V2D navigating flag by Richard Antalik

The goal is to provide thumbnails in the rectangle coloured strips. Works for
movie clips and image sequences. The thumbnails are loaded from source
using separate thread and stores them in cache. The drawing is called inside the
drawing for each strip, and takes images from cache. Drawing is below the
handles from one end of strip to other, inside view only. The job for caching
is called when images are not available, or there is view change.

All strip operations are valid, and overlap of strip adds transparency to the
image. Images are shown only when strip size is wide enough for clear
visibility of images, and the thumbnails represent source footage clearly.

Cache is limited to 5000 thumbnails and performs cleanup of non visible images
when limit crossed.

Related Task : T89143

Differential Revision: https://developer.blender.org/D12266

release/scripts/startup/bl_ui/space_sequencer.py

@@ -250,7 +250,8 @@ class SEQUENCER_PT_sequencer_overlay(Panel):
         layout.prop(st, "show_strip_offset", text="Offsets")
         layout.prop(st, "show_fcurves", text="F-Curves")
         layout.prop(st, "show_grid", text="Grid")
-
+        layout.prop(st, "show_thumbnails", text="Thumbnails")
+        
         layout.separator()
 
         layout.prop_menu_enum(st, "waveform_display_type")

source/blender/blenkernel/BKE_blender_version.h

@@ -39,7 +39,7 @@ extern "C" {
 
 /* Blender file format version. */
 #define BLENDER_FILE_VERSION BLENDER_VERSION
-#define BLENDER_FILE_SUBVERSION 20
+#define BLENDER_FILE_SUBVERSION 21
 
 /* Minimum Blender version that supports reading file written with the current
  * version. Older Blender versions will test this and show a warning if the file

source/blender/blenloader/intern/versioning_300.c

@@ -1111,6 +1111,32 @@ void blo_do_versions_300(FileData *fd, Library *UNUSED(lib), Main *bmain)
     }
   }
 
+  if (!MAIN_VERSION_ATLEAST(bmain, 300, 20)) {
+    LISTBASE_FOREACH (bScreen *, screen, &bmain->screens) {
+      LISTBASE_FOREACH (ScrArea *, area, &screen->areabase) {
+        LISTBASE_FOREACH (SpaceLink *, sl, &area->spacedata) {
+          if (sl->spacetype == SPACE_SEQ) {
+            SpaceSeq *sseq = (SpaceSeq *)sl;
+            sseq->flag |= SEQ_SHOW_THUMBNAILS;
+          }
+        }
+      }
+    }
+  }
+
+  if (!MAIN_VERSION_ATLEAST(bmain, 300, 21)) {
+    LISTBASE_FOREACH (bScreen *, screen, &bmain->screens) {
+      LISTBASE_FOREACH (ScrArea *, area, &screen->areabase) {
+        LISTBASE_FOREACH (SpaceLink *, sl, &area->spacedata) {
+          if (sl->spacetype == SPACE_SEQ) {
+            SpaceSeq *sseq = (SpaceSeq *)sl;
+            sseq->flag |= SEQ_SHOW_THUMBNAILS;
+          }
+        }
+      }
+    }
+  }
+
   /**
    * Versioning code until next subversion bump goes here.
    *

source/blender/blenloader/intern/versioning_defaults.c

@@ -157,7 +157,7 @@ static void blo_update_defaults_screen(bScreen *screen,
       SpaceSeq *seq = area->spacedata.first;
       seq->flag |= SEQ_SHOW_MARKERS | SEQ_SHOW_FCURVES | SEQ_ZOOM_TO_FIT | SEQ_SHOW_STRIP_OVERLAY |
                    SEQ_SHOW_STRIP_SOURCE | SEQ_SHOW_STRIP_NAME | SEQ_SHOW_STRIP_DURATION |
-                   SEQ_SHOW_GRID;
+                   SEQ_SHOW_GRID | SEQ_SHOW_THUMBNAILS;
 
       seq->render_size = SEQ_RENDER_SIZE_PROXY_100;
       seq->flag |= SEQ_USE_PROXIES;

source/blender/editors/interface/interface_templates.c

@@ -5823,6 +5823,11 @@ void uiTemplateRunningJobs(uiLayout *layout, bContext *C)
       icon = ICON_SEQUENCE;
       break;
     }
+    if (WM_jobs_test(wm, scene, WM_JOB_TYPE_SEQ_DRAW_THUMBNAIL)) {
+      handle_event = B_STOPSEQ;
+      icon = ICON_SEQUENCE;
+      break;
+    }
     if (WM_jobs_test(wm, scene, WM_JOB_TYPE_CLIP_BUILD_PROXY)) {
       handle_event = B_STOPCLIP;
       icon = ICON_TRACKER;

source/blender/editors/interface/view2d_ops.c

@@ -147,6 +147,8 @@ static void view_pan_init(bContext *C, wmOperator *op)
   const float winy = (float)(BLI_rcti_size_y(&vpd->region->winrct) + 1);
   vpd->facx = (BLI_rctf_size_x(&vpd->v2d->cur)) / winx;
   vpd->facy = (BLI_rctf_size_y(&vpd->v2d->cur)) / winy;
+
+  vpd->v2d->flag |= V2D_IS_NAVIGATING;
 }
 
 /* apply transform to view (i.e. adjust 'cur' rect) */
@@ -190,6 +192,8 @@ static void view_pan_apply(bContext *C, wmOperator *op)
 /* Cleanup temp custom-data. */
 static void view_pan_exit(wmOperator *op)
 {
+  v2dViewPanData *vpd = op->customdata;
+  vpd->v2d->flag &= ~V2D_IS_NAVIGATING;
   MEM_SAFE_FREE(op->customdata);
 }
 
@@ -305,7 +309,7 @@ static int view_pan_modal(bContext *C, wmOperator *op, const wmEvent *event)
   return OPERATOR_RUNNING_MODAL;
 }
 
