GLMixer Code

Added display of duration in overlay of the range bar.

Added option Exclusive Workspace to show / hide the sources from all
workspaces.

fixed decoding time stamp counter for codecs which do not update pkt_pts
with avcodec_decode_video2 (correct use of reordered_opaque + continuity
check).

Finalized implementation of new Timeline slider. Ready for use.

BUG Fix : improper behavior for non-looping video

Changed behavior of TimelineSlider: sets the begin and end on mouse
release of the cursor.

New example code source ShaderToy

Fixed image inversion of ShaderToy and update of ShaderToy syntax to
accept 'texture' function (new version) instead of texture2D (old).

Added 'Copy Text' to clipboard action in context menu of the source
property tree.

New TimelineSlider (unstable)
New implementation of History Manager (recorder of user actions):
disabled by default, has to enable 'USE_HISTORY_MANAGEMENT' in cmake.