Compositor now uses threaded jobs.
- updates happen per preview node! Check this file for
fun: http://www.blender.org/bf/composite_image.blend
(any compo node could get preview!)
- had to ensure the composite data gets fully copied before
it executes thread, so editing is not frustrated.
- put back node buttons (missing init)
- added WM_jobs api call to check for running job,
illustrated with red light icon in 'use nodes' button.
- added another callback to WM_jobs, to initialize.
use this init to ensure you only do it when job really
starts.
- added an extra notifier option for WM_jobs, to signal
finished job (like redraw image view)
- fixed file read error, it copied the screen it read,
instead of using it.
- commented out annoying prints for missing ops in imagewin
