PiBox » piclock

This is relatively easy although the rotation of the hands is a little confusing (to me, so far). But the background face and overlay (like adding a glass highlight) are straightforward.

• Add support for a theme directory
• Add support for a current theme configuration, defaulting to original drawn face and hands
• Design theme config file format, including validation of the content
  • Maximum face size: 512
  • Scale hands: face size * {.97 second, .85 minute, .65 hour}
  • Hands have rotation point: x/y offset for where rotation should occur
• Write functions for loading hands and rotating them
• If theme available, do drawing:
  • Draw background
  • Call hour hand, draw it
  • Call minute hand, draw it
  • Call second hand, draw it
  • Draw overlay

• Be loaded into their own cairo surface
• Scale the hand
• Rotate the hand
• position the hand after the call
• merged into the main cairo surface

See http://zetcode.com/gfx/cairo/compositing/

Also see this for how to translate and rotate the hands: http://stackoverflow.com/a/35996791. Note that this also shows the use of a Cairo pattern that is generated from the source and is used for translating/rotating.