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  • Finding the centroid of a polygon?

    - by user146780
    I have tried: for each vertex, add to total, divide by number of verities to get center. I'v also tried: Find the topmost, bottommost - get midpoint... find leftmost, rightmost, find midpoint. Both of these did not return the perfect center because I'm relying on the center to scale a polygon. I want to scale my polygons so I may put a border around them. What is the best way to find the centroid of a polygon given that the polygon may be concave, convex and have many many sides of various lengths. Thanks

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  • Interpolating height for a point inside a grid based on a discrete height function.

    - by fastrack20
    Hi, I have been wracking my brain to come up with a solution to this problem. I have a lookup table that returns height values for various points (x,z) on the grid. For instance I can calculate the height at A, B, C and D in Figure 1. However, I am looking for a way to interpolate the height at P (which has a known (x,z)). The lookup table only has values at the grid intervals, and P lies between these intervals. I am trying to calculate values s and t such that: A'(s) = A + s(C-A) B'(t) = B + t(P-B) I would then use the these two equations to find the intersection point of B'(t) with A'(s) to find a point X on the line A-C. With this I can calculate the height at this point X and with that the height at point P. My issue lies in calculating the values for s and t. Any help would be greatly appreciated.

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  • Why I can't draw in a loop? (Using UIView in iPhone)

    - by Tattat
    I can draw many things using this : NSString *imagePath = [[NSBundle mainBundle] pathForResource:@"dummy2.png" ofType:nil]; UIImage *img = [UIImage imageWithContentsOfFile:imagePath]; image = CGImageRetain(img.CGImage); CGRect imageRect; double x = 0; double y = 0; for (int k=0; k<someValue; k++) { x += k; y += k; imageRect.origin = CGPointMake(x, y); imageRect.size = CGSizeMake(25, 25); CGContextDrawImage(UIGraphicsGetCurrentContext(), imageRect, image); } } CGImageRelease(img.CGImage); So, it works, so, I put it into a command object's execute method. Then, I want to do similar thing, but this time, my execute method only do this: NSString *imagePath = [[NSBundle mainBundle] pathForResource:@"dummy2.png" ofType:nil]; UIImage *img = [UIImage imageWithContentsOfFile:imagePath]; image = CGImageRetain(img.CGImage); CGRect imageRect; double x = inComingX; double y = inComingY; imageRect.origin = CGPointMake(x, y); imageRect.size = CGSizeMake(25, 25); CGContextDrawImage(UIGraphicsGetCurrentContext(), imageRect, image); CGImageRelease(img.CGImage); This time, this is also a Command, and it is the execute method. But I take the for loop away. I will have another method that pass the inComingX , and inComingY into my Command object. My Drawing method is simply execute the Cmd that passed in my drawingEngine: -(void)drawInContext:(CGContextRef)context { [self.cmdToBeExecuted execute]; } I also have the assign method to assign the command,: -(void)assignCmd:(Command* )cmd{ self.cmdToBeExecuted = cmd; } And this is the way I called the drawingEngine for(int k=0; k<5; k++){ [self.drawingEngine assignCmd:[DrawingCmd setDrawingInformation:(10*k):0:@"dummy.png"]]; [self.drawingEngine setNeedsDisplay]; } It can draw, but the sad thing is it only draw the last one. Why? and how to fix it? I can draw all the things in my First code, but after I take the loop outside, and use the loop in last code, it just only draw the last one. Plz help

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  • How to distort the desktop screen

    - by HaifengWang
    Hi friends, I want to change the shape of the desktop screen, so what are displayed on the desktop will be distorted at the same time. And the user can still operate the PC with the mouse on the distorted desktop(Run the applications, Open the "My Computer" and so on). I think I must get the projection matrix of the screen coordinate at first. Then transform the matrix, and map the desktop buffer image to the distorted mesh. Are there any interfaces which can modify the shape of the desktop screen in OpenGL or DirectX? Would you please give me some tip on it. Thank you very much in advance. Please refer to the picture from http://oi53.tinypic.com/bhewdx.jpg BR, Haifeng Addition1: I'm sorry! Maybe I didn't express clearly what I want to implement. What I want to implement is to modify the shape of the screen. So we can distort the shapes of all the applications which are run on Windows at the same time. For example that the window of "My Computer" will be distorted with the distortion of the desktop screen. And we can still operate the PC with mouse from the distorted desktop(Click the shortcut to run a program). Addition2: The projection matrix is just my assume. There isn't any desktop projection matrix by which the desktop surface is projected to the screen. What I want to implement is to change the shape of the desktop, as the same with mapping the desktop to an 3D mesh. But the user can still operate the OS on the distorted desktop(Click the shortcut to run a program, open the ie to surf the internet). Addition3: The shapes of all the programs run on the OS are changed with the distortion of the screen. It's realtime. The user can still operate the OS on the distorted screen as usually. Maybe we can intercept or override the GPU itself to implement the effect. I'm investigating GDI, I think I can find some clue for that. The first step is to find how to show the desktop on the screen.

