Render: move editor/render module to c++

Doing this in preparation for some work on asset preview generation.

Differential Revision: https://developer.blender.org/D13676

1 files changed, 1921 insertions, 0 deletions

diff --git a/source/blender/editors/render/render_preview.cc b/source/blender/editors/render/render_preview.cc
new file mode 100644
index 00000000000..779bcd1428c
--- /dev/null
+++ b/source/blender/editors/render/render_preview.cc
@@ -0,0 +1,1921 @@
+/*
+ * 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.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) Blender Foundation.
+ * All rights reserved.
+ */
+
+/** \file
+ * \ingroup edrend
+ */
+
+/* global includes */
+
+#include <math.h>
+#include <stdlib.h>
+#include <string.h>
+
+#ifndef WIN32
+#  include <unistd.h>
+#else
+#  include <io.h>
+#endif
+#include "MEM_guardedalloc.h"
+
+#include "BLI_blenlib.h"
+#include "BLI_math.h"
+#include "BLI_utildefines.h"
+
+#include "PIL_time.h"
+
+#include "BLO_readfile.h"
+
+#include "DNA_brush_types.h"
+#include "DNA_camera_types.h"
+#include "DNA_collection_types.h"
+#include "DNA_light_types.h"
+#include "DNA_material_types.h"
+#include "DNA_mesh_types.h"
+#include "DNA_node_types.h"
+#include "DNA_object_types.h"
+#include "DNA_scene_types.h"
+#include "DNA_screen_types.h"
+#include "DNA_space_types.h"
+#include "DNA_world_types.h"
+
+#include "BKE_animsys.h"
+#include "BKE_appdir.h"
+#include "BKE_armature.h"
+#include "BKE_brush.h"
+#include "BKE_colortools.h"
+#include "BKE_context.h"
+#include "BKE_global.h"
+#include "BKE_icons.h"
+#include "BKE_idprop.h"
+#include "BKE_image.h"
+#include "BKE_layer.h"
+#include "BKE_lib_id.h"
+#include "BKE_light.h"
+#include "BKE_main.h"
+#include "BKE_material.h"
+#include "BKE_node.h"
+#include "BKE_object.h"
+#include "BKE_scene.h"
+#include "BKE_screen.h"
+#include "BKE_texture.h"
+#include "BKE_world.h"
+
+#include "DEG_depsgraph.h"
+#include "DEG_depsgraph_build.h"
+#include "DEG_depsgraph_query.h"
+
+#include "IMB_imbuf.h"
+#include "IMB_imbuf_types.h"
+#include "IMB_thumbs.h"
+
+#include "BIF_glutil.h"
+
+#include "GPU_shader.h"
+
+#include "RE_engine.h"
+#include "RE_pipeline.h"
+#include "RE_texture.h"
+
+#include "WM_api.h"
+#include "WM_types.h"
+
+#include "ED_armature.h"
+#include "ED_datafiles.h"
+#include "ED_render.h"
+#include "ED_screen.h"
+#include "ED_view3d.h"
+#include "ED_view3d_offscreen.h"
+
+#include "UI_interface_icons.h"
+
+#ifndef NDEBUG
+/* Used for database init assert(). */
+#  include "BLI_threads.h"
+#endif
+
+static void icon_copy_rect(ImBuf *ibuf, uint w, uint h, uint *rect);
+
+/* -------------------------------------------------------------------- */
+/** \name Local Structs
+ * \{ */
+
+typedef struct ShaderPreview {
+  /* from wmJob */
+  void *owner;
+  short *stop, *do_update;
+
+  Scene *scene;
+  ID *id, *id_copy;
+  ID *parent;
+  MTex *slot;
+
+  /* datablocks with nodes need full copy during preview render, glsl uses it too */
+  Material *matcopy;
+  Tex *texcopy;
+  Light *lampcopy;
+  World *worldcopy;
+
+  /** Copy of the active objects #Object.color */
+  float color[4];
+
+  int sizex, sizey;
+  uint *pr_rect;
+  ePreviewRenderMethod pr_method;
+  bool own_id_copy;
+
+  Main *bmain;
+  Main *pr_main;
+} ShaderPreview;
+
+typedef struct IconPreviewSize {
+  struct IconPreviewSize *next, *prev;
+  int sizex, sizey;
+  uint *rect;
+} IconPreviewSize;
+
+typedef struct IconPreview {
+  Main *bmain;
+  Depsgraph *depsgraph; /* May be NULL (see #WM_OT_previews_ensure). */
+  Scene *scene;
+  void *owner;
+  ID *id, *id_copy; /* May be NULL! (see ICON_TYPE_PREVIEW case in #ui_icon_ensure_deferred()) */
+  ListBase sizes;
+
+  /* May be NULL, is used for rendering IDs that require some other object for it to be applied on
+   * before the ID can be represented as an image, for example when rendering an Action. */
+  struct Object *active_object;
+} IconPreview;
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Preview for Buttons
+ * \{ */
+
+static Main *G_pr_main = NULL;
+static Main *G_pr_main_grease_pencil = NULL;
+
+#ifndef WITH_HEADLESS
+static Main *load_main_from_memory(const void *blend, int blend_size)
+{
+  const int fileflags = G.fileflags;
+  Main *bmain = NULL;
+  BlendFileData *bfd;
+
+  G.fileflags |= G_FILE_NO_UI;
+  bfd = BLO_read_from_memory(blend, blend_size, BLO_READ_SKIP_NONE, NULL);
+  if (bfd) {
+    bmain = bfd->main;
+
+    MEM_freeN(bfd);
+  }
+  G.fileflags = fileflags;
+
+  return bmain;
+}
+#endif
+
+void ED_preview_ensure_dbase(void)
+{
+#ifndef WITH_HEADLESS
+  static bool base_initialized = false;
+  BLI_assert(BLI_thread_is_main());
+  if (!base_initialized) {
+    G_pr_main = load_main_from_memory(datatoc_preview_blend, datatoc_preview_blend_size);
+    G_pr_main_grease_pencil = load_main_from_memory(datatoc_preview_grease_pencil_blend,
+                                                    datatoc_preview_grease_pencil_blend_size);
+    base_initialized = true;
+  }
+#endif
+}
+
+static bool check_engine_supports_preview(Scene *scene)
+{
+  RenderEngineType *type = RE_engines_find(scene->r.engine);
+  return (type->flag & RE_USE_PREVIEW) != 0;
+}
+
+static bool preview_method_is_render(const ePreviewRenderMethod pr_method)
+{
+  return ELEM(pr_method, PR_ICON_RENDER, PR_BUTS_RENDER);
+}
+
+void ED_preview_free_dbase(void)
+{
+  if (G_pr_main) {
+    BKE_main_free(G_pr_main);
+  }
+
+  if (G_pr_main_grease_pencil) {
+    BKE_main_free(G_pr_main_grease_pencil);
+  }
+}
+
+static Scene *preview_get_scene(Main *pr_main)
+{
+  if (pr_main == NULL) {
+    return NULL;
+  }
+
+  return static_cast<Scene *>(pr_main->scenes.first);
+}
+
+static const char *preview_collection_name(const ePreviewType pr_type)
+{
+  switch (pr_type) {
+    case MA_FLAT:
+      return "Flat";
+    case MA_SPHERE:
+      return "Sphere";
+    case MA_CUBE:
+      return "Cube";
+    case MA_SHADERBALL:
+      return "Shader Ball";
+    case MA_CLOTH:
+      return "Cloth";
+    case MA_FLUID:
+      return "Fluid";
+    case MA_SPHERE_A:
+      return "World Sphere";
+    case MA_LAMP:
+      return "Lamp";
+    case MA_SKY:
+      return "Sky";
+    case MA_HAIR:
+      return "Hair";
+    case MA_ATMOS:
+      return "Atmosphere";
+    default:
+      BLI_assert_msg(0, "Unknown preview type");
+      return "";
+  }
+}
+
+static bool render_engine_supports_ray_visibility(const Scene *sce)
+{
+  return !STREQ(sce->r.engine, RE_engine_id_BLENDER_EEVEE);
+}
+
+static void switch_preview_collection_visibilty(ViewLayer *view_layer, const ePreviewType pr_type)
+{
+  /* Set appropriate layer as visible. */
+  LayerCollection *lc = static_cast<LayerCollection *>(view_layer->layer_collections.first);
+  const char *collection_name = preview_collection_name(pr_type);
+
+  for (lc = static_cast<LayerCollection *>(lc->layer_collections.first); lc; lc = lc->next) {
+    if (STREQ(lc->collection->id.name + 2, collection_name)) {
+      lc->collection->flag &= ~COLLECTION_HIDE_RENDER;
+    }
+    else {
+      lc->collection->flag |= COLLECTION_HIDE_RENDER;
+    }
+  }
+}
+
+static const char *preview_floor_material_name(const Scene *scene,
+                                               const ePreviewRenderMethod pr_method)
+{
+  if (pr_method == PR_ICON_RENDER && render_engine_supports_ray_visibility(scene)) {
+    return "FloorHidden";
+  }
+  return "Floor";
+}
+
+static void switch_preview_floor_material(Main *pr_main,
+                                          Mesh *me,
+                                          const Scene *scene,
+                                          const ePreviewRenderMethod pr_method)
+{
+  if (me->totcol == 0) {
+    return;
+  }
+
+  const char *material_name = preview_floor_material_name(scene, pr_method);
+  Material *mat = static_cast<Material *>(
+      BLI_findstring(&pr_main->materials, material_name, offsetof(ID, name) + 2));
+  if (mat) {
+    me->mat[0] = mat;
+  }
+}
+
+static void switch_preview_floor_visibility(Main *pr_main,
+                                            const Scene *scene,
+                                            ViewLayer *view_layer,
+                                            const ePreviewRenderMethod pr_method)
+{
+  /* Hide floor for icon renders. */
+  LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+    if (STREQ(base->object->id.name + 2, "Floor")) {
+      base->object->visibility_flag &= ~OB_HIDE_RENDER;
+      if (pr_method == PR_ICON_RENDER) {
+        if (!render_engine_supports_ray_visibility(scene)) {
+          base->object->visibility_flag |= OB_HIDE_RENDER;
+        }
+      }
+      if (base->object->type == OB_MESH) {
+        switch_preview_floor_material(
+            pr_main, static_cast<Mesh *>(base->object->data), scene, pr_method);
+      }
+    }
+  }
+}
+
+static void set_preview_visibility(Main *pr_main,
+                                   Scene *scene,
+                                   ViewLayer *view_layer,
+                                   const ePreviewType pr_type,
+                                   const ePreviewRenderMethod pr_method)
+{
+  switch_preview_collection_visibilty(view_layer, pr_type);
+  switch_preview_floor_visibility(pr_main, scene, view_layer, pr_method);
+  BKE_layer_collection_sync(scene, view_layer);
+}
+
+static World *preview_get_localized_world(ShaderPreview *sp, World *world)
+{
+  if (world == NULL) {
+    return NULL;
+  }
+  if (sp->worldcopy != NULL) {
+    return sp->worldcopy;
+  }
+
+  ID *id_copy = BKE_id_copy_ex(NULL,
+                               &world->id,
+                               NULL,
+                               LIB_ID_CREATE_LOCAL | LIB_ID_COPY_LOCALIZE |
+                                   LIB_ID_COPY_NO_ANIMDATA);
+  sp->worldcopy = (World *)id_copy;
+  BLI_addtail(&sp->pr_main->worlds, sp->worldcopy);
+  return sp->worldcopy;
+}
+
+static ID *duplicate_ids(ID *id, const bool allow_failure)
+{
+  if (id == NULL) {
+    /* Non-ID preview render. */
+    return NULL;
+  }
+
+  switch (GS(id->name)) {
+    case ID_OB:
+    case ID_MA:
+    case ID_TE:
+    case ID_LA:
+    case ID_WO: {
+      BLI_assert(BKE_previewimg_id_supports_jobs(id));
+      ID *id_copy = BKE_id_copy_ex(
+          NULL, id, NULL, LIB_ID_CREATE_LOCAL | LIB_ID_COPY_LOCALIZE | LIB_ID_COPY_NO_ANIMDATA);
+      return id_copy;
+    }
+    /* These support threading, but don't need duplicating. */
+    case ID_IM:
+    case ID_BR:
+      BLI_assert(BKE_previewimg_id_supports_jobs(id));
+      return NULL;
+    default:
+      if (!allow_failure) {
+        BLI_assert_msg(0, "ID type preview not supported.");
+      }
+      return NULL;
+  }
+}
+
+static const char *preview_world_name(const Scene *sce,
+                                      const ID_Type id_type,
+                                      const ePreviewRenderMethod pr_method)
+{
+  /* When rendering material icons the floor will not be shown in the output. Cycles will use a
+   * material trick to show the floor in the reflections, but hide the floor for camera rays. For
+   * Eevee we use a transparent world that has a projected grid.
+   *
+   * In the future when Eevee supports vulkan raytracing we can re-evaluate and perhaps remove this
+   * approximation.
+   */
+  if (id_type == ID_MA && pr_method == PR_ICON_RENDER &&
+      !render_engine_supports_ray_visibility(sce)) {
+    return "WorldFloor";
+  }
+  return "World";
+}
+
+static World *preview_get_world(Main *pr_main,
+                                const Scene *sce,
+                                const ID_Type id_type,
+                                const ePreviewRenderMethod pr_method)
+{
+  World *result = NULL;
+  const char *world_name = preview_world_name(sce, id_type, pr_method);
+  result = static_cast<World *>(
+      BLI_findstring(&pr_main->worlds, world_name, offsetof(ID, name) + 2));
+
+  /* No world found return first world. */
+  if (result == NULL) {
+    result = static_cast<World *>(pr_main->worlds.first);
+  }
+
+  BLI_assert_msg(result, "Preview file has no world.");
+  return result;
+}
+
+static void preview_sync_exposure(World *dst, const World *src)
+{
+  BLI_assert(dst);
+  BLI_assert(src);
+  dst->exp = src->exp;
+  dst->range = src->range;
+}
+
+static World *preview_prepare_world(Main *pr_main,
+                                    const Scene *sce,
+                                    const World *world,
+                                    const ID_Type id_type,
+                                    const ePreviewRenderMethod pr_method)
+{
+  World *result = preview_get_world(pr_main, sce, id_type, pr_method);
+  if (world) {
+    preview_sync_exposure(result, world);
+  }
+  return result;
+}
+
+/* call this with a pointer to initialize preview scene */
+/* call this with NULL to restore assigned ID pointers in preview scene */
+static Scene *preview_prepare_scene(
+    Main *bmain, Scene *scene, ID *id, int id_type, ShaderPreview *sp)
+{
+  Scene *sce;
+  Main *pr_main = sp->pr_main;
+
+  memcpy(pr_main->filepath, BKE_main_blendfile_path(bmain), sizeof(pr_main->filepath));
+
+  sce = preview_get_scene(pr_main);
+  if (sce) {
+    ViewLayer *view_layer = static_cast<ViewLayer *>(sce->view_layers.first);
+
+    /* Only enable the combined renderpass */
+    view_layer->passflag = SCE_PASS_COMBINED;
+    view_layer->eevee.render_passes = 0;
+
+    /* this flag tells render to not execute depsgraph or ipos etc */
+    sce->r.scemode |= R_BUTS_PREVIEW;
+    BLI_strncpy(sce->r.engine, scene->r.engine, sizeof(sce->r.engine));
+
+    sce->r.color_mgt_flag = scene->r.color_mgt_flag;
+    BKE_color_managed_display_settings_copy(&sce->display_settings, &scene->display_settings);
+
+    BKE_color_managed_view_settings_free(&sce->view_settings);
+    BKE_color_managed_view_settings_copy(&sce->view_settings, &scene->view_settings);
+
+    if ((id && sp->pr_method == PR_ICON_RENDER) && id_type != ID_WO) {
+      sce->r.alphamode = R_ALPHAPREMUL;
+    }
+    else {
+      sce->r.alphamode = R_ADDSKY;
+    }
+
+    sce->r.cfra = scene->r.cfra;
+
+    /* Setup the world. */
+    sce->world = preview_prepare_world(
+        pr_main, sce, scene->world, static_cast<ID_Type>(id_type), sp->pr_method);
+
+    if (id_type == ID_TE) {
+      /* Texture is not actually rendered with engine, just set dummy value. */
+      BLI_strncpy(sce->r.engine, RE_engine_id_BLENDER_EEVEE, sizeof(sce->r.engine));
+    }
+
+    if (id_type == ID_MA) {
+      Material *mat = NULL, *origmat = (Material *)id;
+
+      if (origmat) {
+        /* work on a copy */
+        BLI_assert(sp->id_copy != NULL);
+        mat = sp->matcopy = (Material *)sp->id_copy;
+        sp->id_copy = NULL;
+        BLI_addtail(&pr_main->materials, mat);
+
+        /* Use current scene world for lighting. */
+        if (mat->pr_flag == MA_PREVIEW_WORLD && sp->pr_method == PR_BUTS_RENDER) {
+          /* Use current scene world to light sphere. */
+          sce->world = preview_get_localized_world(sp, scene->world);
+        }
+        else if (sce->world && sp->pr_method != PR_ICON_RENDER) {
+          /* Use a default world color. Using the current
+           * scene world can be slow if it has big textures. */
+          sce->world->use_nodes = false;
+          sce->world->horr = 0.05f;
+          sce->world->horg = 0.05f;
+          sce->world->horb = 0.05f;
+        }
+
+        /* For grease pencil, always use sphere for icon renders. */
+        const ePreviewType preview_type = static_cast<ePreviewType>(
+            (sp->pr_method == PR_ICON_RENDER && sp->pr_main == G_pr_main_grease_pencil) ?
