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  • RK4 Bouncing a Ball

    - by Jonathan Dickinson
    I am trying to wrap my head around RK4. I decided to do the most basic 'ball with gravity that bounces' simulation. I have implemented the following integrator given Glenn Fiedler's tutorial: /// <summary> /// Represents physics state. /// </summary> public struct State { // Also used internally as derivative. // S: Position // D: Velocity. /// <summary> /// Gets or sets the Position. /// </summary> public Vector2 X; // S: Position // D: Acceleration. /// <summary> /// Gets or sets the Velocity. /// </summary> public Vector2 V; } /// <summary> /// Calculates the force given the specified state. /// </summary> /// <param name="state">The state.</param> /// <param name="t">The time.</param> /// <param name="acceleration">The value that should be updated with the acceleration.</param> public delegate void EulerIntegrator(ref State state, float t, ref Vector2 acceleration); /// <summary> /// Represents the RK4 Integrator. /// </summary> public static class RK4 { private const float OneSixth = 1.0f / 6.0f; private static void Evaluate(EulerIntegrator integrator, ref State initial, float t, float dt, ref State derivative, ref State output) { var state = new State(); // These are a premature optimization. I like premature optimization. // So let's not concentrate on that. state.X.X = initial.X.X + derivative.X.X * dt; state.X.Y = initial.X.Y + derivative.X.Y * dt; state.V.X = initial.V.X + derivative.V.X * dt; state.V.Y = initial.V.Y + derivative.V.Y * dt; output = new State(); output.X.X = state.V.X; output.X.Y = state.V.Y; integrator(ref state, t + dt, ref output.V); } /// <summary> /// Performs RK4 integration over the specified state. /// </summary> /// <param name="eulerIntegrator">The euler integrator.</param> /// <param name="state">The state.</param> /// <param name="t">The t.</param> /// <param name="dt">The dt.</param> public static void Integrate(EulerIntegrator eulerIntegrator, ref State state, float t, float dt) { var a = new State(); var b = new State(); var c = new State(); var d = new State(); Evaluate(eulerIntegrator, ref state, t, 0.0f, ref a, ref a); Evaluate(eulerIntegrator, ref state, t + dt * 0.5f, dt * 0.5f, ref a, ref b); Evaluate(eulerIntegrator, ref state, t + dt * 0.5f, dt * 0.5f, ref b, ref c); Evaluate(eulerIntegrator, ref state, t + dt, dt, ref c, ref d); a.X.X = OneSixth * (a.X.X + 2.0f * (b.X.X + c.X.X) + d.X.X); a.X.Y = OneSixth * (a.X.Y + 2.0f * (b.X.Y + c.X.Y) + d.X.Y); a.V.X = OneSixth * (a.V.X + 2.0f * (b.V.X + c.V.X) + d.V.X); a.V.Y = OneSixth * (a.V.Y + 2.0f * (b.V.Y + c.V.Y) + d.V.Y); state.X.X = state.X.X + a.X.X * dt; state.X.Y = state.X.Y + a.X.Y * dt; state.V.X = state.V.X + a.V.X * dt; state.V.Y = state.V.Y + a.V.Y * dt; } } After reading over the tutorial I noticed a few things that just seemed 'out' to me. Notably how the entire simulation revolves around t at 0 and state at 0 - considering that we are working out a curve over the duration it seems logical that RK4 wouldn't be able to handle this simple scenario. Never-the-less I forged on and wrote a very simple Euler integrator: static void Integrator(ref State state, float t, ref Vector2 acceleration) { if (state.X.Y > 100 && state.V.Y > 0) { // Bounce vertically. acceleration.Y = -state.V.Y * t; } else { acceleration.Y = 9.8f; } } I then ran the code against a simple fixed-time step loop and this is what I got: 0.05 0.20 0.44 0.78 1.23 1.76 ... 74.53 78.40 82.37 86.44 90.60 94.86 99.23 103.05 105.45 106.94 107.86 108.42 108.76 108.96 109.08 109.15 109.19 109.21 109.23 109.23 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 109.24 ... As I said, I was expecting it to break - however I am unsure of how to fix it. I am currently looking into keeping the previous state and time, and working from that - although at the same time I assume that will defeat the purpose of RK4. How would I get this simulation to print the expected results?

