From 63f98a5ec45d9ebf1833b5d1c9bb413e95749116 Mon Sep 17 00:00:00 2001
From: Alex Janka <alex@alexjanka.com>
Date: Fri, 10 Feb 2023 09:26:26 +1100
Subject: [PATCH] window internal lc

---
 src/processor/gpu.rs | 40 ++++++++++++++++++++++++++++++----------
 1 file changed, 30 insertions(+), 10 deletions(-)

diff --git a/src/processor/gpu.rs b/src/processor/gpu.rs
index 0ad6ca0..3fe0de5 100644
--- a/src/processor/gpu.rs
+++ b/src/processor/gpu.rs
@@ -25,6 +25,8 @@ pub struct GPU {
     mode_clock: usize,
     scanline: u8,
     tile_window: Option<TileWindow>,
+    window_lc: u8,
+    has_window_been_enabled: bool,
 }
 
 impl GPU {
@@ -54,6 +56,8 @@ impl GPU {
             mode_clock: 0,
             scanline: 0,
             tile_window,
+            window_lc: 0,
+            has_window_been_enabled: false,
         }
     }
 }
@@ -158,6 +162,8 @@ impl CPU {
     fn exit_vblank(&mut self) {
         self.gpu.mode = DrawMode::Mode2;
         self.gpu.scanline = 0;
+        self.gpu.window_lc = 0;
+        self.gpu.has_window_been_enabled = false;
         if let Some(tile_window) = &mut self.gpu.tile_window {
             tile_window.draw_sprite_window(byte_to_palette(self.memory.get(0xFF47)), &self.memory);
         }
@@ -210,7 +216,11 @@ impl CPU {
         if lcdc.bg_window_enable {
             self.render_scanline_bg(scanline, lcdc, bg_palette);
             if lcdc.window_enable {
+                if !self.gpu.has_window_been_enabled {
+                    self.gpu.window_lc = scanline;
+                }
                 self.render_scanline_window(scanline, lcdc, bg_palette);
+                self.gpu.has_window_been_enabled = true;
             }
         } else {
             for x in 0..WIDTH {
@@ -227,6 +237,7 @@ impl CPU {
         let scroll_y = 0_u8.wrapping_sub(self.memory.get(0xFF42));
         let scroll_x = 0_u8.wrapping_sub(self.memory.get(0xFF43));
         self.render_tiles(
+            scanline,
             scanline,
             &lcdc.bg_tilemap,
             &lcdc.tile_area,
@@ -241,15 +252,23 @@ impl CPU {
         let pos_y = self.memory.get(0xFF4A);
         // subtracting 7 to get the Real Number...
         let pos_x = self.memory.get(0xFF4B);
-        self.render_tiles(
-            scanline,
-            &lcdc.window_tilemap,
-            &lcdc.tile_area,
-            palette,
-            pos_x.wrapping_sub(7),
-            pos_y,
-            false,
-        );
+
+        if pos_y < 143 && pos_x < 166 {
+            // window is on screen
+            self.render_tiles(
+                scanline,
+                self.gpu.window_lc,
+                &lcdc.window_tilemap,
+                &lcdc.tile_area,
+                palette,
+                pos_x.wrapping_sub(7),
+                pos_y,
+                false,
+            );
+
+            self.gpu.window_lc = self.gpu.window_lc.wrapping_add(1);
+            self.gpu.has_window_been_enabled = true;
+        }
     }
 
     fn render_scanline_obj(&mut self, scanline: u8, lcdc: &LCDC, bg_palette: Palette) {
@@ -332,6 +351,7 @@ impl CPU {
     fn render_tiles(
         &mut self,
         scanline: u8,
+        draw_from: u8,
         tilemap: &TilemapArea,
         tiledata: &TiledataArea,
         palette: Palette,
@@ -339,7 +359,7 @@ impl CPU {
         offset_y: u8,
         wrap: bool,
     ) {
-        let (tile_line_y, did_wrap_y) = scanline.overflowing_sub(offset_y);
+        let (tile_line_y, did_wrap_y) = draw_from.overflowing_sub(offset_y);
         if did_wrap_y && !wrap {
             return;
         }