except... Every once in a while, the player will suddenly stick at the edge of one of the tiles as if it is hitting a (nonexistent) wall. Further pushes in the same direction it was traveling will fail, but as soon as I push backwards once in the opposite direction, I can push forwards past the sticking point again. The sticking point seems to be random, except for being on the edge of a tile. Happens while going left or right. For debugging purposes, I keep the Positions/velocity values for the previous two update ticks and print them out when this stop occurs. As an example, here you see the player moving right, decelerating slightly; pos2 should be about 8.7, but it stops dead instead. tick0: pos= 8.4636 vel= 7.1875 tick1: pos= 8.5816 vel= 7.0833 tick2: pos= 8.5816 vel= 0.0000 So, as the player is 0.8 and the tiles 1.0 wide, the player is stopping just as it is about to cross onto the next tile (8.5816 + 0.8/2 = 8.9816). In fact, I get a collision message (which I ignore except noting that it happened). It only seems to happen at x.5816 (or -x.4184) while moving right, and x.4167 (or -x.5833) while moving left I said that it's like hitting a wall, but in fact, when it hits a wall, the numbers look more like: tick0: pos0= 12.4131 vel2= 8.4375 tick1: pos1= 12.5555 vel1= 8.5417 tick2: pos2= 12.5850 vel0= 0.0000 so it moves further right on the last tick, which puts it in contact with the wall. Anyone seen anything like this. Any suggestion on how I could be causing this behavior.

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• Trying to detect collision between two polygons using Separating Axis Theorem

  - by Holly

  The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(vertices[0]); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(vertices[i]); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if( other.x <= y || other.y >= x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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• Error in my Separating Axis Theorem collision code

  - by Holly

  The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; int x; int y; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } public void update(int xPos, int yPos){ x = xPos; y = yPos; } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(new Vect(vertices[0].x+x, vertices[0].y+y)); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(new Vect(vertices[i].x+x, vertices[i].y+y)); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if(y > other.x && other.y > x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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• A detail question when applying genetic algorithm to traveling salesman

  - by burrough

  I read various stuff on this and understand the principle and concepts involved, however, none of paper mentions the details of how to calculate the fitness of a chromosome (which represents a route) involving adjacent cities (in the chromosome) that are not directly connected by an edge (in the graph). For example, given a chromosome 1|3|2|8|4|5|6|7, in which each gene represents the index of a city on the graph/map, how do we calculate its fitness (i.e. the total sum of distances traveled) if, say, there is no direct edge/link between city 2 and 8. Do we follow some sort of greedy algorithm to work out a route between 2 and 8, and add the distance of this route to the total? This problem seems pretty common when applying GA to TSP. Anyone who's done it before please share your experience. Thanks.

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• Sub-classing TreeView in C# WinForms for mouse over tool tips

  - by Matt

  Ok, this is a weird one. The expected behaviour for a TreeView control is that, if ShowNodeToolTips is set to false, then, when a label for a tree node exceeds the width of the control (or, more accurately, it's right hand edge is past the right hand edge of the client area), then a tooltip is shown above the node showing the full item's text. I'd like to disable that, because the above semantic doesn't always work, depending on what the treeview is contained within. So I have rolled my own, and got the tooltips to work (and line up better than the default one!) - but I would like to be able to disable the 'default' behaviour for situations where it would work natively. So, can anyone point me in the right direction as to which message to post to the TreeView in order to disable that behaviour? I have looked at the windows control reference, but couldn't find anything that looked like it might be the one. Thanks Matt

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• image focus calculation

  - by Oren Mazor

  Hi folks, I'm trying to develop an image focusing algorithm for some test automation work. I've chosen to use AForge.net, since it seems like a nice mature .net friendly system. Unfortunately, I can't seem to find information on building autofocus algorithms from scratch, so I've given it my best try: take image. apply sobel edge detection filter, which generates a greyscale edge outline. generate a histogram and save the standard dev. move camera one step closer to subject and take another picture. if the standard dev is smaller than previous one, we're getting more in focus. otherwise, we've past the optimal distance to be taking pictures. is there a better way? update: HUGE flaw in this, by the way. as I get past the optimal focus point, my "image in focus" value continues growing. you'd expect a parabolic-ish function looking at distance/focus-value, but in reality you get something that's more logarithmic

