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• Ray picking - get direction from pitch and yaw

  - by Isaac Waller

  I am attempting to cast a ray from the center of the screen and check for collisions with objects. When rendering, I use these calls to set up the camera: GL11.glRotated(mPitch, 1, 0, 0); GL11.glRotated(mYaw, 0, 1, 0); GL11.glTranslated(mPositionX, mPositionY, mPositionZ); I am having trouble creating the ray, however. This is the code I have so far: ray.origin = new Vector(mPositionX, mPositionY, mPositionZ); ray.direction = new Vector(?, ?, ?); My question is: what should I put in the question mark spots? I.e. how can I create the ray direction from the pitch and roll? Any help would be much appreciated!

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• How would I setup reverse DNS for 2 email servers?

  - by Solignis

  I have an interesting DNS question (well interesting to me atleast). I just installed an hmail server in our remote office to act as an MX backup in the event our exchange server goes down. The 2 host names are mail.campbellsurvey.com mail2.campbellsurvey.com mail points to the address 98.XXX.91.XXX mail2 points to the address 70.XXX.190.XXX How would I setup a PTR record on the ISP end to reflect both hostnames? Does the PTR have to point to EXACTLY mail.campbellsurvey.com or can it point to just campbellsurvey.com? because right now anything passing through the primary static address in our pool (the one used for standard internet) is identified as mail.campbellsurvey.com. My only idea to fix this was to move the mail server to the next available address and give it only it the name mail.campbellsurvey.com but I wanted to see if there was another way. Thanks in advance.

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• Help with Windows 7 BSOD with windbg minidump !analyze -v results

  - by Kurt Harless

  Hi gang, Windows 7 X64 Ultimate is BSODing occasionally. I suspect an overheating issue or something related to the use of my GTX-295 card that runs very hot. Here is an !analyze -v listing of the most recent minidump. Any and all help greatly appreciated. Kurt Microsoft (R) Windows Debugger Version 6.12.0002.633 AMD64 Copyright (c) Microsoft Corporation. All rights reserved. Loading Dump File [C:\Windows\Minidump\122810-31387-01.dmp] Mini Kernel Dump File: Only registers and stack trace are available Symbol search path is: SRV*c:\websymbols*http://msdl.microsoft.com/download/symbols Executable search path is: Windows 7 Kernel Version 7600 MP (8 procs) Free x64 Product: WinNt, suite: TerminalServer SingleUserTS Built by: 7600.16617.amd64fre.win7_gdr.100618-1621 Machine Name: Kernel base = 0xfffff800`03065000 PsLoadedModuleList = 0xfffff800`032a2e50 Debug session time: Tue Dec 28 11:04:03.597 2010 (UTC - 7:00) System Uptime: 2 days 2:28:40.407 Loading Kernel Symbols ............................................................... ................................................................ .............................................. Loading User Symbols Loading unloaded module list ................ ******************************************************************************* * * * Bugcheck Analysis * * * ******************************************************************************* Use !analyze -v to get detailed debugging information. BugCheck 3B, {c0000005, fffff800033b8873, fffff8800e322dc0, 0} Probably caused by : ntkrnlmp.exe ( nt!RtlCompareUnicodeStrings+c3 ) Followup: MachineOwner --------- 1: kd> !analyze -v ******************************************************************************* * * * Bugcheck Analysis * * * ******************************************************************************* SYSTEM_SERVICE_EXCEPTION (3b) An exception happened while executing a system service routine. Arguments: Arg1: 00000000c0000005, Exception code that caused the bugcheck Arg2: fffff800033b8873, Address of the instruction which caused the bugcheck Arg3: fffff8800e322dc0, Address of the context record for the exception that caused the bugcheck Arg4: 0000000000000000, zero. Debugging Details: ------------------ EXCEPTION_CODE: (NTSTATUS) 0xc0000005 - The instruction at 0x%08lx referenced memory at 0x%08lx. The memory could not be %s. FAULTING_IP: nt!RtlCompareUnicodeStrings+c3 fffff800`033b8873 488b7c2418 mov rdi,qword ptr [rsp+18h] CONTEXT: fffff8800e322dc0 -- (.cxr 0xfffff8800e322dc0) rax=0000000000000041 rbx=fffff8a015a3c1c0 rcx=0000000000000024 rdx=0000000000000003 rsi=fffff8800e3238b0 rdi=0000000000000009 rip=fffff800033b8873 rsp=fffff8800e323798 rbp=000000000000000d r8=fffff8a018cb374c r9=000000200a98fdc4 r10=fffff8800e323988 r11=fffff8800e32398e r12=fffff8a018127c18 r13=fffff8800126e550 r14=0000000000000001 r15=fffffa800abe1570 iopl=0 nv up ei pl nz ac po nc cs=0010 ss=0018 ds=002b es=002b fs=0053 gs=002b efl=00010216 nt!RtlCompareUnicodeStrings+0xc3: fffff800`033b8873 488b7c2418 mov rdi,qword ptr [rsp+18h] ss:0018:fffff880`0e3237b0=???????????????? Resetting default scope CUSTOMER_CRASH_COUNT: 1 DEFAULT_BUCKET_ID: VISTA_DRIVER_FAULT BUGCHECK_STR: 0x3B PROCESS_NAME: ccSvcHst.exe CURRENT_IRQL: 0 LAST_CONTROL_TRANSFER: from 0000000000000000 to fffff800033b8873 STACK_TEXT: fffff880`0e323798 00000000`00000000 : 00000000`00000000 00000000`00000000 00000000`00000000 00000000`00000000 : nt!RtlCompareUnicodeStrings+0xc3 FOLLOWUP_IP: nt!RtlCompareUnicodeStrings+c3 fffff800`033b8873 488b7c2418 mov rdi,qword ptr [rsp+18h] SYMBOL_STACK_INDEX: 0 SYMBOL_NAME: nt!RtlCompareUnicodeStrings+c3 FOLLOWUP_NAME: MachineOwner MODULE_NAME: nt IMAGE_NAME: ntkrnlmp.exe DEBUG_FLR_IMAGE_TIMESTAMP: 4c1c44a9 STACK_COMMAND: .cxr 0xfffff8800e322dc0 ; kb FAILURE_BUCKET_ID: X64_0x3B_nt!RtlCompareUnicodeStrings+c3 BUCKET_ID: X64_0x3B_nt!RtlCompareUnicodeStrings+c3 Followup: MachineOwner ---------