+                MA_SPHERE_A :
+                mat->pr_type);
+        set_preview_visibility(pr_main, sce, view_layer, preview_type, sp->pr_method);
+      }
+      else {
+        sce->display.render_aa = SCE_DISPLAY_AA_OFF;
+      }
+
+      LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+        if (base->object->id.name[2] == 'p') {
+          /* copy over object color, in case material uses it */
+          copy_v4_v4(base->object->color, sp->color);
+
+          if (OB_TYPE_SUPPORT_MATERIAL(base->object->type)) {
+            /* don't use BKE_object_material_assign, it changed mat->id.us, which shows in the UI
+             */
+            Material ***matar = BKE_object_material_array_p(base->object);
+            int actcol = max_ii(base->object->actcol - 1, 0);
+
+            if (matar && actcol < base->object->totcol) {
+              (*matar)[actcol] = mat;
+            }
+          }
+          else if (base->object->type == OB_LAMP) {
+            base->flag |= BASE_VISIBLE_DEPSGRAPH;
+          }
+        }
+      }
+    }
+    else if (id_type == ID_TE) {
+      Tex *tex = NULL, *origtex = (Tex *)id;
+
+      if (origtex) {
+        BLI_assert(sp->id_copy != NULL);
+        tex = sp->texcopy = (Tex *)sp->id_copy;
+        sp->id_copy = NULL;
+        BLI_addtail(&pr_main->textures, tex);
+      }
+    }
+    else if (id_type == ID_LA) {
+      Light *la = NULL, *origla = (Light *)id;
+
+      /* work on a copy */
+      if (origla) {
+        BLI_assert(sp->id_copy != NULL);
+        la = sp->lampcopy = (Light *)sp->id_copy;
+        sp->id_copy = NULL;
+        BLI_addtail(&pr_main->lights, la);
+      }
+
+      set_preview_visibility(pr_main, sce, view_layer, MA_LAMP, sp->pr_method);
+
+      if (sce->world) {
+        /* Only use lighting from the light. */
+        sce->world->use_nodes = false;
+        sce->world->horr = 0.0f;
+        sce->world->horg = 0.0f;
+        sce->world->horb = 0.0f;
+      }
+
+      LISTBASE_FOREACH (Base *, base, &view_layer->object_bases) {
+        if (base->object->id.name[2] == 'p') {
+          if (base->object->type == OB_LAMP) {
+            base->object->data = la;
+          }
+        }
+      }
+    }
+    else if (id_type == ID_WO) {
+      World *wrld = NULL, *origwrld = (World *)id;
+
+      if (origwrld) {
+        BLI_assert(sp->id_copy != NULL);
+        wrld = sp->worldcopy = (World *)sp->id_copy;
+        sp->id_copy = NULL;
+        BLI_addtail(&pr_main->worlds, wrld);
+      }
+
+      set_preview_visibility(pr_main, sce, view_layer, MA_SKY, sp->pr_method);
+      sce->world = wrld;
+    }
+
+    return sce;
+  }
+
+  return NULL;
+}
+
+/* new UI convention: draw is in pixel space already. */
+/* uses UI_BTYPE_ROUNDBOX button in block to get the rect */
+static bool ed_preview_draw_rect(ScrArea *area, int split, int first, rcti *rect, rcti *newrect)
+{
+  Render *re;
+  RenderView *rv;
+  RenderResult rres;
+  char name[32];
+  int offx = 0;
+  int newx = BLI_rcti_size_x(rect);
+  int newy = BLI_rcti_size_y(rect);
+  bool ok = false;
+
+  if (!split || first) {
+    sprintf(name, "Preview %p", (void *)area);
+  }
+  else {
+    sprintf(name, "SecondPreview %p", (void *)area);
+  }
+
+  if (split) {
+    if (first) {
+      offx = 0;
+      newx = newx / 2;
+    }
+    else {
+      offx = newx / 2;
+      newx = newx - newx / 2;
+    }
+  }
+
+  /* test if something rendered ok */
+  re = RE_GetRender(name);
+
+  if (re == NULL) {
+    return false;
+  }
+
+  RE_AcquireResultImageViews(re, &rres);
+
+  if (!BLI_listbase_is_empty(&rres.views)) {
+    /* material preview only needs monoscopy (view 0) */
+    rv = RE_RenderViewGetById(&rres, 0);
+  }
+  else {
+    /* possible the job clears the views but we're still drawing T45496 */
+    rv = NULL;
+  }
+
+  if (rv && rv->rectf) {
+
+    if (abs(rres.rectx - newx) < 2 && abs(rres.recty - newy) < 2) {
+
+      newrect->xmax = max_ii(newrect->xmax, rect->xmin + rres.rectx + offx);
+      newrect->ymax = max_ii(newrect->ymax, rect->ymin + rres.recty);
+
+      if (rres.rectx && rres.recty) {
+        uchar *rect_byte = static_cast<uchar *>(
+            MEM_mallocN(rres.rectx * rres.recty * sizeof(int), "ed_preview_draw_rect"));
+        float fx = rect->xmin + offx;
+        float fy = rect->ymin;
+
+        /* material preview only needs monoscopy (view 0) */
+        RE_AcquiredResultGet32(re, &rres, (uint *)rect_byte, 0);
+
+        IMMDrawPixelsTexState state = immDrawPixelsTexSetup(GPU_SHADER_2D_IMAGE_COLOR);
+        immDrawPixelsTex(
+            &state, fx, fy, rres.rectx, rres.recty, GPU_RGBA8, false, rect_byte, 1.0f, 1.0f, NULL);
+
+        MEM_freeN(rect_byte);
+
+        ok = 1;
+      }
+    }
+  }
+
+  RE_ReleaseResultImageViews(re, &rres);
+
+  return ok;
+}
+
+void ED_preview_draw(const bContext *C, void *idp, void *parentp, void *slotp, rcti *rect)
+{
+  if (idp) {
+    wmWindowManager *wm = CTX_wm_manager(C);
+    ScrArea *area = CTX_wm_area(C);
+    ID *id = (ID *)idp;
+    ID *parent = (ID *)parentp;
+    MTex *slot = (MTex *)slotp;
+    SpaceProperties *sbuts = CTX_wm_space_properties(C);
+    ShaderPreview *sp = static_cast<ShaderPreview *>(WM_jobs_customdata(wm, area));
+    rcti newrect;
+    int ok;
+    int newx = BLI_rcti_size_x(rect);
+    int newy = BLI_rcti_size_y(rect);
+
+    newrect.xmin = rect->xmin;
+    newrect.xmax = rect->xmin;
+    newrect.ymin = rect->ymin;
+    newrect.ymax = rect->ymin;
+
+    if (parent) {
+      ok = ed_preview_draw_rect(area, 1, 1, rect, &newrect);
+      ok &= ed_preview_draw_rect(area, 1, 0, rect, &newrect);
+    }
+    else {
+      ok = ed_preview_draw_rect(area, 0, 0, rect, &newrect);
+    }
+
+    if (ok) {
+      *rect = newrect;
+    }
+
+    /* start a new preview render job if signaled through sbuts->preview,
+     * if no render result was found and no preview render job is running,
+     * or if the job is running and the size of preview changed */
+    if ((sbuts != NULL && sbuts->preview) ||
+        (!ok && !WM_jobs_test(wm, area, WM_JOB_TYPE_RENDER_PREVIEW)) ||
+        (sp && (abs(sp->sizex - newx) >= 2 || abs(sp->sizey - newy) > 2))) {
+      if (sbuts != NULL) {
+        sbuts->preview = 0;
+      }
+      ED_preview_shader_job(C, area, id, parent, slot, newx, newy, PR_BUTS_RENDER);
+    }
+  }
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Object Preview
+ * \{ */
+
+struct ObjectPreviewData {
