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• Simple way to implement computer-go board in Java

  - by codingbear

  I want to make a simple Go board to design an Computer Go game. In a go game, you lie a "stone" (white or black) on a position where horizontal and vertical lines intersect. What are some simple ways to restrict users from placing their stones in other locations? Maybe I'm just not seeing a simple solution. EDIT I guess I should rephrase my question better: I want to know how to do the background image of Go board, so that I can lie my stones on the intersection of the horizontal and the vertical lines. I was thinking about getting a just regular Go board image, and when I'm actually rendering stones, I find right position of pixels to lie stones. However, that solution did not seem to be the best solution, since I need to worry about size of stone images and think about proportionality when I either expand or shrink the board window.

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• Finding the centeroid of a polygon?

  - by user146780

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

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• How does an unsharp mask work?

  - by Bob Aman

  I've been playing around with image processing lately, and I'd like to know how the unsharp mask algorithm works. I'm looking at the source code for Gimp and it's implementation, but so far I'm still in the dark about how it actually works. I need to implement it for a project I'm working on, but I'd like to actually understand the algorithm I'm using.

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• Graph paper like drawing software

  - by Algorist

  Hi, I have a college assignment, where I have to draw diagrams of voronoi, delaunay, minimum spanning tree etc for the college. I want to do that in computer. I searched in google with no luck. Is there any good graph drawing software you are aware of? Thank you Bala

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• Any 'pretty' data visualization libraries for Python?

  - by int3

  There are plenty of 'pretty-printing' visualization libraries for Javascript. E.g. those listed here. Googling for 'python visualization libraries' only turns up stuff like VTK and mayavi, which are primarily more for no-nonsense scientific use. So, do you know of any Python libraries similar to those Javascript ones in the above link? I particularly like the Javascript Infovis Toolkit.

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• Turning an NSImage* into a CGImageRef?

  - by Brian Postow

  Is there an easy way to do this that works in 10.5? In 10.6 I can use nsImage CGImageForProposedRect: NULL context: NULL hints: NULL If I'm not using 1b black and white images (Like Group 4 TIFF), I can use bitmaps, but cgbitmaps seem to not like that setup... Is there a general way of doing this? I need to do this because I have an IKImageView that seems to only want to add CGImages, but all I've got are NSImages. Currently, I'm using a private setImage:(NSImage*) method that I'd REALLY REALLY rather not be using...

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• How to view output .mp files from Functional MetaPost

  - by Jared Updike

  I'm interested in using Functional MetaPost on Mac OS X: http://cryp.to/funcmp/ I'm looking for a tutorial like: http://haskell.org/haskellwiki/Haskell_in_5_steps but for a trivial FuncMP example, i.e. using GHC, I can compile something simple such as: import FMP myPicture = text "blah" main = generate "foo" 1 myPicture but I can't figure out how to view this foo.1.mp output. (It gives a runtime error about not finding 'virmp'; my MetaPost binary is 'mpost'; I can't figure out how to override this Parameter or what my .FunMP file is or should be doing...) I can run mpost on that but the output (foo.1.1) is what, PostScript? EPS? How do I use this? (I imagine I just need a simple LaTeX file with an EPS figure in it or something...) Preferably, I'd like to generate output (.ps or .pdf that I can view) so I an actually get somewhere with Functional MetaPost, learning it, playing with it, not banging my head against paths and binaries and shell commands.

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• How to keep text inside a circle using Cairo?

