Cleanup: move image undo into space_image/

This isn't just used for painting.

1 files changed, 1035 insertions, 0 deletions

diff --git a/source/blender/editors/space_image/image_undo.c b/source/blender/editors/space_image/image_undo.c
new file mode 100644
index 00000000000..c3d8bd1b446
--- /dev/null
+++ b/source/blender/editors/space_image/image_undo.c
@@ -0,0 +1,1035 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+/** \file
+ * \ingroup spimage
+ *
+ * Overview
+ * ========
+ *
+ * - Each undo step is a #ImageUndoStep
+ * - Each #ImageUndoStep stores a list of #UndoImageHandle
+ *   - Each #UndoImageHandle stores a list of #UndoImageBuf
+ *     (this is the undo systems equivalent of an #ImBuf).
+ *     - Each #UndoImageBuf stores an array of #UndoImageTile
+ *       The tiles are shared between #UndoImageBuf's to avoid duplication.
+ *
+ * When the undo system manages an image, there will always be a full copy (as a #UndoImageBuf)
+ * each new undo step only stores modified tiles.
+ */
+
+#include "CLG_log.h"
+
+#include "MEM_guardedalloc.h"
+
+#include "BLI_math.h"
+#include "BLI_blenlib.h"
+#include "BLI_utildefines.h"
+#include "BLI_threads.h"
+
+#include "DNA_image_types.h"
+#include "DNA_windowmanager_types.h"
+#include "DNA_object_types.h"
+#include "DNA_screen_types.h"
+#include "DNA_space_types.h"
+
+#include "IMB_imbuf.h"
+#include "IMB_imbuf_types.h"
+
+#include "BKE_context.h"
+#include "BKE_image.h"
+#include "BKE_paint.h"
+#include "BKE_undo_system.h"
+
+#include "DEG_depsgraph.h"
+
+#include "ED_paint.h"
+#include "ED_undo.h"
+#include "ED_util.h"
+#include "ED_object.h"
+
+#include "GPU_draw.h"
+
+#include "WM_api.h"
+
+static CLG_LogRef LOG = {"ed.image.undo"};
+
+/* -------------------------------------------------------------------- */
+/** \name Thread Locking
+ * \{ */
+
+/* this is a static resource for non-globality,
+ * Maybe it should be exposed as part of the
+ * paint operation, but for now just give a public interface */
+static SpinLock paint_tiles_lock;
+
+void image_undo_init_locks(void)
+{
+  BLI_spin_init(&paint_tiles_lock);
+}
+
+void image_undo_end_locks(void)
+{
+  BLI_spin_end(&paint_tiles_lock);
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Paint Tiles
+ *
+ * Created on demand while painting,
+ * use to access the previous state for some paint operations.
+ *
+ * These buffers are also used for undo when available.
+ *
+ * \{ */
+
+static ImBuf *imbuf_alloc_temp_tile(void)
+{
+  return IMB_allocImBuf(IMAPAINT_TILE_SIZE, IMAPAINT_TILE_SIZE, 32, IB_rectfloat | IB_rect);
+}
+
+typedef struct PaintTile {
+  struct PaintTile *next, *prev;
+  Image *image;
+  ImBuf *ibuf;
+  union {
+    float *fp;
+    uint *uint;
+    void *pt;
+  } rect;
+  ushort *mask;
+  bool valid;
+  bool use_float;
+  int x, y;
+} PaintTile;
+
+static void ptile_free(PaintTile *ptile)
+{
+  if (ptile->rect.pt) {
+    MEM_freeN(ptile->rect.pt);
+  }
+  MEM_freeN(ptile);
+}
+
+static void ptile_free_list(ListBase *paint_tiles)
+{
+  for (PaintTile *ptile = paint_tiles->first, *ptile_next; ptile; ptile = ptile_next) {
+    ptile_next = ptile->next;
+    ptile_free(ptile);
+  }
+  BLI_listbase_clear(paint_tiles);
+}
+
+static void ptile_invalidate_list(ListBase *paint_tiles)
+{
+  for (PaintTile *ptile = paint_tiles->first; ptile; ptile = ptile->next) {
+    ptile->valid = false;
+  }
+}
+
+void *image_undo_find_tile(ListBase *paint_tiles,
+                           Image *image,
+                           ImBuf *ibuf,
+                           int x_tile,
+                           int y_tile,
+                           ushort **r_mask,
+                           bool validate)
+{
+  for (PaintTile *ptile = paint_tiles->first; ptile; ptile = ptile->next) {
+    if (ptile->x == x_tile && ptile->y == y_tile) {
+      if (ptile->image == image && ptile->ibuf == ibuf) {
+        if (r_mask) {