-static void view_pan_cancel(bContext *UNUSED(C), wmOperator *op)
+static void view_pan_cancel(bContext *C, wmOperator *op)
 {
   view_pan_exit(op);
 }
@@ -358,6 +362,7 @@ static int view_edge_pan_modal(bContext *C, wmOperator *op, const wmEvent *event
   View2DEdgePanData *vpd = op->customdata;
 
   if (event->val == KM_RELEASE || event->type == EVT_ESCKEY) {
+    vpd->v2d->flag &= ~V2D_IS_NAVIGATING;
     MEM_SAFE_FREE(op->customdata);
     return (OPERATOR_FINISHED | OPERATOR_PASS_THROUGH);
   }
@@ -371,6 +376,8 @@ static int view_edge_pan_modal(bContext *C, wmOperator *op, const wmEvent *event
 
 static void view_edge_pan_cancel(bContext *UNUSED(C), wmOperator *op)
 {
+  v2dViewPanData *vpd = op->customdata;
+  vpd->v2d->flag &= ~V2D_IS_NAVIGATING;
   MEM_SAFE_FREE(op->customdata);
 }
 
@@ -680,6 +687,8 @@ static void view_zoomdrag_init(bContext *C, wmOperator *op)
   vzd->v2d = &vzd->region->v2d;
   /* False by default. Interactive callbacks (ie invoke()) can set it to true. */
   vzd->zoom_to_mouse_pos = false;
+
+  vzd->v2d->flag |= V2D_IS_NAVIGATING;
 }
 
 /* apply transform to view (i.e. adjust 'cur' rect) */
@@ -809,7 +818,8 @@ static void view_zoomstep_apply(bContext *C, wmOperator *op)
 static void view_zoomstep_exit(wmOperator *op)
 {
   UI_view2d_zoom_cache_reset();
-
+  v2dViewZoomData *vzd = op->customdata;
+  vzd->v2d->flag &= ~V2D_IS_NAVIGATING;
   MEM_SAFE_FREE(op->customdata);
 }
 
@@ -1041,6 +1051,7 @@ static void view_zoomdrag_exit(bContext *C, wmOperator *op)
 
   if (op->customdata) {
     v2dViewZoomData *vzd = op->customdata;
+    vzd->v2d->flag &= ~V2D_IS_NAVIGATING;
 
     if (vzd->timer) {
       WM_event_remove_timer(CTX_wm_manager(C), CTX_wm_window(C), vzd->timer);

source/blender/editors/space_sequencer/sequencer_draw.c

@@ -25,6 +25,7 @@
 #include <string.h>
 
 #include "BLI_blenlib.h"
+#include "BLI_ghash.h"
 #include "BLI_math.h"
 #include "BLI_string_utils.h"
 #include "BLI_threads.h"
@@ -1277,6 +1278,391 @@ static void draw_seq_fcurve_overlay(
   }
 }
 