  - by miguelrios

  I a drawing a graph using Cairo (pycairo specifically) and I need to know how can I draw text inside a circle without overlapping it, by keeping it inside the bounds of the circle. I have this simple code snippet that draws a letter "a" inside the circle: ''' Created on May 8, 2010 @author: mrios ''' import cairo, math WIDTH, HEIGHT = 1000, 1000 #surface = cairo.PDFSurface ("/Users/mrios/Desktop/exampleplaces.pdf", WIDTH, HEIGHT) surface = cairo.ImageSurface (cairo.FORMAT_ARGB32, WIDTH, HEIGHT) ctx = cairo.Context (surface) ctx.scale (WIDTH/1.0, HEIGHT/1.0) # Normalizing the canvas ctx.rectangle(0, 0, 1, 1) # Rectangle(x0, y0, x1, y1) ctx.set_source_rgb(255,255,255) ctx.fill() ctx.arc(0.5, 0.5, .4, 0, 2*math.pi) ctx.set_source_rgb(0,0,0) ctx.set_line_width(0.03) ctx.stroke() ctx.arc(0.5, 0.5, .4, 0, 2*math.pi) ctx.set_source_rgb(0,0,0) ctx.set_line_width(0.01) ctx.set_source_rgb(255,0,255) ctx.fill() ctx.set_source_rgb(0,0,0) ctx.select_font_face("Georgia", cairo.FONT_SLANT_NORMAL, cairo.FONT_WEIGHT_BOLD) ctx.set_font_size(1.0) x_bearing, y_bearing, width, height = ctx.text_extents("a")[:4] print ctx.text_extents("a")[:4] ctx.move_to(0.5 - width / 2 - x_bearing, 0.5 - height / 2 - y_bearing) ctx.show_text("a") surface.write_to_png ("/Users/mrios/Desktop/node.png") # Output to PNG The problem is that my labels have variable amount of characters (with a limit of 20) and I need to set the size of the font dynamically. It must fit inside the circle, no matter the size of the circle nor the size of the label. Also, every label has one line of text, no spaces, no line breaks. Any suggestion?

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• How to clip rendering in OpenGL (C++)

  - by topright

  How to clip rendering in OpenGL (simple rectangle area)? Please post a C++ example.

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• deleting HBITMAP causes an access violation at runtime.

  - by Oliver

  Hi, I have the following code to take a screenshot of a window, and get the colour of a specific pixel in it: void ProcessScreenshot(HWND hwnd){ HDC WinDC; HDC CopyDC; HBITMAP hBitmap; RECT rt; GetClientRect (hwnd, &rt); WinDC = GetDC (hwnd); CopyDC = CreateCompatibleDC (WinDC); //Create a bitmap compatible with the DC hBitmap = CreateCompatibleBitmap (WinDC, rt.right - rt.left, //width rt.bottom - rt.top);//height SelectObject (CopyDC, hBitmap); BitBlt (CopyDC, //destination 0,0, rt.right - rt.left, //width rt.bottom - rt.top, //height WinDC, //source 0, 0, SRCCOPY); COLORREF col = ::GetPixel(CopyDC,145,293); // Do some stuff with the pixel colour.... delete hBitmap; ReleaseDC(hwnd, WinDC); ReleaseDC(hwnd, CopyDC); } the line 'delete hBitmap;' causes a runtime error: an access violation. I guess I can't just delete it like that? Because bitmaps take up a lot of space, if I don't get rid of it I will end up with a huge memory leak. My question is: Does releasing the DC the HBITMAP is from deal with this, or does it stick around even after I have released the DC? If the later is the case, how do I correctly get rid of the HBITMAP?

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• LaTeX: How to make a fullpage vertical rule on every page?

  - by Herbert Sitz

  I'm using LaTeX and I would like to have vertical rule along left side of page, topmargin to bottommargin, 0.5in from the left edge of the page. I want this on every page, so I assume that means it must somehow be tied to the header or the footer? Can someone tell me how to do that?

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• Drawing performance with CGImageCreateWithJPEGDataProvider?

