3 files changed, 88 insertions, 4 deletions

diff --git a/source/blender/blenkernel/BKE_multires.h b/source/blender/blenkernel/BKE_multires.h
index b8131d69dfd..5bdea166cce 100644
--- a/source/blender/blenkernel/BKE_multires.h
+++ b/source/blender/blenkernel/BKE_multires.h
@@ -87,6 +87,7 @@ void mdisp_rot_crn_to_face(int S, int corners, int face_side, float x, float y,
 int mdisp_rot_face_to_crn(int corners, int face_side, float u, float v, float *x, float *y);
 void mdisp_apply_weight(int S, int corners, int x, int y, int face_side, float crn_weight[4][2], float *u_r, float *v_r);
 void mdisp_flip_disp(int S, int corners, float axis_x[2], float axis_y[2], float disp[3]);
+void mdisp_join_tris(struct MDisps *dst, struct MDisps *tri1, struct MDisps *tri2);
 
 #endif
 
diff --git a/source/blender/blenkernel/intern/customdata.c b/source/blender/blenkernel/intern/customdata.c
index 2d4e65f8f94..f7606a344c9 100644
--- a/source/blender/blenkernel/intern/customdata.c
+++ b/source/blender/blenkernel/intern/customdata.c
@@ -441,16 +441,55 @@ static void layerInterp_mdisps(void **sources, float *UNUSED(weights),
 	int i, x, y;
 	int side, S, dst_corners, src_corners;
 	float crn_weight[4][2];
-	float (*sw)[4] = NULL;
+	float (*sw)[4] = (void*)sub_weights;
 	float (*disps)[3], (*out)[3];
 
 	s = sources[0];
 	dst_corners = multires_mdisp_corners(d);
 	src_corners = multires_mdisp_corners(s);
 
-	/* XXX: For now, some restrictions on the input
-	        should be implemented to allow quad<->tris face conversion */
-	if(count != 1 || !sub_weights || dst_corners != src_corners) {
+	if(sub_weights && count == 2 && src_corners == 3) {
+		src_corners = multires_mdisp_corners(sources[1]);
+
+		/* special case -- converting two triangles to quad */
+		if(src_corners == 3 && dst_corners == 4) {
+			MDisps tris[2];
+			int vindex[4] = {0};
+
+			S = 0;
+			for(i = 0; i < 2; i++)
+				for(y = 0; y < 4; y++)
+					for(x = 0; x < 4; x++)
+						if(sw[x+i*4][y])
+							vindex[x] = y;
+
+			for(i = 0; i < 2; i++) {
+				float sw[4][4] = {{0}};
+				int a = 7 & ~(1 << vindex[i*2] | 1 << vindex[i*2+1]);
+
+				sw[0][vindex[i*2+1]] = 1;
+				sw[1][vindex[i*2]] = 1;
+
+				for(x = 0; x < 3; x++)
+					if(a & (1 << x))
+						sw[2][x] = 1;
+
+				tris[i] = *((MDisps*)sources[i]);
+				tris[i].disps = MEM_dupallocN(tris[i].disps);
+				layerInterp_mdisps(&sources[i], NULL, (float*)sw, 1, &tris[i]);
+			}
+
+			mdisp_join_tris(d, &tris[0], &tris[1]);
+
+			for(i = 0; i < 2; i++)
+				MEM_freeN(tris[i].disps);
+
+			return;
+		}
+	}
+
+	/* For now, some restrictions on the input */
+	if(count != 1 || !sub_weights) {
 		for(i = 0; i < d->totdisp; ++i)
 			zero_v3(d->disps[i]);
 
diff --git a/source/blender/blenkernel/intern/multires.c b/source/blender/blenkernel/intern/multires.c
index 68ee0d0d0cd..84350127968 100644
--- a/source/blender/blenkernel/intern/multires.c
+++ b/source/blender/blenkernel/intern/multires.c
@@ -1981,3 +1981,47 @@ void mdisp_flip_disp(int S, int corners, float axis_x[2], float axis_y[2], float
 		disp[1] = 0;
 	}
 }
+
+/* Join two triangular displacements into one quad
+	 Corners mapping:
+	 2 -------- 3
+	 | \   tri2 |
+	 |    \     |
+	 | tri1  \  |
+	 0 -------- 1 */
+void mdisp_join_tris(MDisps *dst, MDisps *tri1, MDisps *tri2)
+{
+	int side, st;
+	int S, x, y, crn;
+	float face_u, face_v, crn_u, crn_v;
+	float (*out)[3];
+	MDisps *src;
+
+	if(dst->disps)
+		MEM_freeN(dst->disps);
+
+	side = sqrt(tri1->totdisp / 3);
+	st = (side<<1)-1;
+
+	dst->totdisp = 4 * side * side;
+	out = dst->disps = MEM_callocN(3*dst->totdisp*sizeof(float), "join disps");
+
+	for(S = 0; S < 4; S++)
+		for(y = 0; y < side; ++y)
+			for(x = 0; x < side; ++x, ++out) {
+				mdisp_rot_crn_to_face(S, 4, st, x, y, &face_u, &face_v);
+				face_u = st - 1 - face_u;
+
+				if(face_v > face_u) {
+					src = tri2;
+					face_u = st - 1 - face_u;
+					face_v = st - 1 - face_v;
+				} else src = tri1;
+
+				crn = mdisp_rot_face_to_crn(3, st, face_u, face_v, &crn_u, &crn_v);
+
+				old_mdisps_bilinear((*out), &src->disps[crn*side*side], side, crn_u, crn_v);
+				(*out)[0] = 0;
+				(*out)[1] = 0;
+			}
+}