+          /* allocate mask if requested. */
+          if (!ptile->mask) {
+            ptile->mask = MEM_callocN(sizeof(ushort) * SQUARE(IMAPAINT_TILE_SIZE),
+                                      "UndoImageTile.mask");
+          }
+          *r_mask = ptile->mask;
+        }
+        if (validate) {
+          ptile->valid = true;
+        }
+        return ptile->rect.pt;
+      }
+    }
+  }
+  return NULL;
+}
+
+void image_undo_remove_masks(void)
+{
+  ListBase *paint_tiles = ED_image_undo_get_tiles();
+  for (PaintTile *ptile = paint_tiles->first; ptile; ptile = ptile->next) {
+    MEM_SAFE_FREE(ptile->mask);
+  }
+}
+
+void *image_undo_push_tile(ListBase *paint_tiles,
+                           Image *image,
+                           ImBuf *ibuf,
+                           ImBuf **tmpibuf,
+                           int x_tile,
+                           int y_tile,
+                           ushort **r_mask,
+                           bool **valid,
+                           bool proj,
+                           bool find_prev)
+{
+  const bool has_float = (ibuf->rect_float != NULL);
+
+  /* check if tile is already pushed */
+
+  /* in projective painting we keep accounting of tiles, so if we need one pushed, just push! */
+  if (find_prev) {
+    void *data = image_undo_find_tile(paint_tiles, image, ibuf, x_tile, y_tile, r_mask, true);
+    if (data) {
+      return data;
+    }
+  }
+
+  if (*tmpibuf == NULL) {
+    *tmpibuf = imbuf_alloc_temp_tile();
+  }
+
+  PaintTile *ptile = MEM_callocN(sizeof(PaintTile), "PaintTile");
+
+  ptile->image = image;
+  ptile->ibuf = ibuf;
+
+  ptile->x = x_tile;
+  ptile->y = y_tile;
+
+  /* add mask explicitly here */
+  if (r_mask) {
+    *r_mask = ptile->mask = MEM_callocN(sizeof(ushort) * SQUARE(IMAPAINT_TILE_SIZE),
+                                        "PaintTile.mask");
+  }
+
+  ptile->rect.pt = MEM_mapallocN((ibuf->rect_float ? sizeof(float[4]) : sizeof(char[4])) *
+                                     SQUARE(IMAPAINT_TILE_SIZE),
+                                 "PaintTile.rect");
+
+  ptile->use_float = has_float;
+  ptile->valid = true;
+
+  if (valid) {
+    *valid = &ptile->valid;
+  }
+
+  IMB_rectcpy(*tmpibuf,
+              ibuf,
+              0,
+              0,
+              x_tile * IMAPAINT_TILE_SIZE,
+              y_tile * IMAPAINT_TILE_SIZE,
+              IMAPAINT_TILE_SIZE,
+              IMAPAINT_TILE_SIZE);
+
+  if (has_float) {
+    SWAP(float *, ptile->rect.fp, (*tmpibuf)->rect_float);
+  }
+  else {
+    SWAP(uint *, ptile->rect.uint, (*tmpibuf)->rect);
+  }
+
+  if (proj) {
+    BLI_spin_lock(&paint_tiles_lock);
+  }
+  BLI_addtail(paint_tiles, ptile);
+
+  if (proj) {
+    BLI_spin_unlock(&paint_tiles_lock);
+  }
+  return ptile->rect.pt;
+}
+
+static void ptile_restore_runtime_list(ListBase *paint_tiles)
+{
+  ImBuf *tmpibuf = imbuf_alloc_temp_tile();
+
+  for (PaintTile *ptile = paint_tiles->first; ptile; ptile = ptile->next) {
+    Image *image = ptile->image;
+    ImBuf *ibuf = BKE_image_acquire_ibuf(image, NULL, NULL);
+    const bool has_float = (ibuf->rect_float != NULL);
+
+    if (has_float) {
+      SWAP(float *, ptile->rect.fp, tmpibuf->rect_float);
+    }
+    else {
+      SWAP(uint *, ptile->rect.uint, tmpibuf->rect);
+    }
+
+    IMB_rectcpy(ibuf, tmpibuf, ptile->x, ptile->y, 0, 0, IMAPAINT_TILE_SIZE, IMAPAINT_TILE_SIZE);
+
+    if (has_float) {
+      SWAP(float *, ptile->rect.fp, tmpibuf->rect_float);
+    }
+    else {
+      SWAP(uint *, ptile->rect.uint, tmpibuf->rect);
+    }
+
+    GPU_free_image(image); /* force OpenGL reload (maybe partial update will operate better?) */
+    if (ibuf->rect_float) {
+      ibuf->userflags |= IB_RECT_INVALID; /* force recreate of char rect */
+    }
+    if (ibuf->mipmap[0]) {
+      ibuf->userflags |= IB_MIPMAP_INVALID; /* force mip-map recreation. */
+    }
+    ibuf->userflags |= IB_DISPLAY_BUFFER_INVALID;
+
+    BKE_image_release_ibuf(image, ibuf, NULL);
+  }
+
+  IMB_freeImBuf(tmpibuf);
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Image Undo Tile
+ * \{ */
+
+static uint index_from_xy(uint tile_x, uint tile_y, const uint tiles_dims[2])
+{
+  BLI_assert(tile_x < tiles_dims[0] && tile_y < tiles_dims[1]);
+  return (tile_y * tiles_dims[0]) + tile_x;
+}
+
+typedef struct UndoImageTile {
+  union {
+    float *fp;
+    uint *uint;
+    void *pt;
+  } rect;
+  int users;
+} UndoImageTile;
+
+static UndoImageTile *utile_alloc(bool has_float)
+{
+  UndoImageTile *utile = MEM_callocN(sizeof(*utile), "ImageUndoTile");
+  if (has_float) {
+    utile->rect.fp = MEM_mallocN(sizeof(float[4]) * SQUARE(IMAPAINT_TILE_SIZE), __func__);
+  }
+  else {
+    utile->rect.uint = MEM_mallocN(sizeof(uint) * SQUARE(IMAPAINT_TILE_SIZE), __func__);
+  }
+  return utile;
+}
+
+static void utile_init_from_imbuf(
+    UndoImageTile *utile, const uint x, const uint y, const ImBuf *ibuf, ImBuf *tmpibuf)
+{
+  const bool has_float = ibuf->rect_float;
+
+  if (has_float) {
+    SWAP(float *, utile->rect.fp, tmpibuf->rect_float);
+  }
+  else {
+    SWAP(uint *, utile->rect.uint, tmpibuf->rect);
+  }
+
+  IMB_rectcpy(tmpibuf, ibuf, 0, 0, x, y, IMAPAINT_TILE_SIZE, IMAPAINT_TILE_SIZE);
+
+  if (has_float) {
+    SWAP(float *, utile->rect.fp, tmpibuf->rect_float);
+  }
+  else {
+    SWAP(uint *, utile->rect.uint, tmpibuf->rect);
+  }
+}
+
+static void utile_restore(
+    const UndoImageTile *utile, const uint x, const uint y, ImBuf *ibuf, ImBuf *tmpibuf)
+{
+  const bool has_float = ibuf->rect_float;
+  float *prev_rect_float = tmpibuf->rect_float;
+  uint *prev_rect = tmpibuf->rect;
+
+  if (has_float) {
+    tmpibuf->rect_float = utile->rect.fp;
+  }
+  else {
+    tmpibuf->rect = utile->rect.uint;
+  }
+
+  IMB_rectcpy(ibuf, tmpibuf, x, y, 0, 0, IMAPAINT_TILE_SIZE, IMAPAINT_TILE_SIZE);
+
+  tmpibuf->rect_float = prev_rect_float;
+  tmpibuf->rect = prev_rect;
+}
+
+static void utile_decref(UndoImageTile *utile)
+{
+  utile->users -= 1;
+  BLI_assert(utile->users >= 0);
+  if (utile->users == 0) {
+    MEM_freeN(utile->rect.pt);
+    MEM_freeN(utile);
+  }
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Image Undo Buffer
+ * \{ */
+
+typedef struct UndoImageBuf {
+  struct UndoImageBuf *next, *prev;
+
+  /**
+   * The buffer after the undo step has executed.
+   */
+  struct UndoImageBuf *post;
+
+  char ibuf_name[IMB_FILENAME_SIZE];
+
+  UndoImageTile **tiles;
+
+  /** Can calculate these from dims, just for convenience. */
+  uint tiles_len;
+  uint tiles_dims[2];
+
+  uint image_dims[2];
+
+  /** Store variables from the image. */
+  struct {
+    short source;
+    bool use_float;
+    char gen_type;
+  } image_state;
+
+} UndoImageBuf;
+
+static UndoImageBuf *ubuf_from_image_no_tiles(Image *image, const ImBuf *ibuf)
+{
+  UndoImageBuf *ubuf = MEM_callocN(sizeof(*ubuf), __func__);
+
+  ubuf->image_dims[0] = ibuf->x;
+  ubuf->image_dims[1] = ibuf->y;
+
+  ubuf->tiles_dims[0] = IMAPAINT_TILE_NUMBER(ubuf->image_dims[0]);
+  ubuf->tiles_dims[1] = IMAPAINT_TILE_NUMBER(ubuf->image_dims[1]);
+
+  ubuf->tiles_len = ubuf->tiles_dims[0] * ubuf->tiles_dims[1];
+  ubuf->tiles = MEM_callocN(sizeof(*ubuf->tiles) * ubuf->tiles_len, __func__);
+
+  BLI_strncpy(ubuf->ibuf_name, ibuf->name, sizeof(ubuf->ibuf_name));
+  ubuf->image_state.gen_type = image->gen_type;
+  ubuf->image_state.source = image->source;
+  ubuf->image_state.use_float = ibuf->rect_float != NULL;
+
+  return ubuf;
+}
+
+static void ubuf_from_image_all_tiles(UndoImageBuf *ubuf, const ImBuf *ibuf)
+{
+  ImBuf *tmpibuf = imbuf_alloc_temp_tile();
+
+  const bool has_float = ibuf->rect_float;
+  int i = 0;
+  for (uint y_tile = 0; y_tile < ubuf->tiles_dims[1]; y_tile += 1) {
+    uint y = y_tile << IMAPAINT_TILE_BITS;
+    for (uint x_tile = 0; x_tile < ubuf->tiles_dims[0]; x_tile += 1) {
+      uint x = x_tile << IMAPAINT_TILE_BITS;
+
+      BLI_assert(ubuf->tiles[i] == NULL);
+      UndoImageTile *utile = utile_alloc(has_float);
+      utile->users = 1;
+      utile_init_from_imbuf(utile, x, y, ibuf, tmpibuf);
+      ubuf->tiles[i] = utile;
+
+      i += 1;
+    }
+  }
+
+  IMB_freeImBuf(tmpibuf);
+}
+
+static void ubuf_free(UndoImageBuf *ubuf)
+{
+  UndoImageBuf *ubuf_post = ubuf->post;
+  for (uint i = 0; i < ubuf->tiles_len; i++) {
+    UndoImageTile *utile = ubuf->tiles[i];
+    utile_decref(utile);
+  }
+  MEM_freeN(ubuf->tiles);
+  MEM_freeN(ubuf);
+  if (ubuf_post) {
+    ubuf_free(ubuf_post);
+  }
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Image Undo Handle
+ * \{ */
+
+typedef struct UndoImageHandle {
+  struct UndoImageHandle *next, *prev;
+
+  /** Each undo handle refers to a single image which may have multiple buffers. */
+  UndoRefID_Image image_ref;
+
+  /**
+   * List of #UndoImageBuf's to support multiple buffers per image.
+   *
+   * \note To properly support multiple buffers per image
+   * we would need to store an #ImageUser for each #UndoImageBuf.
+   * since when restoring the image we use:
+   * `BKE_image_acquire_ibuf(image, NULL, NULL)`.
+   */
+  ListBase buffers;
+
+} UndoImageHandle;
+
+static void uhandle_restore_list(ListBase *undo_handles, bool use_init)
+{
+  ImBuf *tmpibuf = imbuf_alloc_temp_tile();
+
+  for (UndoImageHandle *uh = undo_handles->first; uh; uh = uh->next) {
+    /* Tiles only added to second set of tiles. */
+    Image *image = uh->image_ref.ptr;
+    ImBuf *ibuf = BKE_image_acquire_ibuf(image, NULL, NULL);
+    if (UNLIKELY(ibuf == NULL)) {
+      CLOG_ERROR(&LOG, "Unable to get buffer for image '%s'", image->id.name + 2);
+      continue;
+    }
+    bool changed = false;
+    for (UndoImageBuf *ubuf_iter = uh->buffers.first; ubuf_iter; ubuf_iter = ubuf_iter->next) {
+      UndoImageBuf *ubuf = use_init ? ubuf_iter : ubuf_iter->post;
+      IMB_rect_size_set(ibuf, ubuf->image_dims);
+      int i = 0;
+      for (uint y_tile = 0; y_tile < ubuf->tiles_dims[1]; y_tile += 1) {
+        uint y = y_tile << IMAPAINT_TILE_BITS;
+        for (uint x_tile = 0; x_tile < ubuf->tiles_dims[0]; x_tile += 1) {
+          uint x = x_tile << IMAPAINT_TILE_BITS;
+          utile_restore(ubuf->tiles[i], x, y, ibuf, tmpibuf);
+          changed = true;
+          i += 1;
+        }
+      }
+    }
+
+    if (changed) {
+      BKE_image_mark_dirty(image, ibuf);
+      GPU_free_image(image); /* force OpenGL reload */
+
+      if (ibuf->rect_float) {
+        ibuf->userflags |= IB_RECT_INVALID; /* force recreate of char rect */
+      }
+      if (ibuf->mipmap[0]) {
+        ibuf->userflags |= IB_MIPMAP_INVALID; /* force mip-map recreation. */
+      }
+      ibuf->userflags |= IB_DISPLAY_BUFFER_INVALID;
+
+      DEG_id_tag_update(&image->id, 0);
+    }
+    BKE_image_release_ibuf(image, ibuf, NULL);
+  }
+
+  IMB_freeImBuf(tmpibuf);
+}
+
+static void uhandle_free_list(ListBase *undo_handles)
+{
+  LISTBASE_FOREACH_MUTABLE (UndoImageHandle *, uh, undo_handles) {
+    LISTBASE_FOREACH_MUTABLE (UndoImageBuf *, ubuf, &uh->buffers) {
+      ubuf_free(ubuf);
+    }
+    MEM_freeN(uh);
+  }
+  BLI_listbase_clear(undo_handles);
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Image Undo Internal Utilities
+ * \{ */
+
+/** #UndoImageHandle utilities */
+
+static UndoImageBuf *uhandle_lookup_ubuf(UndoImageHandle *uh,
+                                         const Image *UNUSED(image),
+                                         const char *ibuf_name)
+{
+  for (UndoImageBuf *ubuf = uh->buffers.first; ubuf; ubuf = ubuf->next) {
+    if (STREQ(ubuf->ibuf_name, ibuf_name)) {
+      return ubuf;
+    }
+  }
+  return NULL;
+}
+
+static UndoImageBuf *uhandle_add_ubuf(UndoImageHandle *uh, Image *image, ImBuf *ibuf)
+{
+  BLI_assert(uhandle_lookup_ubuf(uh, image, ibuf->name) == NULL);
+  UndoImageBuf *ubuf = ubuf_from_image_no_tiles(image, ibuf);
+  BLI_addtail(&uh->buffers, ubuf);
+
+  ubuf->post = NULL;
+
+  return ubuf;
+}
+
+static UndoImageBuf *uhandle_ensure_ubuf(UndoImageHandle *uh, Image *image, ImBuf *ibuf)
+{
+  UndoImageBuf *ubuf = uhandle_lookup_ubuf(uh, image, ibuf->name);
+  if (ubuf == NULL) {
+    ubuf = uhandle_add_ubuf(uh, image, ibuf);
+  }
+  return ubuf;
+}
+
+static UndoImageHandle *uhandle_lookup_by_name(ListBase *undo_handles, const Image *image)
+{
+  for (UndoImageHandle *uh = undo_handles->first; uh; uh = uh->next) {
+    if (STREQ(image->id.name + 2, uh->image_ref.name + 2)) {
+      return uh;
+    }
+  }
+  return NULL;
+}
+
+static UndoImageHandle *uhandle_lookup(ListBase *undo_handles, const Image *image)
+{
+  for (UndoImageHandle *uh = undo_handles->first; uh; uh = uh->next) {
+    if (image == uh->image_ref.ptr) {
+      return uh;
+    }
+  }
+  return NULL;
+}
+
+static UndoImageHandle *uhandle_add(ListBase *undo_handles, Image *image)
+{
+  BLI_assert(uhandle_lookup(undo_handles, image) == NULL);
+  UndoImageHandle *uh = MEM_callocN(sizeof(*uh), __func__);
+  uh->image_ref.ptr = image;
+  BLI_addtail(undo_handles, uh);
+  return uh;
+}
+
+static UndoImageHandle *uhandle_ensure(ListBase *undo_handles, Image *image)
+{
+  UndoImageHandle *uh = uhandle_lookup(undo_handles, image);
+  if (uh == NULL) {
+    uh = uhandle_add(undo_handles, image);
+  }
+  return uh;
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Implements ED Undo System
+ * \{ */
+
+typedef struct ImageUndoStep {
+  UndoStep step;
+
+  /** #UndoImageHandle */
+  ListBase handles;
+
+  /**
+   * #PaintTile
+   * Run-time only data (active during a paint stroke).
+   */
+  ListBase paint_tiles;
+
+  bool is_encode_init;
+  ePaintMode paint_mode;
+
+} ImageUndoStep;
+
+/**
+ * Find the previous undo buffer from this one.
+ * \note We could look into undo steps even further back.
+ */
+static UndoImageBuf *ubuf_lookup_from_reference(ImageUndoStep *us_prev,
+                                                const Image *image,
+                                                const UndoImageBuf *ubuf)
+{
+  /* Use name lookup because because the pointer is cleared for previous steps. */
+  UndoImageHandle *uh_prev = uhandle_lookup_by_name(&us_prev->handles, image);
+  if (uh_prev != NULL) {
+    UndoImageBuf *ubuf_reference = uhandle_lookup_ubuf(uh_prev, image, ubuf->ibuf_name);
+    if (ubuf_reference) {
+      ubuf_reference = ubuf_reference->post;
+      if ((ubuf_reference->image_dims[0] == ubuf->image_dims[0]) &&
+          (ubuf_reference->image_dims[1] == ubuf->image_dims[1])) {
+        return ubuf_reference;
+      }
+    }
+  }
+  return NULL;
+}
+
+static bool image_undosys_poll(bContext *C)
+{
+  Object *obact = CTX_data_active_object(C);
+
+  ScrArea *sa = CTX_wm_area(C);
+  if (sa && (sa->spacetype == SPACE_IMAGE)) {
+    SpaceImage *sima = (SpaceImage *)sa->spacedata.first;
+    if ((obact && (obact->mode & OB_MODE_TEXTURE_PAINT)) || (sima->mode == SI_MODE_PAINT)) {
+      return true;
+    }
+  }
+  else {
+    if (obact && (obact->mode & OB_MODE_TEXTURE_PAINT)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+static void image_undosys_step_encode_init(struct bContext *UNUSED(C), UndoStep *us_p)
+{
+  ImageUndoStep *us = (ImageUndoStep *)us_p;
+  /* dummy, memory is cleared anyway. */
+  us->is_encode_init = true;
+  BLI_listbase_clear(&us->handles);
+  BLI_listbase_clear(&us->paint_tiles);
+}
+
+static bool image_undosys_step_encode(struct bContext *C,
+                                      struct Main *UNUSED(bmain),
+                                      UndoStep *us_p)
+{
+  /* Encoding is done along the way by adding tiles
+   * to the current 'ImageUndoStep' added by encode_init.
