This tool reads instructions from stdin or args and captures screenshots using the chrome devtools protocol from a running blink-based browser instance at various given breakpoints.

npm install -g chrome-devtools-protocol-screenshot

and then start on your chromium browsers remote debug port.

chrome-devtools-protocol-screenshot.js -p 9222

Stdin

If you have a inst.json like the following (you can use any uri, for example http://example.com)

{
  "uris": {
    "spotify:album:6LBiuhK7PZKjVXyMfPxPoh": {
      "breakPoints": [1200, 800, 400]
    },
    "spotify:artist:7xUZ4069zcyBM4Bn10NQ1c": {
      "breakPoints": [1200, 600]
    }
  }
}

then

cat inst.json | chrome-devtools-protocol-screenshot --outputDir ./captures --remoteDebuggingPort 9222

will output screenshots of these uris at these widths to the output directory.

args

chrome-devtools-protocol-screenshot --outputDir ./captures --remoteDebuggingPort 9222 --breakPoints 1200,800

Will create screenshots at 1200 width and 800 width of the current page in the chromium app and output them to ./captures.

Comparison

You can use whatever image comparison tool you like. I like to use ImageMagik.

convert '(' img1.png ')' \
        '(' img2.png ')' \
        '(' -clone 0-1 -compose darken -composite ')' \
        -channel RGB -combine diff.png

Generates:

compare foo_prod.png foo_dev.png diff.png

Generates: