From 992d6be6ebae56f2e5830abb2f6276fb34fd5bc3 Mon Sep 17 00:00:00 2001
From: Alessio Caiazza <nolith@abisso.org>
Date: Wed, 1 Dec 2021 16:02:54 +0100
Subject: [PATCH] Ensure we do not render before the framebuffer copy completes

---
 platform/drivers/display/display_libSDL.c    | 25 +++++++++++---------
 platform/targets/linux/emulator/sdl_engine.c |  8 +++----
 2 files changed, 18 insertions(+), 15 deletions(-)

diff --git a/platform/drivers/display/display_libSDL.c b/platform/drivers/display/display_libSDL.c
index 4c0653e3..a3fd7815 100644
--- a/platform/drivers/display/display_libSDL.c
+++ b/platform/drivers/display/display_libSDL.c
@@ -130,20 +130,23 @@ void display_renderRows(uint8_t startRow, uint8_t endRow)
 
     if(sdl_ready)
     {
+        // receive a texture pixel map
+        void *fb;
+        chan_recv(&fb_sync, &fb);
 #ifdef PIX_FMT_RGB565
-       chan_send(&fb_sync, frameBuffer);
+	memcpy(fb, frameBuffer, sizeof(PIXEL_SIZE) * SCREEN_HEIGHT * SCREEN_WIDTH);
 #else
-       //TODO free
-       PIXEL_SIZE *pixels = malloc(sizeof(uint16_t) * SCREEN_HEIGHT * SCREEN_WIDTH);
-       for (unsigned int x = 0; x < SCREEN_WIDTH; x++)
-       {
-	   for (unsigned int y = startRow; y < endRow; y++)
-	   {
-	       pixels[x + y * SCREEN_WIDTH] = fetchPixelFromFb(x, y);
-	   }
-       }
-       chan_send(&fb_sync, (void *)pixels);
+        for (unsigned int x = 0; x < SCREEN_WIDTH; x++)
+	{
+	    for (unsigned int y = startRow; y < endRow; y++)
+	    {
+		pixels[x + y * SCREEN_WIDTH] = fetchPixelFromFb(x, y);
+	    }
+	}
 #endif
+	// signal the SDL main loop to proceed with rendering
+	void *done = {0};
+	chan_send(&fb_sync, done);
     }
 
     inProgress = false;
diff --git a/platform/targets/linux/emulator/sdl_engine.c b/platform/targets/linux/emulator/sdl_engine.c
index 26d20efd..83e211c1 100644
--- a/platform/targets/linux/emulator/sdl_engine.c
+++ b/platform/targets/linux/emulator/sdl_engine.c
@@ -278,7 +278,8 @@ void sdl_task()
 	    }
 	}
 
-	if (chan_can_recv(&fb_sync))
+	// we update the window only if there is a something ready to render
+	if (chan_can_send(&fb_sync))
 	{
 	    PIXEL_SIZE *pixels;
 	    int pitch = 0;
@@ -287,9 +288,8 @@ void sdl_task()
 		SDL_Log("SDL_lock failed: %s", SDL_GetError());
 	    }
 
-	    void *fb;
-	    chan_recv(&fb_sync, &fb);
-	    memcpy(pixels, fb, sizeof(PIXEL_SIZE) * SCREEN_HEIGHT * SCREEN_WIDTH);
+	    chan_send(&fb_sync, pixels);
+	    chan_recv(&fb_sync, NULL);
 
 	    SDL_UnlockTexture(displayTexture);
 	    SDL_RenderCopy(renderer, displayTexture, NULL, NULL);