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.

26 files changed, 388 insertions, 293 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 9ced2c13..d5d512e8 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -381,6 +381,8 @@ set(SRCS
     utils/specialfolder.h
     utils/stringutils.cpp
     utils/stringutils.h
+    utils/time.cpp
+    utils/time.h
     utils/mutex.h
     utils/mkdir.cpp
     utils/mkdir.h
diff --git a/src/actorsprite.cpp b/src/actorsprite.cpp
index 62c5d1dc..20e724f5 100644
--- a/src/actorsprite.cpp
+++ b/src/actorsprite.cpp
@@ -20,7 +20,6 @@
 
 #include "actorsprite.h"
 
-#include "client.h"
 #include "configuration.h"
 #include "event.h"
 #include "imagesprite.h"
@@ -35,6 +34,8 @@
 #include "resources/resourcemanager.h"
 #include "resources/theme.h"
 
+#include "utils/time.h"
+
 #include <cassert>
 
 #define EFFECTS_FILE "effects.xml"
@@ -80,7 +81,7 @@ bool ActorSprite::draw(Graphics *graphics, int offsetX, int offsetY) const
     if (mUsedTargetCursor)
     {
         mUsedTargetCursor->reset();
-        mUsedTargetCursor->update(tick_time * MILLISECONDS_IN_A_TICK);
+        mUsedTargetCursor->update(Time::absoluteTimeMs());
         mUsedTargetCursor->draw(graphics, px, py);
     }
 
@@ -101,7 +102,7 @@ bool ActorSprite::drawSpriteAt(Graphics *graphics, int x, int y) const
 void ActorSprite::logic()
 {
     // Update sprite animations
-    update(tick_time * MILLISECONDS_IN_A_TICK);
+    update(Time::absoluteTimeMs());
 
     // Restart status/particle effects, if needed
     if (mMustResetParticles)
diff --git a/src/being.cpp b/src/being.cpp
index 95f7c0d5..88104d74 100644
--- a/src/being.cpp
+++ b/src/being.cpp
@@ -643,7 +643,7 @@ void Being::setAction(Action action, int attackId)
     }
 
     if (currentAction != SpriteAction::MOVE)
-        mActionTime = tick_time;
+        mActionTimer.set();
 }
 
 void Being::lookAt(const Vector &destPos)
@@ -865,13 +865,9 @@ void Being::logic()
 
     // Remove it after 1.5 secs if the dead animation isn't long enough,
     // or simply play it until it's finished.
-    if (!isAlive() && Net::getGameHandler()->removeDeadBeings() &&
-        get_elapsed_time(mActionTime) > std::max(getDuration(), 1500))
-    {
-
-        if (getType() != PLAYER)
+    if (!isAlive() && Net::getGameHandler()->removeDeadBeings() && getType() != PLAYER)
+        if (mActionTimer.elapsed() > std::max(getDuration(), 1500))
             actorSpriteManager->scheduleDelete(this);
-    }
 }
 
 void Being::drawSpeech(int offsetX, int offsetY)
diff --git a/src/being.h b/src/being.h
index 3bd66b06..c8e8a87b 100644
--- a/src/being.h
+++ b/src/being.h
@@ -29,6 +29,8 @@
 #include "position.h"
 #include "vector.h"
 
+#include "utils/time.h"
+
 #include <guichan/color.hpp>
 
 #include <map>
@@ -484,7 +486,7 @@ class Being : public ActorSprite, public EventListener
 
         const BeingInfo *mInfo;
 
-        int mActionTime = 0;    /**< Time spent in current action. TODO: Remove use of it */
+        Timer mActionTimer;     /**< Time spent in current action. TODO: Remove use of it */
 
         /** Time until the last speech sentence disappears */
         int mSpeechTime = 0;
diff --git a/src/client.cpp b/src/client.cpp
index e98006a8..6137a88a 100644
--- a/src/client.cpp
+++ b/src/client.cpp
@@ -70,8 +70,11 @@
 
 #include "utils/gettext.h"
 #include "utils/mkdir.h"
+#if defined(_WIN32) || defined(__APPLE__)
 #include "utils/specialfolder.h"
+#endif
 #include "utils/stringutils.h"
+#include "utils/time.h"
 
 #include <physfs.h>
 #include <SDL_image.h>
@@ -84,12 +87,6 @@
 #include <sys/stat.h>
 #include <cassert>
 
-/**
- * Tells the max tick value,
- * setting it back to zero (and start again).
- */
-static const int MAX_TICK_VALUE = 10000;
-
 // TODO: Get rid fo these globals
 std::string errorMessage;
 LoginData loginData;
@@ -109,23 +106,8 @@ HairDB hairDB;                /**< Hair styles and colors info database */
 
 Sound sound;
 
-volatile int tick_time;       /**< Tick counter */
 volatile int fps = 0;         /**< Frames counted in the last second */
 volatile int frame_count = 0; /**< Counts the frames during one second */
-volatile int cur_time;
-
-/**
- * Advances game logic counter.
- * Called every 10 milliseconds by SDL_AddTimer()
- * @see MILLISECONDS_IN_A_TICK value
- */
-Uint32 nextTick(Uint32 interval, void *param)
-{
-    tick_time++;
-    if (tick_time == MAX_TICK_VALUE)
-        tick_time = 0;
-    return interval;
-}
 
 /**
  * Updates fps.
@@ -139,27 +121,15 @@ Uint32 nextSecond(Uint32 interval, void *param)
     return interval;
 }
 
-int get_elapsed_time(int startTime)
-{
-    if (startTime <= tick_time)
-        return (tick_time - startTime) * MILLISECONDS_IN_A_TICK;
-
-    return (tick_time + (MAX_TICK_VALUE - startTime)) * MILLISECONDS_IN_A_TICK;
-}
-
 bool isDoubleClick(int selected)
 {
-    const Uint32 maximumDelay = 500;
-    static Uint32 lastTime = 0;
+    static Timer timer;
     static int lastSelected = -1;
 
-    if (selected == lastSelected && lastTime + maximumDelay >= SDL_GetTicks())
-    {
-        lastTime = 0;
+    if (selected == lastSelected && !timer.passed())
         return true;
-    }
 
-    lastTime = SDL_GetTicks();
+    timer.set(500);
     lastSelected = selected;
     return false;
 }
@@ -419,9 +389,7 @@ Client::Client(const Options &options):
     if (mState != STATE_ERROR)
         mState = STATE_CHOOSE_SERVER;
 
-    // Initialize logic and seconds counters
-    tick_time = 0;
-    mLogicCounterId = SDL_AddTimer(MILLISECONDS_IN_A_TICK, nextTick, nullptr);
+    // Initialize seconds counter
     mSecondsCounterId = SDL_AddTimer(1000, nextSecond, nullptr);
 
     listen(Event::ConfigChannel);
@@ -437,7 +405,6 @@ Client::Client(const Options &options):
 
 Client::~Client()
 {
-    SDL_RemoveTimer(mLogicCounterId);
     SDL_RemoveTimer(mSecondsCounterId);
 
     // Unload XML databases
@@ -473,12 +440,18 @@ Client::~Client()
 
 int Client::exec()
 {
-    int lastTickTime = tick_time;
+    Time::beginFrame();     // Prevent startup lag influencing the first frame
+
+    // Tick timer, used until logic has been updated to use Time::deltaTimeMs
+    Timer tickTimer;
+    tickTimer.set();
 
     SDL_Event event;
 
     while (mState != STATE_EXIT)
     {
+        Time::beginFrame();
+
         if (mGame)
         {
             // Let the game handle the events while it is active
@@ -512,19 +485,16 @@ int Client::exec()
         if (Net::getGeneralHandler())
             Net::getGeneralHandler()->flushNetwork();
 
-        while (get_elapsed_time(lastTickTime) > 0)
+        while (tickTimer.passed())
         {
             gui->logic();
             if (mGame)
                 mGame->logic();
 
-            sound.logic();
-
-            ++lastTickTime;
+            tickTimer.extend(MILLISECONDS_IN_A_TICK);
         }
 
-        // This is done because at some point tick_time will wrap.
-        lastTickTime = tick_time;
+        sound.logic();
 
         // Update the screen when application is active, delay otherwise.
         if (isActive())
diff --git a/src/client.h b/src/client.h
index 49780a38..a2371a1c 100644
--- a/src/client.h
+++ b/src/client.h
@@ -40,35 +40,16 @@ class LoginData;
 class Window;
 class QuitDialog;
 
-/**
- * Set the milliseconds value of a tick time.
- */
-static const int MILLISECONDS_IN_A_TICK = 10;
-
 //manaserv uses 9601
 //static const short DEFAULT_PORT = 9601;
 static const short DEFAULT_PORT = 6901;
 
 extern volatile int fps;
-extern volatile int tick_time;
-extern volatile int cur_time;
 
 extern std::string errorMessage;
 extern LoginData loginData;
 
 /**
- * @param startTime The value to check in client ticks.
- *
- * @return the elapsed time in milliseconds.
- * between startTime and the current client tick value.
- *
- * @warning This function can't handle delays > 100 seconds.
- * @see MILLISECONDS_IN_A_TICK
- * @see tick_time
- */
-int get_elapsed_time(int startTime);
-
-/**
  * Returns whether this call and the last call were done for the same
  * selected index and within a short time.
  */
@@ -256,7 +237,6 @@ private:
 
     SDL_Surface *mIcon = nullptr;
 
-    SDL_TimerID mLogicCounterId = 0;
     SDL_TimerID mSecondsCounterId = 0;
 
     int mFpsLimit = 0;
diff --git a/src/game.cpp b/src/game.cpp
index a9199817..13928036 100644
--- a/src/game.cpp
+++ b/src/game.cpp
@@ -343,8 +343,6 @@ void Game::logic()
     if (mCurrentMap)
         mCurrentMap->update();
 
-    cur_time = time(nullptr);
-
     // Handle network stuff
     if (!Net::getGameHandler()->isConnected() && !mDisconnected)
     {
diff --git a/src/gui/gui.cpp b/src/gui/gui.cpp
index 26d0913e..2ff697c7 100644
--- a/src/gui/gui.cpp
+++ b/src/gui/gui.cpp
@@ -158,7 +158,7 @@ Gui::~Gui()
 void Gui::logic()
 {
     // Hide mouse cursor after extended inactivity
-    if (get_elapsed_time(mLastMouseActivityTime) > 15000)
+    if (mMouseActivityTimer.passed())
         SDL_ShowCursor(SDL_DISABLE);
 
     Palette::advanceGradients();
@@ -239,7 +239,7 @@ void Gui::updateCursor()
 void Gui::handleMouseMoved(const gcn::MouseInput &mouseInput)
 {
     gcn::Gui::handleMouseMoved(mouseInput);
-    mLastMouseActivityTime = tick_time;
+    mMouseActivityTimer.set(15000);
 
     // Make sure the cursor is visible
     SDL_ShowCursor(SDL_ENABLE);
diff --git a/src/gui/gui.h b/src/gui/gui.h
index 7c3c3afd..fd1dcf94 100644
--- a/src/gui/gui.h
+++ b/src/gui/gui.h
@@ -25,6 +25,8 @@
 #include "eventlistener.h"
 #include "guichanfwd.h"
 
+#include "utils/time.h"
+
 #include <guichan/gui.hpp>
 
 #include <SDL.h>
@@ -137,7 +139,7 @@ class Gui final : public gcn::Gui, public EventListener
         float mCustomCursorScale = 1.0f;
         std::vector<SDL_Cursor *> mSystemMouseCursors;
         std::vector<SDL_Cursor *> mCustomMouseCursors;
-        int mLastMouseActivityTime = 0;
+        Timer mMouseActivityTimer;
         Cursor mCursorType = Cursor::POINTER;
 };
 
diff --git a/src/gui/ministatuswindow.cpp b/src/gui/ministatuswindow.cpp
index d3e01bd2..e22172bc 100644
--- a/src/gui/ministatuswindow.cpp
+++ b/src/gui/ministatuswindow.cpp
@@ -43,8 +43,7 @@
 
