Cycles: Improved robustness of hair motion blur.motion_curve_fix

In some instances, the number of control vertices of a hair could change mid-frame.
Cycles would then be unable to calculate proper motion blur for those hairs. This adds
interpolated CVs to fill in for the missing data. While this will not necessarily result in
a fully accurate reconstruction of the guide hair, it preserves motion blur instead of disabling it.

Reviewers: #cycles, sergey

Reviewed By: #cycles, sergey

Subscribers: sergey, brecht, #cycles

Tags: #cycles

Differential Revision: https://developer.blender.org/D3695

1 files changed, 8 insertions, 2 deletions

diff --git a/source/blender/alembic/intern/abc_customdata.cc b/source/blender/alembic/intern/abc_customdata.cc
index f2ae1c831d1..424475dc61b 100644
--- a/source/blender/alembic/intern/abc_customdata.cc
+++ b/source/blender/alembic/intern/abc_customdata.cc
@@ -185,7 +185,11 @@ static void write_mcol(const OCompoundProperty &prop, const CDStreamConfig &conf
 	MLoop *mloops = config.mloop;
 	MCol *cfaces = static_cast<MCol *>(data);
 
-	std::vector<Imath::C4f> buffer(config.totvert);
+	std::vector<Imath::C4f> buffer;
+	std::vector<uint32_t> indices;
+
+	buffer.reserve(config.totvert);
+	indices.reserve(config.totvert);
 
 	Imath::C4f col;
 
@@ -203,7 +207,8 @@ static void write_mcol(const OCompoundProperty &prop, const CDStreamConfig &conf
 			col[2] = cface->g * cscale;
 			col[3] = cface->b * cscale;
 
-			buffer[mloop->v] = col;
+			buffer.push_back(col);
+			indices.push_back(buffer.size() - 1);
 		}
 	}
 
@@ -211,6 +216,7 @@ static void write_mcol(const OCompoundProperty &prop, const CDStreamConfig &conf
 
 	OC4fGeomParam::Sample sample(
 		C4fArraySample(&buffer.front(), buffer.size()),
+		UInt32ArraySample(&indices.front(), indices.size()),
 		kVertexScope);
 
 	param.set(sample);