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• Finding minimum cut-sets between bounded subgraphs

  - by Tore

  If a game map is partitioned into subgraphs, how to minimize edges between subgraphs? I have a problem, Im trying to make A* searches through a grid based game like pacman or sokoban, but i need to find "enclosures". What do i mean by enclosures? subgraphs with as few cut edges as possible given a maximum size and minimum size for number of vertices for each subgraph that act as a soft constraints. Alternatively you could say i am looking to find bridges between subgraphs, but its generally the same problem. Given a game that looks like this, what i want to do is find enclosures so that i can properly find entrances to them and thus get a good heuristic for reaching vertices inside these enclosures. So what i want is to find these colored regions on any given map. My Motivation The reason for me bothering to do this and not just staying content with the performance of a simple manhattan distance heuristic is that an enclosure heuristic can give more optimal results and i would not have to actually do the A* to get some proper distance calculations and also for later adding competitive blocking of opponents within these enclosures when playing sokoban type games. Also the enclosure heuristic can be used for a minimax approach to finding goal vertices more properly. A possible solution to the problem is the Kernighan-Lin algorithm: function Kernighan-Lin(G(V,E)): determine a balanced initial partition of the nodes into sets A and B do A1 := A; B1 := B compute D values for all a in A1 and b in B1 for (i := 1 to |V|/2) find a[i] from A1 and b[i] from B1, such that g[i] = D[a[i]] + D[b[i]] - 2*c[a][b] is maximal move a[i] to B1 and b[i] to A1 remove a[i] and b[i] from further consideration in this pass update D values for the elements of A1 = A1 / a[i] and B1 = B1 / b[i] end for find k which maximizes g_max, the sum of g[1],...,g[k] if (g_max > 0) then Exchange a[1],a[2],...,a[k] with b[1],b[2],...,b[k] until (g_max <= 0) return G(V,E) My problem with this algorithm is its runtime at O(n^2 * lg(n)), i am thinking of limiting the nodes in A1 and B1 to the border of each subgraph to reduce the amount of work done. I also dont understand the c[a][b] cost in the algorithm, if a and b do not have an edge between them is the cost assumed to be 0 or infinity, or should i create an edge based on some heuristic. Do you know what c[a][b] is supposed to be when there is no edge between a and b? Do you think my problem is suitable to use a multi level problem? Why or why not? Do you have a good idea for how to reduce the work done with the kernighan-lin algorithm for my problem?

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• Data structure for Settlers of Catan map?

  - by templatetypedef

  Hello all- A while back someone asked me if I knew of a nice way to encode the information for the game Settlers of Catan. This would require storing a hexagonal grid in a way where each hex can have data associated with it. More importantly, though, I would need some way of efficiently looking up vertices and edges on the sides of these hexagons, since that's where all the action is. My question is this: is there a good, simple data structure for storing a hexagonal grid while allowing for fast lookup of hexagons, edges between hexagons, and vertices at the intersections of hexagons? I know that general structures like a winged-edge or quad-edge could do this, but that seems like massive overkill. Thanks!

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• Specialization of template after instantiation?

