Self-updating screenshots

Same, I've added a .#screenshots derivation. High up-front effort but almost zero maintenance afterwards.

Bonus: since you're generating screenshots programmatically anyway, you can generate a pair of each with your app's light/dark theme, and swap them in/out depending on prefers-color-scheme: dark. <picture> elements work in GitHub READMEs, too: https://github.com/CyberShadow/CyDo#readme

neobrain 42 days ago | |

+1 for this approach. For a mobile app, I made Nix spawn an ephemeral Android emulator instance for generating up-to-date screenshots, requiring no prior setup and leaving no lingering data around after running. Setting it up wasn't that high-effort in my case either; coming up with the idea was the hard part, the Nix code was one-shot by your favorite LLM.

Granted manually updating the screenshots isn't the most laborious task in the world, but the "upload-apk + take-screenshot + transfer-back-to-PC + edit" process is usually barely annoying enough that you end up almost never doing it otherwise (similar to the OP's experience in the closing paragraph).

Landing7610 41 days ago | | |

That sounds so cool! Is the repo available anywhere?

neobrain 36 days ago | | |

Nothing public yet, but this is the Nix output for taking the screenshot, to be executed via `nix run .#screenshot`:

        outputs.apps.x86_64.screenshot = {
          type = "app";
          program = toString (pkgs.writeShellScript "screenshot-script" ''
            set -euo pipefail

            EMU_SDK="${androidEmulatorComposition.androidsdk}/libexec/android-sdk"
            ADB="$EMU_SDK/platform-tools/adb"
            EMULATOR="$EMU_SDK/emulator/emulator"
            APK="${self.packages.${system}.debug}/myapp-debug.apk"

            SRC_DIR="$(${pkgs.git}/bin/git rev-parse --show-toplevel)"
            AVD_HOME="$(mktemp -d)"
            trap 'kill "$EMU_PID" 2>/dev/null; wait "$EMU_PID" 2>/dev/null; rm -rf "$AVD_HOME"' EXIT

            # Create AVD
            AVD_DIR="$AVD_HOME/screenshot.avd"
            mkdir -p "$AVD_DIR"
            cat > "$AVD_HOME/screenshot.ini" <<EOF
            avd.ini.encoding=UTF-8
            path=$AVD_DIR
            target=android-${platformVersion}
            EOF
            cat > "$AVD_DIR/config.ini" <<EOF
            AvdId=screenshot
            PlayStore.enabled=false
            abi.type=x86_64
            avd.ini.encoding=UTF-8
            hw.cpu.arch=x86_64
            hw.gpu.enabled=yes
            hw.gpu.mode=swiftshader_indirect
            hw.lcd.density=420
            hw.lcd.height=2400
            hw.lcd.width=1080
            hw.ramSize=2048
            image.sysdir.1=system-images/android-${platformVersion}/google_apis/x86_64/
            skin.dynamic=yes
            tag.display=Google APIs
            tag.id=google_apis
            disk.dataPartition.size=2G
            EOF

            echo "==> Starting emulator..."
            ANDROID_AVD_HOME="$AVD_HOME" ANDROID_HOME="$EMU_SDK" \
              "$EMULATOR" -avd screenshot -no-window -no-audio -no-boot-anim \
              -gpu swiftshader_indirect -no-snapshot 2>&1 &
            EMU_PID=$!

            echo "==> Waiting for boot..."
            for i in $(seq 1 90); do
              BOOT=$("$ADB" shell getprop sys.boot_completed 2>/dev/null | tr -d '\r') || true
              if [ "$BOOT" = "1" ]; then
                echo "    Booted after ~$((i * 2))s"
                break
              fi
              sleep 2
            done
            if [ "$BOOT" != "1" ]; then
              echo "ERROR: Emulator failed to boot" >&2
              exit 1
            fi

            # Enable dark mode
            "$ADB" shell cmd uimode night yes

            # Install and launch
            echo "==> Installing APK..."
            "$ADB" install -r "$APK"
            "$ADB" shell pm grant com.me.myapp android.permission.WRITE_SECURE_SETTINGS
            "$ADB" shell am start -n com.me.myapp/.MainActivity
            sleep 3

