Remove Maya style tangents from time splines and add tangent

conversion functions.

Remove Maya style tangent values from the time spline (and related)
code. Tangents are now only stored in "standard" format which is a
typed slope and a TsTime (aka doule) width. Maya style tangent values
which have a height instead of width, stored values scaled by 3, and
which invert the height of the pre-tangent are no longer used
internally.

To continue to support Maya we have added TsConvertToStandardTangent
and TsConvertFromStandardTangent. These functions take standard slope
and width values and perform optional conversions on them that can
convert between slope and height values, scale by 3, and/or negate the
slope or height value.

Note that Hermite curves do not have an explicit tangent width value.
Instead, the value used is 1/3 the width of the segment to which they
belong. The conversion functions, however, require a width in order to
convert between slope and height values. It is up to the caller to
provide a width value to the conversion routines, even when working
with Hermite curves.

(Internal change: 2343223)
(Internal change: 2343286)

Author: o2b3d

pxr/base/ts/CMakeLists.txt

@@ -22,6 +22,7 @@ set(classes
     regressionPreventer
     spline
     splineData
+    tangentConversions
     typeHelpers
     types
 )
@@ -42,6 +43,7 @@ set(pycpp
     wrapRaii.cpp
     wrapRegressionPreventer.cpp
     wrapSpline.cpp
+    wrapTangentConversions.cpp
     wrapTypes.cpp
 )
 
@@ -165,6 +167,16 @@ pxr_build_test(
         tf
 )
 
+pxr_build_test(
+    testTsTangentConversion
+    CPPFILES
+        testenv/testTsTangentConversion.cpp
+    LIBRARIES
+        ts
+        vt
+        tf
+)
+
 pxr_test_scripts(
     testenv/testTsDerivatives.py
     testenv/testTsRegressionPreventer.py
@@ -204,6 +216,11 @@ pxr_register_test(
     COMMAND "${CMAKE_INSTALL_PREFIX}/tests/testTsSplineAPI"
 )
 
+pxr_register_test(
+    testTsTangentConversion
+    COMMAND "${CMAKE_INSTALL_PREFIX}/tests/testTsTangentConversion"
+)
+
 pxr_register_test(
     tsTest_TsFramework
     PYTHON

pxr/base/ts/binary.cpp

@@ -95,13 +95,9 @@ namespace
                 // Bit 0: whether dual-valued.
                 // Bits 1-2: next segment interpolation mode.
                 // Bit 3: curve type.
-                // Bit 4: whether pre-tangent is in Maya form.
-                // Bit 5: whether post-tangent is in Maya form.
                 uint8_t flagByte = knot.dualValued;
                 flagByte |= static_cast<uint8_t>(knot.nextInterp) << 1;
                 flagByte |= static_cast<uint8_t>(knot.curveType) << 3;
-                flagByte |= knot.preTanMayaForm << 4;
-                flagByte |= knot.postTanMayaForm << 5;
                 _WriteBytes<uint8_t>(buf, flagByte);
 
                 // Knot time and value.
@@ -121,8 +117,7 @@ namespace
                     _WriteBytes<double>(buf, knot.postTanWidth);
                 }
 
-                // Tangent slopes or heights.
-                // Interpretation will be governed by the Maya-form flags.
+                // Tangent slopes.
                 _WriteBytes<T>(buf, knot.preTanSlope);
                 _WriteBytes<T>(buf, knot.postTanSlope);
             }
@@ -273,8 +268,6 @@ namespace
                     static_cast<TsInterpMode>((flagByte & 0x06) >> 1);
                 knot.curveType =
                     static_cast<TsCurveType>((flagByte & 0x08) >> 3);
-                knot.preTanMayaForm = flagByte & 0x10;
-                knot.postTanMayaForm = flagByte & 0x20;
 
                 // Knot time and value.
                 READ(&knot.time);
@@ -293,8 +286,7 @@ namespace
                     READ(&knot.postTanWidth);
                 }
 
-                // Tangent slopes or heights.
-                // Interpretation will be governed by the Maya-form flags.
+                // Tangent slopes
                 READ(&knot.preTanSlope);
                 READ(&knot.postTanSlope);
 

pxr/base/ts/eval.cpp

@@ -307,50 +307,6 @@ _EvalHermite(
 ////////////////////////////////////////////////////////////////////////////////
 // EVAL HELPERS
 
-// Find the slope at a knot, facing into a curved segment.
-//
-// Accounts for Maya vs. standard tangent forms, and forced tangent widths for
-// Hermite curves.
-//
-static double
-_GetCurveKnotSlope(
-    const Ts_TypedKnotData<double> &knotData,
-    const TsTime adjacentTime,
-    const TsCurveType curveType,
-    const Ts_EvalLocation location)
-{
-    if (location == Ts_EvalPre)
-    {
-        if (!knotData.preTanMayaForm)
-        {
-            return knotData.preTanSlope;
-        }
-        else if (curveType == TsCurveTypeHermite)
-        {
-            return -knotData.preTanMayaHeight / (knotData.time - adjacentTime);
-        }
-        else
-        {
-            return -knotData.preTanMayaHeight / knotData.preTanWidth;
-        }
-    }
-    else
-    {
-        if (!knotData.postTanMayaForm)
-        {
-            return knotData.postTanSlope;
-        }
-        else if (curveType == TsCurveTypeHermite)
-        {
-            return knotData.postTanMayaHeight / (adjacentTime - knotData.time);
-        }
-        else
-        {
-            return knotData.postTanMayaHeight / knotData.postTanWidth;
-        }
-    }
-}
-
 // Find the slope from one knot to another in a linear segment.  Such slopes are
 // implicit: based on times and values, not tangents.
 //
@@ -424,8 +380,7 @@ _GetExtrapolationSlope(
 
         // Otherwise the first segment is curved.  The slope is continued from
         // the inward-facing side of the first knot.
-        return _GetCurveKnotSlope(
-            endKnotData, adjacentData.time, curveType, Ts_EvalPost);
+        return endKnotData.postTanSlope;
     }
     else
     {
@@ -444,8 +399,7 @@ _GetExtrapolationSlope(
 
         // Otherwise the last segment is curved.  The slope is continued from
         // the inward-facing side of the last knot.
-        return _GetCurveKnotSlope(
-            endKnotData, adjacentData.time, curveType, Ts_EvalPre);
+        return endKnotData.preTanSlope;
     }
 }
 
@@ -1248,8 +1202,7 @@ _EvalMain(
                 }
 
                 // Not a special case.  Return what's stored in the knot.
-                return _GetCurveKnotSlope(
-                    knotData, prevData.time, data->curveType, Ts_EvalPre);
+                return knotData.preTanSlope;
             }
             else
             {
@@ -1275,8 +1228,7 @@ _EvalMain(
                 }
 
                 // Not a special case.  Return what's stored in the knot.
-                return _GetCurveKnotSlope(
-                    knotData, nextData.time, data->curveType, Ts_EvalPost);
+                return knotData.postTanSlope;
             }
         }
     }