 #include "utils/gettext.h"
 #include "utils/stringutils.h"
-
-extern volatile int tick_time;
+#include "utils/time.h"
 
 MiniStatusWindow::MiniStatusWindow():
     Popup("MiniStatus")
@@ -227,7 +226,7 @@ void MiniStatusWindow::logic()
 
     for (auto &icon : mIcons)
         if (icon)
-            icon->update(tick_time * 10);
+            icon->update(Time::absoluteTimeMs());
 }
 
 void MiniStatusWindow::mouseMoved(gcn::MouseEvent &event)
diff --git a/src/gui/palette.cpp b/src/gui/palette.cpp
index aaa3165c..6c6e6f06 100644
--- a/src/gui/palette.cpp
+++ b/src/gui/palette.cpp
@@ -22,18 +22,11 @@
 
 #include "palette.h"
 
-#include "configuration.h"
-#include "client.h"
-
-#include "gui/gui.h"
-
-#include "utils/gettext.h"
-#include "utils/stringutils.h"
-
 #include <cmath>
 
-static const double PI = 3.14159265;
+static constexpr double PI = 3.14159265;
 const gcn::Color Palette::BLACK = gcn::Color(0, 0, 0);
+Timer Palette::mRainbowTimer;
 Palette::Palettes Palette::mInstances;
 
 const gcn::Color Palette::RAINBOW_COLORS[7] = {
@@ -49,7 +42,6 @@ const gcn::Color Palette::RAINBOW_COLORS[7] = {
 const int Palette::RAINBOW_COLOR_COUNT = 7;
 
 Palette::Palette(int size) :
-    mRainbowTime(tick_time),
     mColors(size)
 {
     mInstances.insert(this);
@@ -76,97 +68,85 @@ const gcn::Color &Palette::getColor(char c, bool &valid)
 
 void Palette::advanceGradients()
 {
-    auto it = mInstances.begin();
-    auto it_end = mInstances.end();
+    const int advance = mRainbowTimer.elapsed() / 5;
+    if (advance <= 0)
+        return;
 
-    for (; it != it_end; it++)
-    {
-        (*it)->advanceGradient();
-    }
+    mRainbowTimer.extend(advance * 5);
+
+    for (auto palette : mInstances)
+        palette->advanceGradient(advance);
 }
 
-void Palette::advanceGradient()
+void Palette::advanceGradient(int advance)
 {
-    if (get_elapsed_time(mRainbowTime) > 5)
+    for (auto elem : mGradVector)
     {
-        int pos, colIndex, colVal, delay, numOfColors;
-        // For slower systems, advance can be greater than one (advance > 1
-        // skips advance-1 steps). Should make gradient look the same
-        // independent of the framerate.
-        int advance = get_elapsed_time(mRainbowTime) / 5;
-        double startColVal, destColVal;
-
-        for (auto &elem : mGradVector)
-        {
-            delay = elem->delay;
+        int delay = elem->delay;
 
-            if (elem->grad == PULSE)
-                delay = delay / 20;
+        if (elem->grad == PULSE)
+            delay = delay / 20;
 
-            numOfColors = (elem->grad == SPECTRUM ? 6 :
-                           elem->grad == PULSE ? 127 :
-                           RAINBOW_COLOR_COUNT);
+        const int numOfColors = (elem->grad == SPECTRUM ? 6 :
+                                 elem->grad == PULSE ? 127 :
+                                 RAINBOW_COLOR_COUNT);
 
-            elem->gradientIndex =
-                                    (elem->gradientIndex + advance) %
-                                    (delay * numOfColors);
+        elem->gradientIndex = (elem->gradientIndex + advance) %
+                              (delay * numOfColors);
 
-            pos = elem->gradientIndex % delay;
-            colIndex = elem->gradientIndex / delay;
+        const int pos = elem->gradientIndex % delay;
+        const int colIndex = elem->gradientIndex / delay;
 
-            if (elem->grad == PULSE)
-            {
-                colVal = (int) (255.0 * sin(PI * colIndex / numOfColors));
+        if (elem->grad == PULSE)
+        {
+            const int colVal = (int) (255.0 * sin(PI * colIndex / numOfColors));
+            const gcn::Color &col = elem->testColor;
 
-                const gcn::Color &col = elem->testColor;
+            elem->color.r = ((colVal * col.r) / 255) % (col.r + 1);
+            elem->color.g = ((colVal * col.g) / 255) % (col.g + 1);
+            elem->color.b = ((colVal * col.b) / 255) % (col.b + 1);
+        }
+        if (elem->grad == SPECTRUM)
+        {
+            int colVal;
 
-                elem->color.r = ((colVal * col.r) / 255) % (col.r + 1);
-                elem->color.g = ((colVal * col.g) / 255) % (col.g + 1);
-                elem->color.b = ((colVal * col.b) / 255) % (col.b + 1);
+            if (colIndex % 2)
+            { // falling curve
+                colVal = (int)(255.0 * (cos(PI * pos / delay) + 1) / 2);
             }
-            if (elem->grad == SPECTRUM)
-            {
-                if (colIndex % 2)
-                { // falling curve
-                    colVal = (int)(255.0 * (cos(PI * pos / delay) + 1) / 2);
-                }
-                else
-                { // ascending curve
-                    colVal = (int)(255.0 * (cos(PI * (delay - pos) / delay) +
-                                   1) / 2);
-                }
-
-                elem->color.r =
-                        (colIndex == 0 || colIndex == 5) ? 255 :
-                        (colIndex == 1 || colIndex == 4) ? colVal : 0;
-                elem->color.g =
-                        (colIndex == 1 || colIndex == 2) ? 255 :
-                        (colIndex == 0 || colIndex == 3) ? colVal : 0;
-                elem->color.b =
-                        (colIndex == 3 || colIndex == 4) ? 255 :
-                        (colIndex == 2 || colIndex == 5) ? colVal : 0;
+            else
+            { // ascending curve
+                colVal = (int)(255.0 * (cos(PI * (delay - pos) / delay) +
+                                1) / 2);
             }
-            else if (elem->grad == RAINBOW)
-            {
-                const gcn::Color &startCol = RAINBOW_COLORS[colIndex];
-                const gcn::Color &destCol =
-                        RAINBOW_COLORS[(colIndex + 1) % numOfColors];
 