  - by Onur Cobanoglu

  Hi, My full code is too long, but here is a snippet that will reflect the essence of my problem: class BPCFGParser { public: ... ... class Edge { ... ... }; class ActiveEquivClass { ... ... }; class PassiveEquivClass { ... ... }; struct EqActiveEquivClass { ... ... }; struct EqPassiveEquivClass { ... ... }; unordered_map<ActiveEquivClass, Edge *, hash<ActiveEquivClass>, EqActiveEquivClass> discovered_active_edges; unordered_map<PassiveEquivClass, Edge *, hash<PassiveEquivClass>, EqPassiveEquivClass> discovered_passive_edges; }; namespace std { template <> class hash<BPCFGParser::ActiveEquivClass> { public: size_t operator()(const BPCFGParser::ActiveEquivClass & aec) const { } }; template <> class hash<BPCFGParser::PassiveEquivClass> { public: size_t operator()(const BPCFGParser::PassiveEquivClass & pec) const { } }; } When I compile this code, I get the following errors: In file included from BPCFGParser.cpp:3, from experiments.cpp:2: BPCFGParser.h:408: error: specialization of ‘std::hash<BPCFGParser::ActiveEquivClass>’ after instantiation BPCFGParser.h:408: error: redefinition of ‘class std::hash<BPCFGParser::ActiveEquivClass>’ /usr/include/c++/4.3/tr1_impl/functional_hash.h:44: error: previous definition of ‘class std::hash<BPCFGParser::ActiveEquivClass>’ BPCFGParser.h:445: error: specialization of ‘std::hash<BPCFGParser::PassiveEquivClass>’ after instantiation BPCFGParser.h:445: error: redefinition of ‘class std::hash<BPCFGParser::PassiveEquivClass>’ /usr/include/c++/4.3/tr1_impl/functional_hash.h:44: error: previous definition of ‘class std::hash<BPCFGParser::PassiveEquivClass>’ Now I have to specialize std::hash for these classes (because standard std::hash definition does not include user defined types). When I move these template specializations before the definition of class BPCFGParser, I get a variety of errors for a variety of different things tried, and somewhere (http://www.parashift.com/c++-faq-lite/misc-technical-issues.html) I read that: Whenever you use a class as a template parameter, the declaration of that class must be complete and not simply forward declared. So I'm stuck. I cannot specialize the templates after BPCFGParser definition, I cannot specialize them before BPCFGParser definition, how may I get this working? Thanks in advance, Onur

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• Common Ruby Idioms

  - by DanSingerman

  One thing I love about ruby is that mostly it is a very readable language (which is great for self-documenting code) However, inspired by this question: http://stackoverflow.com/questions/609612/ruby-code-explained and the description of how ||= works in ruby, I was thinking about the ruby idioms I don't use, as frankly, I don't fully grok them. So my question is, similar to the example from the referenced question, what common, but not obvious, ruby idioms do I need to be aware of to be a truly proficient ruby programmer? By the way, from the referenced question a ||= b is equivalent to if a == nil || a == false a = b end (Thanks to Ian Terrell for the correction) Edit: It turns out this point is not totally uncontroversial. The correct expansion is in fact (a || (a = (b))) See these links for why: http://DABlog.RubyPAL.Com/2008/3/25/a-short-circuit-edge-case/ http://DABlog.RubyPAL.Com/2008/3/26/short-circuit-post-correction/ http://ProcNew.Com/ruby-short-circuit-edge-case-response.html Thanks to Jörg W Mittag for pointing this out.

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• Tiling rectangles seamlessly in WPF

  - by Joe White

  I want to seamlessly tile a bunch of different-colored Rectangles in WPF. That is, I want to put a bunch of rectangles edge-to-edge, and not have gaps between them. If everything is aligned to pixels, this works fine. But I also want to support arbitrary zoom, and ideally, I don't want to use SnapsToDevicePixels (because it would compromise quality when the image is zoomed way out). But that means my Rectangles sometimes render with gaps. For example: <Page xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" Background="Black"> <Canvas SnapsToDevicePixels="False"> <Canvas.RenderTransform> <ScaleTransform ScaleX="0.5" ScaleY="0.5"/> </Canvas.RenderTransform> <Rectangle Canvas.Left="25" Width="100" Height="100" Fill="#CFC"/> <Rectangle Canvas.Left="125" Width="100" Height="100" Fill="#CCF"/> </Canvas> </Page> If the ScaleTransform's ScaleX is 1, then the Rectangles fit together seamlessly. When it's 0.5, there's a dark gray streak between them. I understand why -- the combined semi-transparent edge pixels don't combine to be 100% opaque. But I would like a way to fix it. I could always just make the Rectangles overlap, but I won't always know in advance what patterns they'll be in (this is for a game that will eventually support a map editor). Besides, this would cause artifacts around the overlap area when things were zoomed way in (unless I did bevel-cut angles on the underlapping portion, which is an awful lot of work, and still causes problems at corners). Is there some way I can combine these Rectangles into a single combined "shape" that does render without internal gaps? I've played around with GeometryDrawing, which does exactly that, but then I don't see a way to paint each RectangleGeometry with a different-colored brush. Are there any other ways to get shapes to tile seamlessly under an arbitrary transform, without resorting to SnapsToDevicePixels?

