From eebb5b61f489261739d7da55ca64c28bdf193034 Mon Sep 17 00:00:00 2001
From: Isaac Marovitz <isaacryu@icloud.com>
Date: Sun, 10 Dec 2023 14:52:14 -0500
Subject: [PATCH] More GPU boilerplate

---
 src/cpu.rs  |  4 ++--
 src/gