Cleanup: VSE: Clarify selection code

Rename a few functions to more accurately express their intent:
- `sequence_handle_size_get_clamped()` ->`strip_handle_draw_size_get()`
- `clickable_handle_size_get()` -> `inner_clickable_handle_size_get()`

Additionally:
- Move check for making strips unclickable when they are short enough in
  the vertical direction from `sequencer_main_cursor()` to
  `ED_sequencer_get_handle()`.
- Use `inner_clickable_handle_size_get()` in box select with handles.
- Add clarifying comments that calculate exact handle sizes.

There should be no functional changes (barring a tiny change in box
select with handle calculation).

source/blender/editors/space_sequencer/sequencer_intern.hh

@@ -141,7 +141,7 @@ int sequencer_draw_get_transform_preview_frame(Scene *scene);
 
 void sequencer_special_update_set(Strip *strip);
 /* Get handle width in 2d-View space. */
-float sequence_handle_size_get_clamped(const Scene *scene, Strip *strip, float pixelx);
+float strip_handle_draw_size_get(const Scene *scene, Strip *strip, float pixelx);
 
 /* UNUSED */
 /* void seq_reset_imageofs(SpaceSeq *sseq); */

source/blender/editors/space_sequencer/sequencer_select.cc

@@ -897,8 +897,13 @@ static void select_linked_time(const Scene *scene,
   }
 }
 
-/* Similar to `sequence_handle_size_get_clamped()` but allows for larger clickable area. */
-static float clickable_handle_size_get(const Scene *scene, const Strip *strip, const View2D *v2d)
+/* Similar to `strip_handle_draw_size_get()`, but returns a larger clickable area that is
+ * the same for a given zoom level no matter whether "simplified tweaking" is turned off or on.
+ * `strip_clickable_areas_get` will pad this past strip bounds by 1/3 of the inner handle size,
+ * making the full handle size either 15 + 5 = 20px or 1/4 + 1/12 = 1/3 of the strip size. */
+static float inner_clickable_handle_size_get(const Scene *scene,
+                                             const Strip *strip,
+                                             const View2D *v2d)
 {
   const float pixelx = 1 / UI_view2d_scale_get_x(v2d);
   const float strip_len = SEQ_time_right_handle_frame_get(scene, strip) -
@@ -918,6 +923,10 @@ bool ED_sequencer_can_select_handle(const Scene *scene, const Strip *strip, cons
     return false;
   }
 
+  /* This ensures clickable handles are deactivated when the strip gets too small (25 or 15
+   * frames). Since the full handle size for a small strip is 1/3 of the strip size (see
+   * `inner_clickable_handle_size_get`), this means handles cannot be smaller than 25/3 = 8px for
+   * simple tweaking, 15/3 = 5px for legacy behavior. */
   int min_len = 25 * U.pixelsize;
   if ((U.sequencer_editor_flag & USER_SEQ_ED_SIMPLE_TWEAKING) == 0) {
     min_len = 15 * U.pixelsize;
@@ -929,6 +938,11 @@ bool ED_sequencer_can_select_handle(const Scene *scene, const Strip *strip, cons
   if (strip_len / pixelx < min_len) {
     return false;
   }
+
+  if (UI_view2d_scale_get_y(v2d) < 16 * U.pixelsize) {
+    return false;
+  }
+
   return true;
 }
 
@@ -943,11 +957,11 @@ static void strip_clickable_areas_get(const Scene *scene,
   *r_left_handle = *r_body;
   *r_right_handle = *r_body;
 
-  const float handsize = clickable_handle_size_get(scene, strip, v2d);
-  BLI_rctf_pad(r_left_handle, handsize / 3, 0.0f);
-  BLI_rctf_pad(r_right_handle, handsize / 3, 0.0f);
+  const float handsize = inner_clickable_handle_size_get(scene, strip, v2d);
   r_left_handle->xmax = r_body->xmin + handsize;
   r_right_handle->xmin = r_body->xmax - handsize;
+  BLI_rctf_pad(r_left_handle, handsize / 3, 0.0f);
+  BLI_rctf_pad(r_right_handle, handsize / 3, 0.0f);
   BLI_rctf_pad(r_body, -handsize, 0.0f);
 }
 
@@ -2046,9 +2060,8 @@ static int sequencer_box_select_exec(bContext *C, wmOperator *op)
     strip_rectf(scene, strip, &rq);
     if (BLI_rctf_isect(&rq, &rectf, nullptr)) {
       if (handles) {
-        /* Get the handles draw size. */
-        float pixelx = BLI_rctf_size_x(&v2d->cur) / BLI_rcti_size_x(&v2d->mask);
-        float handsize = sequence_handle_size_get_clamped(scene, strip, pixelx) * 4;
+        /* Get the clickable handle size, ignoring padding. */
+        float handsize = inner_clickable_handle_size_get(scene, strip, v2d) * 4;
 
         /* Right handle. */
         if (rectf.xmax > (SEQ_time_right_handle_frame_get(scene, strip) - handsize)) {

source/blender/editors/space_sequencer/sequencer_timeline_draw.cc

@@ -234,7 +234,7 @@ static StripDrawContext strip_draw_context_get(TimelineDrawContext *ctx, Strip *
                                   !strip_ctx.can_draw_strip_content);
   strip_ctx.is_active_strip = strip == SEQ_select_active_get(scene);
   strip_ctx.is_single_image = SEQ_transform_single_image_check(strip);
-  strip_ctx.handle_width = sequence_handle_size_get_clamped(ctx->scene, strip, ctx->pixelx);
+  strip_ctx.handle_width = strip_handle_draw_size_get(ctx->scene, strip, ctx->pixelx);
   strip_ctx.show_strip_color_tag = (ctx->sseq->timeline_overlay.flag &
                                     SEQ_TIMELINE_SHOW_STRIP_COLOR_TAG);
 
@@ -772,7 +772,7 @@ static void draw_handle_transform_text(const TimelineDrawContext *timeline_ctx,
   UI_view2d_text_cache_add(timeline_ctx->v2d, text_x, text_y, numstr, numstr_len, col);
 }
 
-float sequence_handle_size_get_clamped(const Scene *scene, Strip *strip, const float pixelx)
+float strip_handle_draw_size_get(const Scene *scene, Strip *strip, const float pixelx)
 {
   const bool use_thin_handle = (U.sequencer_editor_flag & USER_SEQ_ED_SIMPLE_TWEAKING) != 0;
   const float handle_size = use_thin_handle ? 5.0f : 8.0f;

source/blender/editors/space_sequencer/space_sequencer.cc

@@ -707,9 +707,7 @@ static void sequencer_main_cursor(wmWindow *win, ScrArea *area, ARegion *region)
     return;
   }
 
-  const float scale_y = UI_view2d_scale_get_y(v2d);
-
-  if (!ED_sequencer_can_select_handle(scene, selection.seq1, v2d) || scale_y < 16 * U.pixelsize) {
+  if (!ED_sequencer_can_select_handle(scene, selection.seq1, v2d)) {
     WM_cursor_set(win, wmcursor);
     return;
   }