Don't touch my UV maps!

It's better to trust the artist to know what they are doing if they
provide a uv map for the lightmap modifier to use. Closes #265.

korman/exporter/etlight.py

@@ -15,7 +15,7 @@
 
 import bpy
 
-from contextlib import ExitStack
+from contextlib import contextmanager
 import itertools
 
 from .explosions import *
@@ -375,6 +375,8 @@ class LightBaker(_MeshManager):
         # this tended to create sharp edges. There was already a discussion about this on the
         # Guild of Writers forum, so I'm implementing a code version of dendwaler's process,
         # as detailed here: https://forum.guildofwriters.org/viewtopic.php?p=62572#p62572
+        # This has been amended with Sirius's observations in GH-265 about forced uv map
+        # packing. Namely, don't do it unless modifiers make us.
         uv_base = self._get_lightmap_uvtex(mesh, modifier)
         if uv_base is not None:
             uv_textures.active = uv_base
@@ -384,25 +386,25 @@ class LightBaker(_MeshManager):
             uv_textures.active = uvtex
 
             # if the artist hid any UVs, they will not be baked to... fix this now
-            bpy.ops.object.mode_set(mode="EDIT")
+            with self._set_mode("EDIT"):
                 bpy.ops.uv.reveal()
-            bpy.ops.object.mode_set(mode="OBJECT")
             self._associate_image_with_uvtex(uv_textures.active, im)
-            bpy.ops.object.mode_set(mode="EDIT")
 
-            # prep the uvtex for lightmapping
+            # Meshes with modifiers need to have islands packed to prevent generated vertices
+            # from sharing UVs. Sigh.
+            if self.is_collapsed(bo):
+                self._report.warn("'{}': packing islands in UV Texture '{}' due to modifier collapse", bo.name, uv_base.name)
+                with self._set_mode("EDIT"):
                     bpy.ops.mesh.select_all(action="SELECT")
-            bpy.ops.uv.average_islands_scale()
                     bpy.ops.uv.pack_islands()
         else:
             # same thread, see Sirius's suggestion RE smart unwrap. this seems to yield good
             # results in my tests. it will be good enough for quick exports.
             uvtex = uv_textures.new(self.lightmap_uvtex_name)
             self._associate_image_with_uvtex(uvtex, im)
-            bpy.ops.object.mode_set(mode="EDIT")
+            with self._set_mode("EDIT"):
                 bpy.ops.mesh.select_all(action="SELECT")
-            bpy.ops.uv.smart_project()
+                bpy.ops.uv.smart_project(island_margin=0.05)
-        bpy.ops.object.mode_set(mode="OBJECT")
 
         # Now, set the new LIGHTMAPGEN uv layer as what we want to render to...
         # NOTE that this will need to be reset by us to what the user had previously
@@ -490,3 +492,11 @@ class LightBaker(_MeshManager):
                 elif isinstance(i.data, bpy.types.Mesh) and not self._has_valid_material(i):
                     toggle.track(i, "hide_render", True)
                 i.select = value
+
+    @contextmanager
+    def _set_mode(self, mode):
+        bpy.ops.object.mode_set(mode=mode)
+        try:
+            yield
+        finally:
+            bpy.ops.object.mode_set(mode="OBJECT")

korman/exporter/mesh.py

@@ -232,6 +232,9 @@ class _MeshManager:
                             continue
                         setattr(mod, key, value)
 
+    def is_collapsed(self, bo) -> bool:
+        return bo.name in self._overrides
+
 
 class MeshConverter(_MeshManager):
     def __init__(self, exporter):

korman/properties/modifiers/render.py

@@ -472,7 +472,7 @@ class PlasmaLightMapGen(idprops.IDPropMixin, PlasmaModifierProperties, PlasmaMod
         materials = mat_mgr.get_materials(bo)
 
         # Find the stupid UVTex
-        uvtex_name = "LIGHTMAPGEN"
+        uvtex_name = exporter.oven.lightmap_uvtex_name
         uvw_src = next((i for i, uvtex in enumerate(bo.data.uv_textures) if uvtex.name == uvtex_name), None)
         if uvw_src is None:
             raise ExportError("'{}': Lightmap UV Texture '{}' seems to be missing. Did you delete it?", bo.name, uvtex_name)

korman/ui/modifiers/render.py

@@ -196,6 +196,8 @@ def lightmap(modifier, layout, context):
     col = layout.column()
     col.active = is_texture
     col.prop_search(modifier, "uv_map", context.active_object.data, "uv_textures")
+    if bool(modifier.id_data.modifiers):
+        col.label("UV Map islands will be packed on export.", icon="ERROR")
     col = layout.column()
     col.active = is_texture
     col.prop(modifier, "image", icon="IMAGE_RGB")