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  • Scrolling a canvas as a shape you're moving approaches its edges

    - by Steven Sproat
    Hi, I develop a Python-based drawing program, Whyteboard. I have tools that the user can create new shapes on the canvas, such as text/images/rectangles/circles/polygons. I also have a Select tool that allows the users to modify these shapes - for example, moving a shape's position, resizing, or editing polygon's points' positions. I'm adding in a new feature where moving or resizing a point near the canvas edge will automatically scroll the canvas. I think it's a good idea in terms of program usability, and annoys me when other program's don't have this feature. I've made some good progress on coding this; below is some Python code to demonstrate what I'm doing. These functions demonstrate how some shapes calculate their "edges": def find_edges(self): """A line.""" self.edges = {EDGE_TOP: min(self.y, self.y2), EDGE_RIGHT: max(self.x, self.x2), EDGE_BOTTOM: max(self.y, self.y2), EDGE_LEFT: min(self. x, self.x2)} def find_edges(self): """An image""" self.edges = {EDGE_TOP: self.y, EDGE_RIGHT: self.x + self.image.GetWidth(), EDGE_BOTTOM: self.y + self.image.GetWidth(), EDGE_LEFT: self.x} def find_edges(self): """Get the bounding rectangle for the polygon""" xmin = min(x for x, y in self.points) ymin = min(y for x, y in self.points) xmax = max(x for x, y in self.points) ymax = max(y for x, y in self.points) self.edges = {EDGE_TOP: ymin, EDGE_RIGHT: xmax, EDGE_BOTTOM: ymax, EDGE_LEFT: xmin} And here's the code I have so far to implement the scrolling when a shape nears the edge: def check_canvas_scroll(self, x, y, moving=False): """ We check that the x/y coords are within 50px from the edge of the canvas and scroll the canvas accordingly. If the shape is being moved, we need to check specific edges of the shape (e.g. left/right side of rectangle) """ size = self.board.GetClientSizeTuple() # visible area of the canvas if not self.board.area > size: # canvas is too small to need to scroll return start = self.board.GetViewStart() # user's starting "viewport" scroll = (-1, -1) # -1 means no change if moving: if self.shape.edges[EDGE_RIGHT] > start[0] + size[0] - 50: scroll = (start[0] + 5, -1) if self.shape.edges[EDGE_BOTTOM] > start[1] + size[1] - 50: scroll = (-1, start[1] + 5) # snip others else: if x > start[0] + size[0] - 50: scroll = (start[0] + 5, -1) if y > start[1] + size[1] - 50: scroll = (-1, start[1] + 5) # snip others self.board.Scroll(*scroll) This code actually works pretty well. If we're moving a shape, then we need to know its edges to calculate when they're coming close to the canvas edge. If we're resizing just a single point, then we just use the x/y coords of that point to see if it's close to the edge. The problem I'm having is a little tricky to describe - basically, if you move a shape to the left, and stop moving it, if you positioned the shape within the 50px from the canvas, then the next time you go to move the shape, the code that says "ok, is this shape close to the end?" gets triggered, and the canvas scrolls to the left, even if you're moving the shape to the right. Can anyone think on how to stop this? I created a youtube video to demonstrate the issue. At about 0:54, I move a polygon to the left of the canvas and position it there. The next time I move it, the canvas scrolls to the left even though I'm moving it right Another thing I'd like to add, but I'm stuck on is the scroll gaining momentum the longer a shape is scrolling? So, with a large canvas, you're not moving a shape for ages, moving 5px at a time, when you need to cover a 2000px distance. Any suggestions there? Thanks all - sorry for the super long question!

