From 5d5875499f8f471d8748b6e04c1438edc9963bb9 Mon Sep 17 00:00:00 2001
From: Paul Duncan <pabs@pablotron.org>
Date: Thu, 11 May 2017 16:48:57 -0400
Subject: add fps timer, openmp

---
 Makefile |  4 ++--
 main.c   | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 78 insertions(+), 5 deletions(-)

diff --git a/Makefile b/Makefile
index 46cebbd..f0f7b3a 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
-CFLAGS=-std=c11 -W -Wall -pedantic -O2
+CFLAGS=-std=c11 -fopenmp -W -Wall -pedantic -O2
 APP=compute-test
-LIBS=-lSDL2 -lGLEW -lGL
+LIBS=-fopenmp -lSDL2 -lGLEW -lGL
 OBJS=main.o
 
 .PHONY=all clean test
diff --git a/main.c b/main.c
index 79a9d58..76811ec 100644
--- a/main.c
+++ b/main.c
@@ -7,6 +7,12 @@
 
 #define UNUSED(a) ((void) (a))
 
+// number of time records to keep (must be power of two - 1)
+#define MAX_TIMES 0xFF
+
+// custom SDL_USEREVENT code for timer
+#define EVENT_CODE_TIMER 0
+
 static const float
 verts[] = {
   -0.5,  0.5, 0,
@@ -112,7 +118,7 @@ link_compute_program(
 
 static SDL_Window *
 init(void) {
-  if (SDL_Init(SDL_INIT_VIDEO) < 0) {
+  if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_TIMER) < 0) {
     SDL_Log("SDL_Init() failed: %s", SDL_GetError());
     exit(EXIT_FAILURE);
   }
@@ -182,12 +188,42 @@ init(void) {
   return win;
 }
 
+static Uint32 timer_cb(
+  Uint32 interval,
+  void *arg
+) {
+  SDL_Event ev;
+  UNUSED(arg);
+
+  ev.type = SDL_USEREVENT;
+  ev.user.type = SDL_USEREVENT;
+  ev.user.code = EVENT_CODE_TIMER;
+  ev.user.data1 = NULL;
+  ev.user.data2 = NULL;
+
+  SDL_PushEvent(&ev);
+
+  // return interval
+  return interval;
+}
+
 int main(int argc, char *argv[]) {
   UNUSED(argc);
   UNUSED(argv);
 
+  // init SDL
   SDL_Window *win = init();
 
+  // init times ring buffer
+  struct {
+    uint32_t draw_start,
+             draw_end;
+  } times[MAX_TIMES] = { { 0, 0 } };
+  uint32_t times_ofs = 0;
+
+  // init timer (5 seconds)
+  SDL_TimerID timer_id = SDL_AddTimer(5000, timer_cb, NULL);
+
   // generate vertex array
   GLuint vao;
   glGenVertexArrays(1, &vao);
@@ -209,16 +245,24 @@ int main(int argc, char *argv[]) {
   GLuint prog = link_render_program(vs_src, fs_src);
   GLint u_time = glGetUniformLocation(prog, "time");
 
-  // main loop
+  // init flags
   bool done = false, fullscreen = false;
+
+  // main loop
   while (!done) {
+    // get start time
+    uint32_t now = SDL_GetTicks();
+
+    // save start time
+    times[times_ofs].draw_start = now;
+
     // clear screen
     glClearColor(0, 0, 0, 1);
     glClear(GL_COLOR_BUFFER_BIT);
 
     // use program, set uniform
     glUseProgram(prog);
-    glUniform1f(u_time, SDL_GetTicks() / 1000.0);
+    glUniform1f(u_time, now / 1000.0);
 
     // draw
     glBindVertexArray(vao);
@@ -228,6 +272,10 @@ int main(int argc, char *argv[]) {
     // swap buffer
     SDL_GL_SwapWindow(win);
 
+    // save end time
+    times[times_ofs].draw_end = SDL_GetTicks();
+    times_ofs = (times_ofs + 1) & MAX_TIMES;
+
     // handle events
     {
       SDL_Event ev;
@@ -267,12 +315,37 @@ int main(int argc, char *argv[]) {
             break;
           }
 
+          break;
+        case SDL_USEREVENT:
+          if (ev.user.code == EVENT_CODE_TIMER) {
+            uint32_t sum = 0;
+
+            #pragma omp parallel for reduction(+:sum)
+            for (int i = 0; i < MAX_TIMES; i++) {
+              sum += times[i].draw_end - times[i].draw_start;
+            }
+
+            // print fps
+            SDL_Log("fps: %f", sum * 1.0 / MAX_TIMES);
+          }
+
           break;
         }
       }
     }
   }
 
+  // remove timer
+  if (SDL_RemoveTimer(timer_id) == SDL_FALSE) {
+    SDL_Log("SDL_RemoveTimer() failed");
+  }
+
+  // delete GL context
+  SDL_GLContext context = SDL_GL_GetCurrentContext();
+  if (context) {
+    SDL_GL_DeleteContext(context);
+  }
+
   // destroy window
   SDL_DestroyWindow(win);
 
-- 
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