+  /* The main for the preview, not of the current file. */
+  Main *pr_main;
+  /* Copy of the object to create the preview for. The copy is for thread safety (and to insert
+   * it into an own main). */
+  Object *object;
+  /* Current frame. */
+  int cfra;
+  int sizex;
+  int sizey;
+};
+
+static bool object_preview_is_type_supported(const Object *ob)
+{
+  return OB_TYPE_IS_GEOMETRY(ob->type);
+}
+
+static Object *object_preview_camera_create(Main *preview_main,
+                                            ViewLayer *view_layer,
+                                            Object *preview_object)
+{
+  Object *camera = BKE_object_add(preview_main, view_layer, OB_CAMERA, "Preview Camera");
+
+  float rotmat[3][3];
+  float dummyscale[3];
+  mat4_to_loc_rot_size(camera->loc, rotmat, dummyscale, preview_object->obmat);
+
+  /* Camera is Y up, so needs additional rotations to obliquely face the front. */
+  float drotmat[3][3];
+  const float eul[3] = {M_PI * 0.4f, 0.0f, M_PI * 0.1f};
+  eul_to_mat3(drotmat, eul);
+  mul_m3_m3_post(rotmat, drotmat);
+
+  camera->rotmode = ROT_MODE_QUAT;
+  mat3_to_quat(camera->quat, rotmat);
+
+  /* Nice focal length for close portraiture. */
+  ((Camera *)camera->data)->lens = 85;
+
+  return camera;
+}
+
+static Scene *object_preview_scene_create(const struct ObjectPreviewData *preview_data,
+                                          Depsgraph **r_depsgraph)
+{
+  Scene *scene = BKE_scene_add(preview_data->pr_main, "Object preview scene");
+  /* Preview need to be in the current frame to get a thumbnail similar of what
+   * viewport displays. */
+  CFRA = preview_data->cfra;
+
+  ViewLayer *view_layer = static_cast<ViewLayer *>(scene->view_layers.first);
+  Depsgraph *depsgraph = DEG_graph_new(
+      preview_data->pr_main, scene, view_layer, DAG_EVAL_VIEWPORT);
+
+  BLI_assert(preview_data->object != NULL);
+  BLI_addtail(&preview_data->pr_main->objects, preview_data->object);
+
+  BKE_collection_object_add(preview_data->pr_main, scene->master_collection, preview_data->object);
+
+  Object *camera_object = object_preview_camera_create(
+      preview_data->pr_main, view_layer, preview_data->object);
+
+  scene->camera = camera_object;
+  scene->r.xsch = preview_data->sizex;
+  scene->r.ysch = preview_data->sizey;
+  scene->r.size = 100;
+
+  Base *preview_base = BKE_view_layer_base_find(view_layer, preview_data->object);
+  /* For 'view selected' below. */
+  preview_base->flag |= BASE_SELECTED;
+
+  DEG_graph_build_from_view_layer(depsgraph);
+  DEG_evaluate_on_refresh(depsgraph);
+
+  ED_view3d_camera_to_view_selected(preview_data->pr_main, depsgraph, scene, camera_object);
+
+  BKE_scene_graph_update_tagged(depsgraph, preview_data->pr_main);
+
+  *r_depsgraph = depsgraph;
+  return scene;
+}
+
+static void object_preview_render(IconPreview *preview, IconPreviewSize *preview_sized)
+{
+  Main *preview_main = BKE_main_new();
+  const float pixelsize_old = U.pixelsize;
+  char err_out[256] = "unknown";
+
+  BLI_assert(preview->id_copy && (preview->id_copy != preview->id));
+
+  struct ObjectPreviewData preview_data = {};
+  preview_data.pr_main = preview_main;
+  /* Act on a copy. */
+  preview_data.object = (Object *)preview->id_copy;
+  preview_data.cfra = preview->scene->r.cfra;
+  preview_data.sizex = preview_sized->sizex;
+  preview_data.sizey = preview_sized->sizey;
+
+  Depsgraph *depsgraph;
+  Scene *scene = object_preview_scene_create(&preview_data, &depsgraph);
+
+  /* Ownership is now ours. */
+  preview->id_copy = NULL;
+
+  U.pixelsize = 2.0f;
+
+  View3DShading shading;
+  BKE_screen_view3d_shading_init(&shading);
+  /* Enable shadows, makes it a bit easier to see the shape. */
+  shading.flag |= V3D_SHADING_SHADOW;
+
+  ImBuf *ibuf = ED_view3d_draw_offscreen_imbuf_simple(
+      depsgraph,
+      DEG_get_evaluated_scene(depsgraph),
+      &shading,
+      OB_TEXTURE,
+      DEG_get_evaluated_object(depsgraph, scene->camera),
+      preview_sized->sizex,
+      preview_sized->sizey,
+      IB_rect,
+      V3D_OFSDRAW_OVERRIDE_SCENE_SETTINGS,
+      R_ALPHAPREMUL,
+      NULL,
+      NULL,
+      err_out);
+  /* TODO: color-management? */
+
+  U.pixelsize = pixelsize_old;
+
+  if (ibuf) {
+    icon_copy_rect(ibuf, preview_sized->sizex, preview_sized->sizey, preview_sized->rect);
+    IMB_freeImBuf(ibuf);
+  }
+
+  DEG_graph_free(depsgraph);
+  BKE_main_free(preview_main);
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Action Preview
+ * \{ */
+
+static struct PoseBackup *action_preview_render_prepare(IconPreview *preview)
+{
+  Object *object = preview->active_object;
+  if (object == NULL) {
+    WM_report(RPT_WARNING, "No active object, unable to apply the Action before rendering");
+    return NULL;
+  }
+  if (object->pose == NULL) {
+    WM_reportf(RPT_WARNING,
+               "Object %s has no pose, unable to apply the Action before rendering",
+               object->id.name + 2);
+    return NULL;
+  }
+
+  /* Create a backup of the current pose. */
+  struct bAction *action = (struct bAction *)preview->id;
+  struct PoseBackup *pose_backup = ED_pose_backup_create_all_bones(object, action);
+
+  /* Apply the Action as pose, so that it can be rendered. This assumes the Action represents a
+   * single pose, and that thus the evaluation time doesn't matter. */
+  AnimationEvalContext anim_eval_context = {preview->depsgraph, 0.0f};
+  BKE_pose_apply_action_all_bones(object, action, &anim_eval_context);
+
+  /* Force evaluation of the new pose, before the preview is rendered. */
+  DEG_id_tag_update(&object->id, ID_RECALC_GEOMETRY);
+  DEG_evaluate_on_refresh(preview->depsgraph);
+
+  return pose_backup;
+}
+
+static void action_preview_render_cleanup(IconPreview *preview, struct PoseBackup *pose_backup)
+{
+  if (pose_backup == NULL) {
+    return;
+  }
+  ED_pose_backup_restore(pose_backup);
+  ED_pose_backup_free(pose_backup);
+
+  DEG_id_tag_update(&preview->active_object->id, ID_RECALC_GEOMETRY);
+}
+
+/* Render a pose from the scene camera. It is assumed that the scene camera is
+ * capturing the pose. The pose is applied temporarily to the current object
+ * before rendering. */
+static void action_preview_render(IconPreview *preview, IconPreviewSize *preview_sized)
+{
+  char err_out[256] = "";
+
+  Depsgraph *depsgraph = preview->depsgraph;
+  /* Not all code paths that lead to this function actually provide a depsgraph.
+   * The "Refresh Asset Preview" button (ED_OT_lib_id_generate_preview) does,
+   * but WM_OT_previews_ensure does not. */
+  BLI_assert(depsgraph != NULL);
+  BLI_assert(preview->scene == DEG_get_input_scene(depsgraph));
+
+  /* Apply the pose before getting the evaluated scene, so that the new pose is evaluated. */
+  struct PoseBackup *pose_backup = action_preview_render_prepare(preview);
+
+  Scene *scene_eval = DEG_get_evaluated_scene(depsgraph);
+  Object *camera_eval = scene_eval->camera;
+  if (camera_eval == NULL) {
+    printf("Scene has no camera, unable to render preview of %s without it.\n",
+           preview->id->name + 2);
+    return;
+  }
+
+  /* This renders with the Workbench engine settings stored on the Scene. */
+  ImBuf *ibuf = ED_view3d_draw_offscreen_imbuf_simple(depsgraph,
+                                                      scene_eval,
+                                                      NULL,
+                                                      OB_SOLID,
+                                                      camera_eval,
+                                                      preview_sized->sizex,
+                                                      preview_sized->sizey,
+                                                      IB_rect,
+                                                      V3D_OFSDRAW_NONE,
+                                                      R_ADDSKY,
+                                                      NULL,
+                                                      NULL,
+                                                      err_out);
+
+  action_preview_render_cleanup(preview, pose_backup);
+
+  if (err_out[0] != '\0') {
+    printf("Error rendering Action %s preview: %s\n", preview->id->name + 2, err_out);
+  }
+
+  if (ibuf) {
+    icon_copy_rect(ibuf, preview_sized->sizex, preview_sized->sizey, preview_sized->rect);
+    IMB_freeImBuf(ibuf);
+  }
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name New Shader Preview System
+ * \{ */
+
+/* inside thread, called by renderer, sets job update value */
+static void shader_preview_update(void *spv,
+                                  RenderResult *UNUSED(rr),
+                                  volatile struct rcti *UNUSED(rect))
+{
+  ShaderPreview *sp = static_cast<ShaderPreview *>(spv);
+
+  *(sp->do_update) = true;
+}
+
+/* called by renderer, checks job value */
+static int shader_preview_break(void *spv)
+{
+  ShaderPreview *sp = static_cast<ShaderPreview *>(spv);
+
+  return *(sp->stop);
+}
+
+static void shader_preview_updatejob(void *UNUSED(spv))
+{
+}
+
+/* Renders texture directly to render buffer. */
+static void shader_preview_texture(ShaderPreview *sp, Tex *tex, Scene *sce, Render *re)
+{
+  /* Setup output buffer. */
+  int width = sp->sizex;
+  int height = sp->sizey;
+
+  /* This is needed otherwise no RenderResult is created. */
+  sce->r.scemode &= ~R_BUTS_PREVIEW;
+  RE_InitState(re, NULL, &sce->r, &sce->view_layers, NULL, width, height, NULL);
+  RE_SetScene(re, sce);
+
+  /* Create buffer in empty RenderView created in the init step. */
+  RenderResult *rr = RE_AcquireResultWrite(re);
+  RenderView *rv = (RenderView *)rr->views.first;
+  rv->rectf = static_cast<float *>(
+      MEM_callocN(sizeof(float[4]) * width * height, "texture render result"));
+  RE_ReleaseResult(re);
+
+  /* Get texture image pool (if any) */
+  struct ImagePool *img_pool = BKE_image_pool_new();
+  BKE_texture_fetch_images_for_pool(tex, img_pool);
+
+  /* Fill in image buffer. */
+  float *rect_float = rv->rectf;
+  float tex_coord[3] = {0.0f, 0.0f, 0.0f};
+  bool color_manage = true;
+
+  for (int y = 0; y < height; y++) {
+    /* Tex coords between -1.0f and 1.0f. */
+    tex_coord[1] = ((float)y / (float)height) * 2.0f - 1.0f;
+
+    for (int x = 0; x < width; x++) {
+      tex_coord[0] = ((float)x / (float)height) * 2.0f - 1.0f;
+
+      /* Evaluate texture at tex_coord. */
+      TexResult texres = {0};
+      BKE_texture_get_value_ex(sce, tex, tex_coord, &texres, img_pool, color_manage);
+
+      rect_float[0] = texres.tr;
+      rect_float[1] = texres.tg;
+      rect_float[2] = texres.tb;
+      rect_float[3] = texres.talpha ? texres.ta : 1.0f;
+
+      rect_float += 4;
+    }
+
+    /* Check if we should cancel texture preview. */
+    if (shader_preview_break(sp)) {
+      break;
+    }
+  }
+
+  BKE_image_pool_free(img_pool);
+}
+
+static void shader_preview_render(ShaderPreview *sp, ID *id, int split, int first)
+{
+  Render *re;
+  Scene *sce;
+  float oldlens;
+  short idtype = GS(id->name);
+  char name[32];
+  int sizex;
+  Main *pr_main = sp->pr_main;
+
+  /* in case of split preview, use border render */
+  if (split) {
+    if (first) {
+      sizex = sp->sizex / 2;
+    }
+    else {
+      sizex = sp->sizex - sp->sizex / 2;
+    }
+  }
+  else {
+    sizex = sp->sizex;
+  }
+
+  /* we have to set preview variables first */
+  sce = preview_get_scene(pr_main);
+  if (sce) {
+    sce->r.xsch = sizex;
+    sce->r.ysch = sp->sizey;
+    sce->r.size = 100;
+  }
+
+  /* get the stuff from the builtin preview dbase */
+  sce = preview_prepare_scene(sp->bmain, sp->scene, id, idtype, sp);
+  if (sce == NULL) {
+    return;
+  }
+
+  if (!split || first) {
+    sprintf(name, "Preview %p", sp->owner);
+  }
+  else {
+    sprintf(name, "SecondPreview %p", sp->owner);
+  }
+  re = RE_GetRender(name);
+
+  /* full refreshed render from first tile */
+  if (re == NULL) {
+    re = RE_NewRender(name);
+  }
+
+  /* sce->r gets copied in RE_InitState! */
+  sce->r.scemode &= ~(R_MATNODE_PREVIEW | R_TEXNODE_PREVIEW);
+  sce->r.scemode &= ~R_NO_IMAGE_LOAD;
+
+  if (sp->pr_method == PR_ICON_RENDER) {
+    sce->r.scemode |= R_NO_IMAGE_LOAD;
+    sce->display.render_aa = SCE_DISPLAY_AA_SAMPLES_8;
+  }
+  else { /* PR_BUTS_RENDER */
+    sce->display.render_aa = SCE_DISPLAY_AA_SAMPLES_8;
+  }
+
+  /* Callbacks are cleared on GetRender(). */
+  if (sp->pr_method == PR_BUTS_RENDER) {
+    RE_display_update_cb(re, sp, shader_preview_update);
+  }
+  /* set this for all previews, default is react to G.is_break still */
+  RE_test_break_cb(re, sp, shader_preview_break);
+
+  /* lens adjust */
+  oldlens = ((Camera *)sce->camera->data)->lens;
+  if (sizex > sp->sizey) {
+    ((Camera *)sce->camera->data)->lens *= (float)sp->sizey / (float)sizex;
+  }
+
+  /* entire cycle for render engine */
+  if (idtype == ID_TE) {
+    shader_preview_texture(sp, (Tex *)id, sce, re);
+  }
+  else {
+    /* Render preview scene */
+    RE_PreviewRender(re, pr_main, sce);
+  }
+
+  ((Camera *)sce->camera->data)->lens = oldlens;
+
+  /* handle results */
+  if (sp->pr_method == PR_ICON_RENDER) {
+    // char *rct = (char *)(sp->pr_rect + 32 * 16 + 16);
+
+    if (sp->pr_rect) {
+      RE_ResultGet32(re, sp->pr_rect);
+    }
+  }
+
+  /* unassign the pointers, reset vars */
+  preview_prepare_scene(sp->bmain, sp->scene, NULL, GS(id->name), sp);
+
+  /* XXX bad exception, end-exec is not being called in render, because it uses local main. */
+#if 0
+  if (idtype == ID_TE) {
+    Tex *tex = (Tex *)id;
+    if (tex->use_nodes && tex->nodetree)
+      ntreeEndExecTree(tex->nodetree);
+  }
+#endif
+}
+
+/* runs inside thread for material and icons */
+static void shader_preview_startjob(void *customdata, short *stop, short *do_update)
+{
+  ShaderPreview *sp = static_cast<ShaderPreview *>(customdata);
+
+  sp->stop = stop;
+  sp->do_update = do_update;
+
+  if (sp->parent) {
+    shader_preview_render(sp, sp->id, 1, 1);
+    shader_preview_render(sp, sp->parent, 1, 0);
+  }
+  else {
+    shader_preview_render(sp, sp->id, 0, 0);
+  }
+
+  *do_update = true;
+}
+
+static void preview_id_copy_free(ID *id)
+{
+  struct IDProperty *properties;
+  /* get rid of copied ID */
