problem was that BMesh had tessellation call when undo pushes were called.
if python called an operator with no undo push, tessfaces would not be created.
fix this by making it the responsibility of each editmesh operator to re-tessellate, as it is with notifiers and depsgraph.
added EDBM_update_generic() function to add notifier, tag for depsgraph update and optionally re-tessellate.
Should also fix [#30266], [#29451], and partly [#30316].
Here are the changes made by this commit:
* It adds a "dirty" flag to DerivedMesh struct (for now, only DM_DIRTY_TESS_CDLAYERS, but more might be added as needed).
* It adds a new func, DM_update_tessface_data, which assumes tessfaces themselves are valid, but updates tessellated customdata from their poly/loop counter parts.
* At end of modstack, when valid tessellated faces are present in finaldm , but the cdlayers dirty flag is set, call that function (instead of recomputing the whole tessellation).
* Edits to the codes concerned (UVProject, DynamicPaint, and Subsurf modifiers).
* Also add to subsurf dm generation code the creation of a CD_POLYINDEX layer (mandatory for DM_update_tessface_data to work well, and imho all tessellated dm should have one).
Note: some pieces of old code are just #if 0’ed, will clean them later.
old mesh MCol 'r' was blue, 'b' was red, but theres no reason to keep this for bmesh with MLoopCol.
Loading old files works, saving legacy format works too.
What wont work is loading a file after this revision and loading it in an older revision since the bmesh merge.
(it wont crash but the blue and red will be swapped on vertex color layers).
* Fix: Substep update failed if brush was parented to a canvas vertex. Now substeps are ignored in such case.
* Fix: Wave "open borders" option didn't work for image sequence format.
* Fixed a possible crash after changing surface format to image sequence.
* Some code cleanup.
In fact, we have to add a CD_WEIGHT_MCOL layer (if not yet present) when updating CD_WEIGHT_MLOOPCOL, else with modifiers modifying the topology (like subsurf), it will sigsev.
That step should probably be done at tesselation time, though…
Also simplifies DM_update_weight_mcol: no need to update CD_WEIGHT_MCOL here, as it is anyway recreated from CD_WEIGHT_MLOOPCOL at tesselation time. Only commented out code for now.
User side:
* Preview for DynamicPaint should keep the same behavior (for now). Weight preview should be somawhat quicker, though.
* Preview for WeightVG modifiers is only active in WeightPaint mode, and if the affected vgroup is the active one.
* Last active preview modifier in stack wins!
Note: that modifier preview topic is yet to be further refined, quite raw/incomplete for now.
Dev side:
* In draw code, renamed DRAW_DYNAMIC_PAINT_PREVIEW flag to DRAW_MODIFIERS_PREVIEW
* Removed use of MOD_DPAINT_PREVIEW_READY in DynamicPaint code (seems unecessary, and if it was, should be of more general scope).
* Added eModifierTypeFlag_UsesPreview to ModifierTypeFlag, for modifiers that can generate some preview data.
* Added three new modifier funcs, to handle preview modifiers in draw code / mod stack.
* For weights preview: added the generic DM_update_weight_mcol func, which can update WEIGHT_MCOL layer with either a given array of weights (currently used by DynamicPaint only), or from current active vgroup(s).
So now, draw code is fully generic (i.e. no more modifier-type checking in it). Mod stack code is generic to some extent, but will need more work.
