# HG changeset patch
# User Matti Hamalainen <ccr@tnsp.org>
# Date 1604160857 -7200
# Node ID ff739727dfec322c0c5bc0e53b6cdc976862f038
# Parent  8b34eab13549448c1d04a9ba7bf66f763ef05b99
Compute and display frametime jitter values.

diff -r 8b34eab13549 -r ff739727dfec gldragon.cpp
--- a/gldragon.cpp	Sun Oct 18 14:15:07 2020 +0300
+++ b/gldragon.cpp	Sat Oct 31 18:14:17 2020 +0200
@@ -94,6 +94,8 @@
 
 int main(int argc, char *argv[])
 {
+    int frameDeltas[SET_FRAMES + 1];
+
     bool
         exitFlag = false,
         pauseFlag = false,
@@ -114,6 +116,8 @@
         totalTime = 0,
         totalFrames = 0;
 
+    memset(&frameDeltas, 0, sizeof(frameDeltas));
+
     // Check commandline argument for enabling shaders
     for (int narg = 1; narg < argc; narg++)
     {
@@ -350,6 +354,7 @@
 
         frameDelta = frameEnd - frameStart;
 
+
         // Return true if a full rotation was done
         if (!pauseFlag)
         {
@@ -359,11 +364,30 @@
             cycleTime += frameDelta;
             totalTime += frameDelta;
 
+            memmove(&frameDeltas[0], &frameDeltas[1], sizeof(frameDeltas[0]) * (SET_FRAMES - 1));
+            frameDeltas[SET_FRAMES - 1] = frameDelta;
+
             if (cycleFrames >= SET_FRAMES)
             {
+                float avgCycleFrame = cycleTime / SET_FRAMES;
+                float maxJitter = 0, avgJitter = 0;
+
+                for (int n = 0; n < SET_FRAMES; n++)
+                {
+                    float mjitter = fabs(avgCycleFrame - frameDeltas[n]);
+                    if (mjitter > maxJitter)
+                        maxJitter = mjitter;
+                    avgJitter += mjitter;
+                }
+
+                avgJitter /= SET_FRAMES;
+
                 // Print the current frames per second
-                printf("%d ms for %d frames = %.1lf FPS\n",
-                    cycleTime, cycleFrames, (cycleFrames * 1000.0f) / cycleTime);
+                printf("%d ms for %d frames = %.1lf FPS [framejitter %.1lf ms avg, %.1lf ms max]\n",
+                    cycleTime, cycleFrames,
+                    (cycleFrames * 1000.0f) / cycleTime,
+                    avgJitter, maxJitter
+                    );
 
                 // Reset cycleFrames
                 cycleFrames = 0;