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• Intersection point in silverlight/wpf

  - by Andrei Neagu

  Hello, Given a path like this one : <Path Stretch="Fill" Stroke="#FFD69436" Data="M 0,20 L 22.3,20 L 34,0 L 44.7,20 L 68,20 L 55.8,40 L 68,60 L 44.7,60 L 34,80 L 22.3,60 L 0,60 L 11.16,40 L 0,20 Z"> <Path.Fill> <LinearGradientBrush StartPoint="0,0" EndPoint="0,1"> <LinearGradientBrush.GradientStops> <GradientStop Color="#FFFFFF" Offset="0" /> <GradientStop Color="Orange" Offset="1" /> </LinearGradientBrush.GradientStops> </LinearGradientBrush> </Path.Fill> </Path> How can I get the point that is at the edge of this figure at any angle? Lets say that I want the intersection point between the edge of this figure and a line passing through the center of this figure, at the 30 degrees angle with the OX axe? thanks.

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• Sub-classing TreeView in WinForms for mouse over tool tips

  - by Matt

  Ok, this is a weird one. The expected behaviour for a TreeView control is that, if ShowNodeToolTips is set to false, then, when a label for a tree node exceeds the width of the control (or, more accurately, it's right hand edge is past the right hand edge of the client area), then a tooltip is shown above the node showing the full item's text. I'd like to disable that, because the above semantic doesn't always work, depending on what the treeview is contained within. So I have rolled my own, and got the tooltips to work (and line up better than the default one!) - but I would like to be able to disable the 'default' behaviour for situations where it would work natively. So, can anyone point me in the right direction as to which message to post to the TreeView in order to disable that behaviour? I have looked at the windows control reference, but couldn't find anything that looked like it might be the one.

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• Graph coloring Algorithm

  - by Amitd

  From wiki In its simplest form, it is a way of coloring the vertices of a graph such that no two adjacent vertices share the same color; this is called a vertex coloring. Similarly, an edge coloring assigns a color to each edge so that no two adjacent edges share the same color, and a face coloring of a planar graph assigns a color to each face or region so that no two faces that share a boundary have the same color. Given 'n' colors and m vertices, how easily can a graph coloring algorithm be implemented? Lan

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• iPhone: Activate UISlider and set its value to the location of the current touch programatically

  - by carloe

  Is it possible to set an UISlider as first responder and set its current value to the location of the current touch programatically? The way my app is set up I have a UIView container that takes up the whole screen. Inside the container I have another UIView offscreen at the bottom edge (I'll call this bottomBar). Inside the bottomBar there is a UISlider element. Right now, when the user swipes along the bottom edge of the screen the bottomBar the slider it contains slide up. What I am trying to achieve is to activate the UISlider, and set the position of the slider (the value) to the position of the users touch. Is this possible? Could someone please point me in the right direction?