  - by Rnegi

  I've actually curious about this for the iPhone. I am getting an MJPEG stream from a server and trying to render it natively on the iphone (without the use of safari class). Reasons for this is because the safari class while CAN render MJPEG natively, does not do so at the framerate I would like. So I tried drawing it natively, but I've come up with performance issues, namely a syncing issue between what I'm getting from the server and what I am able to draw onto the screen of the phone. (There should be a little lag, but the drift gets really bad, which is what I want to avoid). So I have a connection set up to my server and I do get the JPEGS. It's just data I insert into a NSMutableArray buffer CFMutableDataRef _t_data_ref = (CFMutableDataRef)[_buffer_array objectAtIndex:0]; //CGDataProviderRef imgDataProvider = CGDataProviderCreateWithCFData (_cf_buffer_data); CGDataProviderRef imgDataProvider = CGDataProviderCreateWithCFData(_t_data_ref); CGImageRef image = CGImageCreateWithJPEGDataProvider(imgDataProvider, NULL, true, kCGRenderingIntentDefault); CGImageRef imgRef = image; CGContextDrawImage(context, CGRectMake(0, 17, 380, 285), imgRef); CGImageRelease(image); CGDataProviderRelease(imgDataProvider); please note this is the gist of my code, but it should summarize what I am trying to accomplish with regards to drawing. Also in order to get the framerate in sync, I had to detach a separate thread that sleeps X seconds and calls [self setNeedsDisplay]. NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init]; // Top-level pool while(1) { //[NSThread sleepForTimeInterval:TIMER_REFRESH_VALUE]; //sleep(unsigned int ); usleep(MICRO_REFRESH_VALUE); if ([_buffer_array count] > 10) { //NSLog(@"stuff %d", [_buffer_array count]); //[self setNeedsDisplay]; [self performSelectorOnMainThread:@selector(setNeedsDisplay) withObject:nil waitUntilDone:NO]; } } [pool release]; // Release the objects in the pool. My buffer of jpeg data actually fills up quite quick, but I can't seem to actually consume what i'm getting at the same rate, actually much slower. Are there any documents that can describe what kind of performance tuning I can do to make it go faster when rendering the JPEG to the screen? Or am I kind of stuck here? Thanks!

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• Reinterpret a CGImageRef using PyObjC in Python

  - by Michael Rondinelli

  Hi, I'm doing something that's a little complicated to sum up in the title, so please bear with me. I'm writing a Python module that provides an interface to my C++ library, which provides some specialized image manipulation functionality. It would be most convenient to be able to access image buffers as CGImageRefs from Python, so they could be manipulated further using Quartz (using PyObjC, which works well). So I have a C++ function that provides a CGImageRef representation from my own image buffers, like this: CGImageRef CreateCGImageRefForImageBuffer(shared_ptr<ImageBuffer> buffer); I'm using Boost::Python to create my Python bridge. What is the easiest way for me to export this function so that I can use the CGImageRef from Python? Problems: The CGImageRef type can't be exported directly because it is a pointer to an undefined struct. So I could make a wrapper function that wraps it in a PyCObject or something to get it to send the pointer to Python. But then how do I "cast" this object to a CGImageRef from Python? Is there a better way to go about this?

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• Python class variables not defined with called from outside module

  - by Jimmy

  I am having some issues with calling a function outside of a module. The scenario is I have a small class library that is using turtle to do some drawing, the function within the module calls the classes also within the module and draws things, etc. This all works fine and dandy when I call the function from within the same file, but if I have another file and call myLib.scene() I get variable undefined errors. Code examples: a class class Rectangle(object): def __init__(self, pen, height=100, width=100, fillcolor=''): self.pen = pen self.height = height self.width = width self.fillcolor = fillcolor def draw(self, x, y): '''draws the rectangle at coordinates x and y''' self.pen.goto(x, y) if self.fillcolor: self.pen.fillcolor(self.fillcolor) self.pen.fill(True) self.pen.down() for i in range(0,4): self.pen.forward(self.height if i%2 else self.width) self.pen.left(90) and the calling function is this def scene(pen): rect = Rectangle(pen) rect.draw(100,100) when I put the line scene(turtle.Turtle()) into the same file I have no issues, the rectangle is drawn and everyone goes home happy. However, if I try to call it from a separate python file like so: myLib.scene(turtle.Turtle()) I get an error: NameError: global name 'pen' is not defined, in the for loop of my draw method. Even if the line above is in the same file it still bombs out. What is going on?

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• Why there is an invalid context error?

  - by Tattat

  Here is the code I use to draw: - (void) drawSomething { CGContextRef context = UIGraphicsGetCurrentContext(); CGContextSetRGBStrokeColor(context, 1, 0, 0, 1); CGContextSetLineWidth(context, 6.0); CGContextMoveToPoint(context, 100.0f, 100.0f); CGContextAddLineToPoint(context, 200.0f, 200.0f); CGContextStrokePath(context); NSLog(@"draw"); } But I got the error like this: [Session started at 2010-04-03 17:51:07 +0800.] Sat Apr 3 17:51:09 MacBook.local MyApp[12869] <Error>: CGContextSetRGBStrokeColor: invalid context Sat Apr 3 17:51:09 MacBook.local MyApp[12869] <Error>: CGContextSetLineWidth: invalid context Sat Apr 3 17:51:09 MacBook.local MyApp[12869] <Error>: CGContextMoveToPoint: invalid context Sat Apr 3 17:51:09 MacBook.local MyApp[12869] <Error>: CGContextAddLineToPoint: invalid context Sat Apr 3 17:51:09 MacBook.local MyApp[12869] <Error>: CGContextDrawPath: invalid context Why it prompt me to say that the context is invalided?

