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• GPGPU programming with OpenGL ES 2.0

  - by Albus Dumbledore

  I am trying to do some image processing on the GPU, e.g. median, blur, brightness, etc. The general idea is to do something like this framework from GPU Gems 1. I am able to write the GLSL fragment shader for processing the pixels as I've been trying out different things in an effect designer app. I am not sure however how I should do the other part of the task. That is, I'd like to be working on the image in image coords and then outputting the result to a texture. I am aware of the gl_FragCoords variable. As far as I understand it it goes like that: I need to set up a view (an orthographic one maybe?) and a quad in such a way so that the pixel shader would be applied once to each pixel in the image and so that it would be rendering to a texture or something. But how can I achieve that considering there's depth that may make things somewhat awkward to me... I'd be very grateful if anyone could help me with this rather simple task as I am really frustrated with myself. UPDATE It seems I'll have to use an FBO, getting one like this: glBindFramebuffer(...)

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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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• QT- QImage and multi-threading problem.

  - by umanga

  Greetings all, Please refer to image at : http://i48.tinypic.com/316qb78.jpg We are developing an application to extract cell edges from MRC images from electron microscope. MRC file format stores volumetric pixel data (http://en.wikipedia.org/wiki/Voxel) and we simply use 3D char array(char***) to load and store data (gray scale values) from a MRC file. As shown in the image,there are 3 viewers to display XY,YZ and ZX planes respectively. Scrollbars on the top of the viewers use to change the image slice along an axis. Here is the steps we do when user changes the scrollbar position. 1) get the new scrollbar value.(this is the selected slice) 2) for the relavant plane (YZ,XY or ZX), generate (char* slice;) array for the selected slice by reading 3D char array (char***) 3) Create a new QImage* (Format_RGB888) and set pixel values by reading 'slice' (using img-setPixel(x,y,c);) 4) This new QImage* is painted in the paintEvent() method. We are going to execute "edge-detection" process in a seperate thread since it is an intensive process.During this process we need to draw detected curve (set of pixels) on top of above QImage*.(as a layer).This means we need to call drawPoint() methods outside the QT thread. Is it the best wayto use QImage for this case? What is the best way to execute QT drawing methods from another thread? thanks in advance,

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• NSString sizeWithFont: returning inconsistent results? known bug?

  - by Olof Hedman

  I'm trying to create a simple custom UIView wich contain a string drawn with a single font, but where the first character is slightly larger. I thought this would be easily implemented with two UILabel:s placed next to eachother. I use NSString sizeWithFont to measure my string to be able to lay it out correctly. But I noticed that the font baseline in the returned rectangle varies with +/- 1 pixel depending on the font size I set. Here is my code: NSString* ctxt = [text substringToIndex:1]; NSString* ttxt = [text substringFromIndex:1]; CGSize sz = [ctxt sizeWithFont: cfont ]; clbl = [[UILabel alloc] initWithFrame:CGRectMake(0, 0, sz.width, sz.height)]; clbl.text = ctxt; clbl.font = cfont; clbl.backgroundColor = [UIColor clearColor]; [contentView addSubview:clbl]; CGSize sz2 = [ttxt sizeWithFont: tfont]; tlbl = [[UILabel alloc] initWithFrame:CGRectMake(sz.width, (sz.height - sz2.height), sz2.width, sz2.height)]; tlbl.text = ttxt; tlbl.font = tfont; tlbl.backgroundColor = [UIColor clearColor]; [contentView addSubview:tlbl]; If I use 12.0 and 14.0 as sizes, it works fine. But if I instead use 13.0 and 15.0, then the first character is 1 pixel too high. Is this a known problem? Any suggestions how to work around it? Creating a UIWebView with a CSS and HTML page seems way overkill for this. and more work to handle dynamic strings. Is that what I'm expected to do?

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• Video-codec rater by image comparison algorithm?

