From f7b5476a7e5eff25a09984e947a0192c82ea20ad Mon Sep 17 00:00:00 2001
From: velllu <91963404+velllu@users.noreply.github.com>
Date: Sun, 7 Apr 2024 19:08:40 +0200
Subject: [PATCH] Implemented basic window rendering

---
 src/consts.rs          |  2 ++
 src/gpu/mod.rs         |  1 +
 src/gpu/states.rs      | 21 ++++++++++++++++++---
 src/gpu/tile_parser.rs |  9 +++++++--
 src/gpu/window.rs      | 11 +++++++++++
 5 files changed, 39 insertions(+), 5 deletions(-)
 create mode 100644 src/gpu/window.rs

diff --git a/src/consts.rs b/src/consts.rs
index bd76279..f070da5 100644
--- a/src/consts.rs
+++ b/src/consts.rs
@@ -20,6 +20,8 @@ pub mod gpu {
     pub const LYC: u16 = 0xFF45;
     pub const OBP0: u16 = 0xFF48;
     pub const OBP1: u16 = 0xFF49;
+    pub const WY: u16 = 0xFF4A;
+    pub const WX: u16 = 0xFF4B;
     pub const IE: u16 = 0xFFFF;
 }
 
diff --git a/src/gpu/mod.rs b/src/gpu/mod.rs
index 53e53ab..73a1bd0 100644
--- a/src/gpu/mod.rs
+++ b/src/gpu/mod.rs
@@ -2,6 +2,7 @@ pub(crate) mod palette;
 pub(crate) mod sprite_parser;
 pub mod states;
 pub mod tile_parser;
+pub(crate) mod window;
 
 #[derive(Clone, Copy, PartialEq, Debug)]
 pub enum Color {
diff --git a/src/gpu/states.rs b/src/gpu/states.rs
index de9354e..3a24d9c 100644
--- a/src/gpu/states.rs
+++ b/src/gpu/states.rs
@@ -2,7 +2,7 @@ use crate::{
     common::Bit,
     consts::{
         display::{DISPLAY_SIZE_X, DISPLAY_SIZE_Y},
-        gpu::{LCDC, LY, SCX, SCY},
+        gpu::{LCDC, LY, SCX, SCY, WX, WY},
     },
     GameBoy,
 };
@@ -36,8 +36,8 @@ pub struct Gpu {
     rendered_sprites_on_line: u8,
 
     // These represent the current position of the "cursor"
-    x: u8,
-    y: u8,
+    pub(crate) x: u8,
+    pub(crate) y: u8,
 
     /// A dot is 1/4 of a CPU cycle
     pub dots: u16,
@@ -98,12 +98,16 @@ impl GameBoy {
             self.gpu.dots += 12;
         }
 
+        // TODO: Scrolling is actually handled a bit differently, read this
+        // "https://gbdev.io/pandocs/Scrolling.html#mid-frame-behavior"
+
         // And we get the background fifo and the sprite fifo
         let background_fifo = match self.bus[LCDC].get_bit(0) {
             false => Line::new_blank(), // When LCDC.0 is 0, the background tile is white
             true => self.get_line_from_coordinates(
                 self.gpu.x.wrapping_add(self.bus[SCX]),
                 self.gpu.y.wrapping_add(self.bus[SCY]),
+                false,
             ),
         };
 
@@ -123,6 +127,17 @@ impl GameBoy {
             self.draw_line(&background_fifo, self.gpu.x as usize, self.gpu.y as usize);
         }
 
+        // Window rendering
+        // `- 7` because WX is always 7 more then the actual value
+        let window_x = self.gpu.x as i32 - (self.bus[WX] as i32 - 7);
+        let window_y = self.gpu.y as i32 - self.bus[WY] as i32;
+
+        // Window doesn't scroll so we don't wrap around like with the background
+        if window_x >= 0 && window_y >= 0 && self.can_render_window() {
+            let window_fifo = self.get_line_from_coordinates(window_x as u8, window_y as u8, true);
+            self.draw_line(&window_fifo, self.gpu.x as usize, self.gpu.y as usize);
+        }
+
         self.gpu.x += 8;
 
         if self.gpu.x == (DISPLAY_SIZE_X as u8) {
diff --git a/src/gpu/tile_parser.rs b/src/gpu/tile_parser.rs
index 5b95414..b8318a9 100644
--- a/src/gpu/tile_parser.rs
+++ b/src/gpu/tile_parser.rs
@@ -80,8 +80,13 @@ impl GameBoy {
 
     /// Returns the line that should be at the given coordinates of the screen (excluding
     /// horizontal and vertical scroll)
-    pub(crate) fn get_line_from_coordinates(&self, x: u8, y: u8) -> Line {
-        let tile_map_address: u16 = match self.bus[0xFF40].get_bit(3) {
+    pub(crate) fn get_line_from_coordinates(&self, x: u8, y: u8, window: bool) -> Line {
+        let lcdc_bit = match window {
+            false => 3,
+            true => 6,
+        };
+
+        let tile_map_address: u16 = match self.bus[LCDC].get_bit(lcdc_bit) {
             false => 0x9800,
             true => 0x9C00,
         };
diff --git a/src/gpu/window.rs b/src/gpu/window.rs
new file mode 100644
index 0000000..2dd7f05
--- /dev/null
+++ b/src/gpu/window.rs
@@ -0,0 +1,11 @@
+use crate::{common::Bit, consts::gpu::LCDC, GameBoy};
+
+impl GameBoy {
+    pub(crate) fn can_render_window(&self) -> bool {
+        if !self.bus[LCDC].get_bit(0) || !self.bus[LCDC].get_bit(5) {
+            return false;
+        }
+
+        true
+    }
+}