Fix T39206: Plane deform works incredibly slow

The issue was caused by the readEWA spending loads of time trying
to sample regions outside of the buffer.Solved by adding an early
exit check.

We could also clamp the sampling region to the rect, but it's
not so much clear whether weight will be correct in such case
so left it for the future.

1 files changed, 9 insertions, 0 deletions

diff --git a/source/blender/compositor/intern/COM_MemoryBuffer.cpp b/source/blender/compositor/intern/COM_MemoryBuffer.cpp
index 65cd74a971f..74991738d7a 100644
--- a/source/blender/compositor/intern/COM_MemoryBuffer.cpp
+++ b/source/blender/compositor/intern/COM_MemoryBuffer.cpp
@@ -288,6 +288,15 @@ void MemoryBuffer::readEWA(float result[4], const float uv[2], const float deriv
 	if (V0 - v1 > EWA_MAXIDX) v1 = V0 - EWA_MAXIDX;
 	if (v2 - V0 > EWA_MAXIDX) v2 = V0 + EWA_MAXIDX;
 
+	/* Early output check for cases the whole region is outside of the buffer. */
+	if ((u2 < m_rect.xmin || u1 >= m_rect.xmax) ||
+	    (v2 < m_rect.ymin || v1 >= m_rect.ymax))
+	{
+		zero_v4(result);
+		return;
+	}
+	/* TODO(sergey): Consider clamping u1/v1/u2/v2 to the m_rect. */
+
 	float DDQ = 2.0f * A;
 	float U = u1 - U0;
 	float ac1 = A * (2.0f * U + 1.0f);