+   *
+   * This function ensures there are previous and current states of the image in the undo buffer.
+   */
+  ImageUndoStep *us = (ImageUndoStep *)us_p;
+
+  BLI_assert(us->step.data_size == 0);
+
+  if (us->is_encode_init) {
+
+    ImBuf *tmpibuf = imbuf_alloc_temp_tile();
+
+    ImageUndoStep *us_reference = (ImageUndoStep *)ED_undo_stack_get()->step_active;
+    while (us_reference && us_reference->step.type != BKE_UNDOSYS_TYPE_IMAGE) {
+      us_reference = (ImageUndoStep *)us_reference->step.prev;
+    }
+
+    /* Initialize undo tiles from ptiles (if they exist). */
+    for (PaintTile *ptile = us->paint_tiles.first, *ptile_next; ptile; ptile = ptile_next) {
+      if (ptile->valid) {
+        UndoImageHandle *uh = uhandle_ensure(&us->handles, ptile->image);
+        UndoImageBuf *ubuf_pre = uhandle_ensure_ubuf(uh, ptile->image, ptile->ibuf);
+
+        UndoImageTile *utile = MEM_callocN(sizeof(*utile), "UndoImageTile");
+        utile->users = 1;
+        utile->rect.pt = ptile->rect.pt;
+        ptile->rect.pt = NULL;
+        const uint tile_index = index_from_xy(ptile->x, ptile->y, ubuf_pre->tiles_dims);
+
+        BLI_assert(ubuf_pre->tiles[tile_index] == NULL);
+        ubuf_pre->tiles[tile_index] = utile;
+      }
+      ptile_next = ptile->next;
+      ptile_free(ptile);
+    }
+    BLI_listbase_clear(&us->paint_tiles);
+
+    for (UndoImageHandle *uh = us->handles.first; uh; uh = uh->next) {
+      for (UndoImageBuf *ubuf_pre = uh->buffers.first; ubuf_pre; ubuf_pre = ubuf_pre->next) {
+
+        ImBuf *ibuf = BKE_image_acquire_ibuf(uh->image_ref.ptr, NULL, NULL);
+
+        const bool has_float = ibuf->rect_float;
+
+        BLI_assert(ubuf_pre->post == NULL);
+        ubuf_pre->post = ubuf_from_image_no_tiles(uh->image_ref.ptr, ibuf);
+        UndoImageBuf *ubuf_post = ubuf_pre->post;
+
+        if (ubuf_pre->image_dims[0] != ubuf_post->image_dims[0] ||
+            ubuf_pre->image_dims[1] != ubuf_post->image_dims[1]) {
+          ubuf_from_image_all_tiles(ubuf_post, ibuf);
+        }
+        else {
+          /* Search for the previous buffer. */
+          UndoImageBuf *ubuf_reference = (us_reference ?