  - by Andreas Hornig

  Hi, perhaps anyone knows if this is possible. comparing image quality is almost imposible to describe without subjective influences. When someone rates an image quality as good there is at least one person, that doesn't think so. human preferences are always different. So, I would like to know if there is away to "rate" the image quality by an algorithm that compares the original image to the produced one in following issues colour change(difference pixel by pixel blur rate artifacts and macroblocking the first one would be the easiest one because you could check just the diffeence in colours and can give 3 values in +- of each hex-value both last once I don't know if this is possible, but the blocking could be detected by edge-finding. and the king's quest would be to do that for more then just one image, because video is done with several frames. perhaps you expert programmers could tell me, if such an automated algo can be done to bring some objective measurement divice into rating image quality. this could perhaps calm down some h.264 is better than x264 and better than vp8 and blaaah people :) Andreas 1st posted here http://www.hdtvtotal.com/index.php?name=PNphpBB2&file=viewtopic&p=9705

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• Saving NSBitmapImageRep as NSBMPFileType file. Wrong BMP headers and bitmap content

  - by niko34

  I save a NSBitmapImageRep to a BMP file (Snow Leopard). It seems ok when i open it on macos. But it makes an error on my multimedia device (which can show any BMP file from internet). I cannot figure out what is wrong, but when i look inside the file (with the cool hexfiend app on macos), 2 things wrong: the header have a wrong value for the biHeight parameter : 4294966216 (hex=C8FBFFFF) the header have a correct biWidth parameter : 1920 the first pixel in the bitmap content (after 54 bytes headers in BMP format) correspond to the upper left corner of the original image. In the original BMP file and as specified in the BMP format, it should be the down left corner pixel first. To explain the full workflow in my app, i have an NSImageView where i can drag a BMP image. This View is bind to an NSImage. After a drag & drop i have an action to save this image (with some text drawing over it) to a BMP file. Here's the code for saving the new BMP file : CGColorSpaceRefcolorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB); CGContextRefcontext = CGBitmapContextCreate(NULL, (int)1920, (int)1080, 8, 4*(int)1920, colorSpace, kCGImageAlphaNoneSkipLast); [duneScreenViewdrawBackgroundWithDuneFolder:self inContext:context inRect:NSMakeRect(0,0,1920,1080) needScale:NO]; if(folderType==DXFolderTypeMovie) { [duneScreenViewdrawSynopsisContentWithDuneFolder:self inContext:context inRect:NSMakeRect(0,0,1920,1080) withScale:1.0]; } CGImageRef backgroundImageRef = CGBitmapContextCreateImage(context); NSBitmapImageRep*bitmapBackgroundImageRef = [[NSBitmapImageRepalloc] initWithCGImage:backgroundImageRef]; NSData*data = [destinationBitmap representationUsingType:NSBMPFileType properties:nil]; [data writeToFile:[NSStringstringWithFormat:@"%@/%@", folderPath,backgroundPath] atomically: YES]; The duneScreenViewdrawSynopsisContentWithDuneFolder method uses CGContextDrawImage to draw the image. The duneScreenViewdrawSynopsis method uses CoreText to draw some text in the same context. Do you know what's wrong?

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• Fast Lightweight Image Comparisson Metric Algorithm

  - by gav

  Hi All, I am developing an application for the Android platform which contains 1000+ image filters that have been 'evolved'. When a user selects a photo I want to present the most relevant filters first. This 'relevance' should be dependent on previous use cases. I have already developed tools that register when a filtered image is saved; this combination of filter and image can be seen as the training data for my system. The issue is that the comparison must occur between selecting an image and the next screen coming up. From a UI point of view I need the whole process to take less that 4 seconds; select an image- obtain a metric to use for similarity - check against use cases - return 6 closest matches. I figure with 4 seconds I can use animations and progress dialogs to keep the user happy. Due to platform contraints I am fairly limited in the computational expense of the algorithm. I have implemented a technique adapted from various online tutorials for running C code on the G1 and hence this language is available Specific Constraints; Qualcomm® MSM7201A™, 528 MHz Processor 320 x 480 Pixel bitmap in 32 bit ARGB ~ 2 seconds computational time for the native method to get the metric ~ 2 seconds to compare the metric of the current image with training data This is an academic project so all ideas are welcome, anything you can think of or have heard about would be of interest to me. My ideas; I want to keep the complexity down (O(n*m)?) by using pixel data only rather than a neighbourhood function I was looking at using the Colour historgram/Greyscale histogram/Texture/Entropy of the image, combining them to make the measure. There will be an obvious loss of information but I need the resultant metric to be substantially smaller than the memory footprint of the image (~0.512 MB) As I said, any ideas to direct my research would be fantastic. Kind regards, Gavin

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• Misalignement in the output Bitmap created from a byte array

  - by Daniel

  I am trying to understand why I have troubles creating a Bitmap from a byte array. I post this after a careful scrutiny of the existing posts about Bitmap creation from byte arrays, like the followings: Creating a bitmap from a byte[], Working with Image and Bitmap in c#?, C#: Bitmap Creation using bytes array My code is aimed to execute a filter on a digital image 8bppIndexed writing the pixel value on a byte [] buffer to be converted again (after some processing to manage gray levels) in a 8BppIndexed Bitmap My input image is a trivial image created by means of specific perl code: https://www.box.com/shared/zqt46c4pcvmxhc92i7ct Of course, after executing the filter the output image has lost the first and last rows and the first and last columns, due to the way the filter manage borders, so from the original 256 x 256 image i get a 254 x 254 image. Just to stay focused on the issue I have commented the code responsible for executing the filter so that the operation really performed is an obvious: ComputedPixel = InputImage.GetPixel(myColumn, myRow).R; I know, i should use lock and unlock but I prefer one headache one by one. Anyway this code should be a sort of identity transform, and at last i use: private unsafe void FillOutputImage() { OutputImage = new Bitmap (OutputImageCols, OutputImageRows , PixelFormat .Format8bppIndexed); ColorPalette ncp = OutputImage.Palette; for (int i = 0; i < 256; i++) ncp.Entries[i] = Color .FromArgb(255, i, i, i); OutputImage.Palette = ncp; Rectangle area = new Rectangle(0, 0, OutputImageCols, OutputImageRows); var data = OutputImage.LockBits(area, ImageLockMode.WriteOnly, OutputImage.PixelFormat); Marshal .Copy (byteBuffer, 0, data.Scan0, byteBuffer.Length); OutputImage.UnlockBits(data); } The output image I get is the following: https://www.box.com/shared/p6tubyi6dsf7cyregg9e It is quite clear that I am losing a pixel per row, but i cannot understand why: I have carefully controlled all the parameters: OutputImageCols, OutputImageRows and the byte [] byteBuffer length and content even writing known values as way to test. The code is nearly identical to other code posted in stackOverflow and elsewhere. Someone maybe could help to identify where the problem is? Thanks a lot

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• ListView Final Column Autosize creates scrollbar

  - by Courtney de Lautour

  Hi There, I am implementing a custom control which derives from ListView. I would like for the final column to fill the remaining space (Quite a common task), I have gone about this via overriding the OnResize method: protected override void OnResize(EventArgs e) { base.OnResize(e); if (Columns.Count == 0) return; Columns[Columns.Count - 1].Width = -2; // -2 = Fill remaining space } or via another method: protected override void OnResize(EventArgs e) { base.OnResize(e); if (!_autoFillLastColumn) return; if (Columns.Count == 0) return; int TotalWidth = 0; int i = 0; for (; i < Columns.Count - 1; i++) { TotalWidth += Columns[i].Width; } Columns[i].Width = this.DisplayRectangle.Width - TotalWidth; } Edit: This works fine until I dock the ListView into a parent container and resize via that control. Every second time the control size shrinks (IE, drag the the border one pixel), I get a scroll bar on the bottom which can't move at all (not even one pixel). The result of which is when I drag the size of the parent I am left with a flickering scroll bar in the ListView, and a 50% chance it will be there when the dragging stops.