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• Camera rotation - First Person Camera using GLM

  - by tempvar

  I've just switched from deprecated opengl functions to using shaders and GLM math library and i'm having a few problems setting up my camera rotations (first person camera). I'll show what i've got setup so far. I'm setting up my ViewMatrix using the glm::lookAt function which takes an eye position, target and up vector // arbitrary pos and target values pos = glm::vec3(0.0f, 0.0f, 10.0f); target = glm::vec3(0.0f, 0.0f, 0.0f); up = glm::vec3(0.0f, 1.0f, 0.0f); m_view = glm::lookAt(pos, target, up); i'm using glm::perspective for my projection and the model matrix is just identity m_projection = glm::perspective(m_fov, m_aspectRatio, m_near, m_far); model = glm::mat4(1.0); I send the MVP matrix to my shader to multiply the vertex position glm::mat4 MVP = camera->getProjection() * camera->getView() * model; // in shader gl_Position = MVP * vec4(vertexPos, 1.0); My camera class has standard rotate and translate functions which call glm::rotate and glm::translate respectively void camera::rotate(float amount, glm::vec3 axis) { m_view = glm::rotate(m_view, amount, axis); } void camera::translate(glm::vec3 dir) { m_view = glm::translate(m_view, dir); } and i usually just use the mouse delta position as the amount for rotation Now normally in my previous opengl applications i'd just setup the yaw and pitch angles and have a sin and cos to change the direction vector using (gluLookAt) but i'd like to be able to do this using GLM and matrices. So at the moment i have my camera set 10 units away from the origin facing that direction. I can see my geometry fine, it renders perfectly. When i use my rotation function... camera->rotate(mouseDeltaX, glm::vec3(0, 1, 0)); What i want is for me to look to the right and left (like i would with manipulating the lookAt vector with gluLookAt) but what's happening is It just rotates the model i'm looking at around the origin, like im just doing a full circle around it. Because i've translated my view matrix, shouldn't i need to translate it to the centre, do the rotation then translate back away for it to be rotating around the origin? Also, i've tried using the rotate function around the x axis to get pitch working, but as soon as i rotate the model about 90 degrees, it starts to roll instead of pitch (gimbal lock?). Thanks for your help guys, and if i've not explained it well, basically i'm trying to get a first person camera working with matrix multiplication and rotating my view matrix is just rotating the model around the origin.

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• Shadow mapping with deffered shading for directional lights - shadow map projection problem

  - by Harry

  I'm trying to implement shadow mapping to my engine. I started with directional lights because they seemed to be the easiest one, but I was wrong :) I have implemented deferred shading and I retrieve position from depth. I think that there is the biggest problem but code looks ok for me. Now more about problem: Shadow map projected onto meshes looks bad scaled and translated and also some informations from shadow map texture aren't visible. You can see it on this screen: http://img5.imageshack.us/img5/2254/93dn.png Yelow frustum is light frustum and I have mixed shadow map preview and actual scene. As you can see shadows are in wrong place and shadow of cone and sphere aren't visible. Could you look at my codes and tell me where I have a mistake? // create shadow map if(!_shd)glGenTextures(1, &_shd); glBindTexture(GL_TEXTURE_2D, _shd); glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, 1024, 1024, 0, GL_DEPTH_COMPONENT, GL_FLOAT,NULL); // shadow map size glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE); glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE); glFramebufferTexture2D(GL_DRAW_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, _shd, 0); glDrawBuffer(GL_NONE); // setting camera Vector dire=Vector(0,0,1); ACamera.setLookAt(dire,Vector(0)); ACamera.setPerspectiveView(60.0f,1,0.1f,10.0f); // currently needed for proper frustum corners calculation Vector min(ACamera._point[0]),max(ACamera._point[0]); for(int i=0;i<8;i++){ max=Max(max,ACamera._point[i]); min=Min(min,ACamera._point[i]); } ACamera.setOrthogonalView(min.x,max.x,min.y,max.y,-max.z,-min.z); glBindFramebuffer(GL_DRAW_FRAMEBUFFER, _s_buffer); // framebuffer for shadow map // rendering to depth buffer glBindFramebuffer(GL_DRAW_FRAMEBUFFER, _g_buffer); Shaders["DirLight"].set(true); Matrix4 bias; bias.x.set(0.5,0.0,0.0,0.0); bias.y.set(0.0,0.5,0.0,0.0); bias.z.set(0.0,0.0,0.5,0.0); bias.w.set(0.5,0.5,0.5,1.0); Shaders["DirLight"].set("textureMatrix",ACamera.matrix*Projection3D*bias); // order of multiplications are 100% correct, everything gives mi the same result as using glm glActiveTexture(GL_TEXTURE5); glBindTexture(GL_TEXTURE_2D,_shd); lightDir(dir); // light calculations Vertex Shader makes nothing related to shadow calculatons Pixel shader function which calculates if pixel is in shadow or not: float readShadowMap(vec3 eyeDir) { // retrieve depth of pixel float z = texture2D(depth, gl_FragCoord.xy/screen).z; vec3 pos = vec3(gl_FragCoord.xy/screen, z); // transform by the projection and view inverse vec4 worldSpace = inverse(View)*inverse(ProjectionMatrix)*vec4(pos*2-1,1); worldSpace /= worldSpace.w; vec4 coord=textureMatrix*worldSpace; float vis=1.0f; if(texture2D(shadow, coord.xy).z < coord.z-0.001)vis=0.2f; return vis; } I also have question about shadows specifically for directional light. Currently I always look at 0,0,0 position and in further implementation I have to move light frustum along to camera frustum. I've found how to do this here: http://www.gamedev.net/topic/505893-orthographic-projection-for-shadow-mapping/ but it doesn't give me what I want. Maybe because of problems mentioned above, but I want know your opinion. EDIT: vec4 worldSpace is position read from depht of the scene (not shadow map). Maybe I wasn't precise so I'll try quick explain what is what: View is camera view matrix, ProjectionMatrix is camera projection,. First I try to get world space position from depth map and then multiply it by textureMatrix which is light view *light projection*bias. Rest of code is the same as in many tutorials. I can't use vertex shader to make something like gl_Position=textureMatrix*gl_Vertex and get it interpolated in fragment shader because of deffered rendering use so I want get it from depht buffer. EDIT2: I also tried make it as in Coding Labs tutorial about Shadow Mapping with Deferred Rendering but unfortunately this either works wrong.

