• If your application is already partially translated using Gettext it’s much easier to keep on using it rather than converting all your mo/po files to Qt’s format.
• Another significant advantage of Gettext is that it doesn’t have any dependencies (unlike Qt Linguist which creates a dependency to the Qt Framework) and thus allows creating more portable code.

So for these reasons, I’ve created a small library which parses and manages Gettext catalogues in Qt. The library includes a generic parser and a catalogue manager which can be used in any C++ project. On top of that, a Qt wrapper is provided for easy integration with the Qt framework.

The library can be downloaded from the Google Code project:

Download the Gettext library for the Qt Framework

Setting up and using the library is easy:

#include <QtGettext.h>

QtGettext::instance()->setLocale("cn_TW"); // Set the locale
QtGettext::instance()->setCatalogueName("catalogue"); // Set the name of the mo files
QtGettext::instance()->setCatalogueLocation("Data/Locales"); // Set the catalogue folder

QtGettext is now set to use the file in Data/Locales/cn_TW/catalogue.mo.

Also note that if this file is not available, QtGettext will try to load Data/Locales/cn/catalogue.mo (if available) as an alternative.

To mark a string for translation, simply call:

QtGettext::instance()->getTranslation("Some string to be translated");

Since this is rather long, a _() macro is also provided. It shortens the code to just:

_("Some string to be translated");

These two values in particular can be interesting:

fmt=22: This is an MP4 video in HD quality. On my tests, the resolution can go up to 1280 x 720.

fmt=18: This is a 480 pixels wide version that can be used in portable devices such as iPods.

In order to use this additional parameter, just add an argument to the constructFLVURL method:

// Set "format" to 22 for the high resolution version, or 18 for the iPod one. Or just
// leave to -1 for the low res version.
private function constructFLVURL (video_id:String, t:String, format:Number = -1):String {
  var str:String = "http://www.youtube.com/get_video.php?";
  str += "video_id=" + video_id;
  str += "&t=" + t;
  if (format >= 0) {
    str += "&fmt=" + format;
  }
  return str;
}

SHFILEOPSTRUCT operation;
operation.wFunc = FO_DELETE;
operation.pFrom = "c:\\file\to\delete.txt";
operation.fFlags = FOF_ALLOWUNDO;

SHFileOperation(&operation);

However, getting the extra large (48×48) and jumbo (256×256) icons introduced respectively by XP and Vista is slighly more complex. This is normally done by:

1. Getting the file information, in particular the icon index, for the given file using SHGetFileInfo
2. Retrieving the system image list where all the icons are stored
3. Casting the image list to an IImageList interface and getting the icon from there

Below is the code I’m using in Appetizer to retrieve the extra large icon. If needed it can easily be adapted to get the jumbo icon.

Update: To do the same thing in C#, see the link in the comments below.

#include <shlobj.h>
#include <shlguid.h>
#include <shellapi.h>
#include <commctrl.h>
#include <commoncontrols.h>

// Get the icon index using SHGetFileInfo
SHFILEINFOW sfi = {0};
SHGetFileInfo(filePath, -1, &sfi, sizeof(sfi), SHGFI_SYSICONINDEX);

// Retrieve the system image list.
// To get the 48x48 icons, use SHIL_EXTRALARGE
// To get the 256x256 icons (Vista only), use SHIL_JUMBO
HIMAGELIST* imageList;
HRESULT hResult = SHGetImageList(SHIL_EXTRALARGE, IID_IImageList, (void**)&imageList);

if (hResult == S_OK) {
  // Get the icon we need from the list. Note that the HIMAGELIST we retrieved
  // earlier needs to be casted to the IImageList interface before use.
  HICON hIcon;
  hResult = ((IImageList*)imageList)->GetIcon(sfi.iIcon, ILD_TRANSPARENT, &hIcon);

  if (hResult == S_OK) {
    // Do something with the icon here.
    // For example, in wxWidgets:
    wxIcon* icon = new wxIcon();
    icon->SetHICON((WXHICON)hIcon);
    icon->SetSize(48, 48);
  }
}

The application also supports the PortableApps USB format. So if you use Appetizer on a USB key in the PortableApps format, the application will detect it and automatically import all your applications along with the ‘Documents’, ‘Videos’, ‘Music’ and ‘Pictures’ folders.

Follow this link to download it.

svnadmin dump http://projectname.googlecode.com/svn > repodump

svnadmin: 'http://projectname.googlecode.com/svn' is an URL when it should be a path

One way around that is to use svnsync. This utility allows you to synchronize a local depository with a remote one. So the technique here is to create an empty repository, synchronize it with the remote one, and, finally, dump the local repository.