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• Ideas for jumping in 2D with Actionscript 3 [included attempt]

  - by befall

  So, I'm working on the basics of Actionscript 3; making games and such. I designed a little space where everything is based on location of boundaries, using pixel-by-pixel movement, etc. So far, my guy can push a box around, and stops when running into the border, or when try to the push the box when it's against the border. So, next, I wanted to make it so when I bumped into the other box, it shot forward; a small jump sideways. I attempted to use this (foolishly) at first: // When right and left borders collide. if( (box1.x + box1.width/2) == (box2.x - box2.width/2) ) { // Nine times through for (var a:int = 1; a < 10; a++) { // Adds 1, 2, 3, 4, 5, 4, 3, 2, 1. if (a <= 5) { box2.x += a; } else { box2.x += a - (a - 5)*2 } } } Though, using this in the function I had for the movement (constantly checking for keys up, etc) does this all at once. Where should I start going about a frame-by-frame movement like that? Further more, it's not actually frames in the scene, just in the movement. This is a massive pile of garbage, I apologize, but any help would be appreciated.

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• How to map coordinates in AxesImage to coordinates in saved image file?

  - by Vebjorn Ljosa

  I use matplotlib to display a matrix of numbers as an image, attach labels along the axes, and save the plot to a PNG file. For the purpose of creating an HTML image map, I need to know the pixel coordinates in the PNG file for a region in the image being displayed by imshow. I have found an example of how to do this with a regular plot, but when I try to do the same with imshow, the mapping is not correct. Here is my code, which saves an image and attempts to print the pixel coordinates of the center of each square on the diagonal: import numpy as np import matplotlib.pyplot as plt fig = plt.figure() ax = fig.add_axes([0.1, 0.1, 0.8, 0.8]) axim = ax.imshow(np.random.random((27,27)), interpolation='nearest') for x, y in axim.get_transform().transform(zip(range(28), range(28))): print int(x), int(fig.get_figheight() * fig.get_dpi() - y) plt.savefig('foo.png', dpi=fig.get_dpi()) Here is the resulting foo.png, shown as a screenshot in order to include the rulers: The output of the script starts and ends as follows: 73 55 92 69 111 83 130 97 149 112 … 509 382 528 396 547 410 566 424 585 439 As you see, the y-coordinates are correct, but the x-coordinates are stretched: they range from 73 to 585 instead of the expected 135 to 506, and they are spaced 19 pixels o.c. instead of the expected 14. What am I doing wrong?

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• Location redirect - is tracking possible ?

  - by Gerald Ferreira

  Hi there, I was wondering if someone can help me, I have the following script that redirect users to an affiliate link when they click on a banner. <?php $targets = array( 'site1' => 'http://www.site1.com/', 'site2' => 'http://www.site2.com/', 'site3' => 'http://www.site3.com/', 'site4' => 'http://www.site4.com/', ); if (isset($targets[$_GET['id']])) { header('Location: '.$targets[$_GET['id']]); exit; } ?> Is it possible to track when a user hits the banner telling me the referer site as well as the ip address of the person clicking on the banner. hmmmm something like pixel tracking? I have tried to add an iframe that does the tracking but it creates an error Hope it makes sense Thanks! This is more or less how I would have done it in asp <% var Command1 = Server.CreateObject ("ADODB.Command"); Command1.ActiveConnection = MM_cs_stats_STRING; Command1.CommandText = "INSERT INTO stats.g_stats (g_stats_ip, g_stats_referer) VALUES (?, ? ) "; Command1.Parameters.Append(Command1.CreateParameter("varg_stats_ip", 200, 1, 20, (String(Request.ServerVariables("REMOTE_ADDR")) != "undefined" && String(Request.ServerVariables("REMOTE_ADDR")) != "") ? String(Request.ServerVariables("REMOTE_ADDR")) : String(Command1__varg_stats_ip))); Command1.Parameters.Append(Command1.CreateParameter("varg_stats_referer", 200, 1, 255, (String(Request.ServerVariables("HTTP_REFERER")) != "undefined" && String(Request.ServerVariables("HTTP_REFERER")) != "") ? String(Request.ServerVariables("HTTP_REFERER")) : String(Command1__varg_stats_referer))); Command1.CommandType = 1; Command1.CommandTimeout = 0; Command1.Prepared = true; Command1.Execute(); %> I am not sure how to do it in php - unfortunately for me the hosting is only supporting php so I am more or less clueless on how to do it in php I was thinking if I can somehow call a picture I can do it with pixel tracking in anoter asp page, on another server. Hope this makes better sense

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• Multi-dimensional array edge/border conditions

  - by kirbuchi

  Hi, I'm iterating over a 3 dimensional array (which is an image with 3 values for each pixel) to apply a 3x3 filter to each pixel as follows: //For each value on the image for (i=0;i<3*width*height;i++){ //For each filter value for (j=0;j<9;j++){ if (notOutsideEdgesCondition){ *(**(outArray)+i)+= *(**(pixelArray)+i-1+(j%3)) * (*(filter+j)); } } } I'm using pointer arithmetic because if I used array notation I'd have 4 loops and I'm trying to have the least possible number of loops. My problem is my notOutsideEdgesCondition is getting quite out of hands because I have to consider 8 border cases. I have the following handled conditions Left Column: ((i%width)==0) && (j%3==0) Right Column: ((i-1)%width ==0) && (i>1) && (j%3==2) Upper Row: (i<width) && (j<2) Lower Row: (i>(width*height-width)) && (j>5) and still have to consider the 4 corner cases which will have longer expressions. At this point I've stopped and asked myself if this is the best way to go because If I have a 5 line long conditional evaluation it'll not only be truly painful to debug but will slow the inner loop. That's why I come to you to ask if there's a known algorithm to handle this cases or if there's a better approach for my problem. Thanks a lot.

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• Image drawing library for Haskell?

  - by absz

  I'm working on a Haskell program for playing spatial games: I have a graph of a bunch of "individuals" playing the Prisoner's Dilemma, but only with their immediate neighbors, and copying the strategies of the people who do best. I've reached a point where I need to draw an image of the world, and this is where I've hit problems. Two of the possible geometries are easy: if people have four or eight neighbors each, then I represent each one as a filled square (with color corresponding to strategy) and tile the plane with these. However, I also have a situation where people have six neighbors (hexagons) or three neighbors (triangles). My question, then, is: what's a good Haskell library for creating images and drawing shapes on them? I'd prefer that it create PNGs, but I'm not incredibly picky. I was originally using Graphics.GD, but it only exports bindings to functions for drawing points, lines, arcs, ellipses, and non-rotated rectangles, which is not sufficient for my purposes (unless I want to draw hexagons pixel by pixel*). I looked into using foreign import, but it's proving a bit of a hassle (partly because the polygon-drawing function requires an array of gdPoint structs), and given that my requirements may grow, it would be nice to use an in-Haskell solution and not have to muck about with the FFI (though if push comes to shove, I'm willing to do that). Any suggestions? * That is also an option, actually; any tips on how to do that would also be appreciated, though I think a library would be easier.

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• Bilinear interpolation - DirectX vs. GDI+

  - by holtavolt

  I have a C# app for which I've written GDI+ code that uses Bitmap/TextureBrush rendering to present 2D images, which can have various image processing functions applied. This code is a new path in an application that mimics existing DX9 code, and they share a common library to perform all vector and matrix (e.g. ViewToWorld/WorldToView) operations. My test bed consists of DX9 output images that I compare against the output of the new GDI+ code. A simple test case that renders to a viewport that matches the Bitmap dimensions (i.e. no zoom or pan) does match pixel-perfect (no binary diff) - but as soon as the image is zoomed up (magnified), I get very minor differences in 5-10% of the pixels. The magnitude of the difference is 1 (occasionally 2)/256. I suspect this is due to interpolation differences. Question: For a DX9 ortho projection (and identity world space), with a camera perpendicular and centered on a textured quad, is it reasonable to expect DirectX.Direct3D.TextureFilter.Linear to generate identical output to a GDI+ TextureBrush filled rectangle/polygon when using the System.Drawing.Drawing2D.InterpolationMode.Bilinear setting? For this (magnification) case, the DX9 code is using this (MinFilter,MipFilter set similarly): Device.SetSamplerState(0, SamplerStageStates.MagFilter, (int)TextureFilter.Linear); and the GDI+ path is using: g.InterpolationMode = InterpolationMode.Bilinear; I thought that "Bilinear Interpolation" was a fairly specific filter definition, but then I noticed that there is another option in GDI+ for "HighQualityBilinear" (which I've tried, with no difference - which makes sense given the description of "added prefiltering for shrinking") Followup Question: Is it reasonable to expect pixel-perfect output matching between DirectX and GDI+ (assuming all external coordinates passed in are equal)? If not, why not? Finally, there are a number of other APIs I could be using (Direct2D, WPF, GDI, etc.) - and this question generally applies to comparing the output of "equivalent" bilinear interpolated output images across any two of these. Thanks!