+typedef struct ThumbnailDrawJob {
+  SeqRenderData context;
+  GHash *sequences_ghash;
+  Scene *scene;
+  rctf *view_area;
+  float pixelx;
+  float pixely;
+} ThumbnailDrawJob;
+
+typedef struct ThumbDataItem {
+  Sequence *seq_dupli;
+  Scene *scene;
+} ThumbDataItem;
+
+static void thumbnail_hash_data_free(void *val)
+{
+  ThumbDataItem *item = val;
+  SEQ_sequence_free(item->scene, item->seq_dupli, 0);
+  MEM_freeN(val);
+}
+
+static void thumbnail_freejob(void *data)
+{
+  ThumbnailDrawJob *tj = data;
+  BLI_ghash_free(tj->sequences_ghash, NULL, thumbnail_hash_data_free);
+  MEM_freeN(tj->view_area);
+  MEM_freeN(tj);
+}
+
+static void thumbnail_endjob(void *data)
+{
+  ThumbnailDrawJob *tj = data;
+  WM_main_add_notifier(NC_SCENE | ND_SEQUENCER, tj->scene);
+}
+
+static bool check_seq_need_thumbnails(Sequence *seq, rctf *view_area)
+{
+  if (seq->type != SEQ_TYPE_MOVIE && seq->type != SEQ_TYPE_IMAGE) {
+    return false;
+  }
+  if (min_ii(seq->startdisp, seq->start) > view_area->xmax) {
+    return false;
+  }
+  else if (max_ii(seq->enddisp, seq->start + seq->len) < view_area->xmin) {
+    return false;
+  }
+  else if (seq->machine + 1.0f < view_area->ymin) {
+    return false;
+  }
+  else if (seq->machine > view_area->ymax) {
+    return false;
+  }
+
+  return true;
+}
+
+static void seq_get_thumb_image_dimensions(Sequence *seq,
+                                           float pixelx,
+                                           float pixely,
+                                           float *r_thumb_width,
+                                           float *r_thumb_height,
+                                           float *r_image_width,
+                                           float *r_image_height)
+{
+  float image_width = seq->strip->stripdata->orig_width;
+  float image_height = seq->strip->stripdata->orig_height;
+
+  /* Fix the dimensions to be max SEQ_RENDER_THUMB_SIZE (256) for x or y. */
+  float aspect_ratio = (float)image_width / image_height;
+  if (image_width > image_height) {
+    image_width = SEQ_RENDER_THUMB_SIZE;
+    image_height = round_fl_to_int(image_width / aspect_ratio);
+  }
+  else {
+    image_height = SEQ_RENDER_THUMB_SIZE;
+    image_width = round_fl_to_int(image_height * aspect_ratio);
+  }
+
+  /* Calculate thumb dimensions. */
+  float thumb_height = (SEQ_STRIP_OFSTOP - SEQ_STRIP_OFSBOTTOM) - (20 * U.dpi_fac * pixely);
+  aspect_ratio = ((float)image_width) / image_height;
+  float thumb_h_px = thumb_height / pixely;
+  float thumb_width = aspect_ratio * thumb_h_px * pixelx;
+
+  if (r_thumb_height == NULL) {
+    *r_thumb_width = thumb_width;
+    return;
+  }
+
+  *r_thumb_height = thumb_height;
+  *r_image_width = image_width;
+  *r_image_height = image_height;
+  *r_thumb_width = thumb_width;
+}
+
+static float seq_thumbnail_get_start_frame(Sequence *seq, float frame_step, rctf *view_area)
+{
+  if (seq->start > view_area->xmin) {
+    return seq->start;
+  }
+
+  /* Drawing and caching both check to see if stristart_framep is in view area or not before
+   * calling this function so assuming strip/part of strip in view. */
+
+  int no_invisible_thumbs = (view_area->xmin - seq->start) / frame_step;
+  return ((no_invisible_thumbs - 1) * frame_step) + seq->start;
+}
+
+static void thumbnail_start_job(void *data, short *stop, short *do_update, float *progress)
+{
+  ThumbnailDrawJob *tj = data;
+  float start_frame, frame_step;
+
+  GHashIterator gh_iter;
+  BLI_ghashIterator_init(&gh_iter, tj->sequences_ghash);
+  while (!BLI_ghashIterator_done(&gh_iter) & !*stop) {
+    Sequence *seq_orig = BLI_ghashIterator_getKey(&gh_iter);
+    ThumbDataItem *val = BLI_ghash_lookup(tj->sequences_ghash, seq_orig);
+
+    if (check_seq_need_thumbnails(seq_orig, tj->view_area)) {
+      seq_get_thumb_image_dimensions(
+          val->seq_dupli, tj->pixelx, tj->pixely, &frame_step, NULL, NULL, NULL);
+      start_frame = seq_thumbnail_get_start_frame(seq_orig, frame_step, tj->view_area);
+      SEQ_render_thumbnails(
+          &tj->context, val->seq_dupli, seq_orig, start_frame, frame_step, tj->view_area, stop);
+    }
+    BLI_ghashIterator_step(&gh_iter);
+  }
+  UNUSED_VARS(do_update, progress);
+}
+
+static SeqRenderData sequencer_thumbnail_context_init(const bContext *C)
+{
+  struct Main *bmain = CTX_data_main(C);
+  struct Depsgraph *depsgraph = CTX_data_depsgraph_pointer(C);
+  Scene *scene = CTX_data_scene(C);
+  SpaceSeq *sseq = CTX_wm_space_seq(C);
+  SeqRenderData context = {0};
+
+  /* Taking rectx and recty as 0 as dimensions not known here, and context is used to calculate
+   * hash key but not necessary as other variables of SeqRenderData are unique enough. */
+  SEQ_render_new_render_data(bmain, depsgraph, scene, 0, 0, sseq->render_size, false, &context);
+  context.view_id = BKE_scene_multiview_view_id_get(&scene->r, STEREO_LEFT_NAME);
+  context.use_proxies = false;
+
+  return context;
+}
+
+static GHash *sequencer_thumbnail_ghash_init(const bContext *C, View2D *v2d, Editing *ed)
+{
+  Scene *scene = CTX_data_scene(C);
+
+  /* Set the data for thumbnail caching job. */
+  GHash *thumb_data_hash = BLI_ghash_ptr_new("seq_duplicates_and_origs");
+
+  LISTBASE_FOREACH (Sequence *, seq, ed->seqbasep) {
+    ThumbDataItem *val_need_update = BLI_ghash_lookup(thumb_data_hash, seq);
+    if (val_need_update == NULL && check_seq_need_thumbnails(seq, &v2d->cur)) {
+      ThumbDataItem *val = MEM_callocN(sizeof(ThumbDataItem), "Thumbnail Hash Values");
+      val->seq_dupli = SEQ_sequence_dupli_recursive(scene, scene, NULL, seq, 0);
+      val->scene = scene;
+      BLI_ghash_insert(thumb_data_hash, seq, val);
+    }
+    else {
+      if (val_need_update != NULL) {
+        val_need_update->seq_dupli->start = seq->start;
+        val_need_update->seq_dupli->startdisp = seq->startdisp;
+      }
+    }
+  }
+
+  return thumb_data_hash;
+}
+
+static void sequencer_thumbnail_init_job(const bContext *C, View2D *v2d, Editing *ed)
+{
+  wmJob *wm_job;
+  ThumbnailDrawJob *tj = NULL;
+  ScrArea *area = CTX_wm_area(C);
+  wm_job = WM_jobs_get(CTX_wm_manager(C),
+                       CTX_wm_window(C),
+                       CTX_data_scene(C),
+                       "Draw Thumbnails",
+                       0,
+                       WM_JOB_TYPE_SEQ_DRAW_THUMBNAIL);
+
+  /* Get the thumbnail job if it exists. */
+  tj = WM_jobs_customdata_get(wm_job);
+  if (!tj) {
+    tj = MEM_callocN(sizeof(ThumbnailDrawJob), "Thumbnail cache job");
+
+    /* Duplicate value of v2d->cur and v2d->tot to have module separation. */
+    rctf *view_area = MEM_callocN(sizeof(struct rctf), "viewport area");
+    view_area->xmax = v2d->cur.xmax;
+    view_area->xmin = v2d->cur.xmin;
+    view_area->ymax = v2d->cur.ymax;
+    view_area->ymin = v2d->cur.ymin;
+
+    tj->scene = CTX_data_scene(C);
+    tj->view_area = view_area;
+    tj->context = sequencer_thumbnail_context_init(C);
+    tj->sequences_ghash = sequencer_thumbnail_ghash_init(C, v2d, ed);
+    tj->pixelx = BLI_rctf_size_x(&v2d->cur) / BLI_rcti_size_x(&v2d->mask);
+    tj->pixely = BLI_rctf_size_y(&v2d->cur) / BLI_rcti_size_y(&v2d->mask);
+    WM_jobs_customdata_set(wm_job, tj, thumbnail_freejob);
+    WM_jobs_timer(wm_job, 0.1, NC_SCENE | ND_SEQUENCER, NC_SCENE | ND_SEQUENCER);
+    WM_jobs_callbacks(wm_job, thumbnail_start_job, NULL, NULL, thumbnail_endjob);
+  }
+
+  if (!WM_jobs_is_running(wm_job)) {
+    G.is_break = false;
+    WM_jobs_start(CTX_wm_manager(C), wm_job);
+  }
+  else {
+    WM_event_add_notifier(C, NC_SCENE | ND_SEQUENCER, NULL);
+  }
+
+  ED_area_tag_redraw(area);
+}
+
+static void sequencer_thumbnail_start_job_if_necessary(const bContext *C,
+                                                       Editing *ed,
+                                                       View2D *v2d,
+                                                       bool thumbnail_is_missing)
+{
+  SpaceSeq *sseq = CTX_wm_space_seq(C);
+
+  if ((v2d->flag & V2D_IS_NAVIGATING) != 0) {
+    WM_event_add_notifier(C, NC_SCENE | ND_SEQUENCER, NULL);
+    return;
+  }
+
+  /* Leftover is set to true if missing image in strip. False when normal call to all strips done.
+   */
+  if (v2d->cur.xmax != sseq->runtime.last_thumbnail_area.xmax ||
+      v2d->cur.ymax != sseq->runtime.last_thumbnail_area.ymax || thumbnail_is_missing) {
+
+    /* Stop the job first as view has changed. Pointless to continue old job. */
+    if (v2d->cur.xmax != sseq->runtime.last_thumbnail_area.xmax ||
+        v2d->cur.ymax != sseq->runtime.last_thumbnail_area.ymax) {
+      WM_jobs_stop(CTX_wm_manager(C), NULL, thumbnail_start_job);
+    }
+
+    sequencer_thumbnail_init_job(C, v2d, ed);
+    sseq->runtime.last_thumbnail_area = v2d->cur;
+  }
+}
+
+/* Don't display thumbnails only when zooming. Panning doesn't cause issues. */
+static bool sequencer_thumbnail_v2d_is_navigating(const bContext *C)
+{
+  ARegion *region = CTX_wm_region(C);
+  View2D *v2d = &region->v2d;
+  SpaceSeq *sseq = CTX_wm_space_seq(C);
+
+  if ((v2d->flag & V2D_IS_NAVIGATING) == 0) {
+    return false;
+  }
+
+  double x_diff = fabs(BLI_rctf_size_x(&sseq->runtime.last_thumbnail_area) -
+                       BLI_rctf_size_x(&v2d->cur));
+  double y_diff = fabs(BLI_rctf_size_y(&sseq->runtime.last_thumbnail_area) -
+                       BLI_rctf_size_y(&v2d->cur));
+  return x_diff > 0.01 || y_diff > 0.01;
+}
+
+static void draw_seq_strip_thumbnail(View2D *v2d,
+                                     const bContext *C,
+                                     Scene *scene,
+                                     Sequence *seq,
+                                     float y1,
+                                     float y2,
+                                     float pixelx,
+                                     float pixely)
+{
+  bool clipped = false;
+  float image_height, image_width, thumb_width, thumb_height;
+  rcti crop;
+
+  /* If width of the strip too small ignore drawing thumbnails. */
+  if ((y2 - y1) / pixely <= 40 * U.dpi_fac)
+    return;
+
+  if (sequencer_thumbnail_v2d_is_navigating(C)) {
+    WM_event_add_notifier(C, NC_SCENE | ND_SEQUENCER, NULL);
+    return;
+  }
+
+  SeqRenderData context = sequencer_thumbnail_context_init(C);
+  seq_get_thumb_image_dimensions(
+      seq, pixelx, pixely, &thumb_width, &thumb_height, &image_width, &image_height);
+
+  float thumb_y_end = y1 + thumb_height - pixely;
+  float thumb_x_start = seq->start;
+
+  float cut_off = 0;
+  float upper_thumb_bound = (seq->endstill) ? (seq->start + seq->len) : seq->enddisp;
+  if (seq->type == SEQ_TYPE_IMAGE) {
+    upper_thumb_bound = seq->enddisp;
+  }
+
+  /* Start drawing. */
+
+  thumb_x_start = seq_thumbnail_get_start_frame(seq, thumb_width, &v2d->cur);
+  float thumb_x_end;
+  while (thumb_x_start < upper_thumb_bound) {
+    thumb_x_end = thumb_x_start + thumb_width;
+    clipped = false;
+
+    /* Checks to make sure that thumbs are loaded only when in view and within the confines of the
+     * strip. Some may not be required but better to have conditions for safety as x1 here is
+     * point to start caching from and not drawing. */
+    if (thumb_x_start > v2d->cur.xmax)
+      break;
+
+    if (thumb_x_end < v2d->cur.xmin) {
+      thumb_x_start = thumb_x_end;
+      continue;
+    }
+
+    /* Ignore thumbs to the left of strip. */
+    if (thumb_x_end < seq->startdisp) {
+      thumb_x_start = thumb_x_end;
+      continue;
+    }
+
+    /* Set the clipping bound to show the left handle moving over thumbs and not shift thumbs. */
+    if (IN_RANGE_INCL(seq->startdisp, thumb_x_start, thumb_x_end)) {
+      cut_off = seq->startdisp - thumb_x_start;
+      clipped = true;
+    }
+
+    /* Clip if full thumbnail cannot be displayed. */
+    if (thumb_x_end > (upper_thumb_bound)) {
+      thumb_x_end = upper_thumb_bound;
+      clipped = true;
+      if (thumb_x_end - thumb_x_start < 1)
+        break;
+    }
+
+    float zoom_x = thumb_width / image_width;
+    float zoom_y = thumb_height / image_height;
+
+    float cropx_min = (cut_off / pixelx) / (zoom_y / pixely);
+    float cropx_max = ((thumb_x_end - thumb_x_start) / pixelx) / (zoom_y / pixely);
+    if (cropx_max == (thumb_x_end - thumb_x_start)) {
+      cropx_max = cropx_max + 1;
+    }
+    BLI_rcti_init(&crop, (int)(cropx_min), (int)cropx_max, 0, (int)(image_height)-1);
+
+    /* Get the image. */
+    ImBuf *ibuf = SEQ_get_thumbnail(&context, seq, roundf(thumb_x_start), &crop, clipped);
+
+    if (!ibuf) {
+      sequencer_thumbnail_start_job_if_necessary(C, scene->ed, v2d, true);
+      break;
+    }
+
+    /* Transparency on overlap. */
+    if (seq->flag & SEQ_OVERLAP) {
+      GPU_blend(GPU_BLEND_ALPHA);
+      unsigned char *buf = (unsigned char *)ibuf->rect;
+      for (int pixel = ibuf->x * ibuf->y; pixel--; buf += 4) {
+        buf[3] = OVERLAP_ALPHA;
+      }
+    }
+
+    ED_draw_imbuf_ctx_clipping(C,
+                               ibuf,
+                               thumb_x_start + cut_off,
+                               y1,
+                               true,
+                               thumb_x_start + cut_off,
+                               y1,
+                               thumb_x_end,
+                               thumb_y_end,
+                               zoom_x,
+                               zoom_y);
+    IMB_freeImBuf(ibuf);
+    GPU_blend(GPU_BLEND_NONE);
+    cut_off = 0;
+    thumb_x_start = thumb_x_end;
+  }
+}
+
 /* Draw visible strips. Bounds check are already made. */
 static void draw_seq_strip(const bContext *C,
                            SpaceSeq *sseq,
@@ -1348,6 +1734,11 @@ static void draw_seq_strip(const bContext *C,
     drawmeta_contents(scene, seq, x1, y1, x2, y2);
   }
 
+  if ((sseq->flag & SEQ_SHOW_STRIP_OVERLAY) && (sseq->flag & SEQ_SHOW_THUMBNAILS) &&
+      (seq->type == SEQ_TYPE_MOVIE || seq->type == SEQ_TYPE_IMAGE)) {
+    draw_seq_strip_thumbnail(v2d, C, scene, seq, y1, y2, pixelx, pixely);
+  }
+
   if ((sseq->flag & SEQ_SHOW_STRIP_OVERLAY) && (sseq->flag & SEQ_SHOW_FCURVES)) {
     draw_seq_fcurve_overlay(scene, v2d, seq, x1, y1, x2, y2, pixelx);
   }
@@ -2194,6 +2585,8 @@ static void draw_seq_strips(const bContext *C, Editing *ed, ARegion *region)
   int sel = 0, j;
   float pixelx = BLI_rctf_size_x(&v2d->cur) / BLI_rcti_size_x(&v2d->mask);
 
+  sequencer_thumbnail_start_job_if_necessary(C, ed, v2d, false);
+
   /* Loop through twice, first unselected, then selected. */
   for (j = 0; j < 2; j++) {
     Sequence *seq;

source/blender/editors/space_sequencer/sequencer_edit.c

@@ -579,7 +579,6 @@ static int sequencer_slip_invoke(bContext *C, wmOperator *op, const wmEvent *eve
 static bool sequencer_slip_recursively(Scene *scene, SlipData *data, int offset)
 {
   /* Only data types supported for now. */
-  Editing *ed = SEQ_editing_get(scene);
   bool changed = false;
 
   /* Iterate in reverse so meta-strips are iterated after their children. */
@@ -633,7 +632,10 @@ static bool sequencer_slip_recursively(Scene *scene, SlipData *data, int offset)
     }
   }
   if (changed) {
-    SEQ_relations_free_imbuf(scene, &ed->seqbase, false);
+    for (int i = data->num_seq - 1; i >= 0; i--) {
+      Sequence *seq = data->seq_array[i];
+      SEQ_relations_invalidate_cache_preprocessed(scene, seq);
+    }
   }
   return changed;
 }

source/blender/editors/space_sequencer/space_sequencer.c

@@ -100,8 +100,11 @@ static SpaceLink *sequencer_create(const ScrArea *UNUSED(area), const Scene *sce
   sseq->mainb = SEQ_DRAW_IMG_IMBUF;
   sseq->flag = SEQ_SHOW_GPENCIL | SEQ_USE_ALPHA | SEQ_SHOW_MARKERS | SEQ_SHOW_FCURVES |
                SEQ_ZOOM_TO_FIT | SEQ_SHOW_STRIP_OVERLAY | SEQ_SHOW_STRIP_NAME |
-               SEQ_SHOW_STRIP_SOURCE | SEQ_SHOW_STRIP_DURATION | SEQ_SHOW_GRID;
+               SEQ_SHOW_STRIP_SOURCE | SEQ_SHOW_STRIP_DURATION | SEQ_SHOW_GRID |
+               SEQ_SHOW_THUMBNAILS;
 
+  struct rctf temp = {0, 0, 0, 0};
+  sseq->runtime.last_thumbnail_area = temp;
   /* Tool header. */
   region = MEM_callocN(sizeof(ARegion), "tool header for sequencer");
 

source/blender/makesdna/DNA_sequence_types.h

@@ -722,6 +722,7 @@ enum {
 
   SEQ_CACHE_PREFETCH_ENABLE = (1 << 10),
   SEQ_CACHE_DISK_CACHE_ENABLE = (1 << 11),
+  SEQ_CACHE_STORE_THUMBNAIL = (1 << 12),
 };
 
 #ifdef __cplusplus

source/blender/makesdna/DNA_space_types.h

@@ -576,6 +576,10 @@ typedef enum eSpaceNla_Flag {
 /** \name Sequence Editor
  * \{ */
 
+typedef struct SpaceSeqRuntime {
+  struct rctf last_thumbnail_area;
+} SpaceSeqRuntime;
+
 /* Sequencer */
 typedef struct SpaceSeq {
   SpaceLink *next, *prev;
@@ -616,6 +620,10 @@ typedef struct SpaceSeq {
   /** Multiview current eye - for internal use. */
   char multiview_eye;
   char _pad2[7];
+
+  /** Required for Thumbnail caching job call condition */
+  SpaceSeqRuntime runtime;
+
 } SpaceSeq;
 
 /* SpaceSeq.mainb */
@@ -655,6 +663,7 @@ typedef enum eSpaceSeq_Flag {
   SEQ_SHOW_STRIP_DURATION = (1 << 16),
   SEQ_USE_PROXIES = (1 << 17),
   SEQ_SHOW_GRID = (1 << 18),
+  SEQ_SHOW_THUMBNAILS = (1 << 19),
 } eSpaceSeq_Flag;
 
 /* SpaceSeq.view */

source/blender/makesdna/DNA_view2d_types.h

@@ -132,6 +132,8 @@ enum {
   V2D_PIXELOFS_X = (1 << 2),
   /* apply pixel offsets on y-axis when setting view matrices */
   V2D_PIXELOFS_Y = (1 << 3),
+  /* zoom, pan or similar action is in progress */
+  V2D_IS_NAVIGATING = (1 << 9),
   /* view settings need to be set still... */
   V2D_IS_INIT = (1 << 10),
 };

source/blender/makesrna/intern/rna_space.c

@@ -5561,6 +5561,11 @@ static void rna_def_space_sequencer(BlenderRNA *brna)
   RNA_def_property_boolean_sdna(prop, NULL, "flag", SEQ_SHOW_GRID);
   RNA_def_property_ui_text(prop, "Show Grid", "Show vertical grid lines");
   RNA_def_property_update(prop, NC_SPACE | ND_SPACE_SEQUENCER, NULL);
+
+  prop = RNA_def_property(srna, "show_thumbnails", PROP_BOOLEAN, PROP_NONE);
+  RNA_def_property_boolean_sdna(prop, NULL, "flag", SEQ_SHOW_THUMBNAILS);
+  RNA_def_property_ui_text(prop, "Show Thumbnails", "Show strip thumbnails");
+  RNA_def_property_update(prop, NC_SPACE | ND_SPACE_SEQUENCER, NULL);
 }
 
 static void rna_def_space_text(BlenderRNA *brna)

source/blender/sequencer/SEQ_render.h

@@ -27,6 +27,8 @@
 extern "C" {
 #endif
 
+#define SEQ_RENDER_THUMB_SIZE 256
+
 struct ListBase;
 struct Main;
 struct Scene;
@@ -67,6 +69,15 @@ struct ImBuf *SEQ_render_give_ibuf(const SeqRenderData *context,
 struct ImBuf *SEQ_render_give_ibuf_direct(const SeqRenderData *context,
                                           float timeline_frame,
                                           struct Sequence *seq);
+void SEQ_render_thumbnails(struct SeqRenderData *context,
+                           struct Sequence *seq,
+                           struct Sequence *seq_orig,
+                           float start_frame,
+                           float frame_step,
+                           rctf *view_area,
+                           short *stop);
+struct ImBuf *SEQ_get_thumbnail(
+    SeqRenderData *context, struct Sequence *seq, float timeline_frame, rcti *crop, bool clipped);
 void SEQ_render_init_colorspace(struct Sequence *seq);
 void SEQ_render_new_render_data(struct Main *bmain,
                                 struct Depsgraph *depsgraph,

source/blender/sequencer/intern/image_cache.c

@@ -104,6 +104,7 @@
 #define DCACHE_IMAGES_PER_FILE 100
 #define DCACHE_CURRENT_VERSION 2
 #define COLORSPACE_NAME_MAX 64 /* XXX: defined in imb intern */
+#define THUMB_CACHE_LIMIT 5000
 
 typedef struct DiskCacheHeaderEntry {
   unsigned char encoding;
@@ -148,6 +149,7 @@ typedef struct SeqCache {
   struct BLI_mempool *items_pool;
   struct SeqCacheKey *last_key;
   SeqDiskCache *disk_cache;
+  int thumbnail_count;
 } SeqCache;
 
 typedef struct SeqCacheItem {
@@ -776,7 +778,7 @@ static float seq_cache_timeline_frame_to_frame_index(Sequence *seq, float timeli
   /* With raw images, map timeline_frame to strip input media frame range. This means that static
    * images or extended frame range of movies will only generate one cache entry. No special
    * treatment in converting frame index to timeline_frame is needed. */
-  if (type == SEQ_CACHE_STORE_RAW) {
+  if (type == SEQ_CACHE_STORE_RAW || type == SEQ_CACHE_STORE_THUMBNAIL) {
     return seq_give_frame_index(seq, timeline_frame);
   }
 
@@ -875,7 +877,7 @@ static void seq_cache_put_ex(Scene *scene, SeqCacheKey *key, ImBuf *ibuf)
   if (BLI_ghash_reinsert(cache->hash, key, item, seq_cache_keyfree, seq_cache_valfree)) {
     IMB_refImBuf(ibuf);
 
-    if (!key->is_temp_cache) {
+    if (!key->is_temp_cache || key->type != SEQ_CACHE_STORE_THUMBNAIL) {
       cache->last_key = key;
     }
   }
@@ -1161,6 +1163,7 @@ static void seq_cache_create(Main *bmain, Scene *scene)
     cache->hash = BLI_ghash_new(seq_cache_hashhash, seq_cache_hashcmp, "SeqCache hash");
     cache->last_key = NULL;
     cache->bmain = bmain;
+    cache->thumbnail_count = 0;
     BLI_mutex_init(&cache->iterator_mutex);
     scene->ed->cache = cache;
 
@@ -1217,7 +1220,7 @@ void seq_cache_free_temp_cache(Scene *scene, short id, int timeline_frame)
     SeqCacheKey *key = BLI_ghashIterator_getKey(&gh_iter);
     BLI_ghashIterator_step(&gh_iter);
 
