WindowStitcher takes a screen capture of a window and centres it over a specified background. This script should be useful for anyone writing about apps.
WindowStitcher takes this window capture (PNG with transparency mask):
And this magnificent wallpaper:
To make this composite:
The padding around the window is user-configurable. The window is centred over the wallpaper, but the position will be user-configurable in a future release. The width of the output file is fixed at 1200px (plus twice the specified padding), but will be user-configurable in a future release.
python3 window-stitcher.py [-h] [-p PADDING] background window