Try recovering everything

Not working, have to adapt for ImBuf

@@ -718,6 +719,18 @@ class NodeTreeMainUpdater {
     blender::bke::node_preview_remove_unused(&ntree);
   }
 
+  void needs_preview_redraw(bNodeTree &ntree)

@@ -721,0 +724,4 @@
+    ntree.preview_refresh_state++;
+    ntree.ensure_topology_cache();
+    for (bNode *node : ntree.group_nodes()) {
+      bNodeTree *nested_tree = (bNodeTree *)node->id;

@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright 2005 Blender Foundation */

@@ -0,0 +10,4 @@
+#include "RE_pipeline.h"
+
+#ifdef __cplusplus
+extern "C" {

@@ -0,0 +20,4 @@
+
+struct NestedTreePreviews {
+  Render *previews_render;
+  int pr_size;

@@ -2233,3 +2230,1 @@
-        BKE_node_instance_hash_lookup(previews, key));
-    if (preview_compositor) {
-      preview = preview_compositor->ibuf;
+  /* Overlay atop the node. */

@@ -107,6 +109,10 @@ struct SpaceNode_Runtime {
   /** Temporary data for node insert offset (in UI called Auto-offset). */
   struct NodeInsertOfsData *iofsd;
 
+  /** Use this to store data for the displayed node tree. It has an entry for every distinct

@@ -0,0 +12,4 @@
+ *
+ * We separate the previewed nodes in two categories: the shader ones and the non-shader ones.
+ * - for non-shader nodes, we use AOVs(Arbitrary Output Variable) which highly speed up the
+ * rendering process by rendering every non-shader nodes at the same time. They are rendered in the

@@ -0,0 +53,4 @@
+
+struct ShaderNodesPreviewJob {
+  NestedTreePreviews *tree_previews;
+  Material *mat_orig;

@@ -0,0 +57,4 @@
+  /* Listbase containing bNodeTreePath * guiding to the viewed nodetree of mat_orig. */
+  ListBase *treepath;
+  Scene *scene;
+  bool *stop;

@@ -0,0 +63,4 @@
+  Material *mat_copy;
+  bNode *mat_output_copy;
+  NodeSocketPair mat_displacement_copy;
+  ListBase treepath_copy;

@@ -0,0 +122,4 @@
+  if (auto hash = get_compute_context_hash_for_node_editor(*sn)) {
+    tree_previews = sn->runtime->tree_previews_per_context.lookup_or_add_cb(*hash, [&]() {
+      tree_previews = static_cast<NestedTreePreviews *>(
+          MEM_callocN(sizeof(NestedTreePreviews), __func__));

@@ -0,0 +158,4 @@
+                                    Main *pr_main,
+                                    Material *matcopy)
+{
+  Scene *sce;

@@ -0,0 +315,4 @@
+                                        bNode *final_node,
+                                        bNodeSocket *final_socket)
+{
+  for (bNodeTreePath *path = (bNodeTreePath *)treepath.last(); path->prev != nullptr;

@@ -0,0 +356,4 @@
+
+/* Connect the node to the output of the first nodetree from `treepath`. Last element of `treepath`
+ * should be the path to the node's nodetree */
+static void connect_node_to_surface_output(Vector<const bNodeTreePath *> treepath,

@@ -0,0 +380,4 @@
+
+/* Connect the nodes to some aov nodes located in the first nodetree from `treepath`. Last element
+ * of `treepath` should be the path to the nodes nodetree. */
+static void connect_nodes_to_aovs(const Vector<const bNodeTreePath *> &treepath,

@@ -0,0 +651,4 @@
+                              "Shader Previews",
+                              WM_JOB_EXCL_RENDER,
+                              WM_JOB_TYPE_RENDER_PREVIEW);
+  ShaderNodesPreviewJob *nt_previews = MEM_new<ShaderNodesPreviewJob>("shader previews");

@@ -332,1 +333,4 @@
 
+static void node_exit(wmWindowManager *wm, ScrArea *area)
+{
+  SpaceNode *snode = (SpaceNode *)area->spacedata.first;

@@ -664,1 +664,4 @@
   bNestedNodeRef *nested_node_refs;
+  /* Contains a number increased for each nodetree update.
+   * The idea here to to store a state var in the preview structures to compare if it differs. */
+  uint16_t preview_refresh_state;

@@ -7640,1 +7640,4 @@
   RNA_def_property_clear_flag(prop, PROP_EDITABLE);
+  RNA_def_property_ui_text(prop,
+                           "Supports Previews",
+                           "Specific to a SpaceNode type to know whether nodes can have previews");

@@ -5422,0 +5424,4 @@
+  RNA_def_property_range(prop, 50, 250);
+  RNA_def_property_ui_text(prop,
+                           "Node Preview Resolution",
+                           "Resolution used for Shader node previews (should be changed for "

@@ -5422,0 +5425,4 @@
+  RNA_def_property_ui_text(prop,
+                           "Node Preview Resolution",
+                           "Resolution used for Shader node previews (should be changed for "
+                           "performances and/or DPI issues)");