-    if (key->is_temp_cache && key->task_id == id) {
+    if (key->is_temp_cache && key->task_id == id && key->type != SEQ_CACHE_STORE_THUMBNAIL) {
       /* Use frame_index here to avoid freeing raw images if they are used for multiple frames. */
       float frame_index = seq_cache_timeline_frame_to_frame_index(
           key->seq, timeline_frame, key->type);
@@ -1278,6 +1281,7 @@ void SEQ_cache_cleanup(Scene *scene)
     BLI_ghash_remove(cache->hash, key, seq_cache_keyfree, seq_cache_valfree);
   }
   cache->last_key = NULL;
+  cache->thumbnail_count = 0;
   seq_cache_unlock(scene);
 }
 
@@ -1345,6 +1349,39 @@ void seq_cache_cleanup_sequence(Scene *scene,
   seq_cache_unlock(scene);
 }
 
+void seq_cache_thumbnail_cleanup(Scene *scene, rctf *view_area_safe)
+{
+  /* Add offsets to the left and right end to keep some frames in cache. */
+  view_area_safe->xmax += 200;
+  view_area_safe->xmin -= 200;
+  view_area_safe->ymin -= 1;
+  view_area_safe->ymax += 1;
+
+  SeqCache *cache = seq_cache_get_from_scene(scene);
+  if (!cache) {
+    return;
+  }
+
+  GHashIterator gh_iter;
+  BLI_ghashIterator_init(&gh_iter, cache->hash);
+  while (!BLI_ghashIterator_done(&gh_iter)) {
+    SeqCacheKey *key = BLI_ghashIterator_getKey(&gh_iter);
+    BLI_ghashIterator_step(&gh_iter);
+
+    if ((key->type & SEQ_CACHE_STORE_THUMBNAIL) &&
+        (key->timeline_frame > view_area_safe->xmax ||
+         key->timeline_frame < view_area_safe->xmin || key->seq->machine > view_area_safe->ymax ||
+         key->seq->machine < view_area_safe->ymin)) {
+      if (key->link_next || key->link_prev) {
+        seq_cache_relink_keys(key->link_next, key->link_prev);
+      }
+      cache->thumbnail_count--;
+      BLI_ghash_remove(cache->hash, key, seq_cache_keyfree, seq_cache_valfree);
+    }
+  }
+  cache->last_key = NULL;
+}
+
 struct ImBuf *seq_cache_get(const SeqRenderData *context,
                             Sequence *seq,
                             float timeline_frame,
@@ -1436,6 +1473,37 @@ bool seq_cache_put_if_possible(
   return false;
 }
 
+void seq_cache_thumbnail_put(
+    const SeqRenderData *context, Sequence *seq, float timeline_frame, ImBuf *i, rctf *view_area)
+{
+  Scene *scene = context->scene;
+
+  if (!scene->ed->cache) {
+    seq_cache_create(context->bmain, scene);
+  }
+
+  seq_cache_lock(scene);
+  SeqCache *cache = seq_cache_get_from_scene(scene);
+  SeqCacheKey *key = seq_cache_allocate_key(
+      cache, context, seq, timeline_frame, SEQ_CACHE_STORE_THUMBNAIL);
+
+  /* Prevent reinserting, it breaks cache key linking. */
+  if (BLI_ghash_haskey(cache->hash, key)) {
+    seq_cache_unlock(scene);
+    return;
+  }
+
+  /* Limit cache to THUMB_CACHE_LIMIT (5000) images stored. */
+  if (cache->thumbnail_count >= THUMB_CACHE_LIMIT) {
+    rctf view_area_safe = *view_area;
+    seq_cache_thumbnail_cleanup(scene, &view_area_safe);
+  }
+
+  seq_cache_put_ex(scene, key, i);
+  cache->thumbnail_count++;
+  seq_cache_unlock(scene);
+}
+
 void seq_cache_put(
     const SeqRenderData *context, Sequence *seq, float timeline_frame, int type, ImBuf *i)
 {

source/blender/sequencer/intern/image_cache.h

@@ -46,6 +46,11 @@ void seq_cache_put(const struct SeqRenderData *context,
                    float timeline_frame,
                    int type,
                    struct ImBuf *i);
+void seq_cache_thumbnail_put(const struct SeqRenderData *context,
+                             struct Sequence *seq,
+                             float timeline_frame,
+                             struct ImBuf *i,
+                             rctf *view_area);
 bool seq_cache_put_if_possible(const struct SeqRenderData *context,
                                struct Sequence *seq,
                                float timeline_frame,
@@ -60,6 +65,7 @@ void seq_cache_cleanup_sequence(struct Scene *scene,
                                 struct Sequence *seq_changed,
                                 int invalidate_types,
                                 bool force_seq_changed_range);
+void seq_cache_thumbnail_cleanup(Scene *scene, rctf *view_area);
 bool seq_cache_is_full(void);
 
 #ifdef __cplusplus

source/blender/sequencer/intern/render.c

@@ -527,6 +527,31 @@ static void sequencer_image_crop_init(const Sequence *seq,
   BLI_rctf_init(r_crop, left, in->x - right, bottom, in->y - top);
 }
 
+static void sequencer_thumbnail_transform(ImBuf *in, ImBuf *out)
+{
+  float image_scale_factor = (float)out->x / in->x;
+  float transform_matrix[3][3];
+
+  /* Set to keep same loc,scale,rot but change scale to thumb size limit. */
+  const float scale_x = 1 * image_scale_factor;
+  const float scale_y = 1 * image_scale_factor;
+  const float image_center_offs_x = (out->x - in->x) / 2;
+  const float image_center_offs_y = (out->y - in->y) / 2;
+  const float pivot[2] = {in->x / 2, in->y / 2};
+  loc_rot_size_to_mat3(transform_matrix,
+                       (const float[]){image_center_offs_x, image_center_offs_y},
+                       0,
+                       (const float[]){scale_x, scale_y});
+  transform_pivot_set_m3(transform_matrix, pivot);
+  invert_m3(transform_matrix);
+
+  /* No crop. */
+  rctf source_crop;
+  BLI_rctf_init(&source_crop, 0, in->x, 0, in->y);
+
+  IMB_transform(in, out, transform_matrix, &source_crop, IMB_FILTER_NEAREST);
+}
+
 static void sequencer_preprocess_transform_crop(
     ImBuf *in, ImBuf *out, const SeqRenderData *context, Sequence *seq, const bool is_proxy_image)
 {
@@ -1989,7 +2014,103 @@ ImBuf *SEQ_render_give_ibuf_direct(const SeqRenderData *context,
   seq_render_state_init(&state);
 