+                                              ubuf_lookup_from_reference(
+                                                  us_reference, uh->image_ref.ptr, ubuf_post) :
+                                              NULL);
+
+          int i = 0;
+          for (uint y_tile = 0; y_tile < ubuf_pre->tiles_dims[1]; y_tile += 1) {
+            uint y = y_tile << IMAPAINT_TILE_BITS;
+            for (uint x_tile = 0; x_tile < ubuf_pre->tiles_dims[0]; x_tile += 1) {
+              uint x = x_tile << IMAPAINT_TILE_BITS;
+
+              if ((ubuf_reference != NULL) && ((ubuf_pre->tiles[i] == NULL) ||
+                                               /* In this case the paint stroke as has added a tile
+                                                * which we have a duplicate reference available. */
+                                               (ubuf_pre->tiles[i]->users == 1))) {
+                if (ubuf_pre->tiles[i] != NULL) {
+                  /* If we have a reference, re-use this single use tile for the post state. */
+                  BLI_assert(ubuf_pre->tiles[i]->users == 1);
+                  ubuf_post->tiles[i] = ubuf_pre->tiles[i];
+                  ubuf_pre->tiles[i] = NULL;
+                  utile_init_from_imbuf(ubuf_post->tiles[i], x, y, ibuf, tmpibuf);
+                }
+                else {
+                  BLI_assert(ubuf_post->tiles[i] == NULL);
+                  ubuf_post->tiles[i] = ubuf_reference->tiles[i];
+                  ubuf_post->tiles[i]->users += 1;
+                }
+                BLI_assert(ubuf_pre->tiles[i] == NULL);
+                ubuf_pre->tiles[i] = ubuf_reference->tiles[i];
+                ubuf_pre->tiles[i]->users += 1;
+
+                BLI_assert(ubuf_pre->tiles[i] != NULL);
+                BLI_assert(ubuf_post->tiles[i] != NULL);
+              }
+              else {
+                UndoImageTile *utile = utile_alloc(has_float);
+                utile_init_from_imbuf(utile, x, y, ibuf, tmpibuf);
+
+                if (ubuf_pre->tiles[i] != NULL) {
+                  ubuf_post->tiles[i] = utile;
+                  utile->users = 1;
+                }
+                else {
+                  ubuf_pre->tiles[i] = utile;
+                  ubuf_post->tiles[i] = utile;
+                  utile->users = 2;
+                }
+              }
+              BLI_assert(ubuf_pre->tiles[i] != NULL);
+              BLI_assert(ubuf_post->tiles[i] != NULL);
+              i += 1;
+            }
+          }
+        }
+        BKE_image_release_ibuf(uh->image_ref.ptr, ibuf, NULL);
+      }
+    }
+
+    IMB_freeImBuf(tmpibuf);
+
+    /* Useful to debug tiles are stored correctly. */
+    if (false) {
+      uhandle_restore_list(&us->handles, false);
+    }
+  }
+  else {
+    /* Happens when switching modes. */
+    ePaintMode paint_mode = BKE_paintmode_get_active_from_context(C);
+    BLI_assert(ELEM(paint_mode, PAINT_MODE_TEXTURE_2D, PAINT_MODE_TEXTURE_3D));
+    us->paint_mode = paint_mode;
+  }
+
+  us_p->is_applied = true;
+
+  return true;
+}
+
+static void image_undosys_step_decode_undo_impl(ImageUndoStep *us, bool is_final)
+{
+  BLI_assert(us->step.is_applied == true);
+  uhandle_restore_list(&us->handles, !is_final);
+  us->step.is_applied = false;
+}
+
+static void image_undosys_step_decode_redo_impl(ImageUndoStep *us)
+{
+  BLI_assert(us->step.is_applied == false);
+  uhandle_restore_list(&us->handles, false);
+  us->step.is_applied = true;
+}
+
+static void image_undosys_step_decode_undo(ImageUndoStep *us, bool is_final)
+{
+  ImageUndoStep *us_iter = us;
+  while (us_iter->step.next && (us_iter->step.next->type == us_iter->step.type)) {
+    if (us_iter->step.next->is_applied == false) {
+      break;
+    }
+    us_iter = (ImageUndoStep *)us_iter->step.next;
+  }
+  while (us_iter != us || (!is_final && us_iter == us)) {
+
+    image_undosys_step_decode_undo_impl(us_iter, is_final);
+    if (us_iter == us) {
+      break;
+    }
+    us_iter = (ImageUndoStep *)us_iter->step.prev;
+  }
+}
+
+static void image_undosys_step_decode_redo(ImageUndoStep *us)
+{
+  ImageUndoStep *us_iter = us;
+  while (us_iter->step.prev && (us_iter->step.prev->type == us_iter->step.type)) {
+    if (us_iter->step.prev->is_applied == true) {
+      break;
+    }
+    us_iter = (ImageUndoStep *)us_iter->step.prev;
+  }
+  while (us_iter && (us_iter->step.is_applied == false)) {
+    image_undosys_step_decode_redo_impl(us_iter);
+    if (us_iter == us) {
+      break;
