Merge pull request #1470 from proberts-cinesite/CurvesPrimitiveEvaluatorTangentPointsInOppositeDirectionForLinearInterpolation

IECoreScene CurvesPrimitiveEvaluator : fix `vTangent()` error

Author: johnhaddon

Changes

@@ -7,6 +7,7 @@ Fixes
 - USDScene :
   - Fixed writing of shutter values from cameras without a `shutter` parameter. The `shutter:open` and `shutter:close` attributes are now omitted instead of being written with Cortex's default -0.5, 0.5 shutter values.
   - Fixed reading of shutter values from cameras without `shutter:open` and `shutter:close` attributes. The `shutter` parameter is now omitted instead of being created with USD's default 0, 0 shutter values.
+- CurvesPrimitiveEvaluator : Fixed error in `Result::vTangent()` function causing tangent to point in opposite direction for curves with `Linear` interpolation.
 
 10.5.x.x (relative to 10.5.15.0)
 ========

src/IECoreScene/CurvesPrimitiveEvaluator.cpp

@@ -260,8 +260,8 @@ void CurvesPrimitiveEvaluator::Result::init( unsigned curveIndex, float v, const
 	{
 		m_coefficients[0] = 1.0f - m_segmentV;
 		m_coefficients[1] = m_segmentV;
-		m_derivativeCoefficients[0] = 1.0f;
-		m_derivativeCoefficients[1] = -1.0f;
+		m_derivativeCoefficients[0] = -1.0f;
+		m_derivativeCoefficients[1] = 1.0f;
 		m_vertexDataIndices[0] = m_varyingDataIndices[0] = o + i;
 		if( periodic )
 		{