delta time 60/90/120 Hz fix

FlappyBird/app/src/main/jni/init.c

@@ -9,10 +9,6 @@
 #include "audio.h"
 #include "game.h"
 
-#include <time.h>
-
-struct timespec lastFrameTime;
-double deltaTime = 0.0f;
 
 bool                 g_Initialized = false;
 EGLDisplay           g_EglDisplay = EGL_NO_DISPLAY;
@@ -155,57 +151,24 @@ void Init(struct android_app* app)
     gColorHandle = glGetUniformLocation(colorProgram, "u_Color");
 
 
-    clock_gettime(CLOCK_MONOTONIC, &lastFrameTime);
-
     Log("FlappyBird is loaded!");
 
     g_Initialized = true;
 }
 
-void Update()
-{
-    struct timespec currentTime;
-    clock_gettime(CLOCK_MONOTONIC, &currentTime);
-
-    deltaTime = (currentTime.tv_sec - lastFrameTime.tv_sec) + (currentTime.tv_nsec - lastFrameTime.tv_nsec) / 1e9;
-    lastFrameTime = currentTime;
-}
-
 void MainLoopStep()
 {
     if (g_EglDisplay == EGL_NO_DISPLAY)
         return;
 
-    static struct timespec lastFrameTime = { 0, 0 };
-    struct timespec currentFrameTime;
-    clock_gettime(CLOCK_MONOTONIC, &currentFrameTime);
-
-    if (lastFrameTime.tv_sec != 0 || lastFrameTime.tv_nsec != 0)
-    {
-        deltaTime = (currentFrameTime.tv_sec - lastFrameTime.tv_sec) +
-            (currentFrameTime.tv_nsec - lastFrameTime.tv_nsec) / 1e9;
-    }
-
     // Setup display size (every frame to accommodate for window resizing)
     glViewport(0, 0, (int)WindowSizeX, (int)WindowSizeY);
     glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
     glClear(GL_COLOR_BUFFER_BIT);
 
-    Update();
     Render();
 
     eglSwapBuffers(g_EglDisplay, g_EglSurface);
-
-    lastFrameTime = currentFrameTime;
-
-    double frameDuration = deltaTime;
-    if (frameDuration < 1.0 / 60.0)
-    {
-        struct timespec sleepTime;
-        sleepTime.tv_sec = 0;
-        sleepTime.tv_nsec = (1.0 / 60.0 - frameDuration) * 1e9;
-        nanosleep(&sleepTime, NULL);
-    }
 }
 
 void Shutdown()

FlappyBird/app/src/main/jni/main.c

@@ -59,6 +59,11 @@ void handle_input(struct android_app* app, AInputEvent* event)
     }
 }
 
+#define TARGET_FPS 60
+#define TARGET_FRAME_TIME (1.0f / TARGET_FPS)
+
+double g_Time = 0.0;
+float DeltaTime = 0.0f;
 
 void android_main(struct android_app* state)
 {
@@ -85,8 +90,31 @@ void android_main(struct android_app* state)
             }
         }
 
-        if (g_Initialized) 
+        if (g_Initialized)
         {
+            struct timespec current_timespec;
+            clock_gettime(CLOCK_MONOTONIC, &current_timespec);
+            double current_time = (double)(current_timespec.tv_sec) + (current_timespec.tv_nsec / 1000000000.0);
+            DeltaTime = g_Time > 0.0 ? (float)(current_time - g_Time) : (float)(1.0f / 60.0f);
+
+            // fps limit
+            if (DeltaTime < TARGET_FRAME_TIME) 
+            {
+                // calc time wait
+                double sleep_time = TARGET_FRAME_TIME - DeltaTime;
+                struct timespec sleep_spec;
+                sleep_spec.tv_sec = (time_t)sleep_time;
+                sleep_spec.tv_nsec = (long)((sleep_time - sleep_spec.tv_sec) * 1000000000.0);
+                nanosleep(&sleep_spec, NULL);
+
+                // update now time after wait
+                clock_gettime(CLOCK_MONOTONIC, &current_timespec);
+                current_time = (double)(current_timespec.tv_sec) + (current_timespec.tv_nsec / 1000000000.0);
+                DeltaTime = (float)(current_time - g_Time);
+            }
+
+            g_Time = current_time;
+
             MainLoopStep();
             MouseReset(&mouse);
         }