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, 31 insertions, 0 deletions

diff --git a/source/blender/editors/space_sequencer/sequencer_intern.h b/source/blender/editors/space_sequencer/sequencer_intern.h
index 33457103ff8..194aa518cd7 100644
--- a/source/blender/editors/space_sequencer/sequencer_intern.h
+++ b/source/blender/editors/space_sequencer/sequencer_intern.h
@@ -25,9 +25,31 @@ struct View2D;
 struct bContext;
 struct rctf;
 struct wmOperator;
+struct ScrArea;
+struct Editing;
+struct ListBase;
 
 #define OVERLAP_ALPHA 180
 
+typedef struct SeqChannelDrawContext {
+  const struct bContext *C;
+  struct ScrArea *area;
+  struct ARegion *region;
+  struct ARegion *timeline_region;
+  struct View2D *v2d;
+  struct View2D *timeline_region_v2d;
+
+  struct Scene *scene;
+  struct Editing *ed;
+  struct ListBase *seqbase;  /* Displayed seqbase. */
+  struct ListBase *channels; /* Displayed channels. */
+
+  float draw_offset;
+  float channel_height;
+  float frame_width;
+  float scale;
+} SeqChannelDrawContext;
+
 /* sequencer_draw.c */
 
 void draw_timeline_seq(const struct bContext *C, struct ARegion *region);
@@ -80,6 +102,12 @@ void draw_seq_strip_thumbnail(struct View2D *v2d,
                               float pixelx,
                               float pixely);
 
+/* sequencer_draw_channels.c */
+void draw_channels(const struct bContext *C, struct ARegion *region);
+void channel_draw_context_init(const struct bContext *C,
+                               struct ARegion *region,
+                               struct SeqChannelDrawContext *r_context);
+
 /* sequencer_edit.c */
 
 struct View2D;
@@ -242,6 +270,9 @@ void SEQUENCER_OT_view_zoom_ratio(struct wmOperatorType *ot);
 void SEQUENCER_OT_view_selected(struct wmOperatorType *ot);
 void SEQUENCER_OT_view_ghost_border(struct wmOperatorType *ot);
 
+/* sequencer_channels_edit.c */
+void SEQUENCER_OT_rename_channel(struct wmOperatorType *ot);
+
 /* sequencer_preview.c */
 
 void sequencer_preview_add_sound(const struct bContext *C, struct Sequence *seq);