VSE: Add channel headers

This patch adds channel region to VSE timeline area for drawing channel
headers. It is synchronizedwith timeline region. 3 basic features are
implemented - channel visibility, locking and name.

Channel data is stored in `SeqTimelineChannel` which can be top-level
owned by `Editing`, or it is owned by meta strip to support nesting.
Strip properties are completely independent and channel properties are
applied on top of particular strip property, thus overriding it.

Implementation is separate from channel regions in other editors. This
is mainly because style and topology is quite different in VSE. But
also code seems to be much more readable this way.

Currently channels use functions similar to VSE timeline to draw
background to provide illusion of transparency, but only for background
and sfra/efra regions.

Great portion of this patch is change from using strip visibility and
lock status to include channel state - this is facilitated by functions
`SEQ_transform_is_locked` and `SEQ_render_is_muted`

Originally this included changes in D14263, but patch was split for
easier review.

Reviewed By: fsiddi, Severin

Differential Revision: https://developer.blender.org/D13836

1 files changed, 6 insertions, 2 deletions

diff --git a/source/blender/sequencer/intern/effects.c b/source/blender/sequencer/intern/effects.c
index a4ab7671eb0..70f83485bb5 100644
--- a/source/blender/sequencer/intern/effects.c
+++ b/source/blender/sequencer/intern/effects.c
@@ -2422,6 +2422,7 @@ static ImBuf *do_multicam(const SeqRenderData *context,
   ImBuf *out;
   Editing *ed;
   ListBase *seqbasep;
+  ListBase *channels = &seq->channels;
 
   if (seq->multicam_source == 0 || seq->multicam_source >= seq->machine) {
     return NULL;
@@ -2436,7 +2437,8 @@ static ImBuf *do_multicam(const SeqRenderData *context,
     return NULL;
   }
 
-  out = seq_render_give_ibuf_seqbase(context, timeline_frame, seq->multicam_source, seqbasep);
+  out = seq_render_give_ibuf_seqbase(
+      context, timeline_frame, seq->multicam_source, channels, seqbasep);
 
   return out;
 }
@@ -2462,6 +2464,7 @@ static ImBuf *do_adjustment_impl(const SeqRenderData *context, Sequence *seq, fl
 {
   Editing *ed;
   ListBase *seqbasep;
+  ListBase *channels = &seq->channels;
   ImBuf *i = NULL;
 
   ed = context->scene->ed;
@@ -2474,7 +2477,8 @@ static ImBuf *do_adjustment_impl(const SeqRenderData *context, Sequence *seq, fl
   timeline_frame = clamp_i(timeline_frame, seq->startdisp, seq->enddisp - 1);
 
   if (seq->machine > 1) {
-    i = seq_render_give_ibuf_seqbase(context, timeline_frame, seq->machine - 1, seqbasep);
+    i = seq_render_give_ibuf_seqbase(
+        context, timeline_frame, seq->machine - 1, channels, seqbasep);
   }
 
   /* Found nothing? so let's work the way up the meta-strip stack, so