Here are some notes on how to do that:

1. Create a local repository

svnadmin create c:/repository

2. Add a “pre-revprop-change” hook to the local repository.

echo > c:\repository\hooks\pre-revprop-change.cmd

This is done by opening the “hooks” folder of the repository and adding a blank “pre-revprop-change.cmd” file into it. This will enable revision property change, which is necessary for synchronization.

On Linux and Mac, please follow the instructions in this comment.

3. Synchronize your new repository with the remote one:

svnsync init file:///c:/repository https://example.googlecode.com/svn

svnsync sync file:///c:/repository

Note: if you get this error: “Cannot initialize a repository with content in it“, it means that you’ve made some changes to the repository. In which case, the best thing to do is to just delete it and start over. The repository must be completely empty for the synchronization to work.

4. Finally, once the synchronization is done, simply dump your local repository:

svnadmin dump c:/repository > repodump

If everything went well, repodump should now contain the exact content of the remote repository.

Everything in one batch script

The batch script below allows to do all that in just one script. Simply replace REPO_PATH and REPO_PATH_NUX by the path to your repository and REPO_URL by the repository URL.

SET REPO_PATH=c:\your\local\repository
SET REPO_PATH_NUX=file:///c:/your/local/repository
SET REPO_URL=https://example.com/remote/repository

REM Uncomment the line below if the repository folder already exists
REM rmdir %REPO_PATH% /s/q
mkdir %REPO_PATH%
svnadmin create %REPO_PATH%
echo > %REPO_PATH%\hooks\pre-revprop-change.cmd
svnsync init %REPO_PATH_NUX% %REPO_URL%
svnsync sync %REPO_PATH_NUX%

1. Downloading the YouTube webpage where the video is embedded
2. Parsing it to extract the “t” and “video_id” parameters
3. Building the FLV URL using the old method.

Obviously, having to download and parse the YouTube web page is a lot slower than the previous method, which was just about reading the HTTP headers, but at least it works.

The code snippet below allows to do just that:

public function getFLVURL(iYouTubeVideoURL) {
  // iYouTubeVideoURL is the "watch" URL such as:
  // http://www.youtube.com/watch?v=OVVvAnU3m6E

  var loader:URLLoader = new URLLoader();
  var req:URLRequest = new URLRequest(iYouTubeVideoURL);
  loader.addEventListener(Event.COMPLETE, this.getFLVURL_complete);
  loader.addEventListener(IOErrorEvent.IO_ERROR, this.getFLVURL_ioError);
  loader.load(req);
}

private function getFLVURL_complete(iEvent) {
  var pageData:String = iEvent.currentTarget.data;

  // Get the "t" parameter
  var regex:RegExp = /"t": "(.*?)"/;
  var result:Array = pageData.match(regex);
  if (result.length < 2) {
    trace("Error parsing YouTube page: Couldn't get 't' parameter");
    return;
  }
  var param_t = result[1];

  // Get the "video_id" parameter
  regex = /"video_id": "(.*?)"/;
  result = pageData.match(regex);
  if (result.length < 2) {
    trace("Error parsing YouTube page: Couldn't get 'video_id' parameter");
    return;
  }
  var param_video_id = result[1];

  var flvURL:String = constructFLVURL(param_video_id, param_t);
  trace("Here's the FLV URL: " + flvURL);

  flvTextBox.text = flvURL;
}

private function getFLVURL_ioError(iEvent) {
  var loader = iEvent.target;
  trace("Couldn't download YouTube web page: " + iEvent);
}

private function constructFLVURL (video_id:String, t:String):String {
  var str:String = "http://www.youtube.com/get_video.php?";
  str += "video_id=" + video_id;
  str += "&t=" + t;
  return str;
}

Update (01/12/2008):

As it turns out, this technique only works from Adobe AIR and not from a web page. This is because YouTube doesn’t allow crossdomain calls, which means that if a Flash application tries to fetch one of their pages, it will fail with a security error.

To go around this issue, it is possible to use a simple PHP stub file, which fetches the YouTube page and send it back to Flash. The PHP file would be as follow:

<?php

$url = urldecode($_GET["url"]);
header("Content-Type: text/html");
readfile($url);

?>

Then, in Flash, instead of calling the YouTube URL directly, you call the PHP URL:

var youTubeURL = "http://uk.youtube.com/watch?v=bxfpMGLMZ7Y"
var stubURL = "http://example.com/stub.php?url=" + escape(youTubeURL)
getFLVURL(stubURL);

This small demo illustrates all that. The source code with PHP stub is available here.