+  properties = IDP_GetProperties(id, false);
+  if (properties) {
+    IDP_FreePropertyContent_ex(properties, false);
+    MEM_freeN(properties);
+  }
+  BKE_libblock_free_datablock(id, 0);
+  MEM_freeN(id);
+}
+
+static void shader_preview_free(void *customdata)
+{
+  ShaderPreview *sp = static_cast<ShaderPreview *>(customdata);
+  Main *pr_main = sp->pr_main;
+  ID *main_id_copy = NULL;
+  ID *sub_id_copy = NULL;
+
+  if (sp->matcopy) {
+    main_id_copy = (ID *)sp->matcopy;
+    BLI_remlink(&pr_main->materials, sp->matcopy);
+  }
+  if (sp->texcopy) {
+    BLI_assert(main_id_copy == NULL);
+    main_id_copy = (ID *)sp->texcopy;
+    BLI_remlink(&pr_main->textures, sp->texcopy);
+  }
+  if (sp->worldcopy) {
+    /* worldcopy is also created for material with `Preview World` enabled */
+    if (main_id_copy) {
+      sub_id_copy = (ID *)sp->worldcopy;
+    }
+    else {
+      main_id_copy = (ID *)sp->worldcopy;
+    }
+    BLI_remlink(&pr_main->worlds, sp->worldcopy);
+  }
+  if (sp->lampcopy) {
+    BLI_assert(main_id_copy == NULL);
+    main_id_copy = (ID *)sp->lampcopy;
+    BLI_remlink(&pr_main->lights, sp->lampcopy);
+  }
+  if (sp->own_id_copy) {
+    if (sp->id_copy) {
+      preview_id_copy_free(sp->id_copy);
+    }
+    if (main_id_copy) {
+      preview_id_copy_free(main_id_copy);
+    }
+    if (sub_id_copy) {
+      preview_id_copy_free(sub_id_copy);
+    }
+  }
+
+  MEM_freeN(sp);
+}
+
+/** \} */
+
+/* -------------------------------------------------------------------- */
+/** \name Icon Preview
+ * \{ */
+
+static ImBuf *icon_preview_imbuf_from_brush(Brush *brush)
+{
+  static const int flags = IB_rect | IB_multilayer | IB_metadata;
+
+  char path[FILE_MAX];
+  const char *folder;
+
+  if (!(brush->icon_imbuf)) {
+    if (brush->flag & BRUSH_CUSTOM_ICON) {
+
+      if (brush->icon_filepath[0]) {
+        /* First use the path directly to try and load the file. */
+
+        BLI_strncpy(path, brush->icon_filepath, sizeof(brush->icon_filepath));
+        BLI_path_abs(path, ID_BLEND_PATH_FROM_GLOBAL(&brush->id));
+
+        /* Use default color-spaces for brushes. */
+        brush->icon_imbuf = IMB_loadiffname(path, flags, NULL);
+
+        /* otherwise lets try to find it in other directories */
+        if (!(brush->icon_imbuf)) {
+          folder = BKE_appdir_folder_id(BLENDER_DATAFILES, "brushicons");
+
+          BLI_make_file_string(
+              BKE_main_blendfile_path_from_global(), path, folder, brush->icon_filepath);
+
+          if (path[0]) {
+            /* Use default color spaces. */
+            brush->icon_imbuf = IMB_loadiffname(path, flags, NULL);
+          }
+        }
+
+        if (brush->icon_imbuf) {
+          BKE_icon_changed(BKE_icon_id_ensure(&brush->id));
+        }
+      }
+    }
+  }
+
+  if (!(brush->icon_imbuf)) {
+    brush->id.icon_id = 0;
+  }
+
+  return brush->icon_imbuf;
+}
+
+static void icon_copy_rect(ImBuf *ibuf, uint w, uint h, uint *rect)
+{
+  struct ImBuf *ima;
+  uint *drect, *srect;
+  float scaledx, scaledy;
+  short ex, ey, dx, dy;
+
+  /* paranoia test */
+  if (ibuf == NULL || (ibuf->rect == NULL && ibuf->rect_float == NULL)) {
+    return;
+  }
+
+  /* Waste of cpu cycles... but the imbuf API has no other way to scale fast (ton). */
+  ima = IMB_dupImBuf(ibuf);
+
+  if (!ima) {
+    return;
+  }
+
+  if (ima->x > ima->y) {
+    scaledx = (float)w;
+    scaledy = ((float)ima->y / (float)ima->x) * (float)w;
+  }
+  else {
+    scaledx = ((float)ima->x / (float)ima->y) * (float)h;
+    scaledy = (float)h;
+  }
+
+  /* Scaling down must never assign zero width/height, see: T89868. */
+  ex = MAX2(1, (short)scaledx);
+  ey = MAX2(1, (short)scaledy);
+
+  dx = (w - ex) / 2;
+  dy = (h - ey) / 2;
+
+  IMB_scalefastImBuf(ima, ex, ey);
+
+  /* if needed, convert to 32 bits */
+  if (ima->rect == NULL) {
+    IMB_rect_from_float(ima);
+  }
+
+  srect = ima->rect;
+  drect = rect;
+
+  drect += dy * w + dx;
+  for (; ey > 0; ey--) {
+    memcpy(drect, srect, ex * sizeof(int));
+    drect += w;
+    srect += ima->x;
+  }
+
+  IMB_freeImBuf(ima);
+}
+
+static void set_alpha(char *cp, int sizex, int sizey, char alpha)
+{
+  int a, size = sizex * sizey;
+
+  for (a = 0; a < size; a++, cp += 4) {
+    cp[3] = alpha;
+  }
+}
+
+static void icon_preview_startjob(void *customdata, short *stop, short *do_update)
+{
+  ShaderPreview *sp = static_cast<ShaderPreview *>(customdata);
+
+  if (sp->pr_method == PR_ICON_DEFERRED) {
+    PreviewImage *prv = static_cast<PreviewImage *>(sp->owner);
+    ImBuf *thumb;
+    char *deferred_data = static_cast<char *>(PRV_DEFERRED_DATA(prv));
+    ThumbSource source = static_cast<ThumbSource>(deferred_data[0]);
+    char *path = &deferred_data[1];
+
+    // printf("generating deferred %d×%d preview for %s\n", sp->sizex, sp->sizey, path);
+
+    thumb = IMB_thumb_manage(path, THB_LARGE, source);
+
+    if (thumb) {
+      /* PreviewImage assumes premultiplied alhpa... */
+      IMB_premultiply_alpha(thumb);
+
+      icon_copy_rect(thumb, sp->sizex, sp->sizey, sp->pr_rect);
+      IMB_freeImBuf(thumb);
+    }
+  }
+  else {
+    ID *id = sp->id;
+    short idtype = GS(id->name);
+
+    BLI_assert(id != NULL);
+
+    if (idtype == ID_IM) {
+      Image *ima = (Image *)id;
+      ImBuf *ibuf = NULL;
+      ImageUser iuser;
+      BKE_imageuser_default(&iuser);
+
+      if (ima == NULL) {
+        return;
+      }
+
+      /* setup dummy image user */
+      iuser.framenr = 1;
+      iuser.scene = sp->scene;
+
+      /* elubie: this needs to be changed: here image is always loaded if not
+       * already there. Very expensive for large images. Need to find a way to
+       * only get existing ibuf */
+      ibuf = BKE_image_acquire_ibuf(ima, &iuser, NULL);
+      if (ibuf == NULL || (ibuf->rect == NULL && ibuf->rect_float == NULL)) {
+        BKE_image_release_ibuf(ima, ibuf, NULL);
+        return;
+      }
+
+      icon_copy_rect(ibuf, sp->sizex, sp->sizey, sp->pr_rect);
+
+      *do_update = true;
+
+      BKE_image_release_ibuf(ima, ibuf, NULL);
+    }
+    else if (idtype == ID_BR) {
+      Brush *br = (Brush *)id;
+
+      br->icon_imbuf = icon_preview_imbuf_from_brush(br);
+
+      memset(sp->pr_rect, 0x88, sp->sizex * sp->sizey * sizeof(uint));
+
+      if (!(br->icon_imbuf) || !(br->icon_imbuf->rect)) {
+        return;
+      }
+
+      icon_copy_rect(br->icon_imbuf, sp->sizex, sp->sizey, sp->pr_rect);
+
+      *do_update = true;
+    }
+    else if (idtype == ID_SCR) {
+      bScreen *screen = (bScreen *)id;
+
+      ED_screen_preview_render(screen, sp->sizex, sp->sizey, sp->pr_rect);
+      *do_update = true;
+    }
+    else {
+      /* re-use shader job */
+      shader_preview_startjob(customdata, stop, do_update);
+
+      /* world is rendered with alpha=0, so it wasn't displayed
+       * this could be render option for sky to, for later */
+      if (idtype == ID_WO) {
+        set_alpha((char *)sp->pr_rect, sp->sizex, sp->sizey, 255);
+      }
+    }
+  }
+}
+
+/* use same function for icon & shader, so the job manager
+ * does not run two of them at the same time. */
+
+static void common_preview_startjob(void *customdata,
+                                    short *stop,
+                                    short *do_update,
+                                    float *UNUSED(progress))
+{
+  ShaderPreview *sp = static_cast<ShaderPreview *>(customdata);
+
+  if (ELEM(sp->pr_method, PR_ICON_RENDER, PR_ICON_DEFERRED)) {
+    icon_preview_startjob(customdata, stop, do_update);
+  }
+  else {
+    shader_preview_startjob(customdata, stop, do_update);
+  }
+}
+
+/**
+ * Some ID types already have their own, more focused rendering (only objects right now). This is
+ * for the other ones, which all share #ShaderPreview and some functions.