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• How to write content in a text file at the end of each line

  - by saravanan

  Hi, I am having one text file which contain following kind of data. "3P","Smith","Richard","3 Point Promotions","3P","[email protected]","IDA","Yes",,,,0,4,5,83.33,10, "A1","Ernest","Amy","TAKE 1 Promotional Products","LCOOK","[email protected]","IDA","Yes",,,,0,6,7,,0, "A2","Derek","Eaton","Advertising Edge Promotions","AE","[email protected]","IDA","Yes",,,,0,8,8,,10, "AAA","Abercrombie","Jerry","AAA Specialty Wholesale Inc","AAA","[email protected]","IDA","Yes",,,,0,9,9,,10, "AAP","Halberstam","Mendy","All About Promotions","AAP","[email protected]","IDA","Yes",,,,0,10,10,,12, Each of them are separate line.Now i want add another column in each like this "3P","Smith","Richard","3 Point Promotions","3P","[email protected]","IDA","Yes",,,,0,4,5,83.33,10,**96** "A1","Ernest","Amy","TAKE 1 Promotional Products","LCOOK","[email protected]","IDA","Yes",,,,0,6,7,,0,**97** "A2","Derek","Eaton","Advertising Edge Promotions","AE","[email protected]","IDA","Yes",,,,0,8,8,,10,**98** "AAA","Abercrombie","Jerry","AAA Specialty Wholesale Inc","AAA","[email protected]","IDA","Yes",,,,0,9,9,,10,**99** "AAP","Halberstam","Mendy","All About Promotions","AAP","[email protected]","IDA","Yes",,,,0,10,10,,12,**100** How i read content in line by line.And also how to write another value in same text file at each line.Please send solution for this problem.I am waiting for your reply.Thanks for reply. -Saravanan

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• Problem with Variable Scoping in Rebol's Object

