VSE: Cleanup speed effect math

Simplify logic of speed effect frame calculation by using discrete math
where possible. Only `SEQ_SPEED_MULTIPLY` mode with animation requires
frame map to be built. Frame map building was simplified by removing
unused branches.

Functional change: Animating strip in negative range will reverse playback.
I assume this was limitation of previous system, where each frame map item
was limited to be within correct frame range. Now frame map can contain
values that point beyond usable range and they are limited by
`seq_speed_effect_target_frame_get`. This way it is possible to control
playback rate in both directions.

Mostly fixes T89120 apart from offset handling.

Reviewed By: mano-wii

Differential Revision: https://developer.blender.org/D11939

1 files changed, 3 insertions, 3 deletions

diff --git a/source/blender/sequencer/intern/strip_relations.c b/source/blender/sequencer/intern/strip_relations.c
index 7c5a3f031db..409b5f6a2e4 100644
--- a/source/blender/sequencer/intern/strip_relations.c
+++ b/source/blender/sequencer/intern/strip_relations.c
@@ -118,7 +118,7 @@ static void sequence_invalidate_cache(Scene *scene,
   }
 
   if (seq->effectdata && seq->type == SEQ_TYPE_SPEED) {
-    seq_effect_speed_rebuild_map(scene, seq, true);
+    seq_effect_speed_rebuild_map(scene, seq);
   }
 
   sequence_do_invalidate_dependent(scene, seq, &ed->seqbase);
@@ -268,7 +268,7 @@ void SEQ_relations_free_imbuf(Scene *scene, ListBase *seqbase, bool for_render)
         SEQ_relations_sequence_free_anim(seq);
       }
       if (seq->type == SEQ_TYPE_SPEED) {
-        seq_effect_speed_rebuild_map(scene, seq, true);
+        seq_effect_speed_rebuild_map(scene, seq);
       }
     }
     if (seq->type == SEQ_TYPE_META) {
@@ -325,7 +325,7 @@ static bool update_changed_seq_recurs(
         SEQ_relations_sequence_free_anim(seq);
       }
       else if (seq->type == SEQ_TYPE_SPEED) {
-        seq_effect_speed_rebuild_map(scene, seq, true);
+        seq_effect_speed_rebuild_map(scene, seq);
       }
     }