From 13ccfb3728eb3dc3a6a5294a8f8754b3c5cbc903 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Sat, 2 Nov 2024 19:36:40 -0400
Subject: frame pacing

---
 balls.c  | 29 +++++++++++++++++++++++++----
 balls.cl |  4 ++--
 2 files changed, 27 insertions(+), 6 deletions(-)

diff --git a/balls.c b/balls.c
index 8d85a89..384f7c1 100644
--- a/balls.c
+++ b/balls.c
@@ -28,7 +28,13 @@
 #define RMAX 0.10 /* Maximum radius. */
 #define VMAX_INIT 0.05 /* Maximum initial velocity. */
 
-enum { WIDTH = 640, HEIGHT = 480 };
+enum {
+	WIDTH = 640,
+	HEIGHT = 640,
+	FPS = 60,
+	MS_PER_S = 1000,
+	FRAME_TIME_MS = MS_PER_S / FPS,
+ };
 enum { KEY_QUIT = 'q' };
 enum { NBALLS_DEFAULT = 3 };
 enum {
@@ -49,6 +55,7 @@ void genVertexBuffer(void);
 void setColors(void);
 void configSharedData(void);
 void setKernelArgs(void);
+void animate(int v);
 void display(void);
 void reshape(int w, int h);
 void keyboard(unsigned char key, int x, int y);
@@ -102,6 +109,7 @@ main(int argc, char *argv[]) {
 	glutDisplayFunc(display);
 	glutReshapeFunc(reshape);
 	glutKeyboardFunc(keyboard);
+	glutTimerFunc(0, animate, 0);
 
 	glutMainLoop();
 
@@ -397,13 +405,27 @@ setKernelArgs(void) {
 }
 
 void
-display(void) {
-	int i;
+animate(int v) {
+	clock_t tstart, elapsed;
+	unsigned int nextFrame;
+
+	tstart = clock();
 
 	move();
 	collideBalls();
 	collideWalls();
 
+	display();
+
+	elapsed = (clock() - tstart) / (CLOCKS_PER_SEC / MS_PER_S);
+	nextFrame = (elapsed > FRAME_TIME_MS) ? 0 : FRAME_TIME_MS-elapsed;
+	glutTimerFunc(nextFrame, animate, 0);
+}
+
+void
+display(void) {
+	int i;
+
 	glClear(GL_COLOR_BUFFER_BIT |GL_DEPTH_BUFFER_BIT);
 
 	genVertices();
@@ -416,7 +438,6 @@ display(void) {
 	frameCount();
 
 	glutSwapBuffers();
-	glutPostRedisplay();
 }
 
 void
diff --git a/balls.cl b/balls.cl
index 6d015fb..05d155c 100644
--- a/balls.cl
+++ b/balls.cl
@@ -1,5 +1,5 @@
-#define G_FACTOR 3600.0f
-#define G (9.81f / G_FACTOR)
+#define FPS 60.0f
+#define G (9.81f / FPS / FPS)
 #define DENSITY 1500.0f
 
 float mass(float radius);
-- 
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