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• What is the best approach to 2D collision detection on the iPhone?

  - by Magic Bullet Dave

  Been working on this problem of collision detection and there appears to be 3 main approaches I could take: Sprite and mask approach. (AND the overlap of the sprites and check for a non-zero number in the resulting sprite pixel data). Bounding circles, rectangles or polygons. (Create one or more shapes that enclose the sprites and do the basic maths to check for overlaps). Use an existing sprite library. The first approach, even though it would have been the way I would have done it in the old days of 16x16 sprite blocks, it appears that there just isn’t an easy way of getting at the individual image pixel data and/or alpha channel within Quartz (or OPENGL for that matter). Detecting the overlap of the bounding box is easy, but then creating a 3rd image from the overlap and then testing it for pixels is complicated and my gut feel is that even if we could get it to work would be slow. Am I missing something neat here? The second approach involves dividing up our sprites into several polygons and testing them for overlaps. The more polygons the more accurate the collision detection. The benefit is that it is fast, and can be accurate. The downside is it makes the sprite creation more complicated. i.e., we have to create the polygons for each sprite. For speed the best approach is to create a tree of polygons. The 3rd approach I’m not sure about as it involves buying code (or using an open source licence). I am not sure what the best library to use is or whether this would make life easier or give us a problem integrating this into our app. So in short I am favouring the polygon and tree approach and would appreciate you views on this before I go and write lots of code. Best regards Dave

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• Using the contents of an array to set individual pixels in a Quartz bitmap context

  - by Magic Bullet Dave

  I have an array that contains the RGB colour values for each pixel in a 320 x 180 display. I would like to be able to set individual pixel values in the a bitmap context of the same size offscreen then display the bitmap context in a view. It appears that I have to create 1x1 rects and either put a stroke on them or a line of length 1 at the point in question. Is that correct? I'm looking for a very efficient way of getting the array data onto the graphics context as you can imagine this is going to be an image buffer that cycles at 25 frames per second and drawing in this way seems inefficient. I guess the other question is should I use OPENGL ES instead? Thoughts/best practice would be much appreciated. Regards Dave OK, have come a short way, but can't make the final hurdle and I am not sure why this isn't working: - (void) displayContentsOfArray1UsingBitmap: (CGContextRef)context { long bitmapData[WIDTH * HEIGHT]; // Build bitmap int i, j, h; for (i = 0; i < WIDTH; i++) { for (j = 0; j < HEIGHT; j++) { h = frameBuffer01[i][j]; bitmapData[i * j] = h; } } // Blit the bitmap to the context CGDataProviderRef providerRef = CGDataProviderCreateWithData(NULL, bitmapData,4 * WIDTH * HEIGHT, NULL); CGColorSpaceRef colorSpaceRef = CGColorSpaceCreateDeviceRGB(); CGImageRef imageRef = CGImageCreate(WIDTH, HEIGHT, 8, 32, WIDTH * 4, colorSpaceRef, kCGImageAlphaFirst, providerRef, NULL, YES, kCGRenderingIntentDefault); CGContextDrawImage(context, CGRectMake(0.0, HEIGHT, WIDTH, HEIGHT), imageRef); CGImageRelease(imageRef); CGColorSpaceRelease(colorSpaceRef); CGDataProviderRelease(providerRef); }

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• 2D Platformer Collision Problems With Both Axes

  - by AusGat

  I'm working on a little 2D platformer/fighting game with C++ and SDL, and I'm having quite a bit of trouble with the collision detection. The levels are made up of an array of tiles, and I use a for loop to go through each one (I know it may not be the best way to do it, and I may need help with that too). For each side of the character, I move it one pixel in that direction and check for a collision (I also check to see if the character is moving in that direction). If there is a collision, I set the velocity to 0 and move the player to the edge of the tile. My problem is that if I check for horizontal collisions first, and the player moves vertically at more than one pixel per frame, it handles the horizontal collision and moves the character to the side of the tile even if the tile is below (or above) the character. If I handle vertical collision first, it does the same, except it does it for the horizontal axis. How can I handle collisions on both axes without having those problems? Is there any better way to handle collision than how I'm doing it?