Update (19/03/2009):

I’ve posted a follow up to this post with some information on how to get the HD quality version of the videos:
Get the URL of an HD-quality Youtube video.

I’ve implemented a version of it in PHP. Just copy and paste the code below and call createBase64UUID()

function createBase64UUID() {
  $uuid = com_create_guid();
  $byteString = "";

  // Remove the dashes from the string
  $uuid = str_replace("-", "", $uuid);

  // Remove the opening and closing brackets
  $uuid = substr($uuid, 1, strlen($uuid) - 2); 

  // Read the UUID string byte by byte
  for($i = 0; $i < strlen($uuid); $i += 2) {
    // Get two hexadecimal characters
    $s = substr($uuid, $i, 2);
    // Convert them to a byte
    $d = hexdec($s);
    // Convert it to a single character
    $c = chr($d);
    // Append it to the byte string
    $byteString = $byteString.$c;
  } 

  // Convert the byte string to a base64 string
  $b64uuid = base64_encode($byteString);
  // Replace the "/" and "+" since they are reserved characters
  $b64uuid = str_replace("/", "_", $b64uuid);
  $b64uuid = str_replace("+", "-", $b64uuid);
  // Remove the trailing "=="
  $b64uuid = substr($b64uuid, 0, strlen($b64uuid) - 2); 

  return $b64uuid;
}

When this happens, there are a number of things you can try to get it back:

» Use Widget Cleaner

This is the simplest solution. Just close the widget then clear the widget preferences using Widget Cleaner. This will reset all the widget preferences to their initial values, including the dimensions and positions of the windows, so the widget should be visible again.

However, it might not always work since Widget Cleaner currently can’t “detect” all the widgets. In that case, try the second solution.

» Check the widget Preferences

Some widget authors add an option in the Preferences to reset the window positions. You can access the Preferences by clicking on the Gear button in the Dock icon, then look for any option that might allow you to reset the windows. If such an option is available, use it and the widget should be visible again.

» Delete the registry settings

The last option is more complicated and only works on Windows, however it will definitely fix the issue in all cases. In order to reset the widget preferences (and therefore its visibility), you can open the registry editor and manually delete the appropriate settings. To do so, follow these instructions:

1. Press the Windows Start button and click on Run
2. Type “regedit” (without the quotes)
3. Navigate to this folder: “HKEY_CURRENT_USER\Software\Yahoo\WidgetEngine\Widgets”
4. Here you will find a number of subfolders. Each of them contains the Preferences of a widget.
5. Find the name of the widget you are looking for, then right-click on its subfolder and select “Delete”.

For example, this is what you should see if you wish to delete the preferences of the “Day Planner Calendar” widget:

After doing so, restart your widget and normally it should be visible again.

• Download the .NET / C# source code
• Download the .NET demo

Background

To detect if two polygons are intersecting, we use the Separating Axis Theorem. The idea is to find a line that separates both polygons - if such a line exists, the polygons are not intersecting (Fig. 1). The implementation of this theorem is relatively simple, and could be summed up in this pseudo code:

• For each edge of both polygons:
  • Find the axis perpendicular to the current edge.
  • Project both polygons on that axis.
  • If these projections don't overlap, the polygons don't intersect (exit the loop).

This can be easily extended to deal with moving polygons by adding one additional step. After having checked that the current projections do not overlap, project the relative velocity of the polygons on the axis. Extend the projection of the first polygon by adding to it the velocity projection (Fig. 2). This will give you the interval spanned by the polygon over the duration of the motion. From there, you can use the technique used for static polygons: if the projections of polygons A and B don’t overlap, the polygons won’t collide. (NB: However, remember that if the intervals do overlap, it doesn’t necessarily mean that the polygons will collide. We need to do the test for all the edges before knowing that.)

Once we have found that the polygons are going to collide, we calculate the translation needed to push the polygons apart. The axis on which the projection overlapping is minimum will be the one on which the collision will take place. We will push the first polygon along this axis. Then, the amount of translation will simply be the amount of overlapping on this axis (Fig. 3).

That is it! Now, each time a collision occurs, the first polygon will nicely slide along the surface of the other polygon.

Figure 1: Projections of the polygons onto an axis.

Figure 2: Projections for moving polygons.

Figure 3: Find the minimum interval overlapping, then calculate the translation required to push the polygons apart.

