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  • Does "epsilon" really guarantees anything in floating-point computations?!

    - by Michal Czardybon
    To make the problem short let's say I want to compute expression: a / (b - c) on float's. To make sure the result is meaningful, I can check if 'b' and 'c' are inequal: float eps = std::numeric_limits<float>::epsilon(); if ((b - c) > EPS || (c - b) > EPS) { return a / (b - c); } but my tests show it is not enough to guarantee either meaningful results nor not failing to provide a result if it is possible. Case 1: a = 1.0f; b = 0.00000003f; c = 0.00000002f; Result: The if condition is NOT met, but the expression would produce a correct result 100000008 (as for the floats' precision). Case 2: a = 1e33f; b = 0.000003; c = 0.000002; Result: The if condition is met, but the expression produces not a meaningful result +1.#INF00. I found it much more reliable to check the result, not the arguments: const float INF = numeric_limits<float>::infinity(); float x = a / (b - c); if (-INF < x && x < INF) { return x; } But what for is the epsilon then and why is everyone saying epsilon is good to use?

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  • How can I compare the performance of log() and fp division in C++?

    - by Ventzi Zhechev
    Hi, I’m using a log-based class in C++ to store very small floating-point values (as the values otherwise go beyond the scope of double). As I’m performing a large number of multiplications, this has the added benefit of converting the multiplications to sums. However, at a certain point in my algorithm, I need to divide a standard double value by an integer value and than do a *= to a log-based value. I have overloaded the *= operator for my log-based class and the right-hand side value is first converted to a log-based value by running log() and than added to the left-hand side value. Thus the operations actually performed are floating-point division, log() and floating-point summation. My question whether it would be faster to first convert the denominator to a log-based value, which would replace the floating-point division with floating-point subtraction, yielding the following chain of operations: twice log(), floating-point subtraction, floating-point summation. In the end, this boils down to whether floating-point division is faster or slower than log(). I suspect that a common answer would be that this is compiler and architecture dependent, so I’ll say that I use gcc 4.2 from Apple on darwin 10.3.0. Still, I hope to get an answer with a general remark on the speed of these two operators and/or an idea on how to measure the difference myself, as there might be more going on here, e.g. executing the constructors that do the type conversion etc. Cheers!

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  • I am trying to access the individual bytes in a floating point number and I am getting unexpected results

    - by oweinh
    So I have this so far: #include <iostream> #include <string> #include <typeinfo> using namespace std; int main () { float f = 3.45; // just an example fp# char* ptr = (char*)&f; // a character pointer to the first byte of the fp#? cout << int(ptr[0]) << endl; // these lines are just to see if I get what I cout << int(ptr[1]) << endl; // am looking for... I want ints that I can cout << int(ptr[2]) << endl; // otherwise manipulate. cout << int(ptr[3]) << endl; } the result is: -51 -52 92 64 so obviously -51 and -52 are not in the byte range that I would expect for a char... I have taken information from similar questions to arrive at this code and from all discussions, a conversion from char to int is straightforward. So why negative values? I am trying to look at a four-byte number, therefore I would expect 4 integers, each in the range 0-255. I am using Codeblocks 13.12 with gcc 4.8.1 with option -std=C++11 on a Windows 8.1 device.