+ */
+static void other_id_types_preview_render(IconPreview *ip,
+                                          IconPreviewSize *cur_size,
+                                          const ePreviewRenderMethod pr_method,
+                                          short *stop,
+                                          short *do_update,
+                                          float *progress)
+{
+  ShaderPreview *sp = MEM_cnew<ShaderPreview>("Icon ShaderPreview");
+
+  /* These types don't use the ShaderPreview mess, they have their own types and functions. */
+  BLI_assert(!ip->id || !ELEM(GS(ip->id->name), ID_OB));
+
+  /* construct shader preview from image size and previewcustomdata */
+  sp->scene = ip->scene;
+  sp->owner = ip->owner;
+  sp->sizex = cur_size->sizex;
+  sp->sizey = cur_size->sizey;
+  sp->pr_method = pr_method;
+  sp->pr_rect = cur_size->rect;
+  sp->id = ip->id;
+  sp->id_copy = ip->id_copy;
+  sp->bmain = ip->bmain;
+  sp->own_id_copy = false;
+  Material *ma = NULL;
+
+  if (sp->pr_method == PR_ICON_RENDER) {
+    BLI_assert(ip->id);
+
+    /* grease pencil use its own preview file */
+    if (GS(ip->id->name) == ID_MA) {
+      ma = (Material *)ip->id;
+    }
+
+    if ((ma == NULL) || (ma->gp_style == NULL)) {
+      sp->pr_main = G_pr_main;
+    }
+    else {
+      sp->pr_main = G_pr_main_grease_pencil;
+    }
+  }
+
+  common_preview_startjob(sp, stop, do_update, progress);
+  shader_preview_free(sp);
+}
+
+/* exported functions */
+
+/**
+ * Find the index to map \a icon_size to data in \a preview_image.
+ */
+static int icon_previewimg_size_index_get(const IconPreviewSize *icon_size,
+                                          const PreviewImage *preview_image)
+{
+  for (int i = 0; i < NUM_ICON_SIZES; i++) {
+    if ((preview_image->w[i] == icon_size->sizex) && (preview_image->h[i] == icon_size->sizey)) {
+      return i;
+    }
+  }
+
+  BLI_assert_msg(0, "The searched icon size does not match any in the preview image");
+  return -1;
+}
+
+static void icon_preview_startjob_all_sizes(void *customdata,
+                                            short *stop,
+                                            short *do_update,
+                                            float *progress)
+{
+  IconPreview *ip = (IconPreview *)customdata;
+  IconPreviewSize *cur_size;
+
+  for (cur_size = static_cast<IconPreviewSize *>(ip->sizes.first); cur_size;
+       cur_size = cur_size->next) {
+    PreviewImage *prv = static_cast<PreviewImage *>(ip->owner);
+    /* Is this a render job or a deferred loading job? */
+    const ePreviewRenderMethod pr_method = (prv->tag & PRV_TAG_DEFFERED) ? PR_ICON_DEFERRED :
+                                                                           PR_ICON_RENDER;
+
+    if (*stop) {
+      break;
+    }
+
+    if (prv->tag & PRV_TAG_DEFFERED_DELETE) {
+      /* Non-thread-protected reading is not an issue here. */
+      continue;
+    }
+
+    /* check_engine_supports_preview() checks whether the engine supports "preview mode" (think:
+     * Material Preview). This check is only relevant when the render function called below is
+     * going to use such a mode. Object and Action render functions use Solid mode, though, so
+     * they can skip this test. */
+    /* TODO: Decouple the ID-type-specific render functions from this function, so that it's not
+     * necessary to know here what happens inside lower-level functions. */
+    const bool use_solid_render_mode = (ip->id != NULL) && ELEM(GS(ip->id->name), ID_OB, ID_AC);
+    if (!use_solid_render_mode && preview_method_is_render(pr_method) &&
+        !check_engine_supports_preview(ip->scene)) {
+      continue;
+    }
+
+#ifndef NDEBUG
+    {
+      int size_index = icon_previewimg_size_index_get(cur_size, prv);
+      BLI_assert(!BKE_previewimg_is_finished(prv, size_index));
+    }
+#endif
+
+    if (ip->id != NULL) {
+      switch (GS(ip->id->name)) {
+        case ID_OB:
+          if (object_preview_is_type_supported((Object *)ip->id)) {
+            /* Much simpler than the ShaderPreview mess used for other ID types. */
+            object_preview_render(ip, cur_size);
+            continue;
+          }
+          break;
+        case ID_AC:
+          action_preview_render(ip, cur_size);
+          continue;
+        default:
+          /* Fall through to the same code as the `ip->id == NULL` case. */
+          break;
+      }
+    }
+    other_id_types_preview_render(ip, cur_size, pr_method, stop, do_update, progress);
+  }
+}
+
+static void icon_preview_add_size(IconPreview *ip, uint *rect, int sizex, int sizey)
+{
+  IconPreviewSize *cur_size = static_cast<IconPreviewSize *>(ip->sizes.first);
+
+  while (cur_size) {
+    if (cur_size->sizex == sizex && cur_size->sizey == sizey) {
+      /* requested size is already in list, no need to add it again */
+      return;
+    }
+
+    cur_size = cur_size->next;
+  }
+
+  IconPreviewSize *new_size = MEM_cnew<IconPreviewSize>("IconPreviewSize");
+  new_size->sizex = sizex;
+  new_size->sizey = sizey;
+  new_size->rect = rect;
+
+  BLI_addtail(&ip->sizes, new_size);
+}
+
+static void icon_preview_endjob(void *customdata)
+{
+  IconPreview *ip = static_cast<IconPreview *>(customdata);
+
+  if (ip->id) {
+
+    if (GS(ip->id->name) == ID_BR) {
+      WM_main_add_notifier(NC_BRUSH | NA_EDITED, ip->id);
+    }
+#if 0
+    if (GS(ip->id->name) == ID_MA) {
+      Material *ma = (Material *)ip->id;
+      PreviewImage *prv_img = ma->preview;
+      int i;
+
+      /* signal to gpu texture */
+      for (i = 0; i < NUM_ICON_SIZES; i++) {
+        if (prv_img->gputexture[i]) {
+          GPU_texture_free(prv_img->gputexture[i]);
+          prv_img->gputexture[i] = NULL;
+          WM_main_add_notifier(NC_MATERIAL | ND_SHADING_DRAW, ip->id);
+        }
+      }
+    }
+#endif
+  }
+
+  if (ip->owner) {
+    PreviewImage *prv_img = static_cast<PreviewImage *>(ip->owner);
+    prv_img->tag &= ~PRV_TAG_DEFFERED_RENDERING;
+
+    LISTBASE_FOREACH (IconPreviewSize *, icon_size, &ip->sizes) {
+      int size_index = icon_previewimg_size_index_get(icon_size, prv_img);
+      BKE_previewimg_finish(prv_img, size_index);
+    }
+
+    if (prv_img->tag & PRV_TAG_DEFFERED_DELETE) {
+      BLI_assert(prv_img->tag & PRV_TAG_DEFFERED);
+      BKE_previewimg_deferred_release(prv_img);
+    }
+  }
+}
+
+static void icon_preview_free(void *customdata)
+{
+  IconPreview *ip = (IconPreview *)customdata;
+
+  if (ip->id_copy) {
+    preview_id_copy_free(ip->id_copy);
+  }
+
+  BLI_freelistN(&ip->sizes);
+  MEM_freeN(ip);
+}
+
+bool ED_preview_id_is_supported(const ID *id)
+{
+  if (id == NULL) {
+    return false;
+  }
+
+  if (GS(id->name) == ID_OB) {
+    return object_preview_is_type_supported((const Object *)id);
+  }