-                startColVal = (cos(PI * pos / delay) + 1) / 2;
-                destColVal = 1 - startColVal;
+            elem->color.r =
+                    (colIndex == 0 || colIndex == 5) ? 255 :
+                    (colIndex == 1 || colIndex == 4) ? colVal : 0;
+            elem->color.g =
+                    (colIndex == 1 || colIndex == 2) ? 255 :
+                    (colIndex == 0 || colIndex == 3) ? colVal : 0;
+            elem->color.b =
+                    (colIndex == 3 || colIndex == 4) ? 255 :
+                    (colIndex == 2 || colIndex == 5) ? colVal : 0;
+        }
+        else if (elem->grad == RAINBOW)
+        {
+            const gcn::Color &startCol = RAINBOW_COLORS[colIndex];
+            const gcn::Color &destCol =
+                    RAINBOW_COLORS[(colIndex + 1) % numOfColors];
 
-                elem->color.r =(int)(startColVal * startCol.r +
-                                               destColVal * destCol.r);
+            const double startColVal = (cos(PI * pos / delay) + 1) / 2;
+            const double destColVal = 1 - startColVal;
 
-                elem->color.g =(int)(startColVal * startCol.g +
-                                               destColVal * destCol.g);
+            elem->color.r =(int)(startColVal * startCol.r +
+                                            destColVal * destCol.r);
 
-                elem->color.b =(int)(startColVal * startCol.b +
-                                               destColVal * destCol.b);
-            }
-        }
+            elem->color.g =(int)(startColVal * startCol.g +
+                                            destColVal * destCol.g);
 
-        if (advance)
-            mRainbowTime = tick_time;
+            elem->color.b =(int)(startColVal * startCol.b +
+                                            destColVal * destCol.b);
+        }
     }
 }
diff --git a/src/gui/palette.h b/src/gui/palette.h
index 41378a43..b81d8865 100644
--- a/src/gui/palette.h
+++ b/src/gui/palette.h
@@ -23,6 +23,8 @@
 #ifndef PALETTE_H
 #define PALETTE_H
 
+#include "utils/time.h"
+
 #include <guichan/color.hpp>
 
 #include <cstdlib>
@@ -121,8 +123,8 @@ class Palette
         static const gcn::Color RAINBOW_COLORS[];
         static const int RAINBOW_COLOR_COUNT;
 
-        /** Time tick, that gradient-type colors were updated the last time. */
-        int mRainbowTime;
+        /** Timer used when updating gradient-type colors. */
+        static Timer mRainbowTimer;
 
         using Palettes = std::set<Palette *>;
         static Palettes mInstances;
@@ -131,7 +133,7 @@ class Palette
 
         ~Palette();
 
-        void advanceGradient();
+        void advanceGradient(int advance);
 
         struct ColorElem
         {
@@ -147,7 +149,7 @@ class Palette
             int delay;
             int committedDelay;
 
-            void set(int type, gcn::Color &color, GradientType grad, int delay)
+            void set(int type, const gcn::Color &color, GradientType grad, int delay)
             {
                 ColorElem::type = type;
                 ColorElem::color = color;
diff --git a/src/gui/socialwindow.cpp b/src/gui/socialwindow.cpp
index 76235306..79a0fd53 100644
--- a/src/gui/socialwindow.cpp
+++ b/src/gui/socialwindow.cpp
@@ -262,7 +262,7 @@ private:
 class PlayerListTab : public SocialTab
 {
 public:
-    PlayerListTab() 
+    PlayerListTab()
     {
         mPlayerList = new PlayerList;
 
@@ -679,10 +679,10 @@ void SocialWindow::setPlayersOnline(const std::vector<Avatar*> &players)
 
 void SocialWindow::logic()
 {
-    if (mLastOnlineListUpdate == 0 || get_elapsed_time(mLastOnlineListUpdate) >= 18000)
+    if (mOnlineListUpdateTimer.passed())
     {
         Net::getChatHandler()->requestOnlineList();
-        mLastOnlineListUpdate = tick_time;
+        mOnlineListUpdateTimer.set(18000);
     }
 
     Window::logic();
diff --git a/src/gui/socialwindow.h b/src/gui/socialwindow.h
index b6865fb2..350f919c 100644
--- a/src/gui/socialwindow.h
+++ b/src/gui/socialwindow.h
@@ -21,6 +21,8 @@
 #ifndef SOCIALWINDOW_H
 #define SOCIALWINDOW_H
 
+#include "utils/time.h"
+
 #include "gui/widgets/window.h"
 
 #include <guichan/actionevent.hpp>
@@ -87,7 +89,7 @@ protected:
     void updateButtons();
 
     int mGuildInvited = 0;
-    int mLastOnlineListUpdate = 0;
+    Timer mOnlineListUpdateTimer;
     ConfirmDialog *mGuildAcceptDialog = nullptr;
     TextDialog *mGuildCreateDialog = nullptr;
 
diff --git a/src/gui/viewport.cpp b/src/gui/viewport.cpp
index cdc4076e..8dbdf7c7 100644
--- a/src/gui/viewport.cpp
+++ b/src/gui/viewport.cpp
@@ -79,8 +79,6 @@ void Viewport::setMap(Map *map)
 
 void Viewport::draw(gcn::Graphics *gcnGraphics)
 {
-    static int lastTick = tick_time;
-
     // Check whether map was successfully loaded since
     // the rest of this function relies on it
     if (!mMap || !local_player)
@@ -95,12 +93,6 @@ void Viewport::draw(gcn::Graphics *gcnGraphics)
 
     auto *graphics = static_cast<Graphics*>(gcnGraphics);
 