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  • Hostapd - WLAN as AP

    - by BBK
    I'm trying to start hostapd but without success. I'm using Headless Ubuntu 11.10 oneiric 3.0.0-16-server x86_64. WLAN driver is rt2800usb and my wireless nic card TP-Link TL-WN727N supports AP mode as shows below: us0# ifconfig wlan0 wlan0 Link encap:Ethernet HWaddr 00:27:19:be:cd:b6 UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) us0# lsusb Bus 003 Device 003: ID 148f:3070 Ralink Technology, Corp. RT2870/RT3070 Wireless Adapter us0# lshw -C network *-network:3 description: Wireless interface physical id: 4 bus info: usb@3:2 logical name: wlan0 serial: 00:27:19:be:cd:b6 capabilities: ethernet physical wireless configuration: broadcast=yes driver=rt2800usb driverversion=3.0.0-16-server firmware=0.29 link=no multicast=yes wireless=IEEE 802.11bgn us0# hostapd /etc/hostapd/hostapd.conf Configuration file: /etc/hostapd/hostapd.conf Could not read interface wlan0 # The int flags: No such device nl80211 driver initialization failed. ELOOP: remaining socket: sock=4 eloop_data=0xd3e4a0 user_data=0xd3ecc0 handler=0x433880 ELOOP: remaining socket: sock=6 eloop_data=0xd411f0 user_data=(nil) handler=0x43cc10 us0# cat /etc/hostapd/hostapd.conf ssid=Home interface=wlan0 # The interface name of the card #driver=rt2800usb driver=nl80211 macaddr_acl=0 ieee80211n=1 channel=1 hw_mode=g auth_algs=1 ignore_broadcast_ssid=0 wpa=2 wpa_passphrase=88888888 wpa_key_mgmt=WPA-PSK wpa_pairwise=TKIP rsn_pairwise=CCMP us0# iw list Wiphy phy0 Band 1: Capabilities: 0x172 HT20/HT40 Static SM Power Save RX Greenfield RX HT20 SGI RX HT40 SGI RX STBC 1-stream Max AMSDU length: 7935 bytes No DSSS/CCK HT40 Maximum RX AMPDU length 65535 bytes (exponent: 0x003) Minimum RX AMPDU time spacing: 2 usec (0x04) HT RX MCS rate indexes supported: 0-7, 32 TX unequal modulation not supported HT TX Max spatial streams: 1 HT TX MCS rate indexes supported may differ Frequencies: * 2412 MHz [1] (20.0 dBm) * 2417 MHz [2] (20.0 dBm) * 2422 MHz [3] (20.0 dBm) * 2427 MHz [4] (20.0 dBm) * 2432 MHz [5] (20.0 dBm) * 2437 MHz [6] (20.0 dBm) * 2442 MHz [7] (20.0 dBm) * 2447 MHz [8] (20.0 dBm) * 2452 MHz [9] (20.0 dBm) * 2457 MHz [10] (20.0 dBm) * 2462 MHz [11] (20.0 dBm) * 2467 MHz [12] (20.0 dBm) (passive scanning, no IBSS) * 2472 MHz [13] (20.0 dBm) (passive scanning, no IBSS) * 2484 MHz [14] (20.0 dBm) (passive scanning, no IBSS) Bitrates (non-HT): * 1.0 Mbps * 2.0 Mbps (short preamble supported) * 5.5 Mbps (short preamble supported) * 11.0 Mbps (short preamble supported) * 6.0 Mbps * 9.0 Mbps * 12.0 Mbps * 18.0 Mbps * 24.0 Mbps * 36.0 Mbps * 48.0 Mbps * 54.0 Mbps max # scan SSIDs: 4 Supported interface modes: * IBSS * managed * AP * AP/VLAN * WDS * monitor * mesh point Supported commands: * new_interface * set_interface * new_key * new_beacon * new_station * new_mpath * set_mesh_params * set_bss * authenticate * associate * deauthenticate * disassociate * join_ibss * Unknown command (68) * Unknown command (55) * Unknown command (57) * Unknown command (59) * Unknown command (67) * set_wiphy_netns * Unknown command (65) * Unknown command (66) * connect * disconnect The question is: Why the hostapd not starting?

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  • A starting point for Use Cases and User Stories

    - by Mike Benkovich
    Originally posted on: http://geekswithblogs.net/benko/archive/2013/07/23/a-starting-point-for-use-cases-and-user-stories.aspxSoftware is a challenging business and is rife with opportunities to go wrong. Over the years a number of methodologies have evolved to help make sure that things go right. In an effort to contribute to this I’ve created a list of user stories that I think should be included and sometimes are just assumed. Note this is a work in progress, so I’m looking for your feedback. I’m curious what you would add or change in my list. · As a DBA I am working with a Normalized data model that reflects an agreed upon logical model for the system · As a DBA I am using consistent names for my fields which match the naming standards of my organization · As a DBA my model supports simple CRUD operations against all the entities · As an Application Architect the UI has been validated against the Business requirements and a complete set of user story’s have been created · As an Application Architect the database model has been validated against the UI · As an Application Architect we have a logical business model that describes all the known and/or expected usage of the system during the software’s expected lifecycle · As an Application Architect we have a Deployment diagram that describes how the application components will be deployed · As an Application Architect we have a navigation diagram that describes the typical application flow · As an Application Architect we have identified points of interaction which describes how the UI interacts with the services and the data storage · As an Application Architect we have identified external systems which may now or in the future use the data of this application and have adapted the logical model to include these interactions · As an Application Architect we have identified existing systems and tools that can be extended and/or reused to help this application achieve it’s business goals · As a Project Manager all team members understand the goals of each release and iteration as they are planned · As a Project Manager all team members understand their role and the roles of others · As a Project Manager we have support of the business to do the right thing even if it is not the expedient thing · As a Test/QA Analyst we have created a simulation environment for testing the system which does not use sensitive data and accurately reflects the scenarios of all the data that will be supported by the system · As a Test/QA Analyst we have identified the matrix of supported clients used to access the system including the likely browsers, mobile devices and other interfaces to work with the application · As a Test/QA Analyst we have created exit criteria for each user story that match the requirements of the business story that was used to create them · As a Test/QA Analyst we have access to a Test environment that is isolated from production and staging environments · As a Test/QA Analyst there we have a way to reset the environment so we can rerun tests when a new version of the software becomes available · As a Test/QA Analyst I am able to automate portions of the test process Thoughts? -mike

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  • How do I translate a point from one rect to a point in a scaled rect?

    - by Bill
    I have an image (i) that's been scaled from its original size (rectLarge) to fit a smaller rectangle (rectSmall). Given a point p in rectSmall, how can I translate this to a point in rectLarge. To make this concrete, suppose I have a 20x20 image that's been scaled to a 10x10 rect. The point (1, 1) in the smaller rect should be scaled up to a point in the larger rect (i.e. (2,2)). I'm trying to achieve this with: result.x = point.x * (destRect.size.width / srcRect.size.width ); result.y = point.y * (destRect.size.height / srcRect.size.height); However, the points generated by this code are not correct - they do not map to the appropriate point in the original image. What am I doing wrong?