   ImBuf *ibuf = seq_render_strip(context, &state, seq, timeline_frame);
-
   return ibuf;
 }
+
+/* Gets the direct image from source and scales to thumbnail size. */
+static ImBuf *seq_get_uncached_thumbnail(SeqRenderData *context,
+                                         SeqRenderState *state,
+                                         Sequence *seq,
+                                         float timeline_frame)
+{
+  bool is_proxy_image = false;
+  ImBuf *ibuf = do_render_strip_uncached(context, state, seq, timeline_frame, &is_proxy_image);
+
+  if (ibuf == NULL) {
+    return NULL;
+  }
+
+  float aspect_ratio = (float)ibuf->x / ibuf->y;
+  int rectx, recty;
+  /* Calculate new dimensions - THUMB_SIZE (256) for x or y. */
+  if (ibuf->x > ibuf->y) {
+    rectx = SEQ_RENDER_THUMB_SIZE;
+    recty = round_fl_to_int(rectx / aspect_ratio);
+  }
+  else {
+    recty = SEQ_RENDER_THUMB_SIZE;
+    rectx = round_fl_to_int(recty * aspect_ratio);
+  }
+
+  /* Scale ibuf to thumbnail size. */
+  ImBuf *scaled_ibuf = IMB_allocImBuf(rectx, recty, 32, ibuf->rect_float ? IB_rectfloat : IB_rect);
+  sequencer_thumbnail_transform(ibuf, scaled_ibuf);
+  seq_imbuf_assign_spaces(context->scene, scaled_ibuf);
+  IMB_freeImBuf(ibuf);
+
+  return scaled_ibuf;
+}
+
+/* Get cached thumbnails. */
+ImBuf *SEQ_get_thumbnail(
+    SeqRenderData *context, Sequence *seq, float timeline_frame, rcti *crop, bool clipped)
+{
+  ImBuf *ibuf = seq_cache_get(context, seq, roundf(timeline_frame), SEQ_CACHE_STORE_THUMBNAIL);
+
+  if (!clipped || ibuf == NULL) {
+    return ibuf;
+  }
+
+  /* Do clipping. */
+  ImBuf *ibuf_cropped = IMB_dupImBuf(ibuf);
+  if (crop->xmin < 0 || crop->ymin < 0) {
+    crop->xmin = 0;
+    crop->ymin = 0;
+  }
+  if (crop->xmax >= ibuf->x || crop->ymax >= ibuf->y) {
+    crop->xmax = ibuf->x - 1;
+    crop->ymax = ibuf->y - 1;
+  }
+  IMB_rect_crop(ibuf_cropped, crop);
+  IMB_freeImBuf(ibuf);
+  return ibuf_cropped;
+}
+
+/* Render the series of thumbnails and store in cache. */
+void SEQ_render_thumbnails(SeqRenderData *context,
+                           Sequence *seq,
+                           Sequence *seq_orig,
+                           float start_frame,
+                           float frame_step,
+                           rctf *view_area,
+                           short *stop)
+{
+  SeqRenderState state;
+  seq_render_state_init(&state);
+
+  /* Adding the hold offset value (seq->anim_startofs) to the start frame. Position of image not
+   * affected, but frame loaded affected. */
+  start_frame = start_frame - 5 * frame_step;
+  float upper_thumb_bound = (seq->endstill) ? (seq->start + seq->len) : seq->enddisp;
+  upper_thumb_bound = (upper_thumb_bound > view_area->xmax) ? view_area->xmax + 5 * frame_step :
+                                                              upper_thumb_bound;
+
+  while ((start_frame < upper_thumb_bound) & !*stop) {
+    ImBuf *ibuf = seq_cache_get(context, seq_orig, roundf(start_frame), SEQ_CACHE_STORE_THUMBNAIL);
+    if (ibuf) {
+      IMB_freeImBuf(ibuf);
+      start_frame += frame_step;
+      continue;
+    }
+
+    ibuf = seq_get_uncached_thumbnail(context, &state, seq, roundf(start_frame));
+
+    if (ibuf) {
+      seq_cache_thumbnail_put(context, seq_orig, roundf(start_frame), ibuf, view_area);
+      IMB_freeImBuf(ibuf);
+    }
+
+    start_frame += frame_step;
+  }
+}
 /** \} */

source/blender/windowmanager/WM_api.h

@@ -781,6 +781,7 @@ enum {
   WM_JOB_TYPE_QUADRIFLOW_REMESH,
   WM_JOB_TYPE_TRACE_IMAGE,
   WM_JOB_TYPE_LINEART,
+  WM_JOB_TYPE_SEQ_DRAW_THUMBNAIL,
   /* add as needed, bake, seq proxy build
    * if having hard coded values is a problem */
 };

source/blender/windowmanager/intern/wm_jobs.c

@@ -230,7 +230,7 @@ bool WM_jobs_test(const wmWindowManager *wm, const void *owner, int job_type)
   LISTBASE_FOREACH (wmJob *, wm_job, &wm->jobs) {
     if (wm_job->owner == owner) {
       if (ELEM(job_type, WM_JOB_TYPE_ANY, wm_job->job_type)) {
-        if (wm_job->running || wm_job->suspended) {
+        if ((wm_job->flag & WM_JOB_PROGRESS) && (wm_job->running || wm_job->suspended)) {
           return true;
         }
       }