@@ -2236,1 +2250,4 @@
+      if (preview && !(preview->x && preview->y)) {
+        preview = nullptr;
+      }
     }

@@ -110,0 +113,4 @@
+   * Use this to store data for the displayed node tree. It has an entry for every distinct
+   * nested nodegroup.
+   */
+  Map<ComputeContextHash, NestedTreePreviews *> tree_previews_per_context;

@@ -0,0 +464,4 @@
+  }
+  Span<bNodeTreePath *> treepath = job_data.treepath_copy;
+
+  /* Disconnect shader, volume and displacement from the material output. */

@@ -97,0 +99,4 @@
+   * The idea here to to store a state var in the `NestedTreePreviews` structure to compare if they
+   * differ.
+   */
+  uint32_t previews_refresh_state;

@@ -31,2 +31,4 @@
   struct Main *main;
 
+  /**
+   * Data for the preview scene to avoid loading in multiple scenarios.

@@ -96,1 +96,4 @@
 
+  /**
+   * Contains a number increased for each nodetree update.
+   * The idea here to to store a state var in the `NestedTreePreviews` structure to compare if they

@@ -721,0 +727,4 @@
+        continue;
+      }
+      bNodeTree *nested_tree = reinterpret_cast<bNodeTree *>(node->id);
+      if (nested_tree) {

@@ -0,0 +12,4 @@
+struct bNodeTree;
+struct ImBuf;
+struct Render;
+

@@ -0,0 +22,4 @@
+  bool restart_needed;
+  uint32_t previews_refresh_state;
+  NestedTreePreviews(const int size)
+      : previews_render(nullptr),

@@ -0,0 +34,4 @@
+    if (this->previews_render) {
+      RE_FreeRender(this->previews_render);
+    }
+    this->previews_map.foreach_item([&](const bNode *, ImBuf *ibuf) { IMB_freeImBuf(ibuf); });

@@ -0,0 +38,4 @@
+  }
+};
+
+void ED_spacenode_free_previews(wmWindowManager *wm, SpaceNode *snode);

@@ -0,0 +43,4 @@
+                                    NestedTreePreviews *tree_previews,
+                                    const bNode *node);
+void ED_node_release_preview_ibuf(NestedTreePreviews *tree_previews);
+NestedTreePreviews *ED_spacenode_get_nested_previews(const bContext *ctx, SpaceNode *sn);

@@ -82,0 +91,4 @@
+                               ePreviewType pr_type,
+                               ePreviewRenderMethod pr_method);
+struct World *ED_preview_prepare_world(struct Main *pr_main,
+                                       const struct Scene *sce,

@@ -0,0 +129,4 @@
+  }
+  NestedTreePreviews *tree_previews = nullptr;
+  if (auto hash = get_compute_context_hash_for_node_editor(*sn)) {
+    tree_previews = &*sn->runtime->tree_previews_per_context.lookup_or_add_cb(

@@ -0,0 +146,4 @@
+
+static Material *duplicate_material(const Material *mat)
+{
+  if (mat == nullptr) {

@@ -0,0 +210,4 @@
+  ED_preview_set_visibility(pr_main,
+                            scene_preview,
+                            view_layer,
+                            static_cast<ePreviewType>(mat_copy->pr_type),

@@ -0,0 +479,4 @@
+static void preview_render(ShaderNodesPreviewJob &job_data)
+{
+  /* Get the stuff from the builtin preview dbase. */
+  Scene *sce = preview_prepare_scene(job_data.bmain, job_data.scene, G.pr_main, job_data.mat_copy);

@@ -141,2 +141,4 @@
   void *tbh = nullptr;
 
+  bool (*prepare_viewlayer)(void *handle, struct ViewLayer *vl, struct Depsgraph *depsgraph);
+  void *pvh;

@@ -0,0 +36,4 @@
+  }
+};
+
+void spacenode_free_previews(wmWindowManager &wm, SpaceNode &snode);

@@ -0,0 +41,4 @@
+                                 NestedTreePreviews &tree_previews,
+                                 const bNode &node);
+void node_release_preview_ibuf(NestedTreePreviews &tree_previews);
+NestedTreePreviews *spacenode_get_nested_previews(const bContext &C, SpaceNode &sn);

@@ -0,0 +51,4 @@
+#include "ED_screen.h"
+#include "node_intern.hh"
+
+using namespace blender;

@@ -0,0 +74,4 @@
+  NodeSocketPair mat_displacement_copy;
+  /* TreePath used to locate the nodetree.
+   * bNodeTreePath elements have some listbase pointers which should not be used. */
+  blender::Vector<bNodeTreePath *> treepath_copy;

@@ -0,0 +239,4 @@
+ * \{ */
+
+/* Return the socket used for previewing the node (should probably follow more precise rules). */
+static bNodeSocket *node_find_preview_socket(const bNode &node)

@@ -0,0 +242,4 @@
+static bNodeSocket *node_find_preview_socket(const bNode &node)
+{
+  LISTBASE_FOREACH (bNodeSocket *, socket, &node.outputs) {
+    if (socket->is_visible()) {