From 6ad3f9f29b30e516c39364776c55cc4d2d74e49d Mon Sep 17 00:00:00 2001
From: Franco Colmenarez <info@francoacg.com>
Date: Thu, 28 Oct 2021 12:58:03 -0500
Subject: [PATCH] Experimental background rendering with scrolling

---
 src/bus.rs |  7 ++++---
 src/ppu.rs | 21 +++++++++++----------
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/src/bus.rs b/src/bus.rs
index 11ec949..773ff52 100644
--- a/src/bus.rs
+++ b/src/bus.rs
@@ -40,8 +40,8 @@ pub struct Bus {
 
 impl Bus {
     pub fn new() -> Self {
-        // let game_rom = match ROM::load_file("ignore/pokemon-yellow.gbc".to_string()) {
-        let game_rom = match ROM::load_file("roms/cpu_instrs_individual/01-special.gb".to_string()) {
+        let game_rom = match ROM::load_file("ignore/dmg-acid2.gb".to_string()) {
+        // let game_rom = match ROM::load_file("roms/cpu_instrs_individual/01-special.gb".to_string()) {
         // let game_rom = match ROM::load_file("roms/cpu_instrs_individual/03-op sp,hl.gb".to_string()) {
         // let game_rom = match ROM::load_file("roms/cpu_instrs_individual/04-op r,imm.gb".to_string()) {
         // let game_rom = match ROM::load_file("roms/cpu_instrs_individual/05-op rp.gb".to_string()) {
@@ -52,7 +52,8 @@ impl Bus {
         // let game_rom = match ROM::load_file("roms/cpu_instrs_individual/10-bit ops.gb".to_string()) {
         // let game_rom = match ROM::load_file("roms/cpu_instrs_individual/11-op a,(hl).gb".to_string()) {
             Ok(rom) => rom,
-            _ => ROM::from_bytes(&[0; 0xFFFF])
+            // _ => ROM::from_bytes(&[0; 0xFFFF])
+            _ => panic!("Could not read ROM"),
         };
         Self {
             data: [0x00; 0x10000],
diff --git a/src/ppu.rs b/src/ppu.rs
index 00db321..c256017 100644
--- a/src/ppu.rs
+++ b/src/ppu.rs
@@ -53,8 +53,8 @@ pub const FRAME_BUFFER_LENGTH: u32 = WIDTH * HEIGHT;
 const LCD_CONTROL_ADDRESS: u16 = 0xFF40;
 const LCD_STATUS_ADDRESS: u16 = 0xFF41;
 
-const SCROLL_X_ADDRESS: u16 = 0xFF42;
-const SCROLL_Y_ADDRESS: u16 = 0xFF43;
+const SCROLL_Y_ADDRESS: u16 = 0xFF42;
+const SCROLL_X_ADDRESS: u16 = 0xFF43;
 const LCD_Y_ADDRESS: u16 = 0xFF44;
 const LCD_Y_COMPARE_ADDRESS: u16 = 0xFF45;
 const DMA_ADDRESS: u16 = 0xFF46;
@@ -180,19 +180,20 @@ impl PPU {
     pub fn draw_background(&mut self, bus: &Bus) {
         let mut idx = 0;
         // let mut tile_line: u16 = 0;
-        let mut lcd_y: u16 = 0;
+        let mut lcd_y: u8 = 0;
         while lcd_y < 144 {
-            let mut lcd_x: u16 = 0;
+            let mut lcd_x: u8 = 0;
             while lcd_x < 160 {
-                let index_x = (lcd_x / 8);
-                let index_y = (lcd_y / 8) * 32;
+                let y = lcd_y.wrapping_add(PPU::get_scroll_y(bus));
+                let x = lcd_x.wrapping_add(PPU::get_scroll_x(bus));
+                let index_x = (x as u16 / 8);
+                let index_y = (y as u16 / 8) * 32;
                 let index = index_x + index_y;
-                let tile_line = (lcd_y + PPU::get_scroll_y(bus) as u16).rem_euclid(8) * 2;
+                let tile_line = (y).rem_euclid(8) * 2;
                 let index_byte = (bus.read(0x9800 + index as u16) as u16) * 16;
 
-                let tile_byte_1 = bus.read(0x8000 + tile_line + index_byte as u16);
-                let tile_byte_2 = bus.read(0x8000 + tile_line + index_byte as u16 + 1);
-                println!("{} {}", tile_byte_1, tile_byte_2);
+                let tile_byte_1 = bus.read(0x8000 + tile_line as u16 + index_byte);
+                let tile_byte_2 = bus.read(0x8000 + tile_line as u16 + index_byte + 1);
 
                 let pixels = PPU::get_byte_pixels(tile_byte_1, tile_byte_2);