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• Drawing CGPathRef in ScrollView using Iphone sdk.

  - by Ann

  Hi all. I want to draw some curve in my scroll view using CGPathRef. I tried to draw this path but i see only the part of my CGPathRef which located at 320x480 pixels. Is it way to do that. Thank you in advance. Here is my code path = CGPathCreateMutable(); CGContextBeginPath(ctx); CGContextMoveToPoint(ctx, [[pathArray objectAtIndex:0]CGPointValue].x,[[pathArray objectAtIndex:0]CGPointValue].y ); for(int i = 1; i < [pathArray count]; ++i) { CGContextAddLineToPoint(ctx, [[pathArray objectAtIndex:i]CGPointValue].x, [[pathArray objectAtIndex:i]CGPointValue].y); } CGContextClosePath(ctx); CGContextSetRGBFillColor(ctx, 0.5, 0.3, 0.2, 0.5); CGContextFillPath(ctx); And when I scroll my view the line does not change its location. My goal is to move this line during scrolling.

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• correct fisheye distortion

  - by Will

  I have some points that describe positions in a picture taken with a fisheye lens. I've found this description of how to generate a fisheye effect, but not how to reverse it. How do you calculate the radial distance from the centre to go from fisheye to rectilinear? My function stub looks like this: Point correct_fisheye(const Point& p,const Size& img) { // to polar const Point centre = {img.width/2,img.height/2}; const Point rel = {p.x-centre.x,p.y-centre.y}; const double theta = atan2(rel.y,rel.x); double R = sqrt((rel.x*rel.x)+(rel.y*rel.y)); // fisheye undistortion in here please //... change R ... // back to rectangular const Point ret = Point(centre.x+R*cos(theta),centre.y+R*sin(theta)); fprintf(stderr,"(%d,%d) in (%d,%d) = %f,%f = (%d,%d)\n",p.x,p.y,img.width,img.height,theta,R,ret.x,ret.y); return ret; }

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• For "draggable" div tags that are NOT nested: JQuery/JavaScript div tag “containment” approach/algor

  - by Pete Alvin

  Background: I've created an online circuit design application where .draggable() div tags are containers that contain smaller div containers and so forth. Question: For any particular div tag I need to quickly identify if it contains other div tags (that may in turn contain other div tags). -- Since the div tags are draggable, in the DOM they are NOT nested inside each other but I think are absolutely positioned. So I think that a "hit testing" approach is the only way to determine containment, unless there is some "secret" routine built-in somewhere that could help with this. I've searched JQuery and I don't see any built-in routine for this. Does anyone know of an algorithm that's quicker than O(n^2)? Seems like I have to walk the list of div tags in an outer loop (n) and have an inner loop (another n) to compare against all other div tags and do a "containment test" (position, width, height), building a list of contained div tags. That's n-squared. Then I have to build a list of all nested div tags by concatenating contained lists. So the total would be O(n^2)+n. There must be a better way?

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• Quartz2D and gradient line

  - by Fry Constantine

  how can i draw gradient line with quartz2d?

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• Building a clip area in a UIView from path objects in its subviews

  - by hkatz

  I'm trying to produce a clipping area in a UIView that's generated from path objects in its subviews. For example, I might have one subview containing a square and another containing a circle. I want to be able to produce a clip in the parent superview that's the union of both these shapes. Can someone explain how to do this? About all I've been able to figure out so far is that: 1 - the superview's drawRect: method is called before its subviews' drawRects are, and 2 - the ContextRef that's accessible in all three instances is the same. Other than that I'm stumped. Thanks, Howard

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• How to write text(using CGContextShowTextAtPoint) dynamically near graph x and y-axis intervals?

