06 Nov 2019

feedPlanet Maemo

Fast wire-frame rendering with OpenCV

Lets say you have mesh data in the typical format, triangulated, vertex buffer and index buffer. E. g. something like

>>> vertices

[[[ 46.27500153  19.2329998   48.5       ]]

 [[  7.12050009  15.28199959  59.59049988]]

 [[ 32.70849991  29.56100082  45.72949982]]


>>> indices

[[1068 1646 1577]
 [1057  908  938]
 [ 420 1175  237]

Typically you would need to feed it into OpenGL to get an image out of it. However, there are occasions when setting up OpenGL would be too much hassle or when you deliberately want to render on the CPU.

In this case we can use the OpenCV to do the rendering in two function calls as:

img = np.full((720, 1280, 3), 64, dtype=np.uint8)

pts2d = cv2.projectPoints(vertices, rot, trans, K, None)[0].astype(int)
cv2.polylines(img, pts2d[indices], True, (255, 255, 255), 1, cv2.LINE_AA)

See the documentation of cv2.projectPoints for the meaning of the parameters.

Note how we only project each vertex once and only apply the mesh topology afterwards. Here, we just use the numpy advanced indexing as pts2d[indices] to perform the expansion.

This is pretty fast as well. The code above only takes about 9ms on my machine.

In case you want filled polygons, this is pretty easy as well

for face in indices:
    cv2.fillConvexPoly(img, pts2d[face], (64, 64, 192))

However, as we need to a python loop in this case and also have quite some overdraw, it is considerable slower at 20ms.

Of course you can also combine both to get an image like in the post title.

From here on you can continue to go crazy and compute face normals to do culling and shading.

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06 Nov 2019 4:26pm GMT

02 Nov 2019

feedPlanet Maemo

Xiaomi AirDots Pro 2 / Air2 Review

So after having made fun of people for "wearing toothbrushes", I finally came to buy such headphones for myself.

Having used non-true wireless Bluetooth headphones before I was curious what the usability advantage would feel like.

Here I went for the Xiaomi AirDots Pro 2 aka Air2 which I could grab for 399 Yuan which is about 51€, which seems like the right price-point for this kind of accessoire.

Keep in mind that the built-in battery only survives so many charging cycles and once it dies you can throw them away.

The Airdots (right) compared to the Airpods (middle) and the Oral-B Precision Clean

The initial feeling of using true wireless headphones is surprisingly relieving - there is simply no cord to untangle or to be aware of while wearing.
This is especially true during phone calls, where one needs to keep the microphone aligned.

The downside is that the headphones are too small to accommodate any buttons for volume and playback control.

The Air 2 kind of make up for it by automatically connecting to your phone once you put them on and by automatically pausing the music when you put one out of the ear. This is achieved by a built-in brightness sensor.

Furthermore you have double-tap actions, which default to play/ pause on the right headphone and launching the voice assistant (e.g. Google Assistant) on the left headphone.

The battery life is stated with 4 hours per-charge with 2 extra charges in the case. I could confirm those on a long distance flight.

Compared to the Airpods 2

Looking at the feature-list above or simply at the images, the similarity to the Apple Airpods is apparent.

Out of curiosity I borrowed some from friend for comparison. The most important point is probably sound quality. Here we found the two virtually in-distinguishable. But keep in mind that we only did a quick test and did not use them extensively.

The second point is likely the form. Here, both earphones have the same ear-part and only differ by the shaft. So if one fits your ear, so should the other.

The shaft however is considerably wider on the Airdots. This is less apparent when viewed from the side as the thickness is similar.

For me, the more important difference is being able to control the headphones from my Android smartphone. This is currently not possible with the Airpods, while there is some way for the Airdots;

Companion app & Software integration

To control the earphones, you have to sideload the Xiao Ai Lite App. The main purpose of it is to provide the Xiaomi voice assistant and the Air2 options likely just ended up there as they offer an always-on assistant integration just like the Airpods.

It handles firmware updates and allows you to configure the douple-tap action per earphone as well as displaying the charging status of the earphones and the case. By default android will only display the charging status of the least charged earphone.

Furthermore, you can use the fast-paring if the app is running. Here, it is sufficient to hold the earphone case close to the phone and just open it. The app will ask for confirmation. This is only slightly more convenient then holding the pairing button and using the normal bluetooth pairing procedure.

The downside is that the app is currently only available in Chinese and consequently the voice assistant only works with Chinese.

Below you find some views of the earphone related settings translated by with google lens

I tried out some voice commands via google translate and everything works as it should. However if you are not fluent in chinese it is far from practical. Most people should disable the assistant in the settings to avoid accidentally triggering it.

A serious advantage of Xiomi/ Huawei phones is the availability of the LHDC Bluetooth Codec which offers a superior bandwidth and latency.
While I am fine with the bandwidth provided by AAC when listening to music, there is still a noticeable and annoying delay when watching videos and playing games.

Active Noise Cancellation

The firmware upgrade to v2.6.9.0 significantly improved the active noise cancellation and thus general sound quality.

There is a very noticeable noise reduction compared to v2.6.2.0 - especially in the lower frequencies; things like your footsteps get filtered out. Higher frequencies like car motor sounds are still perceivable though. This is however a good compromise for me.

Charging issues

Over time I noticed that the left earphone consistently runs out of battery before the right one.
The issue seems to be that it discharges while stored inside the case. Putting it in and out resolves the issue - but only until it is fully charged. This makes keeping the earphones pre-charged and ready quite an issue.

Hopefully this can be addressed with a future firmware update. (reproduced with firmwares up to v2.7.1.0)

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02 Nov 2019 3:56pm GMT

13 Oct 2019

feedPlanet Maemo

Implementing "Open with…" on MacOS with Qt

I just released PhotoTeleport 0.12, which includes the feature mentioned in the title of this blog post. Given that it took me some time to understand how this could work with Qt, I think it might be worth spending a couple of lines about how to implement it.

In the target application

The first step (and the easiest one) is about adding the proper information to your .plist file: this is needed to tell MacOS what file types are supported by your application. The official documentation is here, but given that an example is better than a thousand words, here's what I had to add to PhotoTeleport.plist in order to have it registered as a handler for TIFF files:

    …more dict entries for other supported file formats…

This is enough to have your application appear in Finder's "Open with…" menu and be started when the user selects it from the context menu, but it's only half of the story: to my big surprise, the selected files are not passed to your application as command line parameters, but via some MacOS-specific event which needs to be handled.

By grepping into the Qt source code, I've found out that Qt already handles the event, which is then transformed into a QFileOpenEvent. The documentation here is quite helpful, so I won't waste your time to repeat it here; what has hard for me was to actually find that this functionality exists and is supported by Qt.

In the source application

The above is only half of the story: what if you are writing an application which wants to send some files to some other application? Because of the sandboxing, you cannot just start the desired application in a QProcess and pass the files as parameters: again, we need to use the Apple Launch Services so that the target application would receive the files through the mechanism described above.

Unfortunately, as far as I could find this is not something that Qt supports; sure, with QDesktopServices::openUrlExternally() you can start the default handler for the given url, but what if you need to open more than one file at once? And what if you want to open the files in a specific application, and not just in the default one? Well, you need to get your hands dirty and use some MacOS APIs:

#import <CoreFoundation/CoreFoundation.h>
#import <ApplicationServices/ApplicationServices.h>

void MacOS::runApp(const QString &app, const QList<QUrl> &files)
    CFURLRef appUrl = QUrl::fromLocalFile(app).toCFURL();

    CFMutableArrayRef cfaFiles =
    for (const QUrl &url: files) {
        CFURLRef u = url.toCFURL();
        CFArrayAppendValue(cfaFiles, u);

    LSLaunchURLSpec inspec;
    inspec.appURL = appUrl;
    inspec.itemURLs = cfaFiles;
    inspec.asyncRefCon = NULL;
    inspec.launchFlags = kLSLaunchDefaults + kLSLaunchAndDisplayErrors;
    inspec.passThruParams = NULL;

    OSStatus ret;
    ret = LSOpenFromURLSpec(&inspec, NULL);

In Imaginario I've saved this into a macos.mm file, added it to the source files, and also added the native MacOS libraries to the build (qmake):

LIBS += -framework CoreServices

You can see the commit implementing all this, it really doesn't get more complex than this. The first parameter to the MacOS::runApp() function is the name of the application; I've verified that the form /Applications/YourAppName.app works, but it may be that more human-friendly variants work as well.

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13 Oct 2019 6:51pm GMT

12 Nov 2011

feedPlanet Linux-to-go

Paul 'pfalcon' Sokolovsky: Shopping for 3D TV...

Shopping for 3D TV (again), few findings:

12 Nov 2011 6:55pm GMT

Paul 'pfalcon' Sokolovsky: Hacking Luxeon SP-1

I finally going to get Arduino, and while I'm choosing flavor and waiting for it, I can't help but disassembling all devices I have at home, each time speaking: "This must have Arduino inside!" (meaning of course that I expect it to be based on general-purpose MCU). Gosh, I usually get "blob chip" (uncased chip with blob of epoxy on top).

Well, I finally had my expectations fulfilled - Luxeon SP-1 voltage stabilizer/cutter features ATMEGA48V-10PU (Flash: 4k, EEPROM: 256, RAM:512). Not only that, it is installed in DIP socket! Buy from Luxeon, they're hacker-friendly ;-).

I bought the device actually for a wattmeter it features (which fact is hard to figure out from common specs found in the shops, I accidentally read somebody mentioning it on a forum). The wattmeter is of course not bright - for a lamp rated 100W it shows 88W, and for more powerful equipment (like perforator) understates wattage even more (maybe it's difference between real and apparent power factor).

Still, for $17 you get Arudino-alike with voltage/current sensor and hacking possibility. Woot!