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  • Resizing an image with alpha channel

    - by Hafthor
    I am writing some code to generate images - essentially I have a source image that is large and includes transparent regions. I use GDI+ to open that image and add additional objects. What I want to do next is to save this new image much smaller, so I used the Bitmap constructor that takes a source Image object and a height and width, then saved that. I was expecting the alpha channel to be smoothed like the color channels, but this did not happen -- it did result in a couple of semitransparent pixels, but overall it is very blocky. What gives? Using img As New Bitmap("source100x100.png") ''// Drawing stuff Using simg As New Bitmap(img, 20, 20) simg.Save("target20x20.png") End Using End Using Edit: I think what I want is SuperSampling, like what Paint.NET does when set to "Best Quality"

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  • Getting notification / listener when action is performed (chimpChat / monkeyrunner tool)

    - by Dr. AtZe
    I want to get a notification if someone has performed an action in an android app from outside of the app. I don't want to make any (android) code changes. To do the actions I use the Chimpchat.jar, the .jar that the monkeyrunner tool uses. To be clear: Can I get a notification or register listeners on components from outside of the app? e.g. Run my android app My java application links into the device with chimpChat via the adb The user touches a button My java application gets a notification what was performed = am I able to get that information? If not, am I able to get the information on which position the tab was? Hopefully it's clear what I want to do. Thanks, soeren

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  • Blit Queue Optimization Algorithm

    - by martona
    I'm looking to implement a module that manages a blit queue. There's a single surface, and portions of this surface (bounded by rectangles) are copied to elsewhere within the surface: add_blt(rect src, point dst); There can be any number of operations posted, in order, to the queue. Eventually the user of the queue will stop posting blits, and ask for an optimal set of operations to actually perform on the surface. The task of the module is to ensure that no pixel is copied unnecessarily. This gets tricky because of overlaps of course. A blit could re-blit a previously copied pixel. Ideally blit operations would be subdivided in the optimization phase in such a way that every block goes to its final place with a single operation. It's tricky but not impossible to put this together. I'm just trying to not reinvent the wheel. I looked around on the 'net, and the only thing I found was the SDL_BlitPool Library which assumes that the source surface differs from the destination. It also does a lot of grunt work, seemingly unnecessarily: regions and similar building blocks are a given. I'm looking for something higher-level. Of course, I'm not going to look a gift horse in the mouth, and I also don't mind doing actual work... If someone can come forward with a basic idea that makes this problem seem less complex than it does right now, that'd be awesome too. EDIT: Thinking about aaronasterling's answer... could this work? Implement customized region handler code that can maintain metadata for every rectangle it contains. When the region handler splits up a rectangle, it will automatically associate the metadata of this rectangle with the resulting sub-rectangles. When the optimization run starts, create an empty region handled by the above customized code, call this the master region Iterate through the blt queue, and for every entry: Let srcrect be the source rectangle for the blt beng examined Get the intersection of srcrect and master region into temp region Remove temp region from master region, so master region no longer covers temp region Promote srcrect to a region (srcrgn) and subtract temp region from it Offset temp region and srcrgn with the vector of the current blt: their union will cover the destination area of the current blt Add to master region all rects in temp region, retaining the original source metadata (step one of adding the current blt to the master region) Add to master region all rects in srcrgn, adding the source information for the current blt (step two of adding the current blt to the master region) Optimize master region by checking if adjacent sub-rectangles that are merge candidates have the same metadata. Two sub-rectangles are merge candidates if (r1.x1 == r2.x1 && r1.x2 == r2.x2) | (r1.y1 == r2.y1 && r1.y2 == r2.y2). If yes, combine them. Enumerate master region's sub-rectangles. Every rectangle returned is an optimized blt operation destination. The associated metadata is the blt operation`s source.

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  • Is there a table of OpenGL extensions, versions, and hardware support somewhere?