            # Navigate to settings screen by tapping "Notification Filters" button
            # This uses uiautomator to find the button by text for robustness
            "$ADB" shell uiautomator dump /sdcard/ui.xml
            BOUNDS=$("$ADB" shell cat /sdcard/ui.xml \
              | ${pkgs.gnugrep}/bin/grep -oP 'text="Notification Filters"[^>]*bounds="\K[^"]+' \
              || true)
            if [ -z "$BOUNDS" ]; then
              echo "ERROR: Could not find Notification Filters button" >&2
              exit 1
            fi
            # Parse bounds "[x1,y1][x2,y2]" to compute center tap coordinates
            X1=$(echo "$BOUNDS" | ${pkgs.gnused}/bin/sed 's/\[\([0-9]*\),\([0-9]*\)\]\[\([0-9]*\),\([0-9]*\)\]/\1/')
            Y1=$(echo "$BOUNDS" | ${pkgs.gnused}/bin/sed 's/\[\([0-9]*\),\([0-9]*\)\]\[\([0-9]*\),\([0-9]*\)\]/\2/')
            X2=$(echo "$BOUNDS" | ${pkgs.gnused}/bin/sed 's/\[\([0-9]*\),\([0-9]*\)\]\[\([0-9]*\),\([0-9]*\)\]/\3/')
            Y2=$(echo "$BOUNDS" | ${pkgs.gnused}/bin/sed 's/\[\([0-9]*\),\([0-9]*\)\]\[\([0-9]*\),\([0-9]*\)\]/\4/')
            TAP_X=$(( (X1 + X2) / 2 ))
            TAP_Y=$(( (Y1 + Y2) / 2 ))
            "$ADB" shell input tap "$TAP_X" "$TAP_Y"
            sleep 2

            # Capture and process screenshot
            echo "==> Capturing screenshot..."
            "$ADB" shell screencap -p /sdcard/screenshot.png
            "$ADB" pull /sdcard/screenshot.png "$AVD_HOME/raw.png"

            # Crop to content: remove status bar (top 128px) and empty space below
            # Per-App Overrides, then resize with high-quality Lanczos filter
            ${pkgs.imagemagick}/bin/magick "$AVD_HOME/raw.png" \
              -crop 1080x1100+0+128 +repage \
              -filter Lanczos -resize 540x \
              "$SRC_DIR/fastlane/metadata/android/en-US/images/phoneScreenshots/settings.png"

            echo "==> Screenshot saved to fastlane/metadata/android/en-US/images/phoneScreenshots/settings.png"
          '');
        };

9dev 42 days ago | |

The <picture> in README trick works like magic. Thank you! I'm going to steal it.

Nashooo 42 days ago |

Hey, you need to make your code examples horizontal scrollable on mobile! I could still guess their content based on context clues but still.

amiga386 42 days ago |

If the author is reading this, please note your code blocks don't scroll (and in fact overflow the white text onto the white background) on mobile layouts. You need an "overflow-x: scroll" or such.

spuz 42 days ago |

The only problem with this idea I can forsee is that the application and therefore the screenshots can change but the documentation does not. For example, if the documentation says press "Options > Customize" but the application is updated so this becomes "Preferences > Advanced" then the screenshot will show the new text but the documentation will still show the old labels. This would be very confusing as it would be hard to correlate what is being shown on the screenshot with the text. If the user saw the old screenshot they could more easily identify that they were looking at an out of date documentation.

Having said that, have a process to automatically grab screenshots is going to make it significantly easier for a developer to update the docs so the motivation to keep the text up to date is going to be much higher.

zffr 42 days ago | |

As a next step, it could be cool to write unit tests against these screenshots that look for words like you mentioned. That way if a screenshot is updated and a test breaks you will know what documentation to update

furyofantares 43 days ago |

Very cool.

For the small casual games I've been vibe coding, I always start from a place where the application has a CLI where it can run headless, rendering to offscreen texture, with a a screenshot command as well as performance instrumentation. It takes no time to include all this, and gives the agent a way to automate the ui and inspect important things. It also lets me trivially have the agent update screenshots.

Not as neat as being part of the build process, but I will now add that.

merelysounds 42 days ago |

This is very useful in mobile projects.

App stores require screenshots, but generating N images for NUMBER_OF_SCREEN_SIZES times NUMBER_OF_LOCALIZATIONS can be a chore.