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  • An XEvent a Day (12 of 31) – Using the Extended Events SSMS Addin

    - by Jonathan Kehayias
    The lack of SSMS support for Extended Events, coupled with the fact that a number of the existing Events in SQL Trace were not implemented in SQL Server 2008, has no doubt been a key factor in its slow adoption rate. Since the release of SQL Server Denali CTP1, I have already seen a number of blog posts that talk about the introduction of Extended Events in SQL Server, because there is now a stub for it inside of SSMS. Don’t get excited yet, the functionality in CTP1 is very limited at this point,...(read more)

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  • An XEvent a Day (4 of 31) – Querying the Session Definition and Active Session DMV’s

    - by Jonathan Kehayias
    Yesterdays post, Managing Event Sessions , showed how to manage Event Sessions in Extended Events Sessions inside the Extended Events framework in SQL Server. In today's post, we’ll take a look at how to find information about the defined Event Sessions that already exist inside a SQL Server using the Session Definition DMV’s and how to find information about the Active Event Sessions that exist using the Active Session DMV’s. Session Definition DMV’s The Session Definition DMV’s provide information...(read more)

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  • An XEvent a Day (16 of 31) – How Many Checkpoints are Issued During a Full Backup?

    - by Jonathan Kehayias
    This wasn’t my intended blog post for today, but last night a question came across #SQLHelp on Twitter from Varun ( Twitter ). #sqlhelp how many checkpoints are issued during a full backup? The question was answered by Robert Davis (Blog|Twitter) as: Just 1, at the very start. RT @ 1sql : #sqlhelp how many checkpoints are issued during a full backup? This seemed like a great thing to test out with Extended Events so I ran through the available Events in SQL Server 2008, and the only Event related...(read more)

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  • An XEvent a Day (6 of 31) – Targets Week – asynchronous_file_target

    - by Jonathan Kehayias
    Yesterday’s post, Targets Week - ring_buffer , looked at the ring_buffer Target in Extended Events and how it outputs the raw Event data in an XML document.  Today I’m going to go over the details of the other Target in Extended Events that captures raw Event data, the asynchronous_file_target. What is the asynchronous_file_target? The asynchronous_file_target holds the raw format Event data in a proprietary binary file format that persists beyond server restarts and can be provided to another...(read more)

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  • An XEvent a Day (1 of 31) – An Overview of Extended Events

    - by Jonathan Kehayias
    First introduced in SQL Server 2008, Extended Events provided a new mechanism for capturing information about events inside the Database Engine that was both highly performant and highly configurable. Designed from the ground up with performance as a primary focus, Extended Events may seem a bit odd at first look, especially when you compare it to SQL Trace. However, as you begin to work with Extended Events, you will most likely change how you think about tracing problems, and will find the power...(read more)

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  • An XEvent a Day (8 of 31) – Targets Week – synchronous_event_counter

    - by Jonathan Kehayias
    Yesterday’s post, Targets Week - Bucketizers , looked at the bucketizer Targets in Extended Events and how they can be used to simplify analysis and perform more targeted analysis based on their output.  Today’s post will be fairly short, by comparison to the previous posts, while we look at the synchronous_event_counter target, which can be used to test the impact of an Event Session without actually incurring the cost of Event collection. What is the synchronous_event_counter? The synchronous_event_count...(read more)

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  • An XEvent a Day (2 of 31) – Querying the Extended Events Metadata

    - by Jonathan Kehayias
    In yesterdays post, An Overview of Extended Events , I provided some of the necessary background for Extended Events that you need to understand to begin working with Extended Events in SQL Server. After receiving some feedback by email (thanks Aaron I appreciate it), I have changed the post naming convention associated with the post to reflect “2 of 31” instead of 2/31, which apparently caused some confusion in Paul Randal’s and Glenn Berry’s series which were mentioned in the round up post for...(read more)

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  • gl_PointCoord always zero

    - by Jonathan
    I am trying to draw point sprites in OpenGL with a shader but gl_PointCoord is always zero. Here is my code Setup: //Shader creation..(includes glBindAttribLocation(program, ATTRIB_P, "p");) glEnableVertexAttribArray(ATTRIB_P); In the rendering loop: glUseProgram(shader_particles); float vertices[]={0.0f,0.0f,0.0f}; glEnable(GL_TEXTURE_2D); glEnable(GL_POINT_SPRITE); glEnable(GL_VERTEX_PROGRAM_POINT_SIZE); //glTexEnvi(GL_POINT_SPRITE, GL_COORD_REPLACE, GL_TRUE);(tried with this on/off, doesn't work) glVertexAttribPointer(ATTRIB_P, 3, GL_FLOAT, GL_FALSE, 0, vertices); glDrawArrays(GL_POINTS, 0, 1); Vertex Shader: attribute highp vec4 p; void main() { gl_PointSize = 40.0f; gl_Position = p; } Fragment Shader: void main() { gl_FragColor = vec4(gl_PointCoord.st, 0, 1);//if the coords range from 0-1, this should draw a square with black,red,green,yellow corners } But this only draws a black square with a size of 40. What am I doing wrong? Edit: Point sprites work when i use the fixed function, but I need to use shaders because in the end the code will be for opengl es 2.0 glUseProgram(0); glEnable(GL_TEXTURE_2D); glEnable(GL_POINT_SPRITE); glTexEnvi(GL_POINT_SPRITE, GL_COORD_REPLACE, GL_TRUE); glPointSize(40); glBegin(GL_POINTS); glVertex3f(0.0f,0.0f,0.0f); glEnd(); Is anyone able to get point sprites working with shader? If so, please share some code.

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  • An XEvent a Day (7 of 31) – Targets Week – bucketizers

    - by Jonathan Kehayias
    Yesterday’s post, Targets Week - asynchronous_file_target , looked at the asynchronous_file_target Target in Extended Events and how it outputs the raw Event data in an XML document. Continuing with Targets week today, we’ll look at the bucketizer targets in Extended Events which can be used to group Events based on the Event data that is being returned. What is the bucketizer? The bucketizer performs grouping of Events as they are processed by the target into buckets based on the Event data and...(read more)

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  • Reinventing the Wheel – Automating Data Consistency Checks with Powershell

    - by Jonathan Kehayias
    When I started in my current position at the beginning of the year, one of the first things that I did was to schedule a sit down with the various teams of Analysts that exist in our organization to find out more about their systems.  One thing I am always interested in is the manual processes that people do routinely that might be able to be automated.   A couple of the analyst mentioned that they routinely run queries in their systems to identify issues so that they can proactively...(read more)

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  • Reinventing the Wheel – Automating Data Consistency Checks with Powershell

    - by Jonathan Kehayias
    When I started in my current position at the beginning of the year, one of the first things that I did was to schedule a sit down with the various teams of Analysts that exist in our organization to find out more about their systems.  One thing I am always interested in is the manual processes that people do routinely that might be able to be automated.   A couple of the analyst mentioned that they routinely run queries in their systems to identify issues so that they can proactively...(read more)

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  • An XEvent a Day (9 of 31) – Targets Week – pair_matching

    - by Jonathan Kehayias
    Yesterday’s post, Targets Week – synchronous_event_counter , looked at the counter Target in Extended Events and how it could be used to determine the number of Events a Event Session will generate without actually incurring the cost to collect and store the Events.  Today’s post is coming late, I know, but sometimes that’s just how the ball rolls.  My original planned demo’s for today’s post turned out to only work based on a fluke, though they were very consistent at working as expected,...(read more)

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  • Don’t just P2V that server for Testing!

    - by Jonathan Kehayias
    If you use virtualization in your company, at some point in time you might be tempted to perform a Physical-To-Virtual conversion, also known as P2V.  The ability to create a complete working copy of a physical server as a virtual machine is really useful for migrating to a virtualized datacenter, but it can also wreak havoc in your environment if you use it to generate a copy of a server for testing and the only change you make is the name of the server.  The Problem: Consider that you...(read more)

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  • An XEvent a Day (20 of 31) – Mapping Extended Events to SQL Trace

    - by Jonathan Kehayias
    One of the biggest problems that I had with getting into Extended Events was mapping the Events available in Extended Events to the Events that I knew from SQL Trace. With so many Events to choose from in Extended Events, and a different organization of the Events, it is really easy to get lost when trying to find things. Add to this the fact that Event names don’t match up to Trace Event names in SQL Server 2008 and 2008 R2, and not all of the Events from Trace are implemented in SQL Server 2008...(read more)

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  • An XEvent a Day (27 of 31) – The Future - Tracking Page Splits in SQL Server Denali CTP1

    - by Jonathan Kehayias
    Nearly two years ago Kalen Delaney blogged about Splitting a page into multiple pages , showing how page splits occur inside of SQL Server.  Following her blog post, Michael Zilberstein wrote a post, Monitoring Page Splits with Extended Events , that showed how to see the sqlserver.page_split Events using Extended Events.  Eladio Rincón also blogged about Using XEvents (Extended Events) in SQL Server 2008 to detect which queries are causing Page Splits , but not in relation to Kalen’s blog...(read more)

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  • Some thoughts on the Virtualization Feedback in the SSWUG Newsletters

    - by Jonathan Kehayias
    Last Thursday, March 25, 2010, the topic of Virtualization of SQL Server came up in the SSWUG Newsletter , with Steven Wynkoop asking if peoples perceptions and experiences have changed since the last time he covered virtualizing SQL Server.  I unfortunately missed the last coverage of this topic, but it appears from the newsletter that there was a general consensus that “low-traffic solution could be fine, but if you had a heavy hitting application, the net advise was to avoid a virtual environment...(read more)

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  • Site Icon Hash in stackauth.com/sites

    - by Jonathan
    How do I cache the images properly, I think asked this somewhere before, but it hasn't affected me until gameing site went out of beta. It's HTTP headers or something isn't Ok I used George's answer but frankly the performance is awful, asking the server for the image everytime (even when it doesn't download the image) creates a small delay of about 1/2 a second but because of the huge number of SE sites, the 1/2s add up. Please, please consider adding a hash of the image to the stackauth.com/sites

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  • Some thoughts on the Virtualization Feedback in the SSWUG Newsletters

    - by Jonathan Kehayias
    Last Thursday, March 25, 2010, the topic of Virtualization of SQL Server came up in the SSWUG Newsletter , with Steven Wynkoop asking if peoples perceptions and experiences have changed since the last time he covered virtualizing SQL Server.  I unfortunately missed the last coverage of this topic, but it appears from the newsletter that there was a general consensus that “low-traffic solution could be fine, but if you had a heavy hitting application, the net advise was to avoid a virtual environment...(read more)

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  • Making Use of Plan Explorer in my own Environment

    - by Jonathan Kehayias
    Back in October 2010, I briefly blogged about the SQL Sentry Plan Explorer in my blog post wrap up for SQL Bits 7 and how impressed I was with what I saw from a Alpha demo standpoint from Greg Gonzalez ( Blog | Twitter ) while I was at SQLBits 7 in York.  To be 100% honest and transparent, Greg gave me early access to this tool after discussing it at SQLBits 7, and I had the opportunity to test a number of pre-Beta releases where I was able to offer significant feedback and submit bugs in the...(read more)

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  • SQL Server Installation Checklist

    - by Jonathan Kehayias
    The other night I was asked on Twitter by Todd McDonald (Twitter), for a build list for SQL Server 2005 and 2008.  My initial response was to provide a link to the SQL Server Build List Blog , which documents all of the builds of SQL Server and provides links to the KB articles associated with the builds.  However, this wasn’t what Todd was after, he actually wanted a reference for an installation checklist for SQL Server.  I have a number of these that I use in my job, and they vary...(read more)

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  • Times they are a changing…

    - by Jonathan Kehayias
    If you follow me on twitter ( @SQLSarg ), you already know that this has been a week of big announcements for me. Wednesday afternoon Paul Randal ( Blog | Twitter ) announced that I joined SQLskills.com as a full time employee, and Thursday afternoon, Joe Sack ( Blog | Twitter ) announced that I passed the Microsoft Certified Masters for SQL Server 2008 . As a part of my transition to working for SQLskills.com full time, I will be changing blogs over to the SQLskills.com site. You can read about...(read more)

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  • Want to know how SQL Server logging works?

    - by Jonathan Kehayias
    Have you ever wondered why SQL Server logging works the way it does?  While I have long understood the importance behind the SQL Server Transaction Log, I have never actually understood exactly why it works the way it does, despite having attended Paul Randal’s ( Blog / Twitter ) session at PASS Summit last year.  Over the last few months I have been working on writing a book on troubleshooting the most common problems that I see asked on the forums, and as a part of that I have been digging...(read more)

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  • Making Use of Plan Explorer in my own Environment

    - by Jonathan Kehayias
    Back in October 2010, I briefly blogged about the SQL Sentry Plan Explorer in my blog post wrap up for SQL Bits 7 and how impressed I was with what I saw from a Alpha demo standpoint from Greg Gonzalez ( Blog | Twitter ) while I was at SQLBits 7 in York.  To be 100% honest and transparent, Greg gave me early access to this tool after discussing it at SQLBits 7, and I had the opportunity to test a number of pre-Beta releases where I was able to offer significant feedback and submit bugs in the...(read more)

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  • ID number for sites [closed]

    - by Jonathan
    Possible Duplicate: please add a key fields to stackauth results It would be easier if sites each had an ID, it help with keeping track of them, not only in a numerical way (which is generally easier and smaller than using name strings). Also changes of site names (such as when a site progresses from beta, or decides it's name is not quite right during beta). Everything else has IDs so why not sites?

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