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  • Python point lookup (coordinate binning?)

    - by Rince
    Greetings, I am trying to bin an array of points (x, y) into an array of boxes [(x0, y0), (x1, y0), (x0, y1), (x1, y1)] (tuples are the corner points) So far I have the following routine: def isInside(self, point, x0, x1, y0, y1): pr1 = getProduct(point, (x0, y0), (x1, y0)) if pr1 >= 0: pr2 = getProduct(point, (x1, y0), (x1, y1)) if pr2 >= 0: pr3 = getProduct(point, (x1, y1), (x0, y1)) if pr3 >= 0: pr4 = getProduct(point, (x0, y1), (x0, y0)) if pr4 >= 0: return True return False def getProduct(origin, pointA, pointB): product = (pointA[0] - origin[0])*(pointB[1] - origin[1]) - (pointB[0] - origin[0])*(pointA[1] - origin[1]) return product Is there any better way then point-by-point lookup? Maybe some not-obvious numpy routine? Thank you!

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  • MAMP - Host name changes to first vhost SSL entry for project with two localhosts

    - by user1322092
    I have two projects that are a copy of each other on my Mac with MAMP. They both have SSL pages. However, whenever I hit the a secured SSL page of project 2, the base_url or host changes to project1 instead of remaining project2. I know this is an issue with the vhosts, because if I switch the order of the entries, the reverse happens. Here's my config files: /Applications/MAMP/conf/extra/httpd-ssl.conf <VirtualHost _default_:443> DocumentRoot "/Applications/MAMP/htdocs/proj1" ServerName proj1.localhost:443 ErrorLog "/Applications/MAMP/Library/logs/error_log" TransferLog "/Applications/MAMP/Library/logs/access_log" SSLEngine on SSLCertificateFile "/Applications/MAMP/conf/apache/ssl/server.crt" SSLCertificateKeyFile "/Applications/MAMP/conf/apache/ssl/server.key" </VirtualHost> <VirtualHost _default_:443> DocumentRoot "/Applications/MAMP/htdocs/proj2" ServerName proj2.localhost:443 ErrorLog "/Applications/MAMP/Library/logs/error_log" TransferLog "/Applications/MAMP/Library/logs/access_log" SSLEngine on SSLCertificateFile "/Applications/MAMP/conf/apache/ssl/server.crt" SSLCertificateKeyFile "/Applications/MAMP/conf/apache/ssl/server.key" </VirtualHost> -------------------- cat /etc/hosts ## # Host Database # # localhost is used to configure the loopback interface # when the system is booting. Do not change this entry. ## 127.0.0.1 localhost 255.255.255.255 broadcasthost ::1 localhost fe80::1%lo0 localhost 127.0.0.1 proj1.localhost 127.0.0.1 proj2.localhost

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  • Clicking a link in IE6 doesn't load page (internal DNS entry on our intranet)

    - by Callum
    I have a very strange problem that is only affecting some versions of IE6. The problem does affect IE 6.0.2900.5512, but does not seem to affect 6.0.3790.3959 Basically I work for a company and we have an intranet. While I'm not an expert on "internal DNS pointers", what I was able to do was create a website (let's say about football), and when an employee who is sitting behind the company firewall types the word "football" in to the web address bar of their web browser, they get redirected to a particular server. I am told this is some kind "internally pointing DNS entry". So, I've set one of these up, and I have a placed a link to it on our company intranet page. However, when the link is clicked in IE6.0.2900.5512, the page goes blank. Clicking "refresh" then loads the correct page (the one specified in the link). Can anyone help me out here. I have tried changing the way URL is formed, everything from //football to http://football/ etc. The link works fine in every other browser and IE7+, but unfoturnatly, IE6 is still the most common browser in use at my organisation.

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  • how to remove an entry from system tray?

    - by altvali
    I've searched for an answer to this one and I haven't found one yet. How do i remove a single item from Windows' System tray? I'm targeting Windows XP. Edit: This is not about preventing items from starting up. I want the program to keep running, I just need another script/program to remove the first one's entry from system tray. Second Edit: One approach that I can think of is to try to hide the intended app by modifying registry keys. On several test machines I've found some registry entries that match the System tray information at HKEY_USERS\something-that-looks-like S-1-5-21-682003330-1563985344-725345543-1003\Software\Microsoft\Windows\CurrentVersion\Explorer\TrayNotify with BalloonTip, IconStream and PastIconsStream containing systray information. The important one is IconStream. On other machines, these are found at hkey_classes_root/local/setting/software/microsoft/windows/currentversion/TrayNotify I'm quite sure there's no danger in changing those specific registries, but I don't know how to write code for that. Can anyone help me with the code and with confirming if this has the desired effect of hiding the systray icon for an active program?

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  • One Apache VirtualHost entry overrides another?

