Updated base node class to support several outputs.
Now bricks support 2 outputs : greyscale depth map, and (random) brick color.
Now Voronoi supports 3 outputs : center distance, edge distance and cell color.
Updated bricks example to use brick color output.
- shader updates are delayed by .25 seconds to avouid UI freeze
- fixed GraphNode initialization upon loading
- started obsoleting get_source_rgb and get_source_f functions
- updated colorize node to use gradient
- image node can now be loaded/saved
- removed iqnoise node
- rewrote perlin shader to support a seed parameter (seed is calculated from the node's position, so just move it to reseed)
- Added voronoi noise node
- updated code to use % formats instead of concatenating strings (should solve type problems in shaders)
- reworked the context menu (now has submenus)
- fixes in the gradient editor
