tales from an old nibble
Android Screen Capture for dual screen devices
What’s the problem?
What is keeping me busy lately are dual screen and foldable devices.
I do some work around Jetpack WindowManager and I talk to developers on how to support this new form factors.
Testing new code, I may encounter some “strange behavior” and capture a screenshot is usually a good way to convey my point to someone else.
If you use a tool to capture a screenshot on a dual screen device, you will soon discover that (probably) it assumes that there’s only a screen. These tools capture the screenshot of the default screen. On a dual screen device, there’s a 50% chance that they will capture the image of the wrong screen…
As an example, for a device like the Samsung Z Fold 2, the default/primary screen is the beautiful foldable screen inside the device. If the device is closed and you are using the external display, your tool will probably capture the image of the internal screen:
You will get a black image.
Look for a solution
There’s nothing wrong in Android and its low level tools, they perfectly know that there’s more than one screen. You can ask it yourself to the surface flinger. On a device like the Samsung Z Fold 2 you will get two distinct displays:
screencap? Can it be used to capture both screens?
It looks like that the
-d parameter is what we need. We can then run:
To capture an image from each screen.
So far, so good. My problem is that lately I’m finding myself capturing a lot of screenshot, so I finally decided to automate this process modifying a script by my friend Daniele.
Here is the end result:
This script capture a screenshot for the displays of all the devices connected to your computer.
I’ve this script in my personal
~/bin folder set as executable and I’m running it when needed. I though to write this short notes in case you are also doing some experiments with dual screen devices.
As usual… it works on my machine™