Mirror Modifier: Add offsets for mirrored UVs

The mirror modifier now has two fields that specify a -1 to 1 offset for
the U and V axes when mirroring their coordinates.

D1844 by @circuitfox

4 files changed, 25 insertions, 2 deletions

diff --git a/release/scripts/startup/bl_ui/properties_data_modifier.py b/release/scripts/startup/bl_ui/properties_data_modifier.py
index a098953699e..a37d61dd0af 100644
--- a/release/scripts/startup/bl_ui/properties_data_modifier.py
+++ b/release/scripts/startup/bl_ui/properties_data_modifier.py
@@ -569,6 +569,14 @@ class DATA_PT_modifiers(ModifierButtonsPanel, Panel):
         col.prop(md, "use_mirror_u", text="U")
         col.prop(md, "use_mirror_v", text="V")
 
+        col = layout.column(align=True)
+
+        if md.use_mirror_u:
+            col.prop(md, "mirror_offset_u")
+
+        if md.use_mirror_v:
+            col.prop(md, "mirror_offset_v")
+
         col = layout.column()
 
         if md.use_mirror_merge is True:
diff --git a/source/blender/makesdna/DNA_modifier_types.h b/source/blender/makesdna/DNA_modifier_types.h
index 32b43c7ea55..823a7f0812f 100644
--- a/source/blender/makesdna/DNA_modifier_types.h
+++ b/source/blender/makesdna/DNA_modifier_types.h
@@ -277,6 +277,7 @@ typedef struct MirrorModifierData {
 	short axis  DNA_DEPRECATED; /* deprecated, use flag instead */
 	short flag;
 	float tolerance;
+	float uv_offset[2];
 	struct Object *mirror_ob;
 } MirrorModifierData;
 
diff --git a/source/blender/makesrna/intern/rna_modifier.c b/source/blender/makesrna/intern/rna_modifier.c
index 36cf909b299..1a8dd05a7b5 100644
--- a/source/blender/makesrna/intern/rna_modifier.c
+++ b/source/blender/makesrna/intern/rna_modifier.c
@@ -1526,6 +1526,20 @@ static void rna_def_modifier_mirror(BlenderRNA *brna)
 	RNA_def_property_ui_text(prop, "Mirror V", "Mirror the V texture coordinate around the 0.5 point");
 	RNA_def_property_update(prop, 0, "rna_Modifier_update");
 
+	prop = RNA_def_property(srna, "mirror_offset_u", PROP_FLOAT, PROP_FACTOR);
+	RNA_def_property_float_sdna(prop, NULL, "uv_offset[0]");
+	RNA_def_property_range(prop, -1, 1);
+	RNA_def_property_ui_range(prop, -1, 1, 2, 4);
+	RNA_def_property_ui_text(prop, "U Offset", "Amount to offset mirrored UVs from the 0.5 point on the U axis");
+	RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
+	prop = RNA_def_property(srna, "mirror_offset_v", PROP_FLOAT, PROP_FACTOR);
+	RNA_def_property_float_sdna(prop, NULL, "uv_offset[1]");
+	RNA_def_property_range(prop, -1, 1);
+	RNA_def_property_ui_range(prop, -1, 1, 2, 4);
+	RNA_def_property_ui_text(prop, "V Offset", "Amount to offset mirrored UVs from the 0.5 point on the V axis");
+	RNA_def_property_update(prop, 0, "rna_Modifier_update");
+
 	prop = RNA_def_property(srna, "merge_threshold", PROP_FLOAT, PROP_DISTANCE);
 	RNA_def_property_float_sdna(prop, NULL, "tolerance");
 	RNA_def_property_range(prop, 0, FLT_MAX);
diff --git a/source/blender/modifiers/intern/MOD_mirror.c b/source/blender/modifiers/intern/MOD_mirror.c
index dd127cc255c..9705edc580c 100644
--- a/source/blender/modifiers/intern/MOD_mirror.c
+++ b/source/blender/modifiers/intern/MOD_mirror.c
@@ -274,8 +274,8 @@ static DerivedMesh *doMirrorOnAxis(MirrorModifierData *mmd,
 			int j = maxLoops;
 			dmloopuv += j; /* second set of loops only */
 			for (; j-- > 0; dmloopuv++) {
-				if (do_mirr_u) dmloopuv->uv[0] = 1.0f - dmloopuv->uv[0];
-				if (do_mirr_v) dmloopuv->uv[1] = 1.0f - dmloopuv->uv[1];
+				if (do_mirr_u) dmloopuv->uv[0] = 1.0f - dmloopuv->uv[0] + mmd->uv_offset[0];
+				if (do_mirr_v) dmloopuv->uv[1] = 1.0f - dmloopuv->uv[1] + mmd->uv_offset[1];
 			}
 		}
 	}