From fa7232944f277e4abdadd6edcd3f2bc487aca41f Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Sat, 30 May 2020 01:25:21 +0300
Subject: [PATCH] =?UTF-8?q?Better=20emulation=20of=20CGB=E2=80=99s=20first?=
 =?UTF-8?q?=20frame=20behavior?=
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---
 Core/display.c | 11 +++++++++--
 Core/gb.h      |  1 +
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/Core/display.c b/Core/display.c
index 94d7f77b..2eb8c424 100644
--- a/Core/display.c
+++ b/Core/display.c
@@ -128,7 +128,7 @@ static void display_vblank(GB_gameboy_t *gb)
     
     bool is_ppu_stopped = !GB_is_cgb(gb) && gb->stopped && gb->io_registers[GB_IO_LCDC] & 0x80;
     
-    if (!gb->disable_rendering  && ((!(gb->io_registers[GB_IO_LCDC] & 0x80) || is_ppu_stopped) || gb->frame_skip_state == GB_FRAMESKIP_LCD_TURNED_ON)) {
+    if (!gb->disable_rendering  && ((!(gb->io_registers[GB_IO_LCDC] & 0x80) || is_ppu_stopped) || gb->cgb_repeated_a_frame)) {
         /* LCD is off, set screen to white or black (if LCD is on in stop mode) */
         if (!GB_is_sgb(gb)) {
             uint32_t color = 0;
@@ -796,6 +796,7 @@ void GB_display_run(GB_gameboy_t *gb, uint8_t cycles)
         while (true) {
             GB_SLEEP(gb, display, 1, LCDC_PERIOD);
             display_vblank(gb);
+            gb->cgb_repeated_a_frame = true;
         }
         return;
     }
@@ -1240,11 +1241,17 @@ abort_fetching_object:
                     }
                 }
                 else {
-                    gb->frame_skip_state = GB_FRAMESKIP_SECOND_FRAME_RENDERED;
                     if (!GB_is_sgb(gb) || gb->current_lcd_line < LINES) {
                         gb->is_odd_frame ^= true;
                         display_vblank(gb);
                     }
+                    if (gb->frame_skip_state == GB_FRAMESKIP_FIRST_FRAME_SKIPPED) {
+                        gb->cgb_repeated_a_frame = true;
+                        gb->frame_skip_state = GB_FRAMESKIP_SECOND_FRAME_RENDERED;
+                    }
+                    else {
+                        gb->cgb_repeated_a_frame = false;
+                    }
                 }
             }
             
diff --git a/Core/gb.h b/Core/gb.h
index 68c4ea9b..1376a12d 100644
--- a/Core/gb.h
+++ b/Core/gb.h
@@ -540,6 +540,7 @@ struct GB_gameboy_internal_s {
         bool is_odd_frame;
         uint16_t last_tile_data_address;
         uint16_t last_tile_index_address;
+        bool cgb_repeated_a_frame;
     );
 
     /* Unsaved data. This includes all pointers, as well as everything that shouldn't be on a save state */