Fix (unreported) meshes changing shading when creating empty clnors data.

When you were using autosmooth to generate some custom normals, and
created empty custom loop normal data, you would go back to an 'all
smooth' shading, cancelling some sharp edges generated by the mesh's
smooth threshold.

Now we will first tag such edges as sharp, such that shading remains the
same. This is not crucial in current master, but it is for clnors
editing gsoc branch!

1 files changed, 156 insertions, 58 deletions

diff --git a/source/blender/blenkernel/intern/mesh_evaluate.c b/source/blender/blenkernel/intern/mesh_evaluate.c
index 528a1c0f552..a4cc6913fd9 100644
--- a/source/blender/blenkernel/intern/mesh_evaluate.c
+++ b/source/blender/blenkernel/intern/mesh_evaluate.c
@@ -680,10 +680,11 @@ typedef struct LoopSplitTaskDataCommon {
 	const MEdge *medges;
 	const MLoop *mloops;
 	const MPoly *mpolys;
-	const int (*edge_to_loops)[2];
-	const int *loop_to_poly;
+	int (*edge_to_loops)[2];
+	int *loop_to_poly;
 	const float (*polynors)[3];
 
+	int numEdges;
 	int numLoops;
 	int numPolys;
 } LoopSplitTaskDataCommon;
@@ -693,6 +694,154 @@ typedef struct LoopSplitTaskDataCommon {
 /* See comment about edge_to_loops below. */
 #define IS_EDGE_SHARP(_e2l) (ELEM((_e2l)[1], INDEX_UNSET, INDEX_INVALID))
 