Using the code

The PolygonCollision() function does all of the above, and returns a PolygonCollisionResult structure containing all the necessary information to handle the collision:

// Structure that stores the results of the PolygonCollision function

public struct PolygonCollisionResult {
    // Are the polygons going to intersect forward in time?

    public bool WillIntersect;
    // Are the polygons currently intersecting?

    public bool Intersect;
    // The translation to apply to the first polygon to push the polygons apart.

    public Vector MinimumTranslationVector;
}

Two helper functions are used by the PolygonCollision function. The first one is used to project a polygon onto an axis:

// Calculate the projection of a polygon on an axis

// and returns it as a [min, max] interval

public void ProjectPolygon(Vector axis, Polygon polygon,
                           ref float min, ref float max) {
    // To project a point on an axis use the dot product

    float dotProduct = axis.DotProduct(polygon.Points[0]);
    min = dotProduct;
    max = dotProduct;
    for (int i = 0; i < polygon.Points.Count; i++) {
        dotProduct = polygon.Points[i].DotProduct(axis);
        if (d < min) {
            min = dotProduct;
        } else {
            if (dotProduct> max) {
                max = dotProduct;
            }
        }
    }
}

The second one returns the signed distance between two given projections:

// Calculate the distance between [minA, maxA] and [minB, maxB]

// The distance will be negative if the intervals overlap

public float IntervalDistance(float minA, float maxA, float minB, float maxB) {
    if (minA < minB) {
        return minB - maxA;
    } else {
        return minA - maxB;
    }
}

Finally, here is the main function:

// Check if polygon A is going to collide with polygon B.

// The last parameter is the *relative* velocity 

// of the polygons (i.e. velocityA - velocityB)

public PolygonCollisionResult PolygonCollision(Polygon polygonA,
                              Polygon polygonB, Vector velocity) {
    PolygonCollisionResult result = new PolygonCollisionResult();
    result.Intersect = true;
    result.WillIntersect = true;

    int edgeCountA = polygonA.Edges.Count;
    int edgeCountB = polygonB.Edges.Count;
    float minIntervalDistance = float.PositiveInfinity;
    Vector translationAxis = new Vector();
    Vector edge;

    // Loop through all the edges of both polygons

    for (int edgeIndex = 0; edgeIndex < edgeCountA + edgeCountB; edgeIndex++) {
        if (edgeIndex < edgeCountA) {
            edge = polygonA.Edges[edgeIndex];
        } else {
            edge = polygonB.Edges[edgeIndex - edgeCountA];
        }

        // ===== 1. Find if the polygons are currently intersecting =====

        // Find the axis perpendicular to the current edge

        Vector axis = new Vector(-edge.Y, edge.X);
        axis.Normalize();

        // Find the projection of the polygon on the current axis

        float minA = 0; float minB = 0; float maxA = 0; float maxB = 0;
        ProjectPolygon(axis, polygonA, ref minA, ref maxA);
        ProjectPolygon(axis, polygonB, ref minB, ref maxB);

        // Check if the polygon projections are currentlty intersecting

        if (IntervalDistance(minA, maxA, minB, maxB) > 0)\
            result.Intersect = false;

        // ===== 2. Now find if the polygons *will* intersect =====

        // Project the velocity on the current axis

        float velocityProjection = axis.DotProduct(velocity);

        // Get the projection of polygon A during the movement

        if (velocityProjection < 0) {
            minA += velocityProjection;
        } else {
            maxA += velocityProjection;
        }

        // Do the same test as above for the new projection

        float intervalDistance = IntervalDistance(minA, maxA, minB, maxB);
        if (intervalDistance > 0) result.WillIntersect = false;

        // If the polygons are not intersecting and won't intersect, exit the loop

        if (!result.Intersect && !result.WillIntersect) break;

        // Check if the current interval distance is the minimum one. If so store

        // the interval distance and the current distance.

        // This will be used to calculate the minimum translation vector

        intervalDistance = Math.Abs(intervalDistance);
        if (intervalDistance < minIntervalDistance) {
            minIntervalDistance = intervalDistance;
            translationAxis = axis;

            Vector d = polygonA.Center - polygonB.Center;
            if (d.DotProduct(translationAxis) < 0)
                translationAxis = -translationAxis;
        }
    }

    // The minimum translation vector

    // can be used to push the polygons appart.

    if (result.WillIntersect)
        result.MinimumTranslationVector =
               translationAxis * minIntervalDistance;

    return result;
}

The function can be used this way:

Vector polygonATranslation = new Vector();

PolygonCollisionResult r = PolygonCollision(polygonA, polygonB, velocity);

if (r.WillIntersect) {
  // Move the polygon by its velocity, then move

  // the polygons appart using the Minimum Translation Vector

  polygonATranslation = velocity + r.MinimumTranslationVector;
} else {
  // Just move the polygon by its velocity

  polygonATranslation = velocity;
}

polygonA.Offset(polygonATranslation);

Reference

• GPWiki - Polygon Collision
• Olivier’s code junkyard