Cleanup: Make more VSE functions use const arguments where they can

SEQ_transform_sequence_can_be_translated, SEQ_transform_single_image_check,
SEQ_can_use_proxy can all trivially take const Sequence argument.

Made SEQ_give_frame_index take const Sequence too, by removing the
"modify seq strobe to be at least 1.0" code. The strobe itself is only
ever used inside the same function, and is already guarded by
"is strobe > 1.0" check.

Original code seems to be coming all the way from 2009 with
commit message "2.5. 12k lines of sequencer back!" (03fc5696dc).

Pull Request: https://projects.blender.org/blender/blender/pulls/126021

source/blender/editors/space_sequencer/sequencer_intern.hh

@@ -340,7 +340,7 @@ void SEQUENCER_OT_rename_channel(wmOperatorType *ot);
 
 /* `sequencer_preview.cc` */
 
-void sequencer_preview_add_sound(const bContext *C, Sequence *seq);
+void sequencer_preview_add_sound(const bContext *C, const Sequence *seq);
 
 /* `sequencer_add.cc` */
 

source/blender/editors/space_sequencer/sequencer_preview.cc

@@ -178,7 +178,7 @@ static void preview_endjob(void *data)
   WM_main_add_notifier(NC_SCENE | ND_SEQUENCER, pj->scene);
 }
 
-void sequencer_preview_add_sound(const bContext *C, Sequence *seq)
+void sequencer_preview_add_sound(const bContext *C, const Sequence *seq)
 {
   wmJob *wm_job;
   PreviewJob *pj;

source/blender/editors/space_sequencer/sequencer_timeline_draw.cc

@@ -400,7 +400,7 @@ static void color3ubv_from_seq(const Scene *curscene,
   UI_Theme_Restore(&theme_state);
 }
 
-static void waveform_job_start_if_needed(const bContext *C, Sequence *seq)
+static void waveform_job_start_if_needed(const bContext *C, const Sequence *seq)
 {
   bSound *sound = seq->sound;
 

source/blender/sequencer/SEQ_proxy.hh

@@ -11,9 +11,7 @@
 struct Depsgraph;
 struct GSet;
 struct ListBase;
-struct ListBase;
 struct Main;
-struct ProxyJob;
 struct Scene;
 struct SeqIndexBuildContext;
 struct SeqRenderData;
@@ -31,7 +29,7 @@ bool SEQ_proxy_rebuild_context(Main *bmain,
 void SEQ_proxy_rebuild(SeqIndexBuildContext *context, wmJobWorkerStatus *worker_status);
 void SEQ_proxy_rebuild_finish(SeqIndexBuildContext *context, bool stop);
 void SEQ_proxy_set(Sequence *seq, bool value);
-bool SEQ_can_use_proxy(const SeqRenderData *context, Sequence *seq, int psize);
+bool SEQ_can_use_proxy(const SeqRenderData *context, const Sequence *seq, int psize);
 int SEQ_rendersize_to_proxysize(int render_size);
 double SEQ_rendersize_to_scale_factor(int render_size);
 

source/blender/sequencer/SEQ_time.hh

@@ -65,7 +65,7 @@ int SEQ_time_find_next_prev_edit(Scene *scene,
  */
 bool SEQ_time_strip_intersects_frame(const Scene *scene, const Sequence *seq, int timeline_frame);
 /* Convert timeline frame so strip frame index. */
-float SEQ_give_frame_index(const Scene *scene, Sequence *seq, float timeline_frame);
+float SEQ_give_frame_index(const Scene *scene, const Sequence *seq, float timeline_frame);
 /**
  * Returns true if strip has frames without content to render.
  */

source/blender/sequencer/SEQ_transform.hh

@@ -12,12 +12,12 @@ struct ListBase;
 struct Scene;
 struct Sequence;
 
-bool SEQ_transform_sequence_can_be_translated(Sequence *seq);
+bool SEQ_transform_sequence_can_be_translated(const Sequence *seq);
 /**
  * Used so we can do a quick check for single image seq
  * since they work a bit differently to normal image seq's (during transform).
  */
-bool SEQ_transform_single_image_check(Sequence *seq);
+bool SEQ_transform_single_image_check(const Sequence *seq);
 bool SEQ_transform_test_overlap(const Scene *scene, ListBase *seqbasep, Sequence *test);
 bool SEQ_transform_test_overlap_seq_seq(const Scene *scene, Sequence *seq1, Sequence *seq2);
 void SEQ_transform_translate_sequence(Scene *evil_scene, Sequence *seq, int delta);

source/blender/sequencer/intern/image_cache.cc

@@ -126,7 +126,7 @@ static bool seq_cache_hashcmp(const void *a_, const void *b_)
 }
 
 static float seq_cache_timeline_frame_to_frame_index(Scene *scene,
-                                                     Sequence *seq,
+                                                     const Sequence *seq,
                                                      float timeline_frame,
                                                      int type)
 {

source/blender/sequencer/intern/proxy.cc

@@ -184,7 +184,7 @@ static bool seq_proxy_get_filepath(Scene *scene,
   return true;
 }
 
-bool SEQ_can_use_proxy(const SeqRenderData *context, Sequence *seq, int psize)
+bool SEQ_can_use_proxy(const SeqRenderData *context, const Sequence *seq, int psize)
 {
   if (seq->strip->proxy == nullptr || !context->use_proxies) {
     return false;

source/blender/sequencer/intern/strip_time.cc

@@ -57,7 +57,7 @@ int seq_time_strip_original_content_length_get(const Scene *scene, const Sequenc
   return seq->len / SEQ_time_media_playback_rate_factor_get(scene, seq);
 }
 
-float SEQ_give_frame_index(const Scene *scene, Sequence *seq, float timeline_frame)
+float SEQ_give_frame_index(const Scene *scene, const Sequence *seq, float timeline_frame)
 {
   float frame_index;
   float sta = SEQ_time_start_frame_get(seq);
@@ -95,10 +95,6 @@ float SEQ_give_frame_index(const Scene *scene, Sequence *seq, float timeline_fra
   /* Clamp frame index to strip content frame range. */
   frame_index = clamp_f(frame_index, 0, frame_index_max);
 
-  if (seq->strobe < 1.0f) {
-    seq->strobe = 1.0f;
-  }
-
   if (seq->strobe > 1.0f) {
     frame_index -= fmodf(double(frame_index), double(seq->strobe));
   }

source/blender/sequencer/intern/strip_transform.cc

@@ -30,7 +30,7 @@
 #include "sequencer.hh"
 #include "strip_time.hh"
 
-bool SEQ_transform_single_image_check(Sequence *seq)
+bool SEQ_transform_single_image_check(const Sequence *seq)
 {
   return (seq->flag & SEQ_SINGLE_FRAME_CONTENT) != 0;
 }
@@ -77,7 +77,7 @@ bool SEQ_transform_seqbase_isolated_sel_check(ListBase *seqbase)
   return true;
 }
 
-bool SEQ_transform_sequence_can_be_translated(Sequence *seq)
+bool SEQ_transform_sequence_can_be_translated(const Sequence *seq)
 {
   return !(seq->type & SEQ_TYPE_EFFECT) || (SEQ_effect_get_num_inputs(seq->type) == 0);
 }