Add support to get a bezier curve extreme values

Add logic to get the extreme values of a curve segment. This is used by
the studio to fit an animation curve.

Change-Id: I65564802524bfd49793624a560d98cc67d22e055
Reviewed-by: Miikka Heikkinen <miikka.heikkinen@qt.io>
Reviewed-by: Tomi Korpipää <tomi.korpipaa@qt.io>

1 files changed, 20 insertions, 0 deletions

diff --git a/src/system/Qt3DSBezierEval.h b/src/system/Qt3DSBezierEval.h
index ef99eec..8a6f6b0 100644
--- a/src/system/Qt3DSBezierEval.h
+++ b/src/system/Qt3DSBezierEval.h
@@ -166,4 +166,24 @@ inline float EvaluateBezierKeyframe(long inTime, long inTime1, float inValue1, l
     return 0.0;
 }
 
+inline std::pair<float, float> getBezierCurveExtrema(float inTime1, float inValue1,
+                                                     float inC1Time, float inC1Value,
+                                                     float inC2Time, float inC2Value,
+                                                     float inTime2, float inValue2)
+{
+        auto polynomial = CubicPolynomial(inValue1, inC1Value, inC2Value, inValue2);
+
+        std::pair<float, float> extrema {-FLT_MAX, FLT_MAX}; // <max, min>
+        for (double t : polynomial.extrema()) {
+            const float val = float(evaluateForT(t, inValue1, inC1Value, inC2Value, inValue2));
+
+            if (val > extrema.first)
+                extrema.first = val;
+            if (val < extrema.second)
+                extrema.second = val;
+        }
+
+    return extrema;
+}
+
 } // namespace Qt3DStudio