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• Getting started with Oracle Database In-Memory Part III - Querying The IM Column Store

  - by Maria Colgan

  In my previous blog posts, I described how to install, enable, and populate the In-Memory column store (IM column store). This weeks post focuses on how data is accessed within the IM column store. Let’s take a simple query “What is the most expensive air-mail order we have received to date?” SELECT Max(lo_ordtotalprice) most_expensive_order FROM lineorderWHERE  lo_shipmode = 5; The LINEORDER table has been populated into the IM column store and since we have no alternative access paths (indexes or views) the execution plan for this query is a full table scan of the LINEORDER table. You will notice that the execution plan has a new set of keywords “IN MEMORY" in the access method description in the Operation column. These keywords indicate that the LINEORDER table has been marked for INMEMORY and we may use the IM column store in this query. What do I mean by “may use”? There are a small number of cases were we won’t use the IM column store even though the object has been marked INMEMORY. This is similar to how the keyword STORAGE is used on Exadata environments. You can confirm that the IM column store was actually used by examining the session level statistics, but more on that later. For now let's focus on how the data is accessed in the IM column store and why it’s faster to access the data in the new column format, for analytical queries, rather than the buffer cache. There are four main reasons why accessing the data in the IM column store is more efficient. 1. Access only the column data needed The IM column store only has to scan two columns – lo_shipmode and lo_ordtotalprice – to execute this query while the traditional row store or buffer cache has to scan all of the columns in each row of the LINEORDER table until it reaches both the lo_shipmode and the lo_ordtotalprice column. 2. Scan and filter data in it's compressed format When data is populated into the IM column it is automatically compressed using a new set of compression algorithms that allow WHERE clause predicates to be applied against the compressed formats. This means the volume of data scanned in the IM column store for our query will be far less than the same query in the buffer cache where it will scan the data in its uncompressed form, which could be 20X larger. 3. Prune out any unnecessary data within each column The fastest read you can execute is the read you don’t do. In the IM column store a further reduction in the amount of data accessed is possible due to the In-Memory Storage Indexes(IM storage indexes) that are automatically created and maintained on each of the columns in the IM column store. IM storage indexes allow data pruning to occur based on the filter predicates supplied in a SQL statement. An IM storage index keeps track of minimum and maximum values for each column in each of the In-Memory Compression Unit (IMCU). In our query the WHERE clause predicate is on the lo_shipmode column. The IM storage index on the lo_shipdate column is examined to determine if our specified column value 5 exist in any IMCU by comparing the value 5 to the minimum and maximum values maintained in the Storage Index. If the value 5 is outside the minimum and maximum range for an IMCU, the scan of that IMCU is avoided. For the IMCUs where the value 5 does fall within the min, max range, an additional level of data pruning is possible via the metadata dictionary created when dictionary-based compression is used on IMCU. The dictionary contains a list of the unique column values within the IMCU. Since we have an equality predicate we can easily determine if 5 is one of the distinct column values or not. The combination of the IM storage index and dictionary based pruning, enables us to only scan the necessary IMCUs. 4. Use SIMD to apply filter predicates For the IMCU that need to be scanned Oracle takes advantage of SIMD vector processing (Single Instruction processing Multiple Data values). Instead of evaluating each entry in the column one at a time, SIMD vector processing allows a set of column values to be evaluated together in a single CPU instruction. The column format used in the IM column store has been specifically designed to maximize the number of column entries that can be loaded into the vector registers on the CPU and evaluated in a single CPU instruction. SIMD vector processing enables the Oracle Database In-Memory to scan billion of rows per second per core versus the millions of rows per second per core scan rate that can be achieved in the buffer cache. I mentioned earlier in this post that in order to confirm the IM column store was used; we need to examine the session level statistics. You can monitor the session level statistics by querying the performance views v$mystat and v$statname. All of the statistics related to the In-Memory Column Store begin with IM. You can see the full list of these statistics by typing: display_name format a30 SELECT display_name FROM v$statname WHERE  display_name LIKE 'IM%'; If we check the session statistics after we execute our query the results would be as follow; SELECT Max(lo_ordtotalprice) most_expensive_order FROM lineorderWHERE lo_shipmode = 5; SELECT display_name FROM v$statname WHERE  display_name IN ('IM scan CUs columns accessed',                        'IM scan segments minmax eligible',                        'IM scan CUs pruned'); As you can see, only 2 IMCUs were accessed during the scan as the majority of the IMCUs (44) in the LINEORDER table were pruned out thanks to the storage index on the lo_shipmode column. In next weeks post I will describe how you can control which queries use the IM column store and which don't. +Maria Colgan

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• How do I move the camera sideways in Libgdx?

  - by Bubblewrap

  I want to move the camera sideways (strafe). I had the following in mind, but it doesn't look like there are standard methods to achieve this in Libgdx. If I want to move the camera sideways by x, I think I need to do the following: Create a Matrix4 mat Determine the orthogonal vector v between camera.direction and camera.up Translate mat by v*x Multiply camera.position by mat Will this approach do what I think it does, and is it a good way to do it? And how can I do this in libgdx? I get "stuck" at step 2, as I have not found any standard method in Libgdx to calculate an orthogonal vector. EDIT: I think I can use camera.direction.crs(camera.up) to find v. I'll try this approach tonight and see if it works. EDIT2: I got it working and didn't need the matrix after all: Vector3 right = camera.direction.cpy().crs(camera.up).nor(); camera.position.add(right.mul(x));

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• Parabolic throw with set Height and range (libgdx)

  - by Tauboga

  Currently i'm working on a minigame for android where you have a rotating ball in the center of the display which jumps when touched in the direction of his current angle. I'm simply using a gravity vector and a velocity vector in this way: positionBall = positionBall.add(velocity); velocity = velocity.add(gravity); and velocity.x = (float) Math.cos(angle) * 12; /* 12 to amplify the velocity */ velocity.y = (float) Math.sin(angle) * 15; /* 15 to amplify the velocity */ That works fine. Here comes the problem: I want to make the jump look the same on all possible resolutions. The velocity needs to be scaled in a way that when the ball is thrown straight upwards it will touch the upper display border. When thrown directly left or right the range shall be exactly long enough to touch the left/right display border. Which formula(s) do I need to use and how to implement them correctly? Thanks in advance!

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• DNS - domain conflict?

  - by Stefanos.Ioannou

  I was given two domains: domain.com & domain.info (they are on GoDaddy). And I was also given two servers, 107.105.38.99 - Rails app and 107.107.90.17 - Wordpress platform, on Digital Ocean. At first, I was instructed to associate domain.com with the 107.107.38.99 (Rails app). Then I was instructed to de-associate this IP with domain.com and associated the 107.107.90.17 with the domain name domain.com. Then I was instructed to associated domain.info with the 107.107.38.99 (Rails app). Right now, when I go to domain.com the WordPress platform (107.107.90.17) loads fine and that is what is expected. But when I go to domain.info for the Rails app (107.107.38.99) I get redirected to domain.com. This is not expected and this is really weird for me. When I ping domain.info I get this: PING domain.info (107.107.38.99): 56 data bytes 64 bytes from 107.107.38.99: icmp_seq=0 ttl=50 time=74.601 ms Which is the expected result showing the correct IP but I don't understand why I get redirected to domain.com...(which when I ping is:) domain 64 bytes from 107.107.90.17: icmp_seq=0 ttl=50 time=75.057 ms The PTR Records on Digital Ocean are as follows: IP Address PTR Record 107.107.38.99 domain.info. 107.107.90.17 domain.com. and the DNS configurations on Digital Ocean are: domain.com A: @ 107.107.90.17 CNAME: * @ domain.info A: @ 107.107.38.99 CNAME: * @ I am not sure what the issue is, if you have any clue please let me know, I will be really grateful. If you need any other info let me know.

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• Question about Target parameter of Matrix.CreateLookAt

  - by manning18

  I have a newbie question that's causing me a little bit of confusion when experimenting with cameras and reading other peoples implementations - does this parameter represent a point or a vector? In some examples I've seen people treat it like a specific point they are looking at (eg a position in the world), other times I see people caching the orientation of the camera in a rotation matrix and simply using the Matrix.Forward property as the "target", and other times it's a vector that's the result of targetPos - camPos and also I saw a camPos + orientation.Forward I was also just playing around with hard-coded target positions with same direction eg 1 to 10000 with no discernible difference in what I saw in the scene. Is the "Target" parameter actually a position or a direction (irrespective of magnitude)? Are there any subtle differences in behaviors, common mistakes or gotchas that are associated with what values you provide, or HOW you provide this paramter? Are all the methods I mentioned above equivalent? (sorry, I've only recently started and my math is still catching up)

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• 2D tower defense - A bullet to an enemy

  - by Tashu

  I'm trying to find a good solution for a bullet to hit the enemy. The game is 2D tower defense, the tower is supposed to shoot a bullet and hit the enemy guaranteed. I tried this solution - http://blog.wolfire.com/2009/07/linear-algebra-for-game-developers-part-1/ The link mentioned to subtract the bullet's origin and the enemy as well (vector subtraction). I tried that but a bullet just follows around the enemy. float diffX = enemy.position.x - position.x; float diffY = enemy.position.y - position.y; velocity.x = diffX; velocity.y = diffY; position.add(velocity.x * deltaTime, velocity.y * deltaTime); I'm familiar with vectors but not sure what steps (vector math operations) to be done to get this solution working.

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• b Is it bad to have the Reverse DNS for two IPs point to the same domain name?

  - by Daniel Vandersluis

  I am in the process of setting up a new server for my web application (the site will be moved, it is not for load balancing or the like), which has a different IP address from my existing server. My current server has a reverse DNS PTR record set up pointing its IP to mydomain.com. Is it bad to set up a reverse DNS PTR record for the new IP pointing to mydomain.com as well? Or should I wait until I do my migration to set up the record? Update: I forgot to mention, the A record for the mydomain.com points to the old server's IP address, not the new one, if it matters.

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• Can WinRT really be used at just the boundaries?

  - by Bret Kuhns

  Microsoft (chiefly, Herb Sutter) recommends when using WinRT with C++/CX to keep WinRT at the boundaries of the application and keep the core of the application written in standard ISO C++. I've been writing an application which I would like to leave portable, so my core functionality was written in standard C++, and I am now attempting to write a Metro-style front end for it using C++/CX. I've had a bit of a problem with this approach, however. For example, if I want to push a vector of user-defined C++ types to a XAML ListView control, I have to wrap my user-defined type in a WinRT ref/value type for it to be stored in a Vector^. With this approach, I'm inevitably left with wrapping a large portion of my C++ classes with WinRT classes. This is the first time I've tried to write a portable native application in C++. Is it really practical to keep WinRT along the boundaries like this? How else could this type of portable core with a platform-specific boundary be handled?

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• How to implement a simple bullet trajectory

  - by AirieFenix

  I searched and searched and although it's a fair simple question, I don't find the proper answer but general ideas (which I already have). I have a top-down game and I want to implement a gun which shoots bullets that follow a simple path (no physics nor change of trajectory, just go from A to B thing). a: vector of the position of the gun/player. b: vector of the mouse position (cross-hair). w: the vector of the bullet's trajectory. So, w=b-a. And the position of the bullet = [x=x0+speed*time*normalized w.x , y=y0+speed*time * normalized w.y]. I have the constructor: public Shot(int shipX, int shipY, int mouseX, int mouseY) { //I get mouse with Gdx.input.getX()/getY() ... this.shotTime = TimeUtils.millis(); this.posX = shipX; this.posY = shipY; //I used aVector = aVector.nor() here before but for some reason didn't work float tmp = (float) (Math.pow(mouseX-shipX, 2) + Math.pow(mouseY-shipY, 2)); tmp = (float) Math.sqrt(Math.abs(tmp)); this.vecX = (mouseX-shipX)/tmp; this.vecY = (mouseY-shipY)/tmp; } And here I update the position and draw the shot: public void drawShot(SpriteBatch batch) { this.lifeTime = TimeUtils.millis() - this.shotTime; //position = positionBefore + v*t this.posX = this.posX + this.vecX*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); this.posY = this.posY + this.vecY*this.lifeTime*speed*Gdx.graphics.getDeltaTime(); ... } Now, the behavior of the bullet seems very awkward, not going exactly where my mouse is (it's like the mouse is 30px off) and with a random speed. I know I probably need to open the old algebra book from college but I'd like somebody says if I'm in the right direction (or points me to it); if it's a calculation problem, a code problem or both. Also, is it possible that Gdx.input.getX() gives me non-precise position? Because when I draw the cross-hair it also draws off the cursor position. Sorry for the long post and sorry if it's a very basic question. Thanks!

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• SMTP host name vs. domain in "From:" address vis-a-vis Email Deliverability

  - by Jared Duncan

  I'm trying to implement (or make sure that I'm correctly following) email sending best practices to improve deliverability, but the role of the smtp server's host name vs the domain name of the From: email address seems to be unclear, even after reading dozens of people's articles/input. Specifically, I understand that to satisfy the reverse DNS check, there must be a PTR record for the IP address of the sending machine that yields a domain name that matches the host name of the sending machine / SMTP server. Some say it needs to match the one given by the "hostname" command, most say it's the one provided with the HELO / EHLO statement, and this guy even says they MUST be the same (according to / enforced by what, I don't know; that's only a minor point of confusion, anyhow). First, what I can't find anywhere is whether or not the domain name of the From: email address needs to match the domain name of the SMTP server. So in my case, I have a VPS with linode. It primarily hosts a particular domain of mine, example.com, but I also sometimes do work on other projects: foo.com and bar.com. So what I'm wondering is if I can just leave the default linode PTR record (which resolves to abc.def.linode.com), make sure that abc.def.linode.com is what my mail server (qmail) is configured to say at HELO, and then proceed to use it to send out emails for example.com, foo.com, et al. If so, then I am confused by the advice given here, specifically (in a listing of bad case scenarios): No SPF record for the domain being used in the HELO command Why would THAT domain need an SPF record? And if it does, which domain should it provide whitelisting for: the HELO domain, or the domain of the From: email address (envelope sender)? Also, which domain would need to accept mail sent to [email protected]? If the domains must be the same, that would seem rather limiting to me, because then for every domain you wanted to send email from, you'd have to get another IP address for it. It would also compromise or ruin one's ability to do non-email sending things (e.g. wget) relatively anonymously. However, the upside--if this is the case--is that it would make for a far less confusing setup. I'm currently using the linode.com SMTP+PTR domain and example.com From: address combination without much of any deliverability issue, but my volume is very low and I'd like to know if someone out there has experience with larger volumes and has specifically tested the difference and/or has inside knowledge and/or has an authoritative answer (and source) for this particular question. I'm happy to clarify anything, let me know. Thanks in advance.

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• Evaluating mean and std as simulations are added

  - by Luca Cerone

  I have simulations that evaluate a certain value X. I run the simulations several times and save the value of X in a vector V. When all the runs have finished I evaluate the mean and standard deviation for the vector V. This approach works, but implies saving all the values for X. As my computer is quite old and with limited ram, I was wondering if there is a way to update the mean value M and the standard deviation S, knowing the value of X at the (n+1)-th run, and the values of M and S after n runs. How can I update the mean value and the standard deviation as simulations are added to the set? Please note that this is just a conceptual example, I don't save only one number X but thousands at each simulations, so I really have problems running a big number of runs if I have to keep all the past values into the memory.

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• add collision detection to sprite?

  - by xBroak

  bassically im trying to add collision detection to the sprite below, using the following: self.rect = bounds_rect collide = pygame.sprite.spritecollide(self, wall_list, False) if collide: # yes print("collide") However it seems that when the collide is triggered it continuously prints 'collide' over and over when instead i want them to simply not be able to walk through the object, any help? def update(self, time_passed): """ Update the creep. time_passed: The time passed (in ms) since the previous update. """ if self.state == Creep.ALIVE: # Maybe it's time to change the direction ? # self._change_direction(time_passed) # Make the creep point in the correct direction. # Since our direction vector is in screen coordinates # (i.e. right bottom is 1, 1), and rotate() rotates # counter-clockwise, the angle must be inverted to # work correctly. # self.image = pygame.transform.rotate( self.base_image, -self.direction.angle) # Compute and apply the displacement to the position # vector. The displacement is a vector, having the angle # of self.direction (which is normalized to not affect # the magnitude of the displacement) # displacement = vec2d( self.direction.x * self.speed * time_passed, self.direction.y * self.speed * time_passed) self.pos += displacement # When the image is rotated, its size is changed. # We must take the size into account for detecting # collisions with the walls. # self.image_w, self.image_h = self.image.get_size() global bounds_rect bounds_rect = self.field.inflate( -self.image_w, -self.image_h) if self.pos.x < bounds_rect.left: self.pos.x = bounds_rect.left self.direction.x *= -1 elif self.pos.x > bounds_rect.right: self.pos.x = bounds_rect.right self.direction.x *= -1 elif self.pos.y < bounds_rect.top: self.pos.y = bounds_rect.top self.direction.y *= -1 elif self.pos.y > bounds_rect.bottom: self.pos.y = bounds_rect.bottom self.direction.y *= -1 self.rect = bounds_rect collide = pygame.sprite.spritecollide(self, wall_list, False) if collide: # yes print("collide") elif self.state == Creep.EXPLODING: if self.explode_animation.active: self.explode_animation.update(time_passed) else: self.state = Creep.DEAD self.kill() elif self.state == Creep.DEAD: pass #------------------ PRIVATE PARTS ------------------# # States the creep can be in. # # ALIVE: The creep is roaming around the screen # EXPLODING: # The creep is now exploding, just a moment before dying. # DEAD: The creep is dead and inactive # (ALIVE, EXPLODING, DEAD) = range(3) _counter = 0 def _change_direction(self, time_passed): """ Turn by 45 degrees in a random direction once per 0.4 to 0.5 seconds. """ self._counter += time_passed if self._counter > randint(400, 500): self.direction.rotate(45 * randint(-1, 1)) self._counter = 0 def _point_is_inside(self, point): """ Is the point (given as a vec2d) inside our creep's body? """ img_point = point - vec2d( int(self.pos.x - self.image_w / 2), int(self.pos.y - self.image_h / 2)) try: pix = self.image.get_at(img_point) return pix[3] > 0 except IndexError: return False def _decrease_health(self, n): """ Decrease my health by n (or to 0, if it's currently less than n) """ self.health = max(0, self.health - n) if self.health == 0: self._explode() def _explode(self): """ Starts the explosion animation that ends the Creep's life. """ self.state = Creep.EXPLODING pos = ( self.pos.x - self.explosion_images[0].get_width() / 2, self.pos.y - self.explosion_images[0].get_height() / 2) self.explode_animation = SimpleAnimation( self.screen, pos, self.explosion_images, 100, 300) global remainingCreeps remainingCreeps-=1 if remainingCreeps == 0: print("all dead")

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• Bind: dns not 'spreaded'

  - by realtebo

  I've elfoip.net with bind $ whois elfoip.net | grep 'Name Server' Name Server: NS.ELFOIP.NET I need elfoip.net be able to serve third levels domain, like mickymouse.elfoip.net, etc... Yes, I'm trying to create an other useless dyndns clone. i've added some third level as A RR. Eg: executing this from the server itself $ dig @localhost mattinauno.elfoip.net ;; ANSWER SECTION: mattinauno.elfoip.net. 60 IN A 192.81.221.113 I was expecting in one or two days, from my pc i can digit in browser mattinauno.elfoip.net and get page a 192.81.221.113 But this is not happening. Are there any prerequisites to satisfy to allow dns of my isp to be able to forward dns resolution of *.elfoip.net to MY dns ? (Or to ask to him and then cache ?) TTL of zone is set a 5m I've not AllowQuey directive, is it necessary for other dns to cache from mine ? I've cheched the zone with bind utility named-checkzone but no error detected. How to diagnose why other dns doesn't take in account RR from mine ? from my home pc dig @ns.elfoip.net mattinauno.elfoip.net ;; ANSWER SECTION: mattinauno.elfoip.net. 60 IN A 192.81.221.113 ;; AUTHORITY SECTION: elfoip.net. 300 IN NS ns.elfoip.net. but dig @8.8.8.8 mattinauno.elfoip.net give no answers Whole zone file: note I've used nsupdate, so this file has been re-edited and re-formatted from this utility ! root@mirko:/var/named# cat elfoip.net.db $ORIGIN . $TTL 300 ; 5 minutes elfoip.net IN SOA ns.elfoip.net. hostmaster.elfoip.net. ( 2013062314 ; serial 3600 ; refresh (1 hour) 600 ; retry (10 minutes) 86400 ; expire (1 day) 60 ; minimum (1 minute) ) NS ns.elfoip.net. A 109.168.99.6 $ORIGIN elfoip.net. $TTL 60 ; 1 minute google A 173.194.35.56 maiscai A 192.81.221.113 mattinadue A 192.81.221.113 mattinauno A 192.81.221.113 $TTL 300 ; 5 minutes ns A 109.168.99.6 $TTL 60 ; 1 minute prova A 208.67.222.222 prova2 A 13.23.34.45 A 13.23.34.46 www CNAME elfoip.net. EDIT: added named.conf.local zone "elfoip.net" { type master; // file "/etc/bind/elfoip.net.db"; file "/var/named/elfoip.net.db"; allow-update { key elfoip.net ; }; }; EDIT: I've no setup list-on directive *EDIT Added a TCPDUMP after [email protected] wwww.elfoip.net from a machine which uses my company internal dns, who allow recursive query. root@mirko:~# tcpdump -i eth0 'port 53' tcpdump: verbose output suppressed, use -v or -vv for full protocol decode listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes 11:57:23.293611 IP host9-210-static.22-87-b.business.telecomitalia.it.45958 > mirko.elfoip.net.domain: 61337+ A? www.elfoip.net. (32) 11:57:23.294114 IP mirko.elfoip.net.domain > host9-210-static.22-87-b.business.telecomitalia.it.45958: 61337* 2/1/1 CNAME elfoip.net., A 109.168.99.6 (95) 11:57:23.294554 IP mirko.elfoip.net.59571 > google-public-dns-a.google.com.domain: 45851+ PTR? 9.210.22.87.in-addr.arpa. (42) 11:57:23.330444 IP google-public-dns-a.google.com.domain > mirko.elfoip.net.59571: 45851 1/0/0 PTR host9-210-static.22-87-b.business.telecomitalia.it. (106) 11:57:23.331181 IP mirko.elfoip.net.44171 > google-public-dns-a.google.com.domain: 33339+ PTR? 8.8.8.8.in-addr.arpa. (38) 11:57:23.439405 IP google-public-dns-a.google.com.domain > mirko.elfoip.net.44171: 33339 1/0/0 PTR google-public-dns-a.google.com. (82) 11:57:31.350654 IP host9-210-static.22-87-b.business.telecomitalia.it.30108 > mirko.elfoip.net.domain: 38269 [1au] A? ns.elfoip.net. (42) 11:57:31.351117 IP mirko.elfoip.net.domain > host9-210-static.22-87-b.business.telecomitalia.it.30108: 38269* 1/1/1 A 109.168.99.6 (72) If i dig @8.8.8.8 www.elfoip.net, NOTHING happens in dump log !