In the past I wrote my own scripts for that, today tools like Fastlane[1] help.

I use Fastlane for my logic puzzle game Nonoverse[2], you can see sample screenshots in its App Store page.

I also automated App Preview video recording, complete with multiple scenes. If anyone wants to read more let me know, perhaps this is a good topic for an article.

[1]: https://fastlane.tools/

[2]: https://apps.apple.com/us/app/nonoverse-nonogram-puzzles/id6...

jdnebdbd 42 days ago | |

That sounds enticing! I can't figure out if it's a paid service or a local OS application though

merelysounds 42 days ago | | |

Fastlane is a local, open source CLI tool.

> 100% open source under the MIT license

See: https://docs.fastlane.tools/

It doesn’t support App Preview automation, this is something that I had to script myself.

wahnfrieden 42 days ago | |

These days it can be much easier to(though costlier) to use an agent skill.

boxed 42 days ago |

For web projects, consider not doing screenshots at all and just embedding the html: https://kodare.net/2025/01/14/iframes-not-screenshots.html

You can get responsive design in "screenshots" with this. Super nice, and people can copy paste, look at the code (useful for dev tools), etc.

LeoDaVibeci 43 days ago |

I've needed this so many times. BTW this should be a meme: "I think this might be the neatest thing I’ve built in X that nobody will ever notice."

borplk 42 days ago |

Site appears to be down intermittently with a Django error

If author sees this: Turn off Django debug mode

irishcoffee 43 days ago |

I wrote a gui app once that ran on a safety-critical platform. I ended up stuffing a rendering of the gui (rendered offscreen) into shmem at I think 24hz, and rendered that screenshot into the safety critical application. I passed clicks (no typing for this gui) back from the statically rendered image updating on a cadence, to the offscreen GUI.

Worked well. Not quite the same as this, but that’s what this reminds me of.

yjftsjthsd-h 43 days ago | |

I don't think I follow. What is that giving you that you wouldn't get by just having the user click in the application and see its real interface directly? Or are you saying you were embedding one application inside another?

jfim 43 days ago | | |

My guess is that it's to ensure that the UI logic crashing or hanging doesn't bring down the safety critical process.

irishcoffee 42 days ago | | |

The rendering of the safety-critical application was written completely in C using OpelGLSC (https://www.khronos.org/openglsc/) to render the GUI, and had to pass a formal validation suite (MISRA was the big one IIRC). Simply put, the safety critical application essentially was not allowed to "fail in an unsafe manner" in the DO-178 sense. Using javascript, or some c++ gui library was very much out of the question.

Fortunately, this was not an airborne platform, so failing safely was much simpler than what a true aviation stack or medical stack would need to do.

schneems 43 days ago |

This is neat. I wrote https://github.com/zombocom/rundoc. It has a similar feature. The main driver is to produce tutorials so it also puts the output of commands run back in the document.

markaius 42 days ago |

This reminds me of an small app I wrote and didn't do anything with-- You would choose an API / endpoint to grab data from, then choose how to display that text on a prebuilt or custom uploaded picture. On the ping it would rebuild the image and put the updated text from the api on it so you could have images with more current information (every 5/10/30 mins, etc.) Updating readmes with new screenshots on push is probably a much less cpu and better way to do dynamic image generation, for this use case.

I never ended up using the idea the way I wanted, but this makes me think there's potential in this dynamic image domain yet!

sublinear 42 days ago |

Why wouldn't you want to version the screenshots along with the text? That's a feature, not a bug.

At best, this seems to require an unpublished draft state for all automatic screenshot updates until explicitly approved so that mistakes don't leak out to everyone else.

At worst, this is an unrealistic level of discipline to keep things in sync that is far greater than just updating the docs normally with the next major version release.

My alternative suggestion would be to make sure your test suite takes screenshots with every build. They're already perfectly organized and in the context of what you're documenting.

kalb_almas 43 days ago |

I'm sometimes getting

NoMethodError at /self-updating-screenshots undefined method `name' for nil:NilClass

Ruby title-for: in handle, line 12 Web GET interblah.net/self-updating-screenshots

followed by a very detailed traceback when I try to access the page

Mackser 42 days ago |

Super cool! Love that you can declare the screenshots inline in the markdown document.

