From 699a3e2498112375f8ef8d74724c4589fac05765 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Sybren=20A=2E=20St=C3=BCvel?= <sybren@stuvel.eu>
Date: Wed, 12 Apr 2017 16:33:40 +0200
Subject: [PATCH] Fix T50227: Alembic uv export/load issue

Previously only a CD_MLOOPUV custom data layer was created. Now we also
create the accompanying CD_MTEXPOLY layer too.
---
 source/blender/alembic/intern/abc_mesh.cc | 34 +++++++++++++++--------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/source/blender/alembic/intern/abc_mesh.cc b/source/blender/alembic/intern/abc_mesh.cc
index 5a57e43326a..79b891dbcd4 100644
--- a/source/blender/alembic/intern/abc_mesh.cc
+++ b/source/blender/alembic/intern/abc_mesh.cc
@@ -897,19 +897,31 @@ static void *add_customdata_cb(void *user_data, const char *name, int data_type)
 {
 	DerivedMesh *dm = static_cast<DerivedMesh *>(user_data);
 	CustomDataType cd_data_type = static_cast<CustomDataType>(data_type);
-	void *cd_ptr = NULL;
+	void *cd_ptr;
+	CustomData *loopdata;
+	int numloops;
 
-	if (ELEM(cd_data_type, CD_MLOOPUV, CD_MLOOPCOL)) {
-		cd_ptr = CustomData_get_layer_named(dm->getLoopDataLayout(dm), cd_data_type, name);
+	/* unsupported custom data type -- don't do anything. */
+	if (!ELEM(cd_data_type, CD_MLOOPUV, CD_MLOOPCOL)) {
+		return NULL;
+	}
 
-		if (cd_ptr == NULL) {
-			cd_ptr = CustomData_add_layer_named(dm->getLoopDataLayout(dm),
-			                                    cd_data_type,
-			                                    CD_DEFAULT,
-			                                    NULL,
-			                                    dm->getNumLoops(dm),
-			                                    name);
-		}
+	loopdata = dm->getLoopDataLayout(dm);
+	cd_ptr = CustomData_get_layer_named(loopdata, cd_data_type, name);
+	if (cd_ptr != NULL) {
+		/* layer already exists, so just return it. */
+		return cd_ptr;
+	}
+
+	/* create a new layer, taking care to construct the hopefully-soon-to-be-removed
+	 * CD_MTEXPOLY layer too, with the same name. */
+	numloops = dm->getNumLoops(dm);
+	cd_ptr = CustomData_add_layer_named(loopdata, cd_data_type, CD_DEFAULT,
+	                                    NULL, numloops, name);
+	if (cd_data_type == CD_MLOOPUV) {
+		CustomData_add_layer_named(dm->getPolyDataLayout(dm),
+		                           CD_MTEXPOLY, CD_DEFAULT,
+		                           NULL, numloops, name);
 	}
 
 	return cd_ptr;