    - by johnlai2004
    I can't tell why one apache virtual host entry keeps overriding another. The following file // filename: cbl <VirtualHost 74.207.237.23:80> ServerAdmin [email protected] ServerName completebeautylist.com ServerAlias www.completebeautylist.com DocumentRoot /srv/www/cbl/production/public_html/ ErrorLog /srv/www/cbl/production/logs/error.log CustomLog /srv/www/cbl/production/logs/access.log combined </VirtualHost> keeps overriding this file // filename: theccco.org <VirtualHost 74.207.237.23:80> SuexecUserGroup "#1010" "#1010" ServerName theccco.org ServerAlias www.theccco.org ServerAlias webmail.theccco.org ServerAlias admin.theccco.org DocumentRoot /home/theccco/public_html ErrorLog /var/log/virtualmin/theccco.org_error_log CustomLog /var/log/virtualmin/theccco.org_access_log combined ScriptAlias /cgi-bin/ /home/theccco/cgi-bin/ DirectoryIndex index.html index.htm index.php index.php4 index.php5 <Directory /home/theccco/public_html> Options -Indexes +IncludesNOEXEC +FollowSymLinks allow from all AllowOverride All </Directory> <Directory /home/theccco/cgi-bin> allow from all </Directory> RewriteEngine on RewriteCond %{HTTP_HOST} =webmail.theccco.org RewriteRule ^(.*) https://theccco.org:20000/ [R] RewriteCond %{HTTP_HOST} =admin.theccco.org RewriteRule ^(.*) https://theccco.org:10000/ [R] Alias /dav /home/theccco/public_html <Location /dav> DAV On AuthType Basic AuthName theccco.org AuthUserFile /home/theccco/etc/dav.digest.passwd Require valid-user ForceType text/plain Satisfy All RewriteEngine off </Location> </VirtualHost> I tried a2ensite, a2dissite, and reloading I get this message * Reloading web server config apache2 apache2: Could not reliably determine the server's fully qualified domain name, using 127.0.1.1 for ServerName [Thu Apr 15 10:47:36 2010] [warn] NameVirtualHost 74.207.237.23:443 has no VirtualHosts Aside from that, I don't know what else could be wrong. Can anyone tell me what to do?

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  • Smart card driven membership and door entry system

    - by Rob G
    I'm looking at putting in a smart card driven system at my local sports club (which doesn't have oodles of money), and since they're willing to pay for hardware, and I'm willing to do the technical setup, I was wondering if anyone had any experience in setting something like this up. Writing any software needed is not the problem, I've pretty much got that covered with various open source projects out there and custom code I'll write, but it's more the hardware side I'm not too sure about and I'm looking for advice from people out there. I'm sure there are numerous complications, but on the surface it looks fairly simple. I'd basically like to enable members to swipe/touch a smart card at the door to gain entry to the club, walk up to a touch screen PC and swipe/touch a card reader there to "login" to the system I create, which will allow them to book club facilities etc. I may even want that same card to then activate things like lights or music when they enter the room they've booked. Pretty Eutopian I know, but still, we'd like to get as close as we can. As I said, the software shouldn't be a problem, and on the hardware side, so far I'm looking at: All in one touch screen PC running Windows 7 or Ubuntu USB card reader (not sure which one to buy) Smart Cards (again, never bought these before) Door/lighting hardware that could be triggered (not sure here either) If anyone has any advice on implementing something like this - especially the items I'm not sure about above, and of course anything I've missed out that's crucial, I'd be most grateful. Recommended hardware that you've used for something like this would be fantastic!

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  • Exclude entry from glossary?

    - by draebek
    I'm using the glossaries package in LaTeX. I've got \gls{foo} in my document, but I don't want the entry for "foo" to appear in the glossary. How can I keep a working (i.e. expanding) \gls{foo} in the body of my document, but exclude the entry for "foo" from the glossary?

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  • regsvr32 failed to create an entry under clsid

    - by user1677272
    I have a VC++ dll, which I want to register on my 32-bit Windows 7 machine using regsvr32.exe, however I have some problems with this. When I register my DLL with regsvr32.exe, it shows registration successful, but when I check the entries in regedit, there is no entry in Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Classes\CLSID. There is only one entry in Computer\HKEY_LOCAL_MACHINE\TypeLib with the guid mentioned in the project. Can anyone help me on this?

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  • Python tkInter text entry validation

    - by meade
    I'm trying to validate the entry of text using Python/tkInter def validate_text(): return False text = Entry(textframe, validate="focusout", validatecommand=validate_text) where validate_text is the function - I've tried always returning False and always returning True and there's no difference in the outcome..? Is there a set of arguments in the function that I need to include? Edit - changed from NONE to focusout...still not working

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  • DAO method retrieve single entry

    - by London
    Hello, How can I write DAO method which will return as a result only first entry from the database. For instance lets say I'm looking at Users table and I want to retrieve only the first entry, I'd declare method like: public User getFirstUser(){ //method logic } EDIT: User has primary key id if that matters at all. I apologize if this question is too simple/stupid/whatever I'm beginner with Java so I'm trying new things. thank you

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  • MySql: How to know if an entry is compressed or not

    - by Guy
    I'm working with python and mysql and I want to verify that a certain entry is compressed in the db. Ie: cur = db.getCursor() cur.execute('''select compressed_column from table where id=12345''') res = cur.fetchall() at this point I would like to verify that the entry is compressed (ie in order to work with the data you would have to use select uncompress(compressed_column)..). Ideas?