  - by Rajendra Bhole

  I developed graph using NSObject class and using CGContext method. The following code displaying dynamically in X and Y-axis intervals, CGContextSetRGBStrokeColor(ctx, 2.0, 2.0, 2.0, 1.0); CGContextSetLineWidth(ctx, 2.0); CGContextMoveToPoint(ctx, 30.0, 200.0); CGContextAddLineToPoint(ctx, 30.0, 440.0); for(float y = 400.0; y >= 200.0; y-=30) { CGContextSetRGBStrokeColor(ctx, 2.0, 2.0, 2.0, 1.0); CGContextMoveToPoint(ctx, 28, y); CGContextAddLineToPoint(ctx, 32, y); CGContextStrokePath(ctx); //CGContextClosePath(ctx); } CGContextMoveToPoint(ctx, 10, 420.0); CGContextAddLineToPoint(ctx, 320, 420.0); //CGContextAddLineToPoint(ctx, 320.0, 420.0); //CGContextStrokePath(ctx); for(float x = 60.0; x <= 260.0; x+=30) { CGContextSetRGBStrokeColor(ctx, 2.0, 2.0, 2.0, 1.0); CGContextMoveToPoint(ctx, x, 418.0); CGContextAddLineToPoint(ctx, x, 422.0); CGContextStrokePath(ctx); CGContextClosePath(ctx); } I want to write the dynamic text on the X and Y-axis lines near the intervals (like X-axis is denoting number of days per week and Y-axis denoting something per someting)? Thanks.

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• Soft Paint Bucket Fill: Colour Equality

  - by Bart van Heukelom

  I'm making a small app where children can fill preset illustrations with colours. I've succesfully implemented an MS-paint style paint bucket using the flood fill argorithm. However, near the edges of image elements pixels are left unfilled, because the lines are anti-aliased. This is because the current condition on whether to fill is colourAtCurrentPixel == colourToReplace (the colours are RGB uints) I'd like to add a smoothing/treshold option like in Photoshop and other sophisticated tools, but what's the algorithm to determine the equality/distance between two colours? if (match(pixel(x,y), colourToReplace) setpixel(x,y,colourToReplaceWith) How to fill in match()? Here's my current full code: var b:BitmapData = settings.background; b.lock(); var from:uint = b.getPixel(x,y); var q:Array = []; var xx:int; var yy:int; var w:int = b.width; var h:int = b.height; q.push(y*w + x); while (q.length != 0) { var xy:int = q.shift(); xx = xy % w; yy = (xy - xx) / w; if (b.getPixel(xx,yy) == from) { b.setPixel(xx,yy,to); if (xx != 0) q.push(xy-1); if (xx != w-1) q.push(xy+1); if (yy != 0) q.push(xy-w); if (yy != h-1) q.push(xy+w); } } b.unlock(null);

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• CGPath and Quartz 2D

  - by iphonedevnoob

  I want to create a triangle using Quartz 2D functions. The 3 edges of the triangle should be in different colors. I am able to create the triangle but not able to set the color of each edge or subpath separately. Any suggestions or sample code are much appreciated.

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• iPhone - Is it ok to override UITableViewCell setSelected:animated

  - by Brian

  I am drawing custom UITableViewCells. My cells are opaque and are completely drawn in the drawRect of the cell to help with performance. I want to handle the look of a selected cell myself. If I don't, then the contents of my cell is covered up by the selectedBackgroundView that is added. Is it common or acceptable to override the setSelected:animated method of my cell so this is done properly. I guess if I did that, then I would not call the super's setSelected method since I would be handling how the cell will show that its selected. I would also have to set the selected property of the cell. Any help would be great. Thanks.

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• Metric 3d reconstruction

  - by srand

  I'm trying to reconstruct 3D points from 2D image correspondences. My camera is calibrated. The test images are of a checkered cube and correspondences are hand picked. Radial distortion is removed. After triangulation the construction seems to be wrong however. The X and Y values seem to be correct, but the Z values are about the same and do not differentiate along the cube. The 3D points look like as if the points were flattened along the Z-axis. What is going wrong in the Z values? Do the points need to be normalized or changed from image coordinates at any point, say before the fundamental matrix is computed? (If this is too vague I can explain my general process or elaborate on parts)

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