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• SMTP for multiple domains on virtual interfaces

  - by Pawel Goscicki

  The setup is like this (Ubuntu 9.10): eth0: 1.1.1.1 name.isp.com eth0:0 2.2.2.2 example2.com eth0:1 3.3.3.3 example3.com example2.com and example3.com are web apps which need to send emails to their users. 2.2.2.2 points to example2.com and vice-versa (A/PTR). MX - Google. Google handles all incoming mail. 3.3.3.3 points to example3.com and vice-versa (A/PTR). MX - Google. Google handles all incoming mail. Requirements: Local delivery must be disabled (must deliver to MX specified server), so that the following works (note that there is no local user bob on the machine, but there is an existing bob email user): echo "Test" | mail -s "Test 6" [email protected] I need to be able to specify from which IP/domain name the email is delivered when sending an email. I fought with sendmail. With not much luck. Here's some debug info: sendmail -d0.12 -bt < /dev/null Canonical name: name.isp.com UUCP nodename: host a.k.a.: example2.com a.k.a.: example3.com ... Sendmail always uses canonical name (taken from eth0). I've found no way for it to select one of the UUCP codenames. It uses it for sending email: echo -e "To: [email protected]\nSubject: Test\nTest\n" | sendmail -bm -t -v [email protected]... Connecting to [127.0.0.1] via relay... 220 name.isp.com ESMTP Sendmail 8.14.3/8.14.3/Debian-9ubuntu1; Wed, 31 Mar 2010 16:33:55 +0200; (No UCE/UBE) logging access from: localhost(OK)-localhost [127.0.0.1] >>> EHLO name.isp.com I'm ok with other SMTP solutions. I've looked briefly at nbsmtp, msmtp and nullmailer but I'm not sure thay can deal with disabling local delivery and selecting different domains when sending emails. I also know about spoofing sender field by using mail -a "From: <[email protected]>" but it seems to be a half-solution (mails are still sent from isp.com domain instead of proper example2.com, so PTR records are unused and there's more risk of being flagged as spam/spammer).

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• Marshalling the value of a char* ANSI string DLL API parameter into a C# string

  - by Brian Biales

  For those who do not mix .NET C# code with legacy DLL's that use char* pointers on a regular basis, the process to convert the strings one way or the other is non-obvious. This is not a comprehensive article on the topic at all, but rather an example of something that took me some time to go find, maybe it will save someone else the time. I am utilizing a third party too that uses a call back function to inform my application of its progress.  This callback includes a pointer that under some circumstances is a pointer to an ANSI character string.  I just need to marshal it into a C# string variable.  Seems pretty simple, yes?  Well, it is, (as are most things, once you know how to do them). The parameter of my callback function is of type IntPtr, which implies it is an integer representation of a pointer.  If I know the pointer is pointing to a simple ANSI string, here is a simple static method to copy it to a C# string: private static string GetStringFromCharStar(IntPtr ptr) {     return System.Runtime.InteropServices.Marshal.PtrToStringAnsi(ptr); } The System.Runtime.InteropServices is where to look any time you are mixing legacy unmanaged code with your .NET application.

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• Trying to detect collision between two polygons using Separating Axis Theorem

  - by Holly

  The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(vertices[0]); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(vertices[i]); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if( other.x <= y || other.y >= x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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• Alternatives to NSMutableArray for storing 2D grid - iOS Cocos2d

  - by SundayMonday

  I'm creating a grid-based iOS game using Cocos2d. Currently the grid is stored in an NSMutableArray that contains other NSMutableArrays (the latter are rows in the grid). This works ok and performance so far is pretty good. However the syntax feels bulky and the indexing isn't very elegant (using CGPoints, would prefer integer indices). I'm looking for an alternative. What are some alternatives data structures for 2D arrays in this situation? In my game it's very common to add and remove rows from the bottom of the grid. So the grid might start off 10x10, grow to 17x10, shrink to 8x10 and then finally end with 2x10. Note the column count is constant. I've consider using a vector<vector<Object*>>. Also I'm vaguely aware of some type of "fast array" or similar offered by Cocos2d. I'd just like to learn about best practices from other developers!

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• Understanding how texCUBE works and writing cubemaps properly into a cube rendertarget

  - by cubrman

  My goal is to create accurate reflections, sampled from a dynamic cubemap, for specific 3d objects (mostly lights) in XNA 4.0. To sample the cubemap I compute the 3d reflection vector in a classic way: half3 ReflectionVec = reflect(-directionToCamera, Normal.rgb); I then use the vector to get the actual reflected color: half3 ReflectionCol = texCUBElod(ReflectionSampler, float4(ReflectionVec, 0)); The cubemap I am sampling from is a RenderTarget with 6 flat faces. So my question is, given the 3d world position of an arbitrary 3d object, how can I make sure that I get accurate reflections of this object, when I re-render the cubemap. Should I build the ViewProjection matrix in a specific way? Or is there any other approach?

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• Error in my Separating Axis Theorem collision code

