Fix #34040: Moving Normal Node with enabled Cycles Material Preview crashes

Issue was caused by couple of circumstances:

- Normal Map node requires tesselated faces to compute tangent space
- All temporary meshes needed for Cycles export were adding to G.main
- Undo pushes would temporary set meshes tessfaces to NULL
- Moving node will cause undo push and tree re-evaluate fr preview

All this leads to threading conflict between preview render and undo
system.

Solved it in  way that all temporary meshes are adding to that exact
Main which was passed to Cycles via BlendData. This required couple
of mechanic changes like adding extra parameter to *_add() functions
and adding some *_ex() functions to make it possible RNA adds objects
to Main passed to new() RNA function.

This was tricky to pass Main to RNA function and IMO that's not so
nice to pass main to function, so ended up with such decision:

- Object.to_mesh() will add temp mesh to G.main
- Added Main.meshes.new_from_object() which does the same as to_mesh,
  but adds temporary mesh to specified Main.

So now all temporary meshes needed for preview render would be added
to preview_main which does not conflict with undo pushes.

Viewport render shall not be an issue because object sync happens from
main thread in this case.

It could be some issues with final render, but that's not so much
likely to happen, so shall be fine.

Thanks to Brecht for review!

1 files changed, 1 insertions, 190 deletions

diff --git a/source/blender/makesrna/intern/rna_object_api.c b/source/blender/makesrna/intern/rna_object_api.c
index 40b8d4cce66..51725bda7f9 100644
--- a/source/blender/makesrna/intern/rna_object_api.c
+++ b/source/blender/makesrna/intern/rna_object_api.c
@@ -65,8 +65,6 @@ static EnumPropertyItem space_items[] = {
 #include "BKE_context.h"
 #include "BKE_customdata.h"
 #include "BKE_depsgraph.h"
-#include "BKE_DerivedMesh.h"
-#include "BKE_displist.h"
 #include "BKE_font.h"
 #include "BKE_global.h"
 #include "BKE_main.h"
@@ -113,194 +111,7 @@ static void rna_Scene_mat_convert_space(Object *ob, ReportList *reports, bPoseCh
 /* settings: 0 - preview, 1 - render */
 static Mesh *rna_Object_to_mesh(Object *ob, ReportList *reports, Scene *sce, int apply_modifiers, int settings)
 {
-	Mesh *tmpmesh;
-	Curve *tmpcu = NULL, *copycu;
-	Object *tmpobj = NULL;
-	int render = settings == eModifierMode_Render, i;
-	int cage = !apply_modifiers;
-
-	/* perform the mesh extraction based on type */
-	switch (ob->type) {
-		case OB_FONT:
-		case OB_CURVE:
-		case OB_SURF:
-		{
-			ListBase dispbase = {NULL, NULL};
-			DerivedMesh *derivedFinal = NULL;
-			int uv_from_orco;
-
-			/* copies object and modifiers (but not the data) */
-			tmpobj = BKE_object_copy_with_caches(ob);
-			tmpcu = (Curve *)tmpobj->data;
-			tmpcu->id.us--;
-
-			/* if getting the original caged mesh, delete object modifiers */
-			if (cage)
-				BKE_object_free_modifiers(tmpobj);
-
-			/* copies the data */
-			copycu = tmpobj->data = BKE_curve_copy((Curve *) ob->data);
-
-			/* temporarily set edit so we get updates from edit mode, but
-			 * also because for text datablocks copying it while in edit
-			 * mode gives invalid data structures */
-			copycu->editfont = tmpcu->editfont;
-			copycu->editnurb = tmpcu->editnurb;
-
-			/* get updated display list, and convert to a mesh */
-			BKE_displist_make_curveTypes_forRender(sce, tmpobj, &dispbase, &derivedFinal, FALSE);
-
-			copycu->editfont = NULL;
-			copycu->editnurb = NULL;
-
-			tmpobj->derivedFinal = derivedFinal;
-
-			/* convert object type to mesh */
-			uv_from_orco = (tmpcu->flag & CU_UV_ORCO) != 0;
-			BKE_mesh_from_nurbs_displist(tmpobj, &dispbase, uv_from_orco);
-
-			tmpmesh = tmpobj->data;
-
-			BKE_displist_free(&dispbase);
-
-			/* BKE_mesh_from_nurbs changes the type to a mesh, check it worked */
-			if (tmpobj->type != OB_MESH) {