    - by Thomas
    I'm looking for some resource that can help me decide what OpenGL version my game needs at minimum, and what features to support through extensions. Ideally, a table of the following format: 1.0 1.1 1.2 1.2.1 1.3 ... multitexture - ARB ARB core core texture_float - EXT EXT ARB ARB ... (Not sure about the values I put in, but you get the idea.) The extension specs themselves, at opengl.org, list the minimum OpenGL version they need, so that part is easy. However, many extensions have been accepted and became core standard in subsequent OpenGL versions, but it is very hard to find when that happened. The only way I could find is to compare the full OpenGL standards document for each version. On a related note, I would also very much like to know which extensions/features are supported by which hardware, to help me decide what features I can safely use in my game, and which ones I need to make optional. For example, a big honkin' table like this: MAX_TEXTURE_IMAGE_UNITS MAX_VERTEX_TEXTURE_IMAGE_UNITS ... GeForce 6xxx 8 4 GeForce 7xxx 16 8 ATi x300 8 4 ... (Again, I'm making the values up.) The table could list hardware limitations from glGet but also support for particular extensions, and limitations of such extension support (e.g. what floating-point texture formats are supported in hardware). Any pointers to these or similar resources would be hugely appreciated!

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  • Codebase for making a Flash-based interactive map with SVG vector data?

    - by Mike
    I'm looking for a way to take SVG path info (basically a string of coordinates) and dynamically draw it with Actionscript. Icing on the cake would be if those shapes could detect mouse events to trigger JS and dynamically change their appearance (fill, stroke, etc...). I'm currently trying something similar to this (http://raphaeljs.com/australia.html) using SVG but it's just too slow in IE. I've also tried Google's SVG Web (http://code.google.com/p/svgweb/) which basically does exactly what I'm looking for (it converts SVG to Flash in IE) but again, it's sloooooow - which is why I'm considering doing the whole shebang in Flash. Anyone know of some links to point me in the right direction?

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  • Border in DrawRectangle

    - by undsoft
    Well, I'm coding the OnPaint event for my own control and it is very nescessary for me to make it pixel-accurate. I've got a little problem with borders of rectangles. See picture: These two rectangles were drawn with the same location and size parameters, but using different size of the pen. See what happend? When border became larger it has eaten the free space before the rectangle (on the left). I wonder if there is some kind of property which makes border be drawn inside of the rectangle, so that the distance to rectangle will always be the same. Thanks.

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  • How does Google implement Microsoft Exchange access?

    - by user358041
    I know with Android 2.x there is the ability to tap into Microsoft Exchange, for at least email, if not calendar and contacts. I would like to see how this was accomplished. Particularly because Microsoft Exchange exposes SOAP web services, and I understand there is no native Android support for SOAP. Since this is open source, shouldn't I be able to find something in the Android source? If so, can you point me in the right direction of where to find it in the ~4Gig (!) source? I want to develop an application that accesses Exchange contacts and calendars, but don't want to reinvent that piece. Any other guidance would be appreciated. Thanks.

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  • Access the internal phonebook

    - by L0rdAli3n
    For more than two days now, I'm trying to grab a list of all contacts, from the internal phonebook (no facebook-, gmail- or twittercontacts) with their family- and givenname. I managed to get a list with all contacts, socialcontacts included. So I looked at the account_type and saw that on my HTC Desire they were all "com.htc.android.pcsc" and I was like "Great, I just have to filter the whole list". But then all people with non-htc android cellphones would be unable to use my app, if I would hardcode this filter. Next idea was to let the user choose which account he wants to use, but unfortunately the "com.htc.android.pcsc" didn't appear in the list I got from the AccountManager?!? So my question is: Is there any standardized way to access the internal phonebook? I'm really stuck with that and any hint is highly appreciated!

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  • Merging photo textures - (from calibrated cameras) - projected onto geometry

    - by freakTheMighty
    I am looking for papers/algorithms for merging projected textures onto geometry. To be more specific, given a set of fully calibrated cameras/photographs and geometry, how can we define a metric for choosing which photograph should be used to texture a given patch of the geometry. I can think of a few attributes one may seek minimize including the angle between the surface normal and the camera, the distance of the camera from the surface, as well as minimizing some parameterization of sharpness. The question is how do these things get combined and are there well established existing solutions?

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  • Why are all my masked views unmasked in my view snapshot?

    - by mystify
    I'm taking a snapshot of an view. This view has got some subviews which have layer masks applied to them. For some reason, those masks take no effect in the snapshot and the masked parts are completely visible. UIGraphicsBeginImageContext(theView.frame.size); [theView.layer renderInContext:UIGraphicsGetCurrentContext()]; UIImage *newImage = UIGraphicsGetImageFromCurrentImageContext(); UIGraphicsEndImageContext(); I assume this is a bug in the framework. But maybe it's not? Did I do anything wrong here?

