Added convenient and efficient Timer class

The Timer is efficient because it does not depend on incrementing a
counter to keep track of time, nor does it call SDL_GetTicks every time
its state is checked (this happens once per frame instead).

Along with global functions Time::absoluteTimeMs() and
Time::deltaTimeMs(), this replaces previous globals tick_time, cur_time
and get_elapsed_time().

For now, there is still a fixed 100 times per second logic call rate,
but the new Time::deltaTimeMs() function should allow getting rid of
this.

1 files changed, 63 insertions, 0 deletions

diff --git a/src/utils/time.cpp b/src/utils/time.cpp
new file mode 100644
index 00000000..c89914fa
--- /dev/null
+++ b/src/utils/time.cpp
@@ -0,0 +1,63 @@
+/*
+ *  The Mana Client
+ *  Copyright (C) 2004-2009  The Mana World Development Team
+ *  Copyright (C) 2009-2012  The Mana Developers
+ *
+ *  This file is part of The Mana Client.
+ *
+ *  This program is free software; you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation; either version 2 of the License, or
+ *  any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include "time.h"
+
+#include <algorithm>
+
+#include <SDL.h>
+
+namespace Time
+{
+
+static uint32_t s_absoluteTimeMs;
+static unsigned s_deltaTimeMs;
+
+uint32_t absoluteTimeMs()
+{
+    return s_absoluteTimeMs;
+}
+
+unsigned deltaTimeMs()
+{
+    return s_deltaTimeMs;
+}
+
+static int32_t getElapsedTime(uint32_t timeMs)
+{
+    return static_cast<int32_t>(s_absoluteTimeMs - timeMs);
+}
+
+void beginFrame()
+{
+    // todo: Use SDL_GetTicks64 once we require SDL 2.0.18 or newer.
+
+    const uint32_t previousTime = s_absoluteTimeMs;
+    s_absoluteTimeMs = SDL_GetTicks();
+    s_deltaTimeMs = std::clamp(getElapsedTime(previousTime), 0, 1000);
+}
+
+} // namespace Time
+
+int32_t Timer::elapsed() const
+{
+    return Time::getElapsedTime(mTimeout);
+}