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  • Using JavaCC to infer semantics from a Composite tree

    - by Skice
    Hi all, I am programming (in Java) a very limited symbolic calculus library that manages polynomials, exponentials and expolinomials (sums of elements like "x^n * e^(c x)"). I want the library to be extensible in the sense of new analytic forms (trigonometric, etc.) or new kinds of operations (logarithm, domain transformations, etc.), so a Composite pattern that represent the syntactic structure of an expression, together with a bunch of Visitors for the operations, does the job quite well. My problem arise when I try to implement operations that depends on the semantics more than on the syntax of the Expression (like integrals, for instance: there are a lot of resolution methods for specific classes of functions, but these same classes can be represented with more than a single syntax). So I thought I need something to "parse" the Composite tree to infer its semantics in order to invoke the right integration method (if any). Someone pointed me to JavaCC, but all the examples I've seen deal only with string parsing; so, I don't know if I'm digging in the right direction. Some suggestions? (I hope to have been clear enough!)

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  • How to make an equation span the whole page / line in LaTeX?

    - by Reed Richards
    I have this equation and it's quite big (basically a FDM one) but it aligns with the text and then continues out on the right side to the nothingness. I've tried stuff like \begin{center} and \hspace*{-2.5cm} but to no avail. I want it to use the whole line not just from the left-margin and out to the right. How do I do it and do I need to install some special package for it? I use the \[ instead of the displaymath like this \[ Equation arrays here \] The code \[ \left( \begin{array}{cccccc} -(2\kappa+\frac{hV\rho}{2}) & (\frac{hV\rho}{2}-\kappa) & 0 & \cdots & 0 \\ -\kappa & -(2\kappa+\frac{hV\rho}{2}) & (\frac{hV\rho}{2}-\kappa) & 0 & \cdots \\ 0 & -\kappa & -(2\kappa+\frac{hV\rho}{2}) & (\frac{hV\rho}{2}-\kappa) & 0 & \cdots \\ \vdots & 0 & \ddots & \vdots \\ \vdots & \vdots & \vdots & -\kappa & -(2\kappa+\frac{hV\rho}{2}) & (\frac{hV\rho}{2}-\kappa) \\ 0 & \vdots & \vdots & 0 & \kappa - \frac{2h\kappa_{v}}{\kappa}(\frac{hv\rho}{2} - \kappa) & -2\kappa \\ \end{array} \right) \left( \begin{array}{c} T_{1} \\ T_{2} \\ \vdots \\ T_{n} \\ \end{array} \right) = \left( \begin{array}{c} Q(0) + \kappa T_{0} \\ Q(h) \\ Q(2h) \\ \vdots \\ Q((n-1)h) \\ 2\frac{\kappa_{v}}{\kappa_{v}}T_{out} \\ \end{array} \right) \]

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  • How to solve such system with given parts of it? (maple)

    - by Kabumbus
    So I had a system #for given koefs k:=3; n:=3; #let us solve system: koefSolution:= solve({ sum(a[i], i = 0 .. k) = 0, sum(a[i], i = 0 .. k)-(sum(b[i], i = 0 .. k)) = 0, sum(i^n*a[i], i = 0 .. k)-(sum(i^(n-1)*b[i], i = 0 .. k)) = 0 }); So I have a vector like koefSolution := { a[0] = 7*a[2]+26*a[3]-b[1]-4*b[2]-9*b[3], a[1] = -8*a[2]-27*a[3]+b[1]+4*b[2]+9*b[3], a[2] = a[2], a[3] = a[3], b[0] = -b[1]-b[2]-b[3], b[1] = b[1], b[2] = b[2], b[3] = b[3]} I have a[0] so I try solve({koefSolution, a[0] = 1}); why it does not solve my system for given a[0]? ( main point here is to fill koefSolution with given a[] and b[] and optimize.)

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  • sin v/s sinf fucntion in C

    - by user319873
    Hi Guys, I am trying to use sinf function in my C Program and it does give me undefined reference under MSVC 6.0 but sin works fine. This make me curious to find the difference between sin and sinf. What is the logical difference between sin and sinf(). How can I implement my own sinf functionality?

