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Creating a UEFI + BIOS multi-boot + Data flash drive

This post is slightly different - It is mainly to document the process of creating a flash drive that boots into Grub2 with both a BIOS and UEFI firmware that you can also store data on in Windows.

First of all, you need to make sure that your flash drive has a GPT (GUID Partition Table) and not an MBR. If you don't know, it is safe to assume that you are currently using a MBR (Master Boot Record).

Switching to a GPT

If you don't have a GPT, then you need to backup the contents of your flash drive because you will need to wipe it clean in order to switch it over.

Make sure you are in a linux environment (start a virtual machine and pass the flash drive in if you don't have one). Work out where your flash drive is (in this instance ours is at /dev/sdx) and then execute the following commands:

sudo apt-get install gdisk
sudo sgdisk --zap-all /dev/sdx

The above will wipe all partition tables from the device. Before continuing, you may need to remove and re-plug-in the flash drive you are working in. Run this pair of commands to add a "Microsoft basic data" partition, and format it with FAT32:

sudo sgdisk --new=1:0:0 --typecode=1:0700 /dev/sdx
sudo mkfs.vfat -F32 -n GRUB2EFI /dev/sdx1

The type code 0700 is the bit that determines the type of partition that we are creating. In this case, we are creating a Microsoft basic data partition. The tutorial I followed (see the source at the bottom) set the type ef00, which is a EFI System Partition. If you experience problems, try changing the type to this.

Next up, we need to mount the new partition. Do it like this:

sudo mount -t vfat /dev/sdb1 /mnt -o uid=1000,gid=1000,umask=022

The above will mount it to the directory /mnt. next, you need to go to the first source below and download the zip that can be found under the text pack with all necessary files for you to modify as you need. Extract this to the root of the flash drive (/mnt in our case):

cd ~/Downloads/
unzip usb-pack_efi.zip
rsync -auv usb-pack_efi/ /mnt

Next, we need to install grub2 in BIOS mode. It will complain horribly, but apparently it works :D

sudo grub-install --force --removable --boot-directory=/mnt/boot /dev/sdb

Now you should have a flash drive with Grub2 installed, that you can also see in Windows!

Credit to sysmatck of ubuntuforums.org sudodus for the guide.

Sources:

  1. How to Create a EFI/UEFI GRUB2 Multiboot USB Drive to boot ISO images

File System Performance in PHP

While writing pepperminty wiki, I started seeing a rather nasty in crease in page load times. After looking into it, I drew the conclusion that it must have been the file system that caused the problem. At the time, I had multiple calls to PHP's glob function to find all the wiki pages in the current directory, and I was checking to see if the wiki page existed before reading it into memory.

The solution: A page index. To cut down on the number of reads from the file system, I created a json file that containedd inforamtion about every page on the wiki. This way, it only needs to check the existence of and read in a single file before it can start rendering any one page. If the page index doesn't exist, it is automatically rebuilt with the glob function to find all the wiki pages in the current directory.

In short: to increase the performance of your PHP application, try to reduce the number of reads (and writes!) to the file system to an absolute minimum.

I still need to update the code to allow users to delete pages via the GUI though, because at present you have to have access to the server files to delete a page and then remove it from the page index manually.

Behind the Parallax Stars

Unfortunately I have been busy, so I have been unable to write this post up until now. Anyway, welcome to the second technical post on this blog. This time, we will be looking behind the Parallax Stars.

The FPS and rendering time graphs are drawn by a slightly modified version of stats.js, by mrdoob. It's original github repository can be found here, and the slightly modified version can be found here. The modifications I made allow both the FPS graph and the rendering time graphs to be displayed at once.

The interesting code that makes the stars work is found in stars.js. The function is a constructor that returns an containing everything needed to make the stars appear and animate.

this.build = function() {
    this.data = [];

    for (var i = 0; i < this.number; i++)
    {
        this.data[i] = new star();
    }

    if(this.depthsort == true)
    {
        this.data.sort(depthsort);
    }
};
function star()
{
    this.z = Math.random()*(0.7) + 0.3;

    this.x  = rand(canvas.width);
    this.y  = rand(canvas.height);
    this.radius = Math.floor(this.z * 7);

    var r, g;
    r = rand(200, 255);
    g = rand(200, g - 20);

    this.colour = "rgb(" + r + ", " + g + ", " + 0 + ");"

    this.speed = this.z * 3;
}

The build() function contains some setup code that populates an array with stars, which are constructed by a different function, star(). Each star is assigned an x, y, and z co-ordinate. The x and y co-ordinates determine it's position on the screen. and the z co-ordinate determines it's size and speed. The stars are also given a colour too. The function rand() is a small utility function I sometimes use for generating random numbers:

// EXAMPLES:
// rand(256) returns a whole number between or equal to 0 and 255
// rand(100,201) returns a whole number between or equal to 100 and 200
// rand() returns a decimal between or equal to 0 and less than 1
function rand()
{
    // takes 0-2 arguments (numbers)
    var args = arguments, num;
    if (args[0] && !args[1]) { 
        num = Math.floor(Math.random()*(args[0]));
    } else if (args[0] && args[1]) {
        num = Math.floor(Math.random()*(args[1]-args[0])) + args[0];
    } else {
        num = Math.random();
    }
    return num;
}

The array that hold all the stars is also depth sorted before we start and on each frame to keep the stars in order since stars are leaving the screen and new one coming onto the screen on every frame. The standard array .sort() function is used, along with a custom sort function:

function depthsort(a,b) {
    if(a.z < b.z)
        return -1;
    if(a.z > b.z)
        return 1;
    else
        return 0;
}

The updates that happen every frame are split into two different functions. step() deals with incrementing co-ordinates and keeping the depth sorting up to date, and render() takes the current state and renders it on the canvas.

this.step = function() {
    for (var i = 0; i < this.data.length - 1; i ++)
    {
        this.data[i].x += this.data[i].speed;

        if(this.data[i].x > canvas.width + this.data[i].radius + 1)
        {
            this.data[i].x = new star();
            this.data[i].x = -this.data[i].radius - 1;

            if(this.depthsort == true)
            {
                this.data.sort(depthsort);
            }
        }
    }
}

The this.data array holds all of the stars. For each star, it's x value is incremented by it's speed. If this moves the star off the screen, we replace it with a new star that starts off at the left hand side. The stars are then depth sorted again to keep all the further away stars behind the stars that are (supposed to be) closer to the front.

this.render = function() {
    context.clearRect(0, 0, canvas.width, canvas.height);

    for (var i = 0; i < this.data.length - 1; i ++)
    {
        context.globalAlpha = 1;
        context.globalCompositeOperation = "destination-out";

        context.beginPath();
        context.arc(this.data[i].x, this.data[i].y, this.data[i].radius, 0, Math.PI*2, true);
        context.closePath();
        context.fill();

        context.globalAlpha = this.data[i].z;
        context.globalCompositeOperation = "source-over";

        context.fillStyle = this.data[i].colour;

        context.beginPath();
        context.arc(this.data[i].x, this.data[i].y, this.data[i].radius, 0, Math.PI*2, true);
        context.closePath();
        context.fill();
    }
}

To start off the rendering, the canvas is cleared. After that, For each star, a hole in the canvas is cleared with the destination-out drawing mode. The reason for this is that the z co-ordinate is also used as an alpha value for each star to make it dimmer the further away it is. This gives a slightly more realistic 3d appearance. After clearing a hole, the drawing mode is rest to the default (source-over), and the alpha and fill colours are set up according to the star's current z co-ordinates and colour respectively. Then the star is drawn. Since when this script was written we did not have a canvas drawing function to draw an ellpise, the context.arc(this.data[i].x, this.data[i].y, this.data[i].radius, 0, Math.PI*2, true); code is used to draw circles via context.beginPath() and context.fill().

Finally, One nice neat update() function is provided that calls render() and step() in sequence:

this.update = function() {
    this.render();
    this.step();
}

That concludes this technical post! If you have any questions, please post them below and I will try my best to answer them.

How the trianglfier works

This technical post will be all about how the recently released Image Trianglfier works.

The visible <img /> element that shows the original image has a function called drawimage() attached to it's load event such that every time a new image is selected, it updates the first of two invisible <canvas> elements:

The above code takes the newly loaded image, calculates new dimensions for the image if either side of the image exceeds 1000 pixels, and draws it to the imagecache canvas.

When the render button is clicked, a second <canvas> with an id of main is put to work:

After grabbing a few references to the main canvas (the one we want to draw the image on) and the imagecache canvas (the one with the scaled original image on it), we then extract the pixeldata of the imagecache canvas on line #5 of the gist so that we can use it to out colours for each triangle later.

We then enter a for loop and start drawing triangles. A triangle is drawn by picking 3 random points within a box with a diameter set by the trianglesize setting, and setting these to be the 3 vertices. The central point of the box is picked on lines #17 and #18, and the 3 points are picked on lines #20 through #33.

The colour of the triangle is also set at this point by averaging the colour in a box centred on the central point we picked on lines #17 and #18. This boxes size is set by the coloursampleradius setting. The algorithm is passed the pixeldata we extracted earlier, along with the canvas size, the coordinates of the centralpoint, and the box's diameter and calculates the average by simply adding up all the colour components of each pixel in the box and dividing it by the number pixels it added up the components of. This algorithm is not particularly optimised and is one of the main causes for the hanging that occurs during the rendering process. This algorithm can be found here.

After the colour and point coordinate calculations, all that is left to do is draw the triangle itself. This is done on lines #36 to #42.

After all the triangles have been drawn, the rendering is complete. The finished image is then converted into a jpeg image is displayed on the right hand side.

Got a question? Spotted a mistake? Leave a comment below.

Suggestions for improvement are always appreciated

Art by Mythdael