-				BKE_libblock_free_us(&(G.main->object), tmpobj);
-				BKE_report(reports, RPT_ERROR, "Cannot convert curve to mesh (does the curve have any segments?)");
-				return NULL;
-			}
-
-			BKE_libblock_free_us(&G.main->object, tmpobj);
-			break;
-		}
-
-		case OB_MBALL:
-		{
-			/* metaballs don't have modifiers, so just convert to mesh */
-			Object *basis_ob = BKE_mball_basis_find(sce, ob);
-			/* todo, re-generatre for render-res */
-			/* metaball_polygonize(scene, ob) */
-
-			if (ob != basis_ob)
-				return NULL;  /* only do basis metaball */
-			
-			tmpmesh = BKE_mesh_add("Mesh");
-			/* BKE_mesh_add gives us a user count we don't need */
-			tmpmesh->id.us--;
-
-			if (render) {
-				ListBase disp = {NULL, NULL};
-				BKE_displist_make_mball_forRender(sce, ob, &disp);
-				BKE_mesh_from_metaball(&disp, tmpmesh);
-				BKE_displist_free(&disp);
-			}
-			else
-				BKE_mesh_from_metaball(&ob->disp, tmpmesh);
-
-			break;
-
-		}
-		case OB_MESH:
-			/* copies object and modifiers (but not the data) */
-			if (cage) {
-				/* copies the data */
-				tmpmesh = BKE_mesh_copy(ob->data);
-				/* if not getting the original caged mesh, get final derived mesh */
-			}
-			else {
-				/* Make a dummy mesh, saves copying */
-				DerivedMesh *dm;
-				/* CustomDataMask mask = CD_MASK_BAREMESH|CD_MASK_MTFACE|CD_MASK_MCOL; */
-				CustomDataMask mask = CD_MASK_MESH; /* this seems more suitable, exporter,
-			                                         * for example, needs CD_MASK_MDEFORMVERT */
-
-				/* Write the display mesh into the dummy mesh */
-				if (render)
-					dm = mesh_create_derived_render(sce, ob, mask);
-				else
-					dm = mesh_create_derived_view(sce, ob, mask);
-		
-				tmpmesh = BKE_mesh_add("Mesh");
-				DM_to_mesh(dm, tmpmesh, ob);
-				dm->release(dm);
-			}
-
-			/* BKE_mesh_add/copy gives us a user count we don't need */
-			tmpmesh->id.us--;
-
-			break;
-		default:
-			BKE_report(reports, RPT_ERROR, "Object does not have geometry data");
-			return NULL;
-	}
-
-	/* Copy materials to new mesh */
-	switch (ob->type) {
-		case OB_SURF:
-		case OB_FONT:
-		case OB_CURVE:
-			tmpmesh->totcol = tmpcu->totcol;
-
-			/* free old material list (if it exists) and adjust user counts */
-			if (tmpcu->mat) {
-				for (i = tmpcu->totcol; i-- > 0; ) {
-					/* are we an object material or data based? */
-
-					tmpmesh->mat[i] = ob->matbits[i] ? ob->mat[i] : tmpcu->mat[i];
-
-					if (tmpmesh->mat[i]) {
-						tmpmesh->mat[i]->id.us++;
-					}
-				}
-			}
-			break;
-
-#if 0
-		/* Crashes when assigning the new material, not sure why */
-		case OB_MBALL:
-			tmpmb = (MetaBall *)ob->data;
-			tmpmesh->totcol = tmpmb->totcol;
-
-			/* free old material list (if it exists) and adjust user counts */
-			if (tmpmb->mat) {
-				for (i = tmpmb->totcol; i-- > 0; ) {
-					tmpmesh->mat[i] = tmpmb->mat[i]; /* CRASH HERE ??? */
-					if (tmpmesh->mat[i]) {
-						tmpmb->mat[i]->id.us++;
-					}
-				}
-			}
-			break;
-#endif
-
-		case OB_MESH:
-			if (!cage) {
-				Mesh *origmesh = ob->data;
-				tmpmesh->flag = origmesh->flag;
-				tmpmesh->mat = MEM_dupallocN(origmesh->mat);
-				tmpmesh->totcol = origmesh->totcol;
-				tmpmesh->smoothresh = origmesh->smoothresh;
-				if (origmesh->mat) {
-					for (i = origmesh->totcol; i-- > 0; ) {
-						/* are we an object material or data based? */
-						tmpmesh->mat[i] = ob->matbits[i] ? ob->mat[i] : origmesh->mat[i];
-
-						if (tmpmesh->mat[i]) {
-							tmpmesh->mat[i]->id.us++;
-						}
-					}
-				}
-			}
-			break;
-	} /* end copy materials */
-
-	/* cycles and exporters rely on this still */
-	BKE_mesh_tessface_ensure(tmpmesh);
-
-	/* make sure materials get updated in objects */
-	test_object_materials(&tmpmesh->id);
-
-	return tmpmesh;
+	return rna_Main_meshes_new_from_object(G.main, reports, sce, ob, apply_modifiers, settings);
 }
 
 /* mostly a copy from convertblender.c */