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  • Extended MAPI: How to get the entry ID of messages moved by CopyMessages

    - by marijne
    I have found that if I move a message using IMAPIFolder::CopyMessages (using the MESSAGE_MOVE flag) the message gets a new entry ID. However I do not see any reliable way of getting the entry ID of the message in its new location, or otherwise getting a reference to it. The best suggestion I have had so far involves tagging the message with the old custom property before moving, and then doing a search afterwards, but I was wondering if there is a less convoluted solution.

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  • proxy/vpn by dns entry

    - by rcourtna
    I've been using a service by unblock-us.com, which provides a proxy to Canadians/others allowing access to services that are locked down to only US ip addresses. This is easy enough to achieve by setting up a reverse proxy (eg: squid) on a US-hosted server, and then configuring your browser or OS to use that proxy. However, there is something that unblock-us does that I'm not sure how to duplicate. Rather than configuring your OS to use them as a proxy, you can simply change the DNS Server settings on your router to point to their addresses. Any requests to services they support are automatically proxied. The advantage to this is that you don't have to set up every computer in your house, and it "just works" with clients like ps3, xbox, android, etc. Disadvantage is you really don't have control over what gets proxied, as well as there are privacy concerns I suppose. How can I achieve this same functionality on my own us-based slice?

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  • Point inside Oriented Bounding Box?

