August | 2009 | Can you believe I have another blog?

Archive for August, 2009

links for 2009-08-24

August 25, 2009

SenderScore.org

A free reputation based spam RBL.

(tags: spam antispam sysadmin email free online lookup reputation)
Online LaTeX Equation Editor

A site where you can interactively construct complicated mathematical equations and generate bitmaps and latex source.

(tags: blog programming online webdesign tools latex equation mathematics html equations)

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An easy way to build equation bitmaps

August 23, 2009

Here is a site that provides an easy way to generate equation bitmaps online.

http://www.codecogs.com/components/equationeditor/equationeditor.php

In HTML and actually many environments there is no good way to write complex mathematical equations. Many people fall back to latex to generate bitmaps. This site lets you interactively click on the parts of the equation and generates both the latex and corresponding bitmaps.

So for example, I was trying to save some of my Kalman filter notes. I click edited the Predictor equation and it generated this bitmap:

And it generated this latex:

X^{*}_{n+1,n} = \phi X^{*}_{n,n}

Pretty nice.

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Simple OpenGL Texture Example

August 20, 2009

Here is a simple example of code to use an OpenGL Texture.

// Apple gcc program0.c -framework opengl -framework glut
// A simple OpenGL and glut program 
#include  /* Header File For The GLut Library*/
#include 

//
// You need to generate the texture data that you are going to
// use. GIMP will convert a bitmap, jpg, etc. to a "C" structure
// that you can use almost directly.
//


// GIMP RGBA C-Source image dump (f35_schem_02_edit_4.c) 

static const struct {
  uint32_t     width;
  uint32_t     height;
  uint32_t     bytes_per_pixel; /* 3:RGB, 4:RGBA */
  uint8_t      pixel_data[128 * 128 * 4 + 1];
} planform = {
  128, 128, 4,
  "\377\377\377\377\377\377\377"
  "\377\377\377\377\377\377\377"
  "\377\377\377\377\377\377\377"
  "\377\377\377\377\377\377\377\377"
  // ... much of the texture deleted
  "\377\377\377\377\377\377\377"
  "\377\377\377\377\377\377",
};


// The routine to draw the screen
void display() { 
    // A value to hold our texture handle
    static uint32_t texture = 0;
    static int32_t  firstTimeDone = 0;

    // Clear the display
    glClear(GL_COLOR_BUFFER_BIT); 
    // Set the color to white
    glColor3f(1.0, 1.0, 1.0);
    // Setup the coordinates to what I am used to
    glOrtho(-1.0, 1.0, -1.0, 1.0, -1.0, 1.0); 

    // Get a texture number if we dont have one
    if (!firstTimeDone)
    {
        // Get a texture number
        glGenTextures(1, &texture);

        // Tell OpenGL that we want to use that texture
        glBindTexture(GL_TEXTURE_2D, texture);

        // You have to tell OpenGL how to take the raw bitmap data
        // in the structure above to put it into a texture. We
        // do this with a glTexImage2D() call. We will describe the
        // structure above and how we want it stored internally in 
        // OpenGl.
        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, planform.width, planform.height, 
            0, GL_RGBA, GL_UNSIGNED_BYTE, planform.pixel_data);

        // OpenGl lets you describe how you want to scale the 
        // texture data when the destination is bigger or smaller
        // than the original texture data. In this case, we want
        // simple linear scaling.
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);

        // First Time is done
        firstTimeDone = 1;
    }
    else
    {
        // Tell OpenGL that we want to use that texture
        glBindTexture(GL_TEXTURE_2D, texture);
    }

    // We are going to put the texture on a 2D surface, much
    // like we would apply a decal.
    glTexEnvi(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_DECAL);

    // Normally you leave GL_TEXTURE_2D turned off unless 
    // you are applying a decal to a surface. Since we are
    // doing that, we turn it on here.
    glEnable(GL_TEXTURE_2D);

    // Draw the square
    glBegin(GL_POLYGON);

    // Here we want to associate a point in the texture with the
    // vertex we are drawing on the screen. So these are paired up.
    glTexCoord2f(0.0f, 1.0f); glVertex2f(-0.5, -0.5);
    glTexCoord2f(0.0f, 0.0f); glVertex2f(-0.5, 0.5);
    glTexCoord2f(1.0f, 0.0f); glVertex2f(0.5, 0.5);
    glTexCoord2f(1.0f, 1.0f); glVertex2f(0.5, -0.5);

    // End of the list of verticies
    glEnd();
    // Turn texture drawing back off, normally we leave if off.
    glDisable(GL_TEXTURE_2D);

    // Flush the data. In many drivers, this causes the
    // actual draw to the Frame Buffer.
    glFlush();
} 

int main(int argc, char **argv) { 
    // A minimal GLUT setup to get GLUT up and going.
    // If you use EGL or some other windowing system
    // other than GLUT, you need to replace this.
    glutInit(&argc, argv); 
    glutInitWindowSize(512,512); 
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); 
    glutCreateWindow("The glut hello world program"); 
    glutDisplayFunc(display); 
    glClearColor(0.0, 0.0, 0.0, 1.0); 
    glutMainLoop(); // Infinite event loop 
    return 0; 
}

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Parsing a binary file in Perl

August 20, 2009

This is an example of how to parse a binary file in perl. This reads an mpeg-2 file and chops the first 8 Mbyte chunk out of the file, closing at the next clean sequence header boundary.

#! perl

use Getopt::Std;

use strict;

sub chopMpegFile
{
    my ($fileName) = @_;

    open FILE, "$fileName" or die "Could not open file: $!\n";
    open OUT,  ">out.mpg"   or die "Could not open file: $!\n";

    binmode(FILE);
    binmode(OUT);

    my $buffer = '';
    my $count  = 0;
    my $done   = 0;

    while ((! $done) && ( sysread(FILE, $buffer, 4) ))
    {
        my $value = unpack 'N', $buffer;
        if (($count++ > 2 * 1024 * 1024) && ($value == 0x000001b3))
        {
            print "Closing file.\n";
            $done = 1;
        }
        else
        {
            syswrite(OUT, $buffer, 4);
        }
        if (($count % (1024*100)) == 0)
        {
            print "Count $count\n";
        }
    }
    close(FILE);
    close(OUT);
}


my @args = splice(@ARGV, 0);
foreach my $arg (@args)
{
    print "$arg\n";
    &chopMpegFile($arg);
}