-    // Avoid freaking out when tick_time overflows
-    if (tick_time < lastTick)
-    {
-        lastTick = tick_time;
-    }
-
     // Calculate viewpoint
     int midTileX = (graphics->getWidth() + mScrollCenterOffsetX) / 2;
     int midTileY = (graphics->getHeight() + mScrollCenterOffsetX) / 2;
@@ -109,49 +101,57 @@ void Viewport::draw(gcn::Graphics *gcnGraphics)
     const int player_x = (int) playerPos.x - midTileX;
     const int player_y = (int) playerPos.y - midTileY;
 
-    if (mScrollLaziness < 1)
-        mScrollLaziness = 1; // Avoids division by zero
+    const float ticks = Time::deltaTimeMs() / static_cast<float>(MILLISECONDS_IN_A_TICK);
+    float scrollFraction = 1.0f;
 
-    while (lastTick < tick_time)
+    if (mScrollLaziness > 1)
     {
-        // Apply lazy scrolling
-        if (player_x > mPixelViewX + mScrollRadius)
-        {
-            mPixelViewX += (player_x - mPixelViewX - mScrollRadius) /
-                            mScrollLaziness;
-        }
-        if (player_x < mPixelViewX - mScrollRadius)
-        {
-            mPixelViewX += (player_x - mPixelViewX + mScrollRadius) /
-                            mScrollLaziness;
-        }
-        if (player_y > mPixelViewY + mScrollRadius)
-        {
-            mPixelViewY += (player_y - mPixelViewY - mScrollRadius) /
-                            mScrollLaziness;
-        }
-        if (player_y < mPixelViewY - mScrollRadius)
-        {
-            mPixelViewY += (player_y - mPixelViewY + mScrollRadius) /
-                            mScrollLaziness;
-        }
+        // mScrollLaziness defines the fraction of the desired camera movement
+        // that is applied every 10ms. To make this work independently of the
+        // frame duration, we calculate the actual scroll fraction based on the
+        // time delta.
+        scrollFraction = 1.0f - std::pow(1.0f - 1.0f / mScrollLaziness, ticks);
+    }
+
+    // Apply lazy scrolling
+    if (player_x > mPixelViewX + mScrollRadius)
+    {
+        mPixelViewX += (player_x - mPixelViewX - mScrollRadius) *
+                        scrollFraction;
+    }
+    if (player_x < mPixelViewX - mScrollRadius)
+    {
+        mPixelViewX += (player_x - mPixelViewX + mScrollRadius) *
+                        scrollFraction;
+    }
+    if (player_y > mPixelViewY + mScrollRadius)
+    {
+        mPixelViewY += (player_y - mPixelViewY - mScrollRadius) *
+                        scrollFraction;
+    }
+    if (player_y < mPixelViewY - mScrollRadius)
+    {
+        mPixelViewY += (player_y - mPixelViewY + mScrollRadius) *
+                        scrollFraction;
+    }
+
+    // manage shake effect
+    for (auto i = mShakeEffects.begin(); i != mShakeEffects.end(); i++)
+    {
+        // The decay defines the reduction in amplitude per 10ms. Here
+        // we calculate the reduction based on the ticks.
+        const float decay = std::pow(i->decay, ticks);
+
+        // apply the effect to viewport
+        mPixelViewX += i->x *= -decay;
+        mPixelViewY += i->y *= -decay;
 
-        // manage shake effect
-        for (auto i = mShakeEffects.begin();
-             i != mShakeEffects.end();
-             i++)
+        // check death conditions
+        if (std::abs(i->x) + std::abs(i->y) < 1.0f ||
+            (i->timer.isSet() && i->timer.passed()))
         {
-            // apply the effect to viewport
-            mPixelViewX += i->x *= -i->decay;
-            mPixelViewY += i->y *= -i->decay;
-            // check death conditions
-            if (abs(i->x) + abs(i->y) < 1.0f ||
-                (i->duration > 0 && --i->duration == 0))
-            {
-                i = mShakeEffects.erase(i);
-            }
+            i = mShakeEffects.erase(i);
         }
-        lastTick++;
     }
 
     // Auto center when player is off screen
@@ -264,7 +264,9 @@ void Viewport::shakeScreen(float x, float y, float decay, unsigned duration)
     effect.x = x;
     effect.y = y;
     effect.decay = decay;
-    effect.duration = duration;
+
+    if (duration > 0)
+        effect.timer.set(duration * MILLISECONDS_IN_A_TICK);
 }
 
 void Viewport::logic()
@@ -528,9 +530,9 @@ void Viewport::mouseDragged(gcn::MouseEvent &event)
 
     if (mPlayerFollowMouse && !event.isShiftPressed())
     {
-        if (get_elapsed_time(mLocalWalkTime) >= walkingMouseDelay)
+        if (mLocalWalkTimer.passed())
         {
-            mLocalWalkTime = tick_time;
+            mLocalWalkTimer.set(walkingMouseDelay);
             local_player->setDestination(event.getX() + (int) mPixelViewX,
                                          event.getY() + (int) mPixelViewY);
             local_player->pathSetByMouse();
diff --git a/src/gui/viewport.h b/src/gui/viewport.h
index 32d9bd5c..53edb50f 100644
--- a/src/gui/viewport.h
+++ b/src/gui/viewport.h
@@ -25,6 +25,8 @@
 #include "eventlistener.h"
 #include "position.h"
 
+#include "utils/time.h"
+
 #include "gui/widgets/windowcontainer.h"
 
 #include <guichan/mouselistener.hpp>
@@ -207,15 +209,15 @@ class Viewport : public WindowContainer, public gcn::MouseListener,
             float x;
             float y;
             float decay;
-            unsigned duration;
+            Timer timer;
         };
         std::list<ShakeEffect> mShakeEffects;
 
         bool mPlayerFollowMouse = false;
 
-        int mLocalWalkTime = -1; /**< Timestamp before the next walk can be sent. */
+        Timer mLocalWalkTimer;      /**< Timer for sending walk messages. */
 
-        PopupMenu *mPopupMenu;       /**< Popup menu. */
+        PopupMenu *mPopupMenu;              /**< Popup menu. */
         Being *mHoverBeing = nullptr;       /**< Being mouse is currently over. */
         FloorItem *mHoverItem = nullptr;    /**< FloorItem mouse is currently over. */
         BeingPopup *mBeingPopup;            /**< Being information popup. */
diff --git a/src/gui/widgets/browserbox.cpp b/src/gui/widgets/browserbox.cpp
index 40c9b66a..9eee9448 100644
--- a/src/gui/widgets/browserbox.cpp
+++ b/src/gui/widgets/browserbox.cpp
@@ -22,8 +22,6 @@
 
 #include "gui/widgets/browserbox.h"
 
-#include "client.h"
-
 #include "gui/gui.h"
 #include "gui/truetypefont.h"
 #include "gui/widgets/linkhandler.h"
@@ -32,6 +30,8 @@
 #include "resources/iteminfo.h"
 #include "resources/theme.h"
 
+#include "utils/stringutils.h"
+
 #include <guichan/graphics.hpp>
 #include <guichan/font.hpp>
 #include <guichan/cliprectangle.hpp>
@@ -276,7 +276,7 @@ void BrowserBox::relayoutText()
         layoutTextRow(row, context);
 
     mLastLayoutWidth = getWidth();
-    mLastLayoutTime = tick_time;
+    mLayoutTimer.set(100);
     setHeight(context.y);
 }
 
@@ -507,7 +507,7 @@ void BrowserBox::maybeRelayoutText()
 {
     // Reduce relayouting frequency when there is a lot of text
     if (mTextRows.size() > 100)
-        if (mLastLayoutTime && std::abs(mLastLayoutTime - tick_time) < 10)
+        if (!mLayoutTimer.passed())
             return;
 
     relayoutText();
diff --git a/src/gui/widgets/browserbox.h b/src/gui/widgets/browserbox.h
index d7ff0428..7278bb59 100644
--- a/src/gui/widgets/browserbox.h
+++ b/src/gui/widgets/browserbox.h
@@ -23,6 +23,8 @@
 #ifndef BROWSERBOX_H
 #define BROWSERBOX_H
 
+#include "utils/time.h"
+
 #include <guichan/mouselistener.hpp>
 #include <guichan/widget.hpp>
 
@@ -193,7 +195,7 @@ class BrowserBox : public gcn::Widget,
         std::optional<BrowserLink> mHoveredLink;
         unsigned int mMaxRows = 0;
         int mLastLayoutWidth = 0;
-        int mLastLayoutTime = -1;
+        Timer mLayoutTimer;
 };
 
 #endif
diff --git a/src/localplayer.cpp b/src/localplayer.cpp
index c6031e49..a7969fc3 100644
--- a/src/localplayer.cpp
+++ b/src/localplayer.cpp
@@ -21,7 +21,6 @@
 
 #include "localplayer.h"
 
-#include "client.h"
 #include "configuration.h"
 #include "event.h"
 #include "flooritem.h"
@@ -50,7 +49,10 @@
 #include "utils/gettext.h"
 #include "utils/stringutils.h"
 
-const int AWAY_LIMIT_TIMER = 60;
+constexpr unsigned AWAY_MESSAGE_TIMEOUT = 60 * 1000;
+
+// Actions are allowed at 5.5 per second
+constexpr unsigned ACTION_TIMEOUT = 182;
 
 LocalPlayer *local_player = nullptr;
 
@@ -75,10 +77,6 @@ LocalPlayer::~LocalPlayer()
 
 void LocalPlayer::logic()
 {
-    // Actions are allowed at 5.5 per second
-    if (get_elapsed_time(mLastActionTime) >= 182)
-        mLastActionTime = -1;
-
     // Show XP messages
     if (!mMessages.empty())
     {
@@ -101,10 +99,6 @@ void LocalPlayer::logic()
 
     PlayerInfo::logic();
 
-    // Targeting allowed 4 times a second
-    if (get_elapsed_time(mLastTargetTime) >= 250)
-        mLastTargetTime = -1;
-
     if (mTarget)
     {
         ActorSprite::Type targetType = mTarget->getType();
@@ -173,7 +167,7 @@ void LocalPlayer::setAction(Action action, int attackId)
 {
     if (action == DEAD)
     {
-        mLastTargetTime = -1;
+        mLastTargetTimer.reset();
         setTarget(nullptr);
     }
 
@@ -625,24 +619,18 @@ Being *LocalPlayer::getTarget() const
 
 void LocalPlayer::setTarget(Being *target)
 {
-    if ((mLastTargetTime != -1 || target == this) && target)
+    if ((!mLastTargetTimer.passed() || target == this) && target)
         return;
 
+    // Targeting allowed 4 times a second
     if (target)
-        mLastTargetTime = tick_time;
+        mLastTargetTimer.set(250);
 
     if (target == mTarget)
         return;
 
-    if (target || mAction == ATTACK)
-    {
-        mTargetTime = tick_time;
-    }
-    else
-    {
+    if (!target && mAction != ATTACK)
         mKeepAttacking = false;
-        mTargetTime = -1;
-    }
 
     Being *oldTarget = nullptr;
     if (mTarget)
@@ -793,9 +781,9 @@ void LocalPlayer::stopWalking(bool sendToServer)
 
 void LocalPlayer::toggleSit()
 {
-    if (mLastActionTime != -1)
+    if (!mLastActionTimer.passed())
         return;
-    mLastActionTime = tick_time;
+    mLastActionTimer.set(ACTION_TIMEOUT);
 
     Being::Action newAction;
     switch (mAction)
@@ -810,16 +798,16 @@ void LocalPlayer::toggleSit()
 
 void LocalPlayer::emote(int emoteId)
 {
-    if (mLastActionTime != -1)
+    if (!mLastActionTimer.passed())
         return;
-    mLastActionTime = tick_time;
+    mLastActionTimer.set(ACTION_TIMEOUT);
 