+  return BKE_previewimg_id_get_p(id) != NULL;
+}
+
+void ED_preview_icon_render(
+    const bContext *C, Scene *scene, ID *id, uint *rect, int sizex, int sizey)
+{
+  IconPreview ip = {NULL};
+  short stop = false, update = false;
+  float progress = 0.0f;
+
+  ED_preview_ensure_dbase();
+
+  ip.bmain = CTX_data_main(C);
+  ip.scene = scene;
+  ip.depsgraph = CTX_data_ensure_evaluated_depsgraph(C);
+  ip.owner = BKE_previewimg_id_ensure(id);
+  ip.id = id;
+  /* Control isn't given back to the caller until the preview is done. So we don't need to copy
+   * the ID to avoid thread races. */
+  ip.id_copy = duplicate_ids(id, true);
+  ip.active_object = CTX_data_active_object(C);
+
+  icon_preview_add_size(&ip, rect, sizex, sizey);
+
+  icon_preview_startjob_all_sizes(&ip, &stop, &update, &progress);
+
+  icon_preview_endjob(&ip);
+
+  BLI_freelistN(&ip.sizes);
+  if (ip.id_copy != NULL) {
+    preview_id_copy_free(ip.id_copy);
+  }
+}
+
+void ED_preview_icon_job(
+    const bContext *C, void *owner, ID *id, uint *rect, int sizex, int sizey, const bool delay)
+{
+  wmJob *wm_job;
+  IconPreview *ip, *old_ip;
+
+  ED_preview_ensure_dbase();
+
+  /* suspended start means it starts after 1 timer step, see WM_jobs_timer below */
+  wm_job = WM_jobs_get(CTX_wm_manager(C),
+                       CTX_wm_window(C),
+                       owner,
+                       "Icon Preview",
+                       WM_JOB_EXCL_RENDER,
+                       WM_JOB_TYPE_RENDER_PREVIEW);
+
+  ip = MEM_cnew<IconPreview>("icon preview");
+
+  /* render all resolutions from suspended job too */
+  old_ip = static_cast<IconPreview *>(WM_jobs_customdata_get(wm_job));
+  if (old_ip) {
+    BLI_movelisttolist(&ip->sizes, &old_ip->sizes);
+  }
+
+  /* customdata for preview thread */
+  ip->bmain = CTX_data_main(C);
+  ip->depsgraph = CTX_data_ensure_evaluated_depsgraph(C);
+  ip->scene = DEG_get_input_scene(ip->depsgraph);
+  ip->active_object = CTX_data_active_object(C);
+  ip->owner = owner;
+  ip->id = id;
+  ip->id_copy = duplicate_ids(id, false);
+
+  icon_preview_add_size(ip, rect, sizex, sizey);
+
+  /* Special threading hack:
+   * warn main code that this preview is being rendered and cannot be freed... */
+  {
+    PreviewImage *prv_img = static_cast<PreviewImage *>(owner);
+    if (prv_img->tag & PRV_TAG_DEFFERED) {
+      prv_img->tag |= PRV_TAG_DEFFERED_RENDERING;
+    }
+  }
+
+  /* setup job */
+  WM_jobs_customdata_set(wm_job, ip, icon_preview_free);
+  WM_jobs_timer(wm_job, 0.1, NC_WINDOW, NC_WINDOW);
+  /* Wait 2s to start rendering icon previews, to not bog down user interaction.
+   * Particularly important for heavy scenes and Eevee using OpenGL that blocks
+   * the user interface drawing. */
+  WM_jobs_delay_start(wm_job, (delay) ? 2.0 : 0.0);
+  WM_jobs_callbacks(wm_job, icon_preview_startjob_all_sizes, NULL, NULL, icon_preview_endjob);
+
+  WM_jobs_start(CTX_wm_manager(C), wm_job);
+}
+
+void ED_preview_shader_job(const bContext *C,
+                           void *owner,
+                           ID *id,
+                           ID *parent,
+                           MTex *slot,
+                           int sizex,
+                           int sizey,
+                           ePreviewRenderMethod method)
+{
+  Object *ob = CTX_data_active_object(C);
+  wmJob *wm_job;
+  ShaderPreview *sp;
+  Scene *scene = CTX_data_scene(C);
+  const ID_Type id_type = GS(id->name);
+
+  BLI_assert(BKE_previewimg_id_supports_jobs(id));
+
+  /* Use workspace render only for buttons Window,
+   * since the other previews are related to the datablock. */
+
+  if (preview_method_is_render(method) && !check_engine_supports_preview(scene)) {
+    return;
+  }
+
+  ED_preview_ensure_dbase();
+
+  wm_job = WM_jobs_get(CTX_wm_manager(C),
+                       CTX_wm_window(C),
+                       owner,
+                       "Shader Preview",
+                       WM_JOB_EXCL_RENDER,
+                       WM_JOB_TYPE_RENDER_PREVIEW);
+  sp = MEM_cnew<ShaderPreview>("shader preview");
+
+  /* customdata for preview thread */
+  sp->scene = scene;
+  sp->owner = owner;
+  sp->sizex = sizex;
+  sp->sizey = sizey;
+  sp->pr_method = method;
+  sp->id = id;
+  sp->id_copy = duplicate_ids(id, false);
+  sp->own_id_copy = true;
+  sp->parent = parent;
+  sp->slot = slot;
+  sp->bmain = CTX_data_main(C);
+  Material *ma = NULL;
+
+  /* hardcoded preview .blend for Eevee + Cycles, this should be solved
+   * once with custom preview .blend path for external engines */
+
+  /* grease pencil use its own preview file */
+  if (id_type == ID_MA) {
+    ma = (Material *)id;
+  }
+
+  if ((ma == NULL) || (ma->gp_style == NULL)) {
+    sp->pr_main = G_pr_main;
+  }
+  else {
+    sp->pr_main = G_pr_main_grease_pencil;
+  }
+
+  if (ob && ob->totcol) {
+    copy_v4_v4(sp->color, ob->color);
+  }
+  else {
+    ARRAY_SET_ITEMS(sp->color, 0.0f, 0.0f, 0.0f, 1.0f);
+  }
+
+  /* setup job */
+  WM_jobs_customdata_set(wm_job, sp, shader_preview_free);
+  WM_jobs_timer(wm_job, 0.1, NC_MATERIAL, NC_MATERIAL);
+  WM_jobs_callbacks(wm_job, common_preview_startjob, NULL, shader_preview_updatejob, NULL);
+
+  WM_jobs_start(CTX_wm_manager(C), wm_job);
+}
+
+void ED_preview_kill_jobs(wmWindowManager *wm, Main *UNUSED(bmain))
+{
+  if (wm) {
+    /* This is called to stop all preview jobs before scene data changes, to
+     * avoid invalid memory access. */
+    WM_jobs_kill(wm, NULL, common_preview_startjob);
+    WM_jobs_kill(wm, NULL, icon_preview_startjob_all_sizes);
+  }
+}
+
+typedef struct PreviewRestartQueueEntry {
+  struct PreviewRestartQueueEntry *next, *prev;
+
+  enum eIconSizes size;
+  ID *id;
+} PreviewRestartQueueEntry;
+
+static ListBase /* #PreviewRestartQueueEntry */ G_restart_previews_queue;
+
+void ED_preview_restart_queue_free(void)
+{
+  BLI_freelistN(&G_restart_previews_queue);
+}
+
+void ED_preview_restart_queue_add(ID *id, enum eIconSizes size)
+{
+  PreviewRestartQueueEntry *queue_entry = MEM_new<PreviewRestartQueueEntry>(__func__);
+  queue_entry->size = size;
+  queue_entry->id = id;
+  BLI_addtail(&G_restart_previews_queue, queue_entry);
+}
+
+void ED_preview_restart_queue_work(const bContext *C)
+{
+  LISTBASE_FOREACH_MUTABLE (PreviewRestartQueueEntry *, queue_entry, &G_restart_previews_queue) {
+    PreviewImage *preview = BKE_previewimg_id_get(queue_entry->id);
+    if (!preview) {
+      continue;
+    }
+    if (preview->flag[queue_entry->size] & PRV_USER_EDITED) {
+      /* Don't touch custom previews. */
+      continue;
+    }
+
+    BKE_previewimg_clear_single(preview, queue_entry->size);
+    UI_icon_render_id(C, NULL, queue_entry->id, queue_entry->size, true);
+
+    BLI_freelinkN(&G_restart_previews_queue, queue_entry);
+  }
+}
+
+/** \} */