  - by Rebol Tutorial

  I have modified the rebodex app so that it can be called from rebol's console any time by typing rebodex. To show the title of the app, I need to store it in app-title: system/script/header/title so tha it could be used later in view/new/title dex reform [self/app-title version] That works but as you can see I have named the var name "app-title", but if I use "title" instead, the window caption would show weird stuff (vid code). Why ? REBOL [ Title: "Rebodex" Date: 23-May-2010 Version: 2.1.1 File: %rebodex.r Author: "Carl Sassenrath" Modification: "Rebtut" Purpose: "A simple but useful address book contact database." Email: %carl--rebol--com library: [ level: 'intermediate platform: none type: 'tool domain: [file-handling DB GUI] tested-under: none support: none license: none see-also: none ] ] rebodex.context: context [ app-title: system/script/header/title version: system/script/header/version set 'rebodex func[][ names-path: %names.r ;data file name-list: none fields: [name company title work cell home car fax web email smail notes updat] names: either exists? names-path [load names-path][ [[name "Carl Sassenrath" title "Founder" company "REBOL Technologies" email "%carl--rebol--com" web "http://www.rebol.com"]] ] brws: [ if not empty? web/text [ if not find web/text "http://" [insert web/text "http://"] error? try [browse web/text] ] ] dial: [request [rejoin ["Dial number for " name/text "? (Not implemented.)"] "Dial" "Cancel"]] dex-styles: stylize [ lab: label 60x20 right bold middle font-size 11 btn: button 64x20 font-size 11 edge [size: 1x1] fld: field 200x20 font-size 11 middle edge [size: 1x1] inf: info font-size 11 middle edge [size: 1x1] ari: field wrap font-size 11 edge [size: 1x1] with [flags: [field tabbed]] ] dex-pane1: layout/offset [ origin 0 space 2x0 across styles dex-styles lab "Name" name: fld bold return lab "Title" title: fld return lab "Company" company: fld return lab "Email" email: fld return lab "Web" brws web: fld return lab "Address" smail: ari 200x72 return lab "Updated" updat: inf 200x20 return ] 0x0 updat/flags: none dex-pane2: layout/offset [ origin 0 space 2x0 across styles dex-styles lab "Work #" dial work: fld 140 return lab "Home #" dial home: fld 140 return lab "Cell #" dial cell: fld 140 return lab "Alt #" dial car: fld 140 return lab "Fax #" fax: fld 140 return lab "Notes" notes: ari 140x72 return pad 136x1 btn "Close" #"^q" [store-entry save-file unview] ] 0x0 dex: layout [ origin 8x8 space 0x1 styles dex-styles srch: fld 196x20 bold across rslt: list 180x150 [ nt: txt 178x15 middle font-size 11 [ store-entry curr: cnt find-name nt/text update-entry unfocus show dex ] ] supply [ cnt: count + scroll-off face/text: "" face/color: snow if not n: pick name-list cnt [exit] face/text: select n 'name face/font/color: black if curr = cnt [face/color: system/view/vid/vid-colors/field-select] ] sl: slider 16x150 [scroll-list] return return btn "New" #"^n" [new-name] btn "Del" #"^d" [delete-name unfocus update-entry search-all show dex] btn "Sort" [sort names sort name-list show rslt] return at srch/offset + (srch/size * 1x0) bx1: box dex-pane1/size bx2: box dex-pane2/size return ] bx1/pane: dex-pane1/pane bx2/pane: dex-pane2/pane rslt/data: [] this-name: first names name-list: copy names curr: none search-text: "" scroll-off: 0 srch/feel: make srch/feel [ redraw: func [face act pos][ face/color: pick face/colors face system/view/focal-face if all [face = system/view/focal-face face/text search-text] [ search-text: copy face/text search-all if 1 = length? name-list [this-name: first name-list update-entry show dex] ] ] ] update-file: func [data] [ set [path file] split-path names-path if not exists? path [make-dir/deep path] write names-path data ] save-file: has [buf] [ buf: reform [{REBOL [Title: "Name Database" Date:} now "]^/[^/"] foreach n names [repend buf [mold n newline]] update-file append buf "]" ] delete-name: does [ remove find/only names this-name if empty? names [append-empty] save-file new-name ] clean-names: function [][n][ forall names [ if any [empty? first names none? n: select first names 'name empty? n][ remove names ] ] names: head names ] search-all: function [] [ent flds] [ clean-names clear name-list flds: [name] either empty? search-text [insert name-list names][ foreach nam names [ foreach word flds [ if all [ent: select nam word find ent search-text][ append/only name-list nam break ] ] ] ] scroll-off: 0 sl/data: 0 resize-drag scroll-list curr: none show [rslt sl] ] new-name: does [ store-entry clear-entry search-all append-empty focus name ; update-entry ] append-empty: does [append/only names this-name: copy []] find-name: function [str][] [ foreach nam names [ if str = select nam 'name [ this-name: nam break ] ] ] store-entry: has [val ent flag] [ flag: 0 if not empty? trim name/text [ foreach word fields [ val: trim get in get word 'text either ent: select this-name word [ if ent val [insert clear ent val flag: flag + 1] ][ if not empty? val [repend this-name [word copy val] flag: flag + 1] ] if flag = 1 [flag: 2 updat/text: form now] ] if not zero? flag [save-file] ] ] update-entry: does [ foreach word fields [ insert clear get in get word 'text any [select this-name word ""] ] show rslt ] clear-entry: does [ clear-fields bx1 clear-fields bx2 updat/text: form now unfocus show dex ] show-names: does [ clear rslt/data foreach n name-list [ if n/name [append rslt/data n/name] ] show rslt ] scroll-list: does [ scroll-off: max 0 to-integer 1 + (length? name-list) - (100 / 16) * sl/data show rslt ] do resize-drag: does [sl/redrag 100 / max 1 (16 * length? name-list)] center-face dex new-name focus srch show-names view/new/title dex reform [app-title version] insert-event-func [ either all [event/type = 'close event/face = dex][ store-entry unview ][event] ] do-events ] ]

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• Math for a geodesic sphere

  - by Marcelo Cantos

  I'm trying to create a very specific geodesic tessellation, but I can't find anything online about it. It is normal to subdivide the triangles of an icosahedron into triangle patches and project them onto the sphere. However, I noticed an animated GIF on the Wikipedia entry for Geodesic Domes that appears not to follow this scheme. Geodesic spheres generally comprise a mixture of mostly hexagonal triangle patches, with pentagonal patches forming at the vertices of the original icosahedron; in most cases, these pentagons are linked together; that is, following a straight edge from the center of one pentagon leads to the center of another pentagon. In the Wikipedia animation, however, the edge from the center of one pentagon doesn't appear to intersect the center of an adjacent pentagons; instead it intersects the side of the other pentagon. Hopefully the drawing below makes this clear: Where can I go to learn about the math behind this particular geometry? Ideally, I'd like to know of an algorithm for generating such tessellations.