     Net::getPlayerHandler()->emote(emoteId);
 }
 
 void LocalPlayer::attack(Being *target, bool keep)
 {
-    if (mLastActionTime != -1)
+    if (!mLastActionTimer.passed())
         return;
 
     // Can only attack when standing still
@@ -830,23 +818,23 @@ void LocalPlayer::attack(Being *target, bool keep)
         return;
 
     // Can't attack more times than its attack speed
-    static int lastAttackTime = 0;
-    if (get_elapsed_time(lastAttackTime) < mAttackSpeed)
+    static Timer lastAttackTimer;
+    if (!lastAttackTimer.passed())
         return;
 
-    lastAttackTime = tick_time;
+    lastAttackTimer.set(mAttackSpeed);
 
     mKeepAttacking = keep;
 
     if (mTarget != target || !mTarget)
     {
-        mLastTargetTime = -1;
+        mLastTargetTimer.reset();
         setTarget(target);
     }
 
     lookAt(mTarget->getPosition());
 
-    mLastActionTime = tick_time;
+    mLastActionTimer.set(ACTION_TIMEOUT);
 
     setAction(ATTACK);
 
@@ -872,7 +860,7 @@ void LocalPlayer::stopAttack()
             setAction(STAND);
         setTarget(nullptr);
     }
-    mLastTargetTime = -1;
+    mLastTargetTimer.reset();
     cancelGoToTarget();
 }
 
@@ -964,7 +952,7 @@ void LocalPlayer::setGotoTarget(Being *target)
     if (!target)
         return;
 
-    mLastTargetTime = -1;
+    mLastTargetTimer.reset();
 
     setTarget(target);
     mGoingToTarget = true;
@@ -1039,7 +1027,8 @@ void LocalPlayer::event(Event::Channel channel, const Event &event)
 void LocalPlayer::changeAwayMode()
 {
     mAwayMode = !mAwayMode;
-    mAfkTime = 0;
+    mAfkTimer.reset();
+
     if (mAwayMode)
     {
         mAwayDialog = new OkDialog(_("Away"),
@@ -1061,9 +1050,7 @@ void LocalPlayer::afkRespond(ChatTab *tab, const std::string &nick)
 {
     if (mAwayMode)
     {
-        if (mAfkTime == 0
-            || cur_time < mAfkTime
-            || cur_time - mAfkTime > AWAY_LIMIT_TIMER)
+        if (mAfkTimer.passed())
         {
             std::string msg = "*AFK*: "
                     + config.getValue("afkMessage", "I am away from keyboard");
@@ -1078,7 +1065,8 @@ void LocalPlayer::afkRespond(ChatTab *tab, const std::string &nick)
             {
                 tab->chatLog(getName(), msg);
             }
-            mAfkTime = cur_time;
+
+            mAfkTimer.set(AWAY_MESSAGE_TIMEOUT);
         }
     }
 }
diff --git a/src/localplayer.h b/src/localplayer.h
index 4e3bbc88..9d844339 100644
--- a/src/localplayer.h
+++ b/src/localplayer.h
@@ -26,6 +26,8 @@
 
 #include "resources/userpalette.h"
 
+#include "utils/time.h"
+
 #include <guichan/actionlistener.hpp>
 
 class ChatTab;
@@ -217,9 +219,7 @@ class LocalPlayer final : public Being
 
         int mAttackRange = -1;
 
-        int mTargetTime = -1;   /**< How long the being has been targeted **/
-        /** Time stamp of last targeting action, -1 if none. */
-        int mLastTargetTime = -1;
+        Timer mLastTargetTimer; /**< Timer for last targeting action. */
 
         int mGMLevel = 0;
 
@@ -229,7 +229,7 @@ class LocalPlayer final : public Being
 
         bool mGoingToTarget = false;
         bool mKeepAttacking = false;    /**< Whether or not to continue to attack */
-        int mLastActionTime = -1;       /**< Time stamp of the last action, -1 if none. */
+        Timer mLastActionTimer;         /**< Timeout for the last action. */
         int mWalkingDir = 0;            /**< The direction the player is walking in. */
         bool mPathSetByMouse = false;   /**< Tells if the path was set using mouse */
 
@@ -241,7 +241,7 @@ class LocalPlayer final : public Being
 
         AwayListener *mAwayListener;
         OkDialog *mAwayDialog = nullptr;
-        int mAfkTime = 0;
+        Timer mAfkTimer;
         bool mAwayMode = false;
 };
 
diff --git a/src/map.cpp b/src/map.cpp
index e9d29b61..c4e4c3be 100644
--- a/src/map.cpp
+++ b/src/map.cpp
@@ -22,7 +22,6 @@
 #include "map.h"
 
 #include "actorspritemanager.h"
-#include "client.h"
 #include "configuration.h"
 #include "graphics.h"
 #include "log.h"
@@ -34,6 +33,8 @@
 #include "resources/image.h"
 #include "resources/resourcemanager.h"
 
+#include "utils/time.h"
+
 #include "net/net.h"
 
 #include "utils/dtor.h"
@@ -247,8 +248,8 @@ void Map::initializeAmbientLayers()
         {
             auto &ambientLayer = list.emplace_back(img);
             ambientLayer.mParallax = getFloatProperty(name + "parallax");
-            ambientLayer.mSpeedX = getFloatProperty(name + "scrollX");
-            ambientLayer.mSpeedY = getFloatProperty(name + "scrollY");
+            ambientLayer.mSpeedX = getFloatProperty(name + "scrollX") / MILLISECONDS_IN_A_TICK;
+            ambientLayer.mSpeedY = getFloatProperty(name + "scrollY") / MILLISECONDS_IN_A_TICK;
             ambientLayer.mMask = getIntProperty(name + "mask", 1);
             ambientLayer.mKeepRatio = getBoolProperty(name + "keepratio");
         }
@@ -433,8 +434,6 @@ void Map::drawCollision(Graphics *graphics, int scrollX, int scrollY,
 
 void Map::updateAmbientLayers(float scrollX, float scrollY)
 {
-    static int lastTick = tick_time; // static = only initialized at first call
-
     if (mLastScrollX == 0.0f && mLastScrollY == 0.0f)
     {
         // First call - initialisation
@@ -445,25 +444,23 @@ void Map::updateAmbientLayers(float scrollX, float scrollY)
     // Update Overlays
     float dx = scrollX - mLastScrollX;
     float dy = scrollY - mLastScrollY;
-    int timePassed = get_elapsed_time(lastTick);
 
     for (auto &background : mBackgrounds)
     {
         if ((background.mMask & mMask) == 0)
             continue;
 