    - by Milo
    I have an OBB2D class based on SAT. This is my point in OBB method: public boolean pointInside(float x, float y) { float newy = (float) (Math.sin(angle) * (y - center.y) + Math.cos(angle) * (x - center.x)); float newx = (float) (Math.cos(angle) * (x - center.x) - Math.sin(angle) * (y - center.y)); return (newy > center.y - (getHeight() / 2)) && (newy < center.y + (getHeight() / 2)) && (newx > center.x - (getWidth() / 2)) && (newx < center.x + (getWidth() / 2)); } public boolean pointInside(Vector2D v) { return pointInside(v.x,v.y); } Here is the rest of the class; the parts that pertain: public class OBB2D { private Vector2D projVec = new Vector2D(); private static Vector2D projAVec = new Vector2D(); private static Vector2D projBVec = new Vector2D(); private static Vector2D tempNormal = new Vector2D(); private Vector2D deltaVec = new Vector2D(); private ArrayList<Vector2D> collisionPoints = new ArrayList<Vector2D>(); // Corners of the box, where 0 is the lower left. private Vector2D corner[] = new Vector2D[4]; private Vector2D center = new Vector2D(); private Vector2D extents = new Vector2D(); private RectF boundingRect = new RectF(); private float angle; //Two edges of the box extended away from corner[0]. private Vector2D axis[] = new Vector2D[2]; private double origin[] = new double[2]; public OBB2D(float centerx, float centery, float w, float h, float angle) { for(int i = 0; i < corner.length; ++i) { corner[i] = new Vector2D(); } for(int i = 0; i < axis.length; ++i) { axis[i] = new Vector2D(); } set(centerx,centery,w,h,angle); } public OBB2D(float left, float top, float width, float height) { for(int i = 0; i < corner.length; ++i) { corner[i] = new Vector2D(); } for(int i = 0; i < axis.length; ++i) { axis[i] = new Vector2D(); } set(left + (width / 2), top + (height / 2),width,height,0.0f); } public void set(float centerx,float centery,float w, float h,float angle) { float vxx = (float)Math.cos(angle); float vxy = (float)Math.sin(angle); float vyx = (float)-Math.sin(angle); float vyy = (float)Math.cos(angle); vxx *= w / 2; vxy *= (w / 2); vyx *= (h / 2); vyy *= (h / 2); corner[0].x = centerx - vxx - vyx; corner[0].y = centery - vxy - vyy; corner[1].x = centerx + vxx - vyx; corner[1].y = centery + vxy - vyy; corner[2].x = centerx + vxx + vyx; corner[2].y = centery + vxy + vyy; corner[3].x = centerx - vxx + vyx; corner[3].y = centery - vxy + vyy; this.center.x = centerx; this.center.y = centery; this.angle = angle; computeAxes(); extents.x = w / 2; extents.y = h / 2; computeBoundingRect(); } //Updates the axes after the corners move. Assumes the //corners actually form a rectangle. private void computeAxes() { axis[0].x = corner[1].x - corner[0].x; axis[0].y = corner[1].y - corner[0].y; axis[1].x = corner[3].x - corner[0].x; axis[1].y = corner[3].y - corner[0].y; // Make the length of each axis 1/edge length so we know any // dot product must be less than 1 to fall within the edge. for (int a = 0; a < axis.length; ++a) { float l = axis[a].length(); float ll = l * l; axis[a].x = axis[a].x / ll; axis[a].y = axis[a].y / ll; origin[a] = corner[0].dot(axis[a]); } } public void computeBoundingRect() { boundingRect.left = JMath.min(JMath.min(corner[0].x, corner[3].x), JMath.min(corner[1].x, corner[2].x)); boundingRect.top = JMath.min(JMath.min(corner[0].y, corner[1].y),JMath.min(corner[2].y, corner[3].y)); boundingRect.right = JMath.max(JMath.max(corner[1].x, corner[2].x), JMath.max(corner[0].x, corner[3].x)); boundingRect.bottom = JMath.max(JMath.max(corner[2].y, corner[3].y),JMath.max(corner[0].y, corner[1].y)); } public void set(RectF rect) { set(rect.centerX(),rect.centerY(),rect.width(),rect.height(),0.0f); } // Returns true if other overlaps one dimension of this. private boolean overlaps1Way(OBB2D other) { for (int a = 0; a < axis.length; ++a) { double t = other.corner[0].dot(axis[a]); // Find the extent of box 2 on axis a double tMin = t; double tMax = t; for (int c = 1; c < corner.length; ++c) { t = other.corner[c].dot(axis[a]); if (t < tMin) { tMin = t; } else if (t > tMax) { tMax = t; } } // We have to subtract off the origin // See if [tMin, tMax] intersects [0, 1] if ((tMin > 1 + origin[a]) || (tMax < origin[a])) { // There was no intersection along this dimension; // the boxes cannot possibly overlap. return false; } } // There was no dimension along which there is no intersection. // Therefore the boxes overlap. return true; } public void moveTo(float centerx, float centery) { float cx,cy; cx = center.x; cy = center.y; deltaVec.x = centerx - cx; deltaVec.y = centery - cy; for (int c = 0; c < 4; ++c) { corner[c].x += deltaVec.x; corner[c].y += deltaVec.y; } boundingRect.left += deltaVec.x; boundingRect.top += deltaVec.y; boundingRect.right += deltaVec.x; boundingRect.bottom += deltaVec.y; this.center.x = centerx; this.center.y = centery; computeAxes(); } // Returns true if the intersection of the boxes is non-empty. public boolean overlaps(OBB2D other) { if(right() < other.left()) { return false; } if(bottom() < other.top()) { return false; } if(left() > other.right()) { return false; } if(top() > other.bottom()) { return false; } if(other.getAngle() == 0.0f && getAngle() == 0.0f) { return true; } return overlaps1Way(other) && other.overlaps1Way(this); } public Vector2D getCenter() { return center; } public float getWidth() { return extents.x * 2; } public float getHeight() { return extents.y * 2; } public void setAngle(float angle) { set(center.x,center.y,getWidth(),getHeight(),angle); } public float getAngle() { return angle; } public void setSize(float w,float h) { set(center.x,center.y,w,h,angle); } public float left() { return boundingRect.left; } public float right() { return boundingRect.right; } public float bottom() { return boundingRect.bottom; } public float top() { return boundingRect.top; } public RectF getBoundingRect() { return boundingRect; } public boolean overlaps(float left, float top, float right, float bottom) { if(right() < left) { return false; } if(bottom() < top) { return false; } if(left() > right) { return false; } if(top() > bottom) { return false; } return true; } public static float distance(float ax, float ay,float bx, float by) { if (ax < bx) return bx - ay; else return ax - by; } public Vector2D project(float ax, float ay) { projVec.x = Float.MAX_VALUE; projVec.y = Float.MIN_VALUE; for (int i = 0; i < corner.length; ++i) { float dot = Vector2D.dot(corner[i].x,corner[i].y,ax,ay); projVec.x = JMath.min(dot, projVec.x); projVec.y = JMath.max(dot, projVec.y); } return projVec; } public Vector2D getCorner(int c) { return corner[c]; } public int getNumCorners() { return corner.length; } public boolean pointInside(float x, float y) { float newy = (float) (Math.sin(angle) * (y - center.y) + Math.cos(angle) * (x - center.x)); float newx = (float) (Math.cos(angle) * (x - center.x) - Math.sin(angle) * (y - center.y)); return (newy > center.y - (getHeight() / 2)) && (newy < center.y + (getHeight() / 2)) && (newx > center.x - (getWidth() / 2)) && (newx < center.x + (getWidth() / 2)); } public boolean pointInside(Vector2D v) { return pointInside(v.x,v.y); } public ArrayList<Vector2D> getCollsionPoints(OBB2D b) { collisionPoints.clear(); for(int i = 0; i < corner.length; ++i) { if(b.pointInside(corner[i])) { collisionPoints.add(corner[i]); } } for(int i = 0; i < b.corner.length; ++i) { if(pointInside(b.corner[i])) { collisionPoints.add(b.corner[i]); } } return collisionPoints; } }; What could be wrong? When I getCollisionPoints for 2 OBBs I know are penetrating, it returns no points. Thanks

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  • Point of contact of 2 OBBs?