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• Mulit-dimensional array edge/border conditions

  - by kirbuchi

  Hi, I'm iterating over a 3 dimensional array (which is an image with 3 values for each pixel) to apply a 3x3 filter to each pixel as follows: //For each value on the image for (i=0;i<3*width*height;i++){ //For each filter value for (j=0;j<9;j++){ if (notOutsideEdgesCondition){ *(**(outArray)+i)+= *(**(pixelArray)+i-1+(j%3)) * (*(filter+j)); } } } I'm using pointer arithmetic because if I used array notation I'd have 4 loops and I'm trying to have the least possible number of loops. My problem is my notOutsideEdgesCondition is getting quite out of hands because I have to consider 8 border cases. I have the following handled conditions Left Column: ((i%width)==0) && (j%3==0) Right Column: ((i-1)%width ==0) && (i>1) && (j%3==2) Upper Row: (i<width) && (j<2) Lower Row: (i>(width*height-width)) && (j>5) and still have to consider the 4 corner cases which will have longer expressions. At this point I've stopped and asked myself if this is the best way to go because If I have a 5 line long conditional evaluation it'll not only be truly painful to debug but will slow the inner loop. That's why I come to you to ask if there's a known algorithm to handle this cases or if there's a better approach for my problem. Thanks a lot.

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• In CSS, how to not float a 300px wide Div to the next line?

  - by Jian Lin

  Say, there is a bar that is styled at the bottom of the viewport, using position: fixed; bottom: 0; left: 0; width: 100%; height 50px; overflow: hidden and then there are 4 Divs inside it, each one floated to the left. Each Div is about 300px wide or can be more (depending on the content) Now, when the window is 1200 pixel wide, and we see all 4 Divs, but when the window is resize to be 1180 pixel wide (just 20 pixels less), then the whole 300px wide Div will disappear, because it is "floated" to the next line. So how can this be made so that, the Div will stay there and showing 280px of itself, rather than totally disappear? By the way, white-space: nowrap won't work as that probably has to do with not wrapping inline content. I was thinking of putting another Div inside this Div, having a fixed width of 1200px or 2000px, so that all Divs will float on the same level in this inner Div, and the outer Div will cut it off with the overflow: hidden. But this seems more like a hack... since the wide of all those Divs can be dynamic, and setting a fixed width of 1200px or 2000px seems like too much of a hack.

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• Organizing multiple embed codes with jQuery

  - by Nimbuz

  I have several embed codes on my website, for example: Embed Code #1: <object width="480" height="385"><param name="movie" value="http://www.youtube.com/v/f8Lp2ssd5A9ErAc&hl=en_US&fs=1&"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/f8Lp2A9ErAc&hl=en_US&fs=1&" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385"></embed></object> Embed Code #2: <script type="text/javascript"> _qoptions={ qacct:"p-3asdb5E0g6" }; </script> <script type="text/javascript" src="http://edge.quantserve.com/quant.js"></script> <noscript> <a href="http://www.quantcast.com/p-3asdb5E0g6" target="_blank"><img src="http://pixel.quantserve.com/pixel/p-3asdb5E0g6.gif" style="display: none;" border="0" height="1" width="1" alt="Quantcast"/></a> </noscript> and so on.. How do organize them and separate them into an external single js file to keep the markup clean? Thanks for your help!

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• 60K+ Sprites on the 360?

