convert: attempt to perform an operation not allowed by the security policy `PDF' @ error/constitute.c/IsCoderAuthorized/412.

Edit :
sudo nano /etc/ImageMagick-7/policy.xml
and just before </policymap>
add
 <policy domain="coder" rights="read | write" pattern="PDF" />
ctrl+o and enter and that's it. Now it works.

How to make a gif from Huawei moving picture

I really like moving pictures. They are totally cool way to remember a fun moment and they are really easy to make. The big problem, however, is that they are a nightmare to share. Because they are recognised only by Huawei phones. Which is really a pity. It turned out it's pretty hard to export them to GIF-s as well. So here's what I found after all.
The only app which I've found so far to work with them is "Gif maker-editor". From it, you can choose "More->Motion photo-GIF" and turn your cool motion photo to a GIF. Of course, without the sound, which is also stupid, but whatever.
Then, if you want to edit your GIF (i.e. to remove a particularly ugly frame) you can do it from the app "GIF Maker- Gif Editor" (WTF with the names of those apps). From there, you select Edit->Manager and click on the - signs to remove a frame. Then you save it, and here you go a nice pretty GIF.
And with Motion Stills you can make normal GIFs. But they are not so fun as moving pictures :)

Sudden loss of FPS

To my greatest surprise when I tried playing games this week, I would play about 10mins and then the game would suddenly experience a total FPS drop at which point it has to be killed. I thought it's a problem with the latest KSP update, but then it happened with another game and I was like "What?".
Well, it seems like some genius decided that there should be a 10 mins limit of work for the discrete card (i.e. the Nvidia). Because...why not. Let's stop people from gaming and give them back their life. Oh well.
Anyway, luckily once I realised the problem is on my computer, it was very easy to find a solution using Google. So according to this forum, or Arch Linux's wiki, it's to add in the section Screen (or in my case Devices) of /etc/bumblebee/xorg.conf.nvidia

Option "HardDPMS" "false"

For now, $optirun glxspheres works for more than 10 mins without an FPS drop, so YAY! 

(the other solution, to type in terminal:

$xset s off -dpms

doesn't work, at least, it didn't for me.)