Animation: make it possible to advance() multiple players at once.

Just realized that <functional> is 22k in C++11 and 44k lines in C++17.
SAD. EXTREMELY.

src/Magnum/Animation/Player.h

@@ -258,6 +258,13 @@ template<class T, class K
          */
         typedef std::pair<UnsignedInt, K>(*Scaler)(T, K);
 
+        /**
+         * @brief Advance multiple players at the same time
+         *
+         * Equivalent to calling @ref advance(T) for each item in @p players.
+         */
+        static void advance(T time, std::initializer_list<std::reference_wrapper<Player<T, K>>> players);
+
         /** @brief Constructor */
         explicit Player();
 

src/Magnum/Animation/Player.hpp

@@ -31,6 +31,7 @@
 
 #include "Player.h"
 
+#include <functional>
 #include <Corrade/Containers/Optional.h>
 
 namespace Magnum { namespace Animation {
@@ -70,6 +71,10 @@ template<class T, class K> struct Player<T, K>::Track  {
 };
 #endif
 
+template<class T, class K> void Player<T, K>::advance(const T time, const std::initializer_list<std::reference_wrapper<Player<T, K>>> players) {
+    for(Player<T, K>& p: players) p.advance(time);
+}
+
 template<class T, class K> Player<T, K>::Player(Player<T, K>&&) = default;
 
 template<class T, class K> Player<T, K>& Player<T, K>::operator=(Player<T, K>&&) = default;

src/Magnum/Animation/Test/PlayerTest.cpp

@@ -23,6 +23,7 @@
     DEALINGS IN THE SOFTWARE.
 */
 
+#include <functional>
 #include <sstream>
 #include <Corrade/TestSuite/Tester.h>
 #include <Corrade/TestSuite/Compare/Numeric.h>
@@ -57,6 +58,7 @@ struct PlayerTest: TestSuite::Tester {
     void advancePlayCount();
     void advancePlayCountInfinite();
     void advanceChrono();
+    void advanceList();
     void advanceZeroDurationStop();
     void advanceZeroDurationPause();
     void advanceZeroDurationInfinitePlayCount();
@@ -139,6 +141,7 @@ PlayerTest::PlayerTest() {
               &PlayerTest::advancePlayCount,
               &PlayerTest::advancePlayCountInfinite,
               &PlayerTest::advanceChrono,
+              &PlayerTest::advanceList,
               &PlayerTest::advanceZeroDurationStop,
               &PlayerTest::advanceZeroDurationPause,
               &PlayerTest::advanceZeroDurationInfinitePlayCount,
@@ -759,6 +762,26 @@ void PlayerTest::advanceChrono() {
     CORRADE_COMPARE(value, 4.0f);
 }
 
+void PlayerTest::advanceList() {
+    Float valueA = -1.0f, valueB = -1.0f;
+    Player<std::chrono::nanoseconds, Float> a, b;
+    a.add(Track, valueA)
+     .play(std::chrono::seconds{2});
+    b.add(Track, valueB)
+     .play(std::chrono::seconds{1});
+
+    /* 1.75 secs in for A, 2.75 seconds in for B */
+    Player<std::chrono::nanoseconds, Float>::advance(std::chrono::milliseconds{3750}, {a, b});
+    CORRADE_COMPARE(a.state(), State::Playing);
+    CORRADE_COMPARE(b.state(), State::Playing);
+    CORRADE_COMPARE(a.elapsed(std::chrono::milliseconds{3750}),
+        std::make_pair(0, 1.75f));
+    CORRADE_COMPARE(b.elapsed(std::chrono::milliseconds{3750}),
+        std::make_pair(0, 2.75f));
+    CORRADE_COMPARE(valueA, 4.0f);
+    CORRADE_COMPARE(valueB, 2.75f);
+}
+
 void PlayerTest::advanceZeroDurationStop() {
     Float value = -1.0f;
     Player<Float> player;