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  • KD-Trees and missing values (vector comparison)

    - by labratmatt
    I have a system that stores vectors and allows a user to find the n most similar vectors to the user's query vector. That is, a user submits a vector (I call it a query vector) and my system spits out "here are the n most similar vectors." I generate the similar vectors using a KD-Tree and everything works well, but I want to do more. I want to present a list of the n most similar vectors even if the user doesn't submit a complete vector (a vector with missing values). That is, if a user submits a vector with three dimensions, I still want to find the n nearest vectors (stored vectors are of 11 dimensions) I have stored. I have a couple of obvious solutions, but I'm not sure either one seem very good: Create multiple KD-Trees each built using the most popular subset of dimensions a user will search for. That is, if a user submits a query vector of thee dimensions, x, y, z, I match that query to my already built KD-Tree which only contains vectors of three dimensions, x, y, z. Ignore KD-Trees when a user submits a query vector with missing values and compare the query vector to the vectors (stored in a table in a DB) one by one using something like a dot product. This has to be a common problem, any suggestions? Thanks for the help.

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  • Algorithm possible amounts (over)paid for a specific price, based on denominations

    - by Wrikken
    In a current project, people can order goods delivered to their door and choose 'pay on delivery' as a payment option. To make sure the delivery guy has enough change customers are asked to input the amount they will pay (e.g. delivery is 48,13, they will pay with 60,- (3*20,-)). Now, if it were up to me I'd make it a free field, but apparantly higher-ups have decided is should be a selection based on available denominations, without giving amounts that would result in a set of denominations which could be smaller. Example: denominations = [1,2,5,10,20,50] price = 78.12 possibilities: 79 (multitude of options), 80 (e.g. 4*20) 90 (e.g. 50+2*20) 100 (2*50) It's international, so the denominations could change, and the algorithm should be based on that list. The closest I have come which seems to work is this: for all denominations in reversed order (large=>small) add ceil(price/denomination) * denomination to possibles baseprice = floor(price/denomination) * denomination; for all smaller denominations as subdenomination in reversed order add baseprice + (ceil((price - baseprice) / subdenomination) * subdenomination) to possibles end for end for remove doubles sort Is seems to work, but this has emerged after wildly trying all kinds of compact algorithms, and I cannot defend why it works, which could lead to some edge-case / new countries getting wrong options, and it does generate some serious amounts of doubles. As this is probably not a new problem, and Google et al. could not provide me with an answer save for loads of pages calculating how to make exact change, I thought I'd ask SO: have you solved this problem before? Which algorithm? Any proof it will always work?

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  • Reverse factorial

    - by dada
    Well, we all know that if N is given it's easy to calculate N!. But what about reversing? N! is given and you are about to find N - Is that possible ? I'm curious.

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  • bash: expanding variables with spaces

    - by adam n
    i have a file called physics 1b.sh in bash, if i try x="physics 1b" grep "string" "$x".sh grep complains: grep: physics 1b: No such file or directory. However, when i do grep "string" physics\ 1b.sh it works fine. So i guess the problem is something to do with the variable not being expanded to include the backslash that grep needs to recognize the space. How do i get this to work? using bash 3.2, mac os 10.6.

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  • Power function fit to data set

    - by czerasz
    I have a set of data (in ArrayCollection) and I need to fit a power function { f(x)= B + x^alpha } to it, before display in LineChart. As result I need the alpha and B paremeter. How to do this with Flex?

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  • how to subtract circle from an arbitrary polygon

    - by George
    Given an arbitary polygon with vertices stored in either clockwise/counterclockwise fashion (depicted as a black rectangle in the diagram), I need to be able to subtract an arbitrary number of circles (in red on the diagram) from that polygon. Removing a circle could possibly split the polygon into two seperate polygons (as depicted by the second line in the diagram). I'm not sure where to start. http://www.freeimagehosting.net/image.php?89a0276d9d.jpg

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  • Calculate new position of player