    - by Milo
    I'm working on the physics for my GTA2-like game so I can learn more about game physics. The collision detection and resolution are working great. I'm now just unsure how to compute the point of contact when I hit a wall. Here is my OBB class: public class OBB2D { private Vector2D projVec = new Vector2D(); private static Vector2D projAVec = new Vector2D(); private static Vector2D projBVec = new Vector2D(); private static Vector2D tempNormal = new Vector2D(); private Vector2D deltaVec = new Vector2D(); // Corners of the box, where 0 is the lower left. private Vector2D corner[] = new Vector2D[4]; private Vector2D center = new Vector2D(); private Vector2D extents = new Vector2D(); private RectF boundingRect = new RectF(); private float angle; //Two edges of the box extended away from corner[0]. private Vector2D axis[] = new Vector2D[2]; private double origin[] = new double[2]; public OBB2D(float centerx, float centery, float w, float h, float angle) { for(int i = 0; i < corner.length; ++i) { corner[i] = new Vector2D(); } for(int i = 0; i < axis.length; ++i) { axis[i] = new Vector2D(); } set(centerx,centery,w,h,angle); } public OBB2D(float left, float top, float width, float height) { for(int i = 0; i < corner.length; ++i) { corner[i] = new Vector2D(); } for(int i = 0; i < axis.length; ++i) { axis[i] = new Vector2D(); } set(left + (width / 2), top + (height / 2),width,height,0.0f); } public void set(float centerx,float centery,float w, float h,float angle) { float vxx = (float)Math.cos(angle); float vxy = (float)Math.sin(angle); float vyx = (float)-Math.sin(angle); float vyy = (float)Math.cos(angle); vxx *= w / 2; vxy *= (w / 2); vyx *= (h / 2); vyy *= (h / 2); corner[0].x = centerx - vxx - vyx; corner[0].y = centery - vxy - vyy; corner[1].x = centerx + vxx - vyx; corner[1].y = centery + vxy - vyy; corner[2].x = centerx + vxx + vyx; corner[2].y = centery + vxy + vyy; corner[3].x = centerx - vxx + vyx; corner[3].y = centery - vxy + vyy; this.center.x = centerx; this.center.y = centery; this.angle = angle; computeAxes(); extents.x = w / 2; extents.y = h / 2; computeBoundingRect(); } //Updates the axes after the corners move. Assumes the //corners actually form a rectangle. private void computeAxes() { axis[0].x = corner[1].x - corner[0].x; axis[0].y = corner[1].y - corner[0].y; axis[1].x = corner[3].x - corner[0].x; axis[1].y = corner[3].y - corner[0].y; // Make the length of each axis 1/edge length so we know any // dot product must be less than 1 to fall within the edge. for (int a = 0; a < axis.length; ++a) { float l = axis[a].length(); float ll = l * l; axis[a].x = axis[a].x / ll; axis[a].y = axis[a].y / ll; origin[a] = corner[0].dot(axis[a]); } } public void computeBoundingRect() { boundingRect.left = JMath.min(JMath.min(corner[0].x, corner[3].x), JMath.min(corner[1].x, corner[2].x)); boundingRect.top = JMath.min(JMath.min(corner[0].y, corner[1].y),JMath.min(corner[2].y, corner[3].y)); boundingRect.right = JMath.max(JMath.max(corner[1].x, corner[2].x), JMath.max(corner[0].x, corner[3].x)); boundingRect.bottom = JMath.max(JMath.max(corner[2].y, corner[3].y),JMath.max(corner[0].y, corner[1].y)); } public void set(RectF rect) { set(rect.centerX(),rect.centerY(),rect.width(),rect.height(),0.0f); } // Returns true if other overlaps one dimension of this. private boolean overlaps1Way(OBB2D other) { for (int a = 0; a < axis.length; ++a) { double t = other.corner[0].dot(axis[a]); // Find the extent of box 2 on axis a double tMin = t; double tMax = t; for (int c = 1; c < corner.length; ++c) { t = other.corner[c].dot(axis[a]); if (t < tMin) { tMin = t; } else if (t > tMax) { tMax = t; } } // We have to subtract off the origin // See if [tMin, tMax] intersects [0, 1] if ((tMin > 1 + origin[a]) || (tMax < origin[a])) { // There was no intersection along this dimension; // the boxes cannot possibly overlap. return false; } } // There was no dimension along which there is no intersection. // Therefore the boxes overlap. return true; } public void moveTo(float centerx, float centery) { float cx,cy; cx = center.x; cy = center.y; deltaVec.x = centerx - cx; deltaVec.y = centery - cy; for (int c = 0; c < 4; ++c) { corner[c].x += deltaVec.x; corner[c].y += deltaVec.y; } boundingRect.left += deltaVec.x; boundingRect.top += deltaVec.y; boundingRect.right += deltaVec.x; boundingRect.bottom += deltaVec.y; this.center.x = centerx; this.center.y = centery; computeAxes(); } // Returns true if the intersection of the boxes is non-empty. public boolean overlaps(OBB2D other) { if(right() < other.left()) { return false; } if(bottom() < other.top()) { return false; } if(left() > other.right()) { return false; } if(top() > other.bottom()) { return false; } if(other.getAngle() == 0.0f && getAngle() == 0.0f) { return true; } return overlaps1Way(other) && other.overlaps1Way(this); } public Vector2D getCenter() { return center; } public float getWidth() { return extents.x * 2; } public float getHeight() { return extents.y * 2; } public void setAngle(float angle) { set(center.x,center.y,getWidth(),getHeight(),angle); } public float getAngle() { return angle; } public void setSize(float w,float h) { set(center.x,center.y,w,h,angle); } public float left() { return boundingRect.left; } public float right() { return boundingRect.right; } public float bottom() { return boundingRect.bottom; } public float top() { return boundingRect.top; } public RectF getBoundingRect() { return boundingRect; } public boolean overlaps(float left, float top, float right, float bottom) { if(right() < left) { return false; } if(bottom() < top) { return false; } if(left() > right) { return false; } if(top() > bottom) { return false; } return true; } public static float distance(float ax, float ay,float bx, float by) { if (ax < bx) return bx - ay; else return ax - by; } public Vector2D project(float ax, float ay) { projVec.x = Float.MAX_VALUE; projVec.y = Float.MIN_VALUE; for (int i = 0; i < corner.length; ++i) { float dot = Vector2D.dot(corner[i].x,corner[i].y,ax,ay); projVec.x = JMath.min(dot, projVec.x); projVec.y = JMath.max(dot, projVec.y); } return projVec; } public Vector2D getCorner(int c) { return corner[c]; } public int getNumCorners() { return corner.length; } public static float collisionResponse(OBB2D a, OBB2D b, Vector2D outNormal) { float depth = Float.MAX_VALUE; for (int i = 0; i < a.getNumCorners() + b.getNumCorners(); ++i) { Vector2D edgeA; Vector2D edgeB; if(i >= a.getNumCorners()) { edgeA = b.getCorner((i + b.getNumCorners() - 1) % b.getNumCorners()); edgeB = b.getCorner(i % b.getNumCorners()); } else { edgeA = a.getCorner((i + a.getNumCorners() - 1) % a.getNumCorners()); edgeB = a.getCorner(i % a.getNumCorners()); } tempNormal.x = edgeB.x -edgeA.x; tempNormal.y = edgeB.y - edgeA.y; tempNormal.normalize(); projAVec.equals(a.project(tempNormal.x,tempNormal.y)); projBVec.equals(b.project(tempNormal.x,tempNormal.y)); float distance = OBB2D.distance(projAVec.x, projAVec.y,projBVec.x,projBVec.y); if (distance > 0.0f) { return 0.0f; } else { float d = Math.abs(distance); if (d < depth) { depth = d; outNormal.equals(tempNormal); } } } float dx,dy; dx = b.getCenter().x - a.getCenter().x; dy = b.getCenter().y - a.getCenter().y; float dot = Vector2D.dot(dx,dy,outNormal.x,outNormal.y); if(dot > 0) { outNormal.x = -outNormal.x; outNormal.y = -outNormal.y; } return depth; } public Vector2D getMoveDeltaVec() { return deltaVec; } }; Thanks!

