From 496c5589e6a1506596c116026a268b76b25daac0 Mon Sep 17 00:00:00 2001
From: Lior Halphon <LIJI32@gmail.com>
Date: Sat, 3 Mar 2018 19:36:21 +0200
Subject: [PATCH] Added window support

---
 Core/display.c | 54 ++++++++++++++++++++++++++++++++++++++++++--------
 Core/gb.h      |  2 +-
 2 files changed, 47 insertions(+), 9 deletions(-)

diff --git a/Core/display.c b/Core/display.c
index fa5a40c7..f227724d 100755
--- a/Core/display.c
+++ b/Core/display.c
@@ -419,14 +419,37 @@ static void render_pixel_if_possible(GB_gameboy_t *gb)
         gb->position_in_line++;
         return;
     }
-    
     if (gb->fifo_paused) return;
     
-    uint8_t pixel = ((gb->io_registers[GB_IO_BGP] >> (fifo_item->pixel << 1)) & 3);
-    gb->screen[gb->position_in_line + gb->current_line * WIDTH] = gb->background_palettes_rgb[pixel];
+    /* Mixing */
+    bool bg_enabled = true, bg_behind = false;
+    
+    if ((gb->io_registers[GB_IO_LCDC] & 0x1) == 0) {
+        if (gb->cgb_mode) {
+            bg_behind = true;
+        }
+        else {
+            bg_enabled = false;
+        }
+    }
+    if (!bg_enabled) {
+        gb->screen[gb->position_in_line + gb->current_line * WIDTH] = gb->rgb_encode_callback(gb, 0xFF, 0xFF, 0xFF);
+    }
+    else {
+        uint8_t pixel = fifo_item->pixel;
+        if (!gb->cgb_mode) {
+            pixel = ((gb->io_registers[GB_IO_BGP] >> (pixel << 1)) & 3);
+        }
+        gb->screen[gb->position_in_line + gb->current_line * WIDTH] = gb->background_palettes_rgb[pixel];
+    }
     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)
 {
     
@@ -546,16 +569,31 @@ void GB_display_run(GB_gameboy_t *gb, uint8_t cycles)
             gb->fetcher_divisor = false;
             gb->fetcher_state = GB_FETCHER_GET_TILE;
             gb->fifo_paused = true;
+            gb->in_window = false;
             while (true) {
+                /* Handle window */
+                /* Todo: Timing not verified by test ROM */
+                if (!gb->in_window && window_enabled(gb) &&
+                    gb->current_line >= gb->io_registers[GB_IO_WY] + gb->wy_diff &&
+                    gb->position_in_line + 7 == gb->io_registers[GB_IO_WX]) {
+                    gb->in_window = true;
+                    fifo_clear(&gb->bg_fifo);
+                    gb->fifo_paused =  true;
+                    gb->fetcher_x = 0;
+                    gb->fetcher_state = GB_FETCHER_GET_TILE;
+                }
+                
                 if (gb->fetcher_divisor) {
                     switch (gb->fetcher_state) {
                         case GB_FETCHER_GET_TILE: {
                             uint16_t map = 0x1800;
-                            if (gb->io_registers[GB_IO_LCDC] & 0x08) {
+                            if (gb->io_registers[GB_IO_LCDC] & 0x08 && !gb->in_window) {
                                 map = 0x1C00;
                             }
-                            uint8_t y = gb->current_line + gb->io_registers[GB_IO_SCY];
-                            gb->current_tile = gb->vram[map + gb->fetcher_x + y / 8 * 32];
+                            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_x++;
                             gb->fetcher_x &= 0x1f;
                         }
@@ -569,13 +607,13 @@ 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 + ((gb->current_line + gb->io_registers[GB_IO_SCY]) & 7) * 2];
+                            gb->vram[gb->current_tile_address + (scrolled_y(gb) & 7) * 2];
                         }
                         break;
                         
                         case GB_FETCHER_GET_TILE_DATA_HIGH: {
                             gb->current_tile_data[1] =
-                            gb->vram[gb->current_tile_address + ((gb->current_line + gb->io_registers[GB_IO_SCY]) & 7) * 2 + 1];
+                            gb->vram[gb->current_tile_address + (scrolled_y(gb) & 7) * 2 + 1];
                         }
                         break;
                             
diff --git a/Core/gb.h b/Core/gb.h
index 68c7c0db..b4ff2abc 100644
--- a/Core/gb.h
+++ b/Core/gb.h
@@ -419,7 +419,7 @@ struct GB_gameboy_internal_s {
         } fetcher_state:8;
         bool fetcher_divisor; // The fetcher runs at 2MHz
         bool fifo_paused;
-        
+        bool in_window;
     );
 
     /* Unsaved data. This includes all pointers, as well as everything that shouldn't be on a save state */