High-power board:

MCU board:

12 Nov 2011 5:58pm GMT

10 Nov 2011

feedPlanet Linux-to-go

Paul 'pfalcon' Sokolovsky: Links for November 2011


Linux kernel module tricks:

10 Nov 2011 3:21pm GMT

19 Oct 2011

feedPlanet OpenEZX

Antonio Ospite: Gnome 3: go to Shell? Not just yet, thanks.

In Debian Unstable the transition to Gnome 3 is taking place; when Gnome 3.0 firstly came out some unnamed geeky users complained loudly about the design decisions of the development team to push strongly towards gnome-shell as a new default UI; gnome-shell was designed focusing on usability (usability is a metric relative to a certain target audience BTW) and simplicity, hiding a lot of details from the users. Obviously you can never make everyone happy so some of us simply happened to be "out of target": you know us computer people (*cough cough*), we like to be in charge and control The Machine... I must admit I still don't have a definitive opinion about the gnome-shell concept, for now I just know that it does not suit me; I am going to try it eventually, maybe I'll get used to it, but in the mean time I need my desktop back just like I shaped it through the years; can this be done without loosing all the good Gnome technologies (Empathy over all of them)?

To be completely fair I have to say that there is little to complain about with Gnome developers, we can still get our good old GNOME desktop fully back by using the fall-back mode based on gnome-panel and live happily ever after, let's take a look at how this can be accomplished.

NOTE: GNOME people state that the fall-back mode is meant for systems with older graphic cards which cannot run gnome-shell, however it can very well be seen as a good opportunity for those who do not want to run gnome-shell just yet.

Getting back to the topic: some minor touches are needed to make the panel look more like what we are used to, maybe some of these settings could even become default for fall-back mode, we'll see.

First, enable fall-back mode (on Debian there is a dedicated session you can choose from the Log-in Manager for that) and change some desktop settings, in a terminal type:

$ gsettings set org.gnome.desktop.session session-name 'gnome-fallback'
$ gsettings set org.gnome.desktop.interface 'menus-have-icons' true
$ gsettings set org.gnome.desktop.interface 'buttons-have-icons' true
$ gsettings set org.gnome.desktop.background 'show-desktop-icons' true

gnome-tweak-tool can be used for some of these settings like shown in the attached images.

Then rearrange the applets on the panel as you please (use Alt-RightClick to access the panel properties), and fix the theming using this patch to have a light panel again (against gnome-themes-standard=3.0.2-1):

$ mkdir $HOME/.themes
$ cd $HOME/.themes
$ cp -r /usr/share/themes/Adwaita Adwaita-fallback
$ cd Adwaita-fallback
$ patch -p1 < $HOME/adwaita-fallback-panel-theme.patch
$ gsettings set org.gnome.desktop.interface 'gtk-theme' 'Adwaita-fallback'

Some final touches for the Metacity window manager and to the clock applet, and we are all set:

$ gconftool-2 --type string --set /apps/metacity/general/focus_mode mouse
$ gconftool-2 --type boolean --set /apps/metacity/general/compositing_manager true
$ gconftool-2 --type string --set /apps/panel3-applets/clock/custom_format '<span color="#333">%a %d %b</span> <b>%H:%M</b>'
$ gconftool-2 --type string --set /apps/panel3-applets/clock/format custom

Ah, in the new gnome-panel based on Gtk3 there are still some details to take care of, I hope issues like that will be addressed and that the panel will be supported for quite some time.

Attached images:
Gnome Shell default look on Debian
gnome-tweak-tool show desktop icons
Gnome 3 fall-back mode default look on Debian
Gnome 3 fall-back mode applets rearranged
Gnome 3 fall-back mode rethemed to have a light panel
Attached files:
text/x-diff iconAdwaita theme patch for fall-back mode

19 Oct 2011 9:37pm GMT

09 Jun 2011

feedPlanet OpenEZX

Michael Lauer: The Eagle Has Landed!

After letting us wait for a bit longer than scheduled (13 days), the hospital initiated the contractions. For the first couple of hours, everything went just perfect, but then the little one got stuck on the way and we had to resort to a cesarean section. Lara Marie Lauer was born 8th of June at 04:41 (AM) with 3460 gramms and 49 cm.

Mummy was still on intensive care and so they gave her to me. I can't express the feelings I had in this very moment. I'm still kind of overwhelmed every time I see her. Thanks for all of you who waited anxiously with me and those who prayed for us. The most important tasks for the near future is getting Mummy to recover and Lara Marie to become accustomed to us and the rest of the outside world.

Please bear with me if in the next time I'm not as responsive as usually :)

Lara Marie Lauer

09 Jun 2011 4:06pm GMT

30 May 2011

feedPlanet OpenEZX

Michael Lauer: German Post on time!

And now for something completely different… while we are all waiting for my baby to arrive (who was scheduled for 25th of May), she just received her first greeting card - together with a personalized bib and a towel (with integrated hood - pretty fancy!) from my good friends at #openmoko-cdevel.

Guys, seeing this card was very heartwarming - it means a lot to me that you share my anticipation, thanks a lot! And I'm 100% sure she will appreciate her gifts… now let's cross fingers it won't take much longer… waiting is the hardest part of it :)



30 May 2011 8:54am GMT