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• How to find relation between change in latitudes at centre of map and top/bottom

  - by Imran

  Hi, Im having little trouble finding a relation between the movement at centre and edge of a circle, Im doing for panning world map,my map extent is 180,89:-180,-89, my map pans by adding change(dx,dY) to its extents and not its centre. Now a situation has arrrised where I have to move the map to a specific centre, to calculate the change in longitudes is very easy and simple, but its the change in lattitudes that has caused problem. It seems the change in centreY of map is more than the change at edge of the mapY, or simply if I have to move the map centre from 0long,0lat to 73long,33lat, for dX I simply get 73, but for dY apparently it looks 33 but if i add 33 to top of map that is 89 , it will be 122 which is incorrect since Latitudes are between 90 and -90 . It seems a case a projection of a circle on 2D plane where the edge of circle since is moving backward due to angle expereinces less change and the centre expereinces more change, now is there a relation between these two factors? I tried converting the difference between OriginY and destinationY into radians and then add to Top and Bottom of Map, but it did'nt really work for me. Please note that the map is project on a virtual canvas whose width starts from 256 and increases by 256*2^z , z=0 is default and whole world is visible at that extent of canvas code: public void moveMapTo(double destinationLongitude,double destinationLattitude) // moves map to the new centre { double dXLong=destinationLongitude-centreLongitude; double atanhsinO = atanh(Math.sin(destinationLattitude * Math.PI / 180.00)); double atanhsinD = atanh(Math.sin(centreLatitude * Math.PI / 180.00)); double atanhCentre = (atanhsinD + atanhsinO) / 2; double latitudeSpan =destinationLattitude - centreLatitude; double radianOfCentreLatitude = Math.atan(Math.sinh(atanhCentre)); double dXLat=latitudeSpan / Math.cos(radianOfCentreLatitude); dXLat*=getLattitudeSpan()*(Math.PI/180); <--- HERE IS THE PORBLEM System.out.println("dxLong:"+dXLong+"_dxLat:"+dXLat); mapLeft+=dXLong; mapRight+=dXLong; mapTop+=dXLat; mapBottom+=dXLat; } ////latitude span function private double getLattitudeSpan() { double latitudeSpan = mapTop - mapBottom; latitudeSpan = latitudeSpan / Math.cos(radianOfCentreLatitude); return Math.abs(latitudeSpan); } //ht

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• How to position an element so that it does not flow off the visible screen

  - by rjray

  I am creating pseudo-tooltips on a page that has a lot of "a" and "span" elements that have these tips associated with them. Everything in the creation of the element is fine, and it displays fine. However, since this is a page with a lot of data, as you get towards the bottom of the visual area the tooltips start to flow past the bottom edge of the window. My initial attempt to compensate for this with window.innerWidth/innerHeight didn't come out too well. I'm using jQuery for DOM manipulation (but not jQuery UI). Given the event itself, and the height and width of the tooltip (which I can get with getBoundingClientRect()), how can I position this element so that the bottom of the tooltip is never below the edge of the window?

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• iPhone: scroll view with arbitrary page/"settling" boundaries?

  - by Ben

  Hi all, I'm trying to figure out if I can get what I want out of UIScrollView through some trickery or whether I need to roll my own scroll view: I have a series of items in row that I want to scroll through. One item should always be centered in the view, but other items should be visible to either side. In other words, I want normal scrolling and edge bouncing, but I want the deceleration when the user ends a touch to naturally settle at some specified stop point. (Actually now that I think of it, this behavior is similar to coverflow in this respect.) I know UIScrollView doesn't do this out of the box, but does anyone have suggestions for how it might be made to do this, or if anyone's spotted any code that accomplishes something similar (I'm loathe to reimplement all the math for deceleration and edge bounce) Thanks!

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