  - by Holly

  The only collision experience i've had was with simple rectangles, i wanted to find something that would allow me to define polygonal areas for collision and have been trying to make sense of SAT using these two links Though i'm a bit iffy with the math for the most part i feel like i understand the theory! Except my implementation somewhere down the line must be off as: (excuse the hideous font) As mentioned above i have defined a CollisionPolygon class where most of my theory is implemented and then have a helper class called Vect which was meant to be for Vectors but has also been used to contain a vertex given that both just have two float values. I've tried stepping through the function and inspecting the values to solve things but given so many axes and vectors and new math to work out as i go i'm struggling to find the erroneous calculation(s) and would really appreciate any help. Apologies if this is not suitable as a question! CollisionPolygon.java: package biz.hireholly.gameplay; import android.graphics.Canvas; import android.graphics.Color; import android.graphics.Paint; import biz.hireholly.gameplay.Types.Vect; public class CollisionPolygon { Paint paint; private Vect[] vertices; private Vect[] separationAxes; int x; int y; CollisionPolygon(Vect[] vertices){ this.vertices = vertices; //compute edges and separations axes separationAxes = new Vect[vertices.length]; for (int i = 0; i < vertices.length; i++) { // get the current vertex Vect p1 = vertices[i]; // get the next vertex Vect p2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; // subtract the two to get the edge vector Vect edge = p1.subtract(p2); // get either perpendicular vector Vect normal = edge.perp(); // the perp method is just (x, y) => (-y, x) or (y, -x) separationAxes[i] = normal; } paint = new Paint(); paint.setColor(Color.RED); } public void draw(Canvas c, int xPos, int yPos){ for (int i = 0; i < vertices.length; i++) { Vect v1 = vertices[i]; Vect v2 = vertices[i + 1 == vertices.length ? 0 : i + 1]; c.drawLine( xPos + v1.x, yPos + v1.y, xPos + v2.x, yPos + v2.y, paint); } } public void update(int xPos, int yPos){ x = xPos; y = yPos; } /* consider changing to a static function */ public boolean intersects(CollisionPolygon p){ // loop over this polygons separation exes for (Vect axis : separationAxes) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // loop over the other polygons separation axes Vect[] sepAxesOther = p.getSeparationAxes(); for (Vect axis : sepAxesOther) { // project both shapes onto the axis Vect p1 = this.minMaxProjection(axis); Vect p2 = p.minMaxProjection(axis); // do the projections overlap? if (!p1.overlap(p2)) { // then we can guarantee that the shapes do not overlap return false; } } // if we get here then we know that every axis had overlap on it // so we can guarantee an intersection return true; } /* Note projections wont actually be acurate if the axes aren't normalised * but that's not necessary since we just need a boolean return from our * intersects not a Minimum Translation Vector. */ private Vect minMaxProjection(Vect axis) { float min = axis.dot(new Vect(vertices[0].x+x, vertices[0].y+y)); float max = min; for (int i = 1; i < vertices.length; i++) { float p = axis.dot(new Vect(vertices[i].x+x, vertices[i].y+y)); if (p < min) { min = p; } else if (p > max) { max = p; } } Vect minMaxProj = new Vect(min, max); return minMaxProj; } public Vect[] getSeparationAxes() { return separationAxes; } public Vect[] getVertices() { return vertices; } } Vect.java: package biz.hireholly.gameplay.Types; /* NOTE: Can also be used to hold vertices! Projections, coordinates ect */ public class Vect{ public float x; public float y; public Vect(float x, float y){ this.x = x; this.y = y; } public Vect perp() { return new Vect(-y, x); } public Vect subtract(Vect other) { return new Vect(x - other.x, y - other.y); } public boolean overlap(Vect other) { if(y > other.x && other.y > x){ return true; } return false; } /* used specifically for my SAT implementation which i'm figuring out as i go, * references for later.. * http://www.gamedev.net/page/resources/_/technical/game-programming/2d-rotated-rectangle-collision-r2604 * http://www.codezealot.org/archives/55 */ public float scalarDotProjection(Vect other) { //multiplier = dot product / length^2 float multiplier = dot(other) / (x*x + y*y); //to get the x/y of the projection vector multiply by x/y of axis float projX = multiplier * x; float projY = multiplier * y; //we want to return the dot product of the projection, it's meaningless but useful in our SAT case return dot(new Vect(projX,projY)); } public float dot(Vect other){ return (other.x*x + other.y*y); } }

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• Bullet Physics - Casting a ray straight down from a rigid body (first person camera)

  - by Hydrocity

  I've implemented a first person camera using Bullet--it's a rigid body with a capsule shape. I've only been using Bullet for a few days and physics engines are new to me. I use btRigidBody::setLinearVelocity() to move it and it collides perfectly with the world. The only problem is the Y-value moves freely, which I temporarily solved by setting the Y-value of the translation vector to zero before the body is moved. This works for all cases except when falling from a height. When the body drops off a tall object, you can still glide around since the translate vector's Y-value is being set to zero, until you stop moving and fall to the ground (the velocity is only set when moving). So to solve this I would like to try casting a ray down from the body to determine the Y-value of the world, and checking the difference between that value and the Y-value of the camera body, and disable or slow down movement if the difference is large enough. I'm a bit stuck on simply casting a ray and determining the Y-value of the world where it struck. I've implemented this callback: struct AllRayResultCallback : public btCollisionWorld::RayResultCallback{ AllRayResultCallback(const btVector3& rayFromWorld, const btVector3& rayToWorld) : m_rayFromWorld(rayFromWorld), m_rayToWorld(rayToWorld), m_closestHitFraction(1.0){} btVector3 m_rayFromWorld; btVector3 m_rayToWorld; btVector3 m_hitNormalWorld; btVector3 m_hitPointWorld; float m_closestHitFraction; virtual btScalar addSingleResult(btCollisionWorld::LocalRayResult& rayResult, bool normalInWorldSpace) { if(rayResult.m_hitFraction < m_closestHitFraction) m_closestHitFraction = rayResult.m_hitFraction; m_collisionObject = rayResult.m_collisionObject; if(normalInWorldSpace){ m_hitNormalWorld = rayResult.m_hitNormalLocal; } else{ m_hitNormalWorld = m_collisionObject->getWorldTransform().getBasis() * rayResult.m_hitNormalLocal; } m_hitPointWorld.setInterpolate3(m_rayFromWorld, m_rayToWorld, m_closestHitFraction); return 1.0f; } }; And in the movement function, I have this code: btVector3 from(pos.x, pos.y + 1000, pos.z); // pos is the camera's rigid body position btVector3 to(pos.x, 0, pos.z); // not sure if 0 is correct for Y AllRayResultCallback callback(from, to); Base::getSingletonPtr()->m_btWorld->rayTest(from, to, callback); So I have the callback.m_hitPointWorld vector, which seems to just show the position of the camera each frame. I've searched Google for examples of casting rays, as well as the Bullet documentation, and it's been hard to just find an example. An example is really all I need. Or perhaps there is some method in Bullet to keep the rigid body on the ground? I'm using Ogre3D as a rendering engine, and casting a ray down is quite straightforward with that, however I want to keep all the ray casting within Bullet for simplicity. Could anyone point me in the right direction? Thanks.

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