    - by user1439111
    Edit: I will summerize my question since it is very long (Thanks Len for pointing it out) What I'm trying to find out is to get a new position of a player after an X amount of time. The following variables are known: - Speed - Length between the 2 points - Source position (X, Y) - Destination position (X, Y) How can I calculate a position between the source and destion with these variables given? For example: source: 0, 0 destination: 10, 0 speed: 1 so after 1 second the players position would be 1, 0 The code below works but it's quite long so I'm looking for something shorter/more logical ====================================================================== I'm having a hard time figuring out how to calculate a new position of a player ingame. This code is server sided used to track a player(It's a emulator so I don't have access to the clients code). The collision detection of the server works fine I'm using bresenham's line algorithm and a raycast to determine at which point a collision happens. Once I deteremined the collision I calculate the length of the path the player is about to walk and also the total time. I would like to know the new position of a player each second. This is the code I'm currently using. It's in C++ but I am porting the server to C# and I haven't written the code in C# yet. // Difference between the source X - destination X //and source y - destionation Y float xDiff, yDiff; xDiff = xDes - xSrc; yDiff = yDes - ySrc; float walkingLength = 0.00F; float NewX = xDiff * xDiff; float NewY = yDiff * yDiff; walkingLength = NewX + NewY; walkingLength = sqrt(walkingLength); const float PI = 3.14159265F; float Angle = 0.00F; if(xDes >= xSrc && yDes >= ySrc) { Angle = atanf((yDiff / xDiff)); Angle = Angle * 180 / PI; } else if(xDes < xSrc && yDes >= ySrc) { Angle = atanf((-xDiff / yDiff)); Angle = Angle * 180 / PI; Angle += 90.00F; } else if(xDes < xSrc && yDes < ySrc) { Angle = atanf((yDiff / xDiff)); Angle = Angle * 180 / PI; Angle += 180.00F; } else if(xDes >= xSrc && yDes < ySrc) { Angle = atanf((xDiff / -yDiff)); Angle = Angle * 180 / PI; Angle += 270.00F; } float WalkingTime = (float)walkingLength / (float)speed; bool Done = false; float i = 0; while(i < walkingLength) { if(Done == true) { break; } if(WalkingTime >= 1000) { Sleep(1000); i += speed; WalkTime -= 1000; } else { Sleep(WalkTime); i += speed * WalkTime; WalkTime -= 1000; Done = true; } if(Angle >= 0 && Angle < 90) { float xNew = cosf(Angle * PI / 180) * i; float yNew = sinf(Angle * PI / 180) * i; float NewCharacterX = xSrc + xNew; float NewCharacterY = ySrc + yNew; } I have cut the last part of the loop since it's just 3 other else if statements with 3 other angle conditions and the only change is the sin and cos. The given speed parameter is the speed/second. The code above works but as you can see it's quite long so I'm looking for a new way to calculate this. btw, don't mind the while loop to calculate each new position I'm going to use a timer in C# Thank you very much

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  • Using bitwise operators on > 32 bit integers

    - by dqhendricks
    I am using bitwise operations in order to represent many access control flags within one integer. ADMIN_ACCESS = 1; EDIT_ACCOUNT_ACCESS = 2; EDIT_ORDER_ACCESS = 4; var myAccess = 3; // ie: ( ADMIN_ACCESS | EDIT_ACCOUNT_ACCESS ) if ( myAccess & EDIT_ACCOUNT_ACCESS ) { // check for correct access // allow for editing of account } Most of this is occurring on the PHP side of my project. There is one piece however where Javascript is used to join several access flags using | when saving someone's access level. This works fine to a point. I have found that once an integer (flag) gets too large ( 32bit), it no longer works correctly with bitwise operators in Javascript. For instance: alert( 4294967296 | 1 ); // equals 1, but should equal 4294967297 I am trying to find a workaround for this so that I do not have to limit my number of access control flags to 32. Each access control flag is two times the previous control flag so that each control flag will not interfere with other control flags. dec(4) = bin(100) dec(8) = bin(1000) dec(16) = bin(10000) I have noticed that when adding two of these flags together with a simple +, it seems to come out with the same answer as a bitwise or operation, but am having trouble wrapping my head around whether this is a simple substitution, or if there might be problems with doing this. Can anyone comment on the validity of this workaround? Example: (4294967296 | 262144 | 524288) == (4294967296 + 262144 + 524288)