+static void mesh_edges_sharp_tag(
+        LoopSplitTaskDataCommon *data,
+        const bool check_angle, const float split_angle, const bool do_sharp_edges_tag)
+{
+	MVert *mverts = data->mverts;
+	MEdge *medges = data->medges;
+	MLoop *mloops = data->mloops;
+	MPoly *mpolys = data->mpolys;
+
+	const int numEdges = data->numEdges;
+	const int numPolys = data->numPolys;
+
+	float (*loopnors)[3] = data->loopnors;  /* Note: loopnors may be NULL here. */
+	const float (*polynors)[3] = data->polynors;
+
+	int (*edge_to_loops)[2] = data->edge_to_loops;
+	int *loop_to_poly = data->loop_to_poly;
+
+	BLI_bitmap *sharp_edges = do_sharp_edges_tag ? BLI_BITMAP_NEW(numEdges, __func__) : NULL;
+
+	MPoly *mp;
+	int mp_index;
+
+	const float split_angle_cos = check_angle ? cosf(split_angle) : -1.0f;
+
+	for (mp = mpolys, mp_index = 0; mp_index < numPolys; mp++, mp_index++) {
+		MLoop *ml_curr;
+		int *e2l;
+		int ml_curr_index = mp->loopstart;
+		const int ml_last_index = (ml_curr_index + mp->totloop) - 1;
+
+		ml_curr = &mloops[ml_curr_index];
+
+		for (; ml_curr_index <= ml_last_index; ml_curr++, ml_curr_index++) {
+			MEdge *me = &medges[ml_curr->e];
+
+			e2l = edge_to_loops[ml_curr->e];
+
+			loop_to_poly[ml_curr_index] = mp_index;
+
+			/* Pre-populate all loop normals as if their verts were all-smooth, this way we don't have to compute
+			 * those later!
+			 */
+			if (loopnors) {
+				normal_short_to_float_v3(loopnors[ml_curr_index], mverts[ml_curr->v].no);
+			}
+
+			/* Check whether current edge might be smooth or sharp */
+			if ((e2l[0] | e2l[1]) == 0) {
+				/* 'Empty' edge until now, set e2l[0] (and e2l[1] to INDEX_UNSET to tag it as unset). */
+				e2l[0] = ml_curr_index;
+				/* We have to check this here too, else we might miss some flat faces!!! */
+				e2l[1] = (mp->flag & ME_SMOOTH) ? INDEX_UNSET : INDEX_INVALID;
+			}
+			else if (e2l[1] == INDEX_UNSET) {
+				const bool is_angle_sharp = (check_angle &&
+				                             dot_v3v3(polynors[loop_to_poly[e2l[0]]], polynors[mp_index]) < split_angle_cos);
+
+				/* Second loop using this edge, time to test its sharpness.
+				 * An edge is sharp if it is tagged as such, or its face is not smooth,
+				 * or both poly have opposed (flipped) normals, i.e. both loops on the same edge share the same vertex,
+				 * or angle between both its polys' normals is above split_angle value.
+				 */
+				if (!(mp->flag & ME_SMOOTH) || (me->flag & ME_SHARP) ||
+				    ml_curr->v == mloops[e2l[0]].v ||
+				    is_angle_sharp)
+				{
+					/* Note: we are sure that loop != 0 here ;) */
+					e2l[1] = INDEX_INVALID;
+
+					/* We want to avoid tagging edges as sharp when it is already defined as such by
+					 * other causes than angle threshold... */
+					if (do_sharp_edges_tag && is_angle_sharp) {
+						BLI_BITMAP_SET(sharp_edges, ml_curr->e, true);
+					}
+				}
+				else {
+					e2l[1] = ml_curr_index;
+				}
+			}
+			else if (!IS_EDGE_SHARP(e2l)) {
+				/* More than two loops using this edge, tag as sharp if not yet done. */
+				e2l[1] = INDEX_INVALID;
+
+				/* We want to avoid tagging edges as sharp when it is already defined as such by
+				 * other causes than angle threshold... */
+				if (do_sharp_edges_tag) {
+					BLI_BITMAP_SET(sharp_edges, ml_curr->e, false);
+				}
+			}
+			/* Else, edge is already 'disqualified' (i.e. sharp)! */
+		}
+	}
+
+	/* If requested, do actual tagging of edges as sharp in another loop. */
+	if (do_sharp_edges_tag) {
+		MEdge *me;
+		int me_index;
+		for (me = medges, me_index = 0; me_index < numEdges; me++, me_index++) {
+			if (BLI_BITMAP_TEST(sharp_edges, me_index)) {
+				me->flag |= ME_SHARP;
+			}
+		}
+
+		MEM_freeN(sharp_edges);
+	}
+}
+
+/** Define sharp edges as needed to mimic 'autosmooth' from angle threshold.
+ *
+ * Used when defining an empty custom loop normals data layer, to keep same shading as with autosmooth!
+ */
+void BKE_edges_sharp_from_angle_set(
+        const struct MVert *mverts, const int UNUSED(numVerts),
+        struct MEdge *medges, const int numEdges,
+        struct MLoop *mloops, const int numLoops,
+        struct MPoly *mpolys, const float (*polynors)[3], const int numPolys,
+        const float split_angle)
+{
+	if (split_angle >= (float)M_PI) {
+		/* Nothing to do! */
+		return;
+	}
+
+	/* Mapping edge -> loops. See BKE_mesh_normals_loop_split() for details. */
+	int (*edge_to_loops)[2] = MEM_calloc_arrayN((size_t)numEdges, sizeof(*edge_to_loops), __func__);
+
+	/* Simple mapping from a loop to its polygon index. */
+	int *loop_to_poly = MEM_malloc_arrayN((size_t)numLoops, sizeof(*loop_to_poly), __func__);
+
+	LoopSplitTaskDataCommon common_data = {
+	    .mverts = mverts,
+	    .medges = medges,
+	    .mloops = mloops,
+	    .mpolys = mpolys,
+	    .edge_to_loops = edge_to_loops,
+	    .loop_to_poly = loop_to_poly,
+	    .polynors = polynors,
+	    .numEdges = numEdges,
+	    .numPolys = numPolys,
+	};
+
+	mesh_edges_sharp_tag(&common_data, true, split_angle, true);
+
+	MEM_freeN(edge_to_loops);
+	MEM_freeN(loop_to_poly);
+}
+
 static void loop_manifold_fan_around_vert_next(
         const MLoop *mloops, const MPoly *mpolys,
         const int *loop_to_poly, const int *e2lfan_curr, const uint mv_pivot_index,
@@ -1313,12 +1462,8 @@ void BKE_mesh_normals_loop_split(
 	/* Simple mapping from a loop to its polygon index. */
 	int *loop_to_poly = r_loop_to_poly ? r_loop_to_poly : MEM_malloc_arrayN((size_t)numLoops, sizeof(*loop_to_poly), __func__);
 