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  • RaphaelJS HTML5 Library pathIntersection() bug or alternative optimisation (screenshots)

    - by user1236048
    I have a chart generated using RaphaelJS library. It is just on long path: M 50 122 L 63.230769230769226 130 L 76.46153846153845 130 L 89.6923076923077 128 L 102.92307692307692 56 L 116.15384615384615 106 L 129.3846153846154 88 L 142.6153846153846 114 L 155.84615384615384 52 L 169.07692307692307 30 L 182.3076923076923 62 L 195.53846153846152 130 L 208.76923076923077 74 L 222 130 L 235.23076923076923 66 L 248.46153846153845 102 L 261.6923076923077 32 L 274.9230769230769 130 L 288.15384615384613 130 L 301.38461538461536 32 L 314.6153846153846 86 L 327.8461538461538 130 L 341.07692307692304 70 L 354.30769230769226 130 L 367.53846153846155 102 L 380.7692307692308 120 L 394 112 L 407.2307692307692 68 L 420.46153846153845 48 L 433.6923076923077 92 L 446.9230769230769 128 L 460.15384615384613 110 L 473.38461538461536 78 L 486.6153846153846 130 L 499.8461538461538 56 L 513.0769230769231 116 L 526.3076923076923 80 L 539.5384615384614 58 L 552.7692307692307 40 L 566 130 L 579.2307692307692 94 L 592.4615384615385 64 L 605.6923076923076 122 L 618.9230769230769 98 L 632.1538461538461 120 L 645.3846153846154 70 L 658.6153846153845 82 L 671.8461538461538 76 L 685.0769230769231 124 L 698.3076923076923 110 L 711.5384615384615 94 L 724.7692307692307 130 L 738 130 L 751.2307692307692 66 L 764.4615384615385 118 L 777.6923076923076 70 L 790.9230769230769 130 L 804.1538461538461 44 L 817.3846153846154 130 L 830.6153846153845 36 L 843.8461538461538 92 L 857.076923076923 130 L 870.3076923076923 76 L 883.5384615384614 130 L 896.7692307692307 60 L 910 88 Also below these chart I have a jqueryUI slider of the same width (860px) and centered with the chart. I want when I move the slider to move a dot on the chart accordingly with the slider position. See attached screenshot: As you can see it seems to work fine. I've implemented this behaviour using the pathIntersection() method. On the slide event at each ui.value (x coordinate) I intersect my chartPath (the one from above) with a vertical straight line at the x coordinate. But still there are some problems. One of them is that it runs very hard, and it kinda freezes sometimes.. and very weird sometimes it doesn't seem to intersect at all even it should.. I'll example below 2 cases I identified: M 499.8461538461538 0 L 499.8461538461538 140 M 910 0 L 910 140 Could you please explain why this intersect behaviour happens (it should return a dot).. and the worst part it seems like it happens randomly.. if I use another chartdata. Also if you can identify another (better) solution to syncronise the slider position with the dot on the chart.. would be perfect. I thought about using Element.getPointAtLength(length), but I don't know how. I think I should save the pathSegments and for each to compute the start Length and the finish Length.

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  • Simulating brush strokes for painting application

    - by DrRobot
    I'm trying to write an application that can be used to create pictures that look like paintings using simulated brush strokes. Are there any good sources for simple ways of simulating brush strokes? For example, given a list of mouse positions that the user has dragged the mouse through, a brush width and a brush texture, how do I determine what to draw to the canvas? I've tried angling the brush texture in the direction of the mouse movement and dabbing several brush texture images along the path, but it doesn't look great. I think I'm missing something where the brush texture should shrink and grow on corners. Any simple to follow links would be appreciated. I've found complex academic papers on simulating e.g. oil paints but I just want a basic algorithm to use that produces OK results if possible.

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  • Optimally place a pie slice in a rectangle.

    - by Lisa
    Given a rectangle (w, h) and a pie slice with start angle and end angle, how can I place the slice optimally in the rectangle so that it fills the room best (from an optical point of view, not mathematically speaking)? I'm currently placing the pie slice's center in the center of the rectangle and use the half of the smaller of both rectangle sides as the radius. This leaves plenty of room for certain configurations. Examples to make clear what I'm after, based on the precondition that the slice is drawn like a unit circle: A start angle of 0 and an end angle of PI would lead to a filled lower half of the rectangle and an empty upper half. A good solution here would be to move the center up by 1/4*h. A start angle of 0 and an end angle of PI/2 would lead to a filled bottom right quarter of the rectangle. A good solution here would be to move the center point to the top left of the rectangle and to set the radius to the smaller of both rectangle sides. This is fairly easy for the cases I've sketched but it becomes complicated when the start and end angles are arbitrary. I am searching for an algorithm which determines center of the slice and radius in a way that fills the rectangle best. Pseudo code would be great since I'm not a big mathematician.

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