GLMixer Code

Bug Fix: update once to ensure FFGL source is filled even if created
without playing.

Bug Fix: Algorithm source display first frame when not played initially,
and fixed random seed.

Bug Fix: cleanup the image buffer before SVG rendering.

Add keyboard shortcut Ctrl + [0] for workspace exclusive display mode.

Cleanup GLSL shadertoy examples code.

Updated support to ShadeToy; switched to iTime variable (deprecated
iGlobalTime) and added informative warnings about syntax changes.

Bug Fix: idem previous, but cleaner implementation.

Bug Fix: correct management of picture queue on changes of marks for
begin and end (clean_until_time_picture_queue)

Fixed GUI: disabling / enabling timeline according to source type and
status.

Bug Fix : clamp rotation angles of source in range [0..360] (not a real
issue for rendering, just for display of angle property.