+    }
+    us_iter = (ImageUndoStep *)us_iter->step.next;
+  }
+}
+
+static void image_undosys_step_decode(
+    struct bContext *C, struct Main *bmain, UndoStep *us_p, int dir, bool is_final)
+{
+  ImageUndoStep *us = (ImageUndoStep *)us_p;
+  if (dir < 0) {
+    image_undosys_step_decode_undo(us, is_final);
+  }
+  else {
+    image_undosys_step_decode_redo(us);
+  }
+
+  if (us->paint_mode == PAINT_MODE_TEXTURE_3D) {
+    ED_object_mode_set(C, OB_MODE_TEXTURE_PAINT);
+  }
+
+  /* Refresh texture slots. */
+  ED_editors_init_for_undo(bmain);
+}
+
+static void image_undosys_step_free(UndoStep *us_p)
+{
+  ImageUndoStep *us = (ImageUndoStep *)us_p;
+  uhandle_free_list(&us->handles);
+
+  /* Typically this list will have been cleared. */
+  ptile_free_list(&us->paint_tiles);
+}
+
+static void image_undosys_foreach_ID_ref(UndoStep *us_p,
+                                         UndoTypeForEachIDRefFn foreach_ID_ref_fn,
+                                         void *user_data)
+{
+  ImageUndoStep *us = (ImageUndoStep *)us_p;
+  for (UndoImageHandle *uh = us->handles.first; uh; uh = uh->next) {
+    foreach_ID_ref_fn(user_data, ((UndoRefID *)&uh->image_ref));
+  }
+}
+
+/* Export for ED_undo_sys. */
+void ED_image_undosys_type(UndoType *ut)
+{
+  ut->name = "Image";
+  ut->poll = image_undosys_poll;
+  ut->step_encode_init = image_undosys_step_encode_init;
+  ut->step_encode = image_undosys_step_encode;
+  ut->step_decode = image_undosys_step_decode;
+  ut->step_free = image_undosys_step_free;
+
+  ut->step_foreach_ID_ref = image_undosys_foreach_ID_ref;
+
+  ut->use_context = true;
+
+  ut->step_size = sizeof(ImageUndoStep);
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Utilities
+ * \{ */
+
+ListBase *ED_image_undo_get_tiles(void)
+{
+  UndoStack *ustack = ED_undo_stack_get();
+  UndoStep *us_prev = ustack->step_init;
+  UndoStep *us_p = BKE_undosys_stack_init_or_active_with_type(ustack, BKE_UNDOSYS_TYPE_IMAGE);
+  ImageUndoStep *us = (ImageUndoStep *)us_p;
+  /* We should always have an undo push started when accessing tiles,
+   * not doing this means we won't have paint_mode correctly set. */
+  BLI_assert(us_p == us_prev);
+  if (us_p != us_prev) {
+    /* Fallback value until we can be sure this never happens. */
+    us->paint_mode = PAINT_MODE_TEXTURE_2D;
+  }
+  return &us->paint_tiles;
+}
+
+/* restore painting image to previous state. Used for anchored and drag-dot style brushes*/
+void ED_image_undo_restore(UndoStep *us)
+{
+  ListBase *paint_tiles = &((ImageUndoStep *)us)->paint_tiles;
+  ptile_restore_runtime_list(paint_tiles);
+  ptile_invalidate_list(paint_tiles);
+}
+
+static ImageUndoStep *image_undo_push_begin(const char *name, int paint_mode)
+{
+  UndoStack *ustack = ED_undo_stack_get();
+  bContext *C = NULL; /* special case, we never read from this. */
+  UndoStep *us_p = BKE_undosys_step_push_init_with_type(ustack, C, name, BKE_UNDOSYS_TYPE_IMAGE);
+  ImageUndoStep *us = (ImageUndoStep *)us_p;
+  BLI_assert(ELEM(paint_mode, PAINT_MODE_TEXTURE_2D, PAINT_MODE_TEXTURE_3D));
+  us->paint_mode = paint_mode;
+  return us;
+}
+
+void ED_image_undo_push_begin(const char *name, int paint_mode)
+{
+  image_undo_push_begin(name, paint_mode);
+}
+
+void ED_image_undo_push_begin_with_image(const char *name, Image *image, ImBuf *ibuf)
+{
+  ImageUndoStep *us = image_undo_push_begin(name, PAINT_MODE_TEXTURE_2D);
+
+  UndoImageHandle *uh = uhandle_ensure(&us->handles, image);
+  UndoImageBuf *ubuf_pre = uhandle_ensure_ubuf(uh, image, ibuf);
+  BLI_assert(ubuf_pre->post == NULL);
+
+  ImageUndoStep *us_reference = (ImageUndoStep *)ED_undo_stack_get()->step_active;
+  while (us_reference && us_reference->step.type != BKE_UNDOSYS_TYPE_IMAGE) {
+    us_reference = (ImageUndoStep *)us_reference->step.prev;
+  }
+  UndoImageBuf *ubuf_reference = (us_reference ?
+                                      ubuf_lookup_from_reference(us_reference, image, ubuf_pre) :
+                                      NULL);
+
+  if (ubuf_reference) {
+    memcpy(ubuf_pre->tiles, ubuf_reference->tiles, sizeof(*ubuf_pre->tiles) * ubuf_pre->tiles_len);
+    for (uint i = 0; i < ubuf_pre->tiles_len; i++) {
+      UndoImageTile *utile = ubuf_pre->tiles[i];
+      utile->users += 1;
+    }
+  }
+  else {
+    ubuf_from_image_all_tiles(ubuf_pre, ibuf);
+  }
+}
+
+void ED_image_undo_push_end(void)
+{
+  UndoStack *ustack = ED_undo_stack_get();
+  BKE_undosys_step_push(ustack, NULL, NULL);
+  WM_file_tag_modified();
+}
+
+/** \} */