-        background.update(timePassed, dx, dy);
+        background.update(Time::deltaTimeMs(), dx, dy);
     }
     for (auto &foreground : mForegrounds)
     {
         if ((foreground.mMask & mMask) == 0)
             continue;
 
-        foreground.update(timePassed, dx, dy);
+        foreground.update(Time::deltaTimeMs(), dx, dy);
     }
     mLastScrollX = scrollX;
     mLastScrollY = scrollY;
-    lastTick = tick_time;
 }
 
 void Map::drawAmbientLayers(Graphics *graphics, LayerType type,
diff --git a/src/net/tmwa/playerhandler.cpp b/src/net/tmwa/playerhandler.cpp
index 431137fd..c9baf27b 100644
--- a/src/net/tmwa/playerhandler.cpp
+++ b/src/net/tmwa/playerhandler.cpp
@@ -40,8 +40,9 @@
 #include "net/tmwa/messageout.h"
 #include "net/tmwa/protocol.h"
 
-#include "utils/stringutils.h"
 #include "utils/gettext.h"
+#include "utils/stringutils.h"
+#include "utils/time.h"
 
 extern OkDialog *weightNotice;
 extern OkDialog *deathNotice;
@@ -563,17 +564,17 @@ void PlayerHandler::increaseSkill(int skillId)
 
 void PlayerHandler::pickUp(FloorItem *floorItem)
 {
-    static Uint32 lastTime = 0;
+    static Timer lastPickupTimer;
 
     // Avoid spamming the server with pick-up requests to prevent the player
     // from being kicked.
-    if (!floorItem || SDL_GetTicks() < lastTime + 100)
+    if (!floorItem || !lastPickupTimer.passed())
         return;
 
     MessageOut outMsg(CMSG_ITEM_PICKUP);
     outMsg.writeInt32(floorItem->getId());
 
-    lastTime = SDL_GetTicks();
+    lastPickupTimer.set(100);
 }
 
 void PlayerHandler::setDirection(char direction)
diff --git a/src/resources/ambientlayer.cpp b/src/resources/ambientlayer.cpp
index b292070b..a238afcc 100644
--- a/src/resources/ambientlayer.cpp
+++ b/src/resources/ambientlayer.cpp
@@ -34,8 +34,8 @@ AmbientLayer::~AmbientLayer() = default;
 void AmbientLayer::update(int timePassed, float dx, float dy)
 {
     // Self scrolling of the overlay
-    mPosX -= mSpeedX * timePassed / 10;
-    mPosY -= mSpeedY * timePassed / 10;
+    mPosX -= mSpeedX * timePassed;
+    mPosY -= mSpeedY * timePassed;
 
     // Parallax scrolling
     mPosX += dx * mParallax;
diff --git a/src/resources/userpalette.h b/src/resources/userpalette.h
index 93056867..6eba44b2 100644
--- a/src/resources/userpalette.h
+++ b/src/resources/userpalette.h
@@ -90,7 +90,7 @@ class UserPalette : public Palette, public gcn::ListModel
          * @param type the color type requested
          * @param color the color that should be tested
          */
-        void setTestColor(int type, gcn::Color color)
+        void setTestColor(int type, const gcn::Color &color)
         {
             mColors[type].testColor = color;
         }
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);
+}
diff --git a/src/utils/time.h b/src/utils/time.h
new file mode 100644
index 00000000..ac7cd351
--- /dev/null
+++ b/src/utils/time.h
@@ -0,0 +1,106 @@
+/*
+ *  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/>.
+ */
+
+ #ifndef UTILS_TIME_H
+ #define UTILS_TIME_H
+
+#include <cstdint>
+
+/**
+ * The amount of milliseconds in a logic tick.
+ */
+static constexpr unsigned MILLISECONDS_IN_A_TICK = 10;
+
+namespace Time
+{
+
+/**
+ * The time in milliseconds since the program started (wraps around after ~49
+ * days).
+ */
+uint32_t absoluteTimeMs();
+
+/**
+ * The time in milliseconds since the last frame, maximized to 1000ms.
+ */
+unsigned deltaTimeMs();
+
+/**
+ * Called at the start of each frame, updates the above variables.
+ */
+void beginFrame();
+
+} // namespace Time
+
+/**
+ * Simple timer that can be used to check if a certain amount of time
+ * has passed.
+ */
+class Timer
+{
+public:
+    Timer() = default;
+
+    /**
+     * Sets the timer with an optional duration in milliseconds.
+     */
+    void set(uint32_t ms = 0)
+    { mTimeout = Time::absoluteTimeMs() + ms; }
+
+    /**
+     * Reset the timer.
+     */
+    void reset()
+    { mTimeout = 0; }
+
+    /**
+     * Returns whether the timer has been set.
+     */
+    bool isSet() const
+    { return mTimeout != 0; }
+
+    /**
+     * Returns whether the timer has passed.
+     * A timer that wasn't set will always return true.
+     */
+    bool passed() const
+    { return elapsed() >= 0; }
+
+    /**
+     * Extend the timer by the given number of milliseconds.
+     */
+    void extend(uint32_t ms)
+    { mTimeout += ms; }
+
+    /**
+     * Returns the number of milliseconds elapsed since the set time, or a
+     * negative value if the timer hasn't passed.
+     *
+     * Due to wrapping, this function is not suitable for measuring long
+     * periods of time (tens of days).
+     */
+    int32_t elapsed() const;
+
+private:
+    uint32_t mTimeout = 0;
+};
+
+#endif // UTILS_TIME_H