-	MPoly *mp;
-	int mp_index;
-
 	/* When using custom loop normals, disable the angle feature! */
 	const bool check_angle = (split_angle < (float)M_PI) && (clnors_data == NULL);
-	const float split_angle_cos = check_angle ? cosf(split_angle) : -1.0f;
 
 	MLoopNorSpaceArray _lnors_spacearr = {NULL};
 
@@ -1334,57 +1479,6 @@ void BKE_mesh_normals_loop_split(
 		BKE_lnor_spacearr_init(r_lnors_spacearr, numLoops);
 	}
 
-	/* This first loop check which edges are actually smooth, and compute edge vectors. */
-	for (mp = mpolys, mp_index = 0; mp_index < numPolys; mp++, mp_index++) {
-		MLoop *ml_curr;
-		int *e2l;
-		int ml_curr_index = mp->loopstart;
-		const int ml_last_index = (ml_curr_index + mp->totloop) - 1;
-
-		ml_curr = &mloops[ml_curr_index];
-
-		for (; ml_curr_index <= ml_last_index; ml_curr++, ml_curr_index++) {
-			e2l = edge_to_loops[ml_curr->e];
-
-			loop_to_poly[ml_curr_index] = mp_index;
-
-			/* Pre-populate all loop normals as if their verts were all-smooth, this way we don't have to compute
-			 * those later!
-			 */
-			normal_short_to_float_v3(r_loopnors[ml_curr_index], mverts[ml_curr->v].no);
-
-			/* Check whether current edge might be smooth or sharp */
-			if ((e2l[0] | e2l[1]) == 0) {
-				/* 'Empty' edge until now, set e2l[0] (and e2l[1] to INDEX_UNSET to tag it as unset). */
-				e2l[0] = ml_curr_index;
-				/* We have to check this here too, else we might miss some flat faces!!! */
-				e2l[1] = (mp->flag & ME_SMOOTH) ? INDEX_UNSET : INDEX_INVALID;
-			}
-			else if (e2l[1] == INDEX_UNSET) {
-				/* Second loop using this edge, time to test its sharpness.
-				 * An edge is sharp if it is tagged as such, or its face is not smooth,
-				 * or both poly have opposed (flipped) normals, i.e. both loops on the same edge share the same vertex,
-				 * or angle between both its polys' normals is above split_angle value.
-				 */
-				if (!(mp->flag & ME_SMOOTH) || (medges[ml_curr->e].flag & ME_SHARP) ||
-				    ml_curr->v == mloops[e2l[0]].v ||
-				    (check_angle && dot_v3v3(polynors[loop_to_poly[e2l[0]]], polynors[mp_index]) < split_angle_cos))
-				{
-					/* Note: we are sure that loop != 0 here ;) */
-					e2l[1] = INDEX_INVALID;
-				}
-				else {
-					e2l[1] = ml_curr_index;
-				}
-			}
-			else if (!IS_EDGE_SHARP(e2l)) {
-				/* More than two loops using this edge, tag as sharp if not yet done. */
-				e2l[1] = INDEX_INVALID;
-			}
-			/* Else, edge is already 'disqualified' (i.e. sharp)! */
-		}
-	}
-
 	/* Init data common to all tasks. */
 	LoopSplitTaskDataCommon common_data = {
 	    .lnors_spacearr = r_lnors_spacearr,
@@ -1394,13 +1488,17 @@ void BKE_mesh_normals_loop_split(
 	    .medges = medges,
 	    .mloops = mloops,
 	    .mpolys = mpolys,
-	    .edge_to_loops = (const int(*)[2])edge_to_loops,
+	    .edge_to_loops = edge_to_loops,
 	    .loop_to_poly = loop_to_poly,
 	    .polynors = polynors,
+	    .numEdges = numEdges,
 	    .numLoops = numLoops,
 	    .numPolys = numPolys,
 	};
 
+	/* This first loop check which edges are actually smooth, and compute edge vectors. */
+	mesh_edges_sharp_tag(&common_data, check_angle, split_angle, false);
+
 	if (numLoops < LOOP_SPLIT_TASK_BLOCK_SIZE * 8) {
 		/* Not enough loops to be worth the whole threading overhead... */
 		loop_split_generator(NULL, &common_data);