From d8c96b82fa68bdc5b3a89780d0d2178a329f3293 Mon Sep 17 00:00:00 2001
From: Shaun Inman <shaun@panic.com>
Date: Fri, 13 Jan 2023 20:12:47 -0500
Subject: [PATCH] only wait for vsync if under frame budget

---
 src/common/api.c   | 18 +++++++++++-------
 src/common/api.h   |  1 +
 src/minarch/main.c |  1 +
 src/minui/main.c   | 11 +++++++----
 4 files changed, 20 insertions(+), 11 deletions(-)

diff --git a/src/common/api.c b/src/common/api.c
index 11f38ed..fee0de9 100644
--- a/src/common/api.c
+++ b/src/common/api.c
@@ -192,18 +192,22 @@ void GFX_clearAll(void) {
 	memset(gfx.map, 0, gfx.map_size);
 }
 
+static int frame_start = 0;
+void GFX_startFrame(void) {
+	frame_start = SDL_GetTicks();
+}
 void GFX_flip(SDL_Surface* screen) {
+	static int ticks = 0;
+	ticks += 1;
 #ifdef GFX_ENABLE_VSYNC
-	int arg = 1;
-	ioctl(gfx.fb, OWLFB_WAITFORVSYNC, &arg); // TODO: this doesn't wait but it also doesn't error out like FBIO_WAITFORVSYNC...
+#define FRAME_BUDGET 17 // 60fps
+	if (frame_start==0 || SDL_GetTicks()-frame_start<FRAME_BUDGET) { // only wait if we're under frame budget
+		int arg = 1;
+		ioctl(gfx.fb, OWLFB_WAITFORVSYNC, &arg);
+	}
 #endif
 
 #ifdef GFX_ENABLE_BUFFER
-    // TODO: this would be moved to a thread
-	// I'm not clear on why that would be necessary
-	// if it's non-blocking and the pan will wait
-	// until the next vblank...
-	// what if the scaling was also moved to a thread?
 	gfx.vinfo.yoffset = gfx.buffer * SCREEN_HEIGHT;
 	ioctl(gfx.fb, FBIOPAN_DISPLAY, &gfx.vinfo);
 
diff --git a/src/common/api.h b/src/common/api.h
index fb0d855..aa2ec84 100644
--- a/src/common/api.h
+++ b/src/common/api.h
@@ -28,6 +28,7 @@ void LOG_note(int level, const char* fmt, ...);
 SDL_Surface* GFX_init(void);
 void GFX_clear(SDL_Surface* screen);
 void GFX_clearAll(void);
+void GFX_startFrame(void);
 void GFX_flip(SDL_Surface* screen);
 void GFX_quit(void);
 
diff --git a/src/minarch/main.c b/src/minarch/main.c
index de08f97..39a64c4 100644
--- a/src/minarch/main.c
+++ b/src/minarch/main.c
@@ -926,6 +926,7 @@ int main(int argc , char* argv[]) {
 	
 	sec_start = SDL_GetTicks();
 	while (1) {
+		GFX_startFrame();
 		if (PAD_justReleased(BTN_POWER)) break; // TODO: tmp
 		core.run();
 		cpu_ticks += 1;
diff --git a/src/minui/main.c b/src/minui/main.c
index 094042f..ae88638 100644
--- a/src/minui/main.c
+++ b/src/minui/main.c
@@ -1262,6 +1262,7 @@ int main (int argc, char *argv[]) {
 	unsigned long cancel_start = SDL_GetTicks();
 	unsigned long power_start = 0;
 	while (!quit) {
+		GFX_startFrame();
 		unsigned long frame_start = SDL_GetTicks();
 		
 		PAD_poll();
@@ -1556,10 +1557,12 @@ int main (int argc, char *argv[]) {
 			GFX_flip(screen);
 			dirty = 0;
 		}
-		// // slow down to 60fps
-		// unsigned long frame_duration = SDL_GetTicks() - frame_start;
-		// #define TARGET_FRAME_DURATION 17
-		// if (frame_duration<TARGET_FRAME_DURATION) SDL_Delay(TARGET_FRAME_DURATION-frame_duration);
+		else {
+			// slow down to 60fps
+			unsigned long frame_duration = SDL_GetTicks() - frame_start;
+			#define TARGET_FRAME_DURATION 17
+			if (frame_duration<TARGET_FRAME_DURATION) SDL_Delay(TARGET_FRAME_DURATION-frame_duration);
+		}
 	}
 	
 	if (version) SDL_FreeSurface(version);