For my desktop app I created a solution that generates screenshots in multiple languages, light/dark mode, removes noise and adds Windows/macOS window frames.

Wrote about it here: https://maxschmitt.me/posts/cakedesk-website-redesign#screen...

It's currently a separate script (which is a pain to maintain). I should look into making it a part of the markdown/mdx. Thanks for the inspiration!

taspeotis 43 days ago |

I’ve wondered about doing screenshots from the e2e test run, even keeping docs/ all together in the same repo so when you update the documentation and need a new screenshot you add a new test

immanuwell 43 days ago |

nice, embedding the capture instructions right in the markdown as comments is a dead-simple solution that'll age way better than any fancy external tooling

oneeyedpigeon 42 days ago | |

Except that it's brittle—HTML comments can be stripped. I wonder why they chose this approach vs. frontmatter.

martylamb 42 days ago |

Very nice. I did something in a similar spirit eons ago for capturing CLI tool output directly into my docbook-based documentation. In my case it was also part of a build, generating intermediate .xml prior to running the docbook build.

Ancient historical reference: https://martiansoftware.com/lab/rundoc

Biganon 42 days ago |

You should set DEBUG=False in your Django settings.

amelius 42 days ago |

Speaking of screenshots.

Can we please agree that the OS should not send any event to applications while a screenshot is being made?

It is very annoying if you press a screenshot button and suddenly menus disappear. Or much worse, the application sends a "screenshot taken" message back to the social media platform.

reddalo 42 days ago | |

I also can't stand Android preventing me from taking a screenshot. It's on my screen, I have the right to take a screenshot.

I understand the technical limit of taking screenshots of DRM-protected content (e.g. Netflix), but why would my bank app be allowed to stop me from taking screenshots?

hebelehubele 42 days ago | | |

You can mod the APK and remove those detections using ReVanced Manager

https://github.com/revanced/revanced-manager

https://gitlab.com/ReVanced/revanced-patches/-/blob/main/ext...

pwdisswordfishs 42 days ago | | |

Solution: don't use mobile bank apps.

reddalo 42 days ago | | |

I'm forced to use a bank app in order to authenticate, even if I want to login on the desktop website. I think it's because of an EU regulation for strong authentication.

dgellow 42 days ago | | |

The implementation causing you issues is from the bank, not from the EU regulation.

See https://en.wikipedia.org/wiki/Strong_customer_authentication for details

Ylpertnodi 42 days ago | | |

Ask them?

cbm-vic-20 42 days ago | |

The MacOS built-in screenshot tool has an optional "timed delay" feature, where you can click "screenshot in 5 seconds". With that time, you can open menus, or do anything that requires events to be processed by the application. Very handy for screenshots that require something to be clicked on.

amelius 42 days ago | | |

I mean, I can probably do the same in X11 using xwd, with a sleep.

But I just don't want my screenshot button to do anything else than taking a screenshot.

maderalabs 43 days ago |

Nice! I actually started to build this exact thing a couple years back, and ended up abstracting it out to something more generic with https://picshift.io/. That said, I still love the screenshot use case - the original name of this project was ScreenSync ;)

Barbing 42 days ago | |

Neat, good job, and good to have these different approaches out there

efortis 43 days ago |

same here, but linking to the screenshots used for pixel diffing, which get committed to the repo.

https://github.com/ericfortis/mockaton/tree/main/pixaton-tes...

cocoto 42 days ago |

Wouldn’t a real live render approach work in this case? Have a live preview of your tool inside a rectangle. If the tool is light it should be optimal visually: it will respect browser rendering settings like accessibility parameters or custom addons.

boxed 42 days ago | |

Or just statically build the HTML. That's what we do for iommi docs: https://kodare.net/2025/01/14/iframes-not-screenshots.html

kristopherleads 42 days ago | |

Don't we already have this in HTML5?

npodbielski 42 days ago | |

Also it would be a security issue?

npodbielski 42 days ago |

I do not know why but looking at the title I was sure that this involves something like webserver that updates static file it serves by some external webhook.

ekjhgkejhgk 42 days ago |

> Your users might not notice, but you know, and it gnaws at you.

The users WILL DEFINITELY notice if the screenshots don't match what they have in front of their eyes.