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  • Google DNS Same Entry Different Results

    - by Henrik P. Hessel
    Why is this happening? The Rootserver returns a wrong entry I fixed containing 5269.XXX.com. instead of 5269 XXX.com. Macbook @ Home ; <<>> DiG 9.6.0-APPLE-P2 <<>> @8.8.8.8 srv _xmpp-server._tcp.XXX.com. ; (1 server found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 18412 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;_xmpp-server._tcp.XXX.com. IN SRV ;; ANSWER SECTION: _xmpp-server._tcp.XXX.com. 64328 IN SRV 10 0 5269 XXX.com. ;; Query time: 21 msec ;; SERVER: 8.8.8.8#53(8.8.8.8) ;; WHEN: Tue Dec 28 03:16:45 2010 ;; MSG SIZE rcvd: 86 Rootserver ; <<>> DiG 9.6-ESV-R1 <<>> @8.8.8.8 srv _xmpp-server._tcp.XXX.com. ; (1 server found) ;; global options: +cmd ;; Got answer: ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 27240 ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0 ;; QUESTION SECTION: ;_xmpp-server._tcp.XXX.com. IN SRV ;; ANSWER SECTION: _xmpp-server._tcp.XXX.com. 52139 IN SRV 0 10 0 5269.XXX.com. ;; Query time: 7 msec ;; SERVER: 8.8.8.8#53(8.8.8.8) ;; WHEN: Tue Dec 28 03:23:23 2010 ;; MSG SIZE rcvd: 91

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  • Point sample opacity/alpha in Adobe Photoshop?

    - by Josh
    I opened a PNG containing an alpha channel in Photoshop and wanted to get the opacity / alpha of a given point in the PNG file, so that I could match that opacity in a new photoshop layer. How can I do this? is there any way to get an alpha value at a point the way the color sample tool gives RGB values at a given point?

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  • Is an Ethernet point to point connection without a switch real time capable?

    - by funksoulbrother
    In automation and control, it is commonly stated that ethernet can't be used as a bus because it is not real time capable due to packet collisions. If important control packets collide, they often can't keep the hard real time conditions needed for control. But what if I have a single point to point connection with Ethernet, no switch in between? To be more precise, I have an FPGA board with a giga-Ethernet port that is connected directly to my control PC. I think the benefits of giga Ethernet over CAN or USB for a p2p connection are huge, especially for high sampling rates and lots of data generation on the FPGA board. Am I correct that with a point to point connection there can't be any packet collisions and therefore a real time environment is given even with ethernet? Thanks in advance! ~fsb

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