From 476133abd04fc27cdff5ab22d90cca13090de3d7 Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Sat, 3 Mar 2018 20:51:38 +0200
Subject: [PATCH] The scrolled y value is cached and not recalculated

---
 Core/display.c | 14 +++++---------
 Core/gb.h      |  5 +++--
 2 files changed, 8 insertions(+), 11 deletions(-)

diff --git a/Core/display.c b/Core/display.c
index 22cd847..f6c0e57 100755
--- a/Core/display.c
+++ b/Core/display.c
@@ -444,12 +444,6 @@ static void render_pixel_if_possible(GB_gameboy_t *gb)
     }
     gb->position_in_line++;
 }
-
-static inline uint8_t scrolled_y(GB_gameboy_t *gb)
-{
-    return gb->current_line + (gb->in_window? - gb->io_registers[GB_IO_WY] - gb->wy_diff : gb->io_registers[GB_IO_SCY]);
-}
-
 void GB_display_run(GB_gameboy_t *gb, uint8_t cycles)
 {
     
@@ -593,7 +587,9 @@ void GB_display_run(GB_gameboy_t *gb, uint8_t cycles)
                             else if (gb->io_registers[GB_IO_LCDC] & 0x40 && gb->in_window) {
                                 map = 0x1C00;
                             }
-                            gb->current_tile = gb->vram[map + gb->fetcher_x + scrolled_y(gb) / 8 * 32];
+                            gb->fetcher_y =
+                                gb->current_line + (gb->in_window? - gb->io_registers[GB_IO_WY] - gb->wy_diff : gb->io_registers[GB_IO_SCY]);
+                            gb->current_tile = gb->vram[map + gb->fetcher_x + gb->fetcher_y / 8 * 32];
                             gb->fetcher_x++;
                             gb->fetcher_x &= 0x1f;
                         }
@@ -607,13 +603,13 @@ void GB_display_run(GB_gameboy_t *gb, uint8_t cycles)
                                 gb->current_tile_address =  (int8_t)gb->current_tile * 0x10 + 0x1000;
                             }
                             gb->current_tile_data[0] =
-                            gb->vram[gb->current_tile_address + (scrolled_y(gb) & 7) * 2];
+                            gb->vram[gb->current_tile_address + (gb->fetcher_y & 7) * 2];
                         }
                         break;
                         
                         case GB_FETCHER_GET_TILE_DATA_HIGH: {
                             gb->current_tile_data[1] =
-                            gb->vram[gb->current_tile_address + (scrolled_y(gb) & 7) * 2 + 1];
+                            gb->vram[gb->current_tile_address + (gb->fetcher_y & 7) * 2 + 1];
                         }
                         break;
                             
diff --git a/Core/gb.h b/Core/gb.h
index b4ff2ab..56215c1 100644
--- a/Core/gb.h
+++ b/Core/gb.h
@@ -401,14 +401,15 @@ struct GB_gameboy_internal_s {
         bool oam_write_blocked;
         bool vram_write_blocked;
         bool window_disabled_while_active;
-        uint8_t effective_scy; // SCY is latched when starting to draw a tile
+        uint8_t effective_scy; // Todo: delete me!
         uint8_t current_line;
         uint16_t ly_for_comparison;
         GB_fifo_t bg_fifo, oam_fifo;
         uint8_t fetcher_x;
+        uint8_t fetcher_y;
         uint16_t cycles_for_line;
         uint8_t current_tile;
-        uint16_t current_tile_address; // TODO: is this actually cached? If not, it could be used to "mix" two tiles
+        uint16_t current_tile_address;
         uint8_t current_tile_data[2];
         enum {
             GB_FETCHER_GET_TILE,