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  • Need some help understanding this problem about maximizing graph connectivity

    - by Legend
    I was wondering if someone could help me understand this problem. I prepared a small diagram because it is much easier to explain it visually. Problem I am trying to solve: 1. Constructing the dependency graph Given the connectivity of the graph and a metric that determines how well a node depends on the other, order the dependencies. For instance, I could put in a few rules saying that node 3 depends on node 4 node 2 depends on node 3 node 3 depends on node 5 But because the final rule is not "valuable" (again based on the same metric), I will not add the rule to my system. 2. Execute the request order Once I built a dependency graph, execute the list in an order that maximizes the final connectivity. I am not sure if this is a really a problem but I somehow have a feeling that there might exist more than one order in which case, it is required to choose the best order. First and foremost, I am wondering if I constructed the problem correctly and if I should be aware of any corner cases. Secondly, is there a closely related algorithm that I can look at? Currently, I am thinking of something like Feedback Arc Set or the Secretary Problem but I am a little confused at the moment. Any suggestions? PS: I am a little confused about the problem myself so please don't flame on me for that. If any clarifications are needed, I will try to update the question.

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  • reflection paths between points in2d

    - by Chris H
    Just wondering if there was a nice (already implemented/documented) algorithm to do the following Given any shape (without crossing edges) and two points inside that shape, compute all the paths between the two points such that all reflections are perfect reflections. The path lengths should be limited to a certain length otherwise there are infinite solutions. I'm not interested in just shooting out rays to try to guess how close I can get, I'm interested in algorithms that can do it perfectly. Search based, not guess/improvement based.

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  • Evaluating a function at a particular value in parallel

    - by Gaurav Kalra
    Hi. The question may seem vague, but let me explain it. Suppose we have a function f(x,y,z ....) and we need to find its value at the point (x1,y1,z1 .....). The most trivial approach is to just replace (x,y,z ...) with (x1,y1,z1 .....). Now suppose that the function is taking a lot of time in evaluation and I want to parallelize the algorithm to evaluate it. Obviously it will depend on the nature of function, too. So my question is: what are the constraints that I have to look for while "thinking" to parallelize f(x,y,z...)? If possible, please share links to study.

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  • Write number N in basis M

    - by VaioIsBorn
    I know how to do it mathematically, but i want it now to do it in c++ using some easy algorithm. Is is possible ? The question is that i need some methods/ideas for writing a number N in basis M, for ex. 14 in basis 3 = 2*(3^0) + 1*(3^1) + 1*(3^2) etc.

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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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  • Sparse quadratic program solver

    - by Jacob
    This great SO answer points to a good sparse solver, but I've got constraints on x (for Ax = b) such that each element in x is >=0 an <=N. The first thing which comes to mind is an QP solver for large sparse matrices. Also, A is huge (around 2e6x2e6) but very sparse with <=4 elements per row. Any ideas/recommendations?

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  • Check if BigInteger is not a perfect square

    - by Ender
    I have a BigInteger value, let's say it is 282 and is inside the variable x. I now want to write a while loop that states: while b2 isn't a perfect square: a ? a + 1 b2 ? a*a - N endwhile How would I do such a thing using BigInteger? EDIT: The purpose for this is so I can write this method. As the article states one must check if b2 is not square.

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  • Drawing Directed Acyclic Graphs: Minimizing edge crossing?

    - by Robert Fraser
    Laying out the verticies in a DAG in a tree form (i.e. verticies with no in-edges on top, verticies dependent only on those on the next level, etc.) is rather simple without graph drawing algorithms such as Efficient Sugimiya. However, is there a simple algorithm to do this that minimizes edge crossing? (For some graphs, it may be impossible to completely eliminate edge crossing.) A picture says a thousand words, so is there an algorithm that would suggest: instead of: EDIT: As the picture suggests, a vertex's inputs are always on top and outputs are always below, which is another barrier to just pasting in an existing layout algorithm.

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