  - by Jeffrey Kern

  Hey everyone, Just wondering - throwing ideas in my head - about starting a new XNA project for the 360. I would like it to be retro-old school, and emulating scanlines and color palettes and such. As part of this idea, what I would ideally like to do is manually draw each and every pixel of the screen. So, worst-case scenario I would have to draw about 60K sprites on a 252x240 resolution (I think thats correct). 60K sprites on the screen at a time. So, before I even attempt to code this - would the XBOX 360 be able to keep up with this even? That is a lot of sprites, but they aren't big sprites, and the texture data needed would be non-existant. However, I guess how this project would be implemented would make it or break it, but all I was thinking was coming up with a 2D array and mapping which color value would need to be drawn at that point. Of course, this is watered down talk right now. But what you all suggest? EDIT: Each sprite would represent one pixel. E.g., a sprite at 0,0. Another at 0,1. etc.

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• C# getpixels() gets the correct value on xp and vista but is slightly off when used on windows 7

  - by user352288

  I have a C# program that works correctly on xp and vista but it needs to be used on windows 7, I have not been able to come up with a solution, it appears that getpixels just doesn't work right on windows 7. I am getting one of the RGB values because I am dealing with tiff grayscale images. System.Drawing.Bitmap image;// this is in a separate class image = new Bitmap(destination);// this is in the constructor Color t = image.GetPixel(j, i); // this is in a separate function int s = t.R when I print s, for example, image(0,0), it is supposed to be 220, it will be 221 I am doing edge detection on an image and I have to go through the image pixel by pixel, I have run the exact same program on XP,Vista,windows7 and windows 7 got different values. It wouldn't let me post images at all and only one link. The first image is the original image, the second is the correct image, also the one I get with XP and Vista, the final image is the image when running the same program in Windows 7. There is not much of a visible difference but it matters for what I am doing. Thanks for the help, it seems that I am having a hard time explaining my problem.

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• How to disable scaling in JFreeChart?

  - by Alex Arnon

  Hi All, We're using JFreeChart to build an engine to display graphs. This is a web service that runs on Tomcat + Java 1.5.0, and renders charts to PNGs and JPEGs (using ChartUtilities.writeChartAs{PNG,JPEG}() ). We've run into a problem where JFreeChart seems to scale everything inside the Plot area, but only by a few pixels. The result is that the graph looks inconsistent, e.g.: Minor ticks are sometimes stretched horizontally, so that they seem to be two pixels wide instead of one. We use a small image in the top-right of the plot area as a watermark. This is stretched by one pixel horizontally and vertically somewhere near (but not exactly) its middle. Background grid lines seem to appear on sub-pixel boundaries. I have not found a way to create an accurately dotted grid line. We have tried both 1.0.9 and 1.0.13, with exactly the same results (except for the minor ticks, which were not available in the older version). Also, rendering the image to a Frame instead of JPEG/PNG produced an identical result. Help is greatly appreciated, in advance :)

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• C# image drawing colours are incorrect

  - by Jon Tackabury

  I have a source bitmap that is 1x1 and I am trying to take that image and draw it to a new bitmap. The source bitmap is all red, but for some reason the new bitmap ends up with a gradient (see image). Using the code below, shouldn't the new bitmap be completely red? Where is it getting the white/alpha from? private void DrawImage() { Bitmap bmpSOURCE = new Bitmap(1, 1, PixelFormat.Format32bppArgb); using (Graphics g = Graphics.FromImage(bmpSOURCE)) { g.Clear(Color.Red); } Bitmap bmpTest = new Bitmap(300, 100, PixelFormat.Format32bppArgb); using (Graphics g = Graphics.FromImage(bmpTest)) { g.CompositingMode = CompositingMode.SourceCopy; g.CompositingQuality = CompositingQuality.AssumeLinear; g.InterpolationMode = InterpolationMode.HighQualityBicubic; g.PageUnit = GraphicsUnit.Pixel; g.PixelOffsetMode = PixelOffsetMode.None; g.SmoothingMode = SmoothingMode.None; Rectangle rectDest = new Rectangle(0, 0, bmpTest.Width, bmpTest.Height); Rectangle rectSource = new Rectangle(0, 0, 1, 1); g.DrawImage(bmpSOURCE, rectDest, rectSource, GraphicsUnit.Pixel); } pictureBox1.Image = bmpTest; }

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