Animation: make it possible to have integer keys.

src/Magnum/Animation/Interpolation.h

@@ -188,7 +188,7 @@ template<class K, class V, class R> R interpolate(const Containers::StridedArray
     }
 
     return interpolator(values[hint], values[hint + 1],
-        Math::lerpInverted(keys[hint], keys[hint + 1], frame));
+        Math::lerpInverted(Float(keys[hint]), Float(keys[hint + 1]), Float(frame)));
 }
 
 template<class K, class V, class R> R interpolateStrict(const Containers::StridedArrayView<const K>& keys, const Containers::StridedArrayView<const V>& values, R(*const interpolator)(const V&, const V&, Float), const K frame, std::size_t& hint) {
@@ -203,7 +203,7 @@ template<class K, class V, class R> R interpolateStrict(const Containers::Stride
         ++hint;
 
     return interpolator(values[hint], values[hint + 1],
-        Math::lerpInverted(keys[hint], keys[hint + 1], frame));
+        Math::lerpInverted(Float(keys[hint]), Float(keys[hint + 1]), Float(frame)));
 }
 
 }}

src/Magnum/Animation/Test/InterpolationTest.cpp

@@ -48,6 +48,9 @@ struct InterpolationTest: TestSuite::Tester {
     void interpolateError();
     void interpolateStrictError();
 
+    void interpolateIntegerKey();
+    void interpolateStrictIntegerKey();
+
     void debugExtrapolation();
 };
 
@@ -141,6 +144,9 @@ InterpolationTest::InterpolationTest() {
               &InterpolationTest::interpolateError,
               &InterpolationTest::interpolateStrictError,
 
+              &InterpolationTest::interpolateIntegerKey,
+              &InterpolationTest::interpolateStrictIntegerKey,
+
               &InterpolationTest::debugExtrapolation});
 }
 
@@ -236,6 +242,24 @@ void InterpolationTest::interpolateStrictDifferentResultType() {
     CORRADE_COMPARE(hint, 2);
 }
 
+namespace {
+    constexpr Int IntegerKeys[]{0, 48, 96, 120};
+}
+
+void InterpolationTest::interpolateIntegerKey() {
+    std::size_t hint{};
+    CORRADE_COMPARE((Animation::interpolate<Int, Float>(
+        IntegerKeys, Values, Extrapolation::Extrapolated, Extrapolation::Extrapolated, Math::lerp, 114, hint)), 1.0f);
+    CORRADE_COMPARE(hint, 2);
+}
+
+void InterpolationTest::interpolateStrictIntegerKey() {
+    std::size_t hint{};
+    CORRADE_COMPARE((Animation::interpolateStrict<Int, Float>(
+        IntegerKeys, Values, Math::lerp, 114, hint)), 1.0f);
+    CORRADE_COMPARE(hint, 2);
+}
+
 void InterpolationTest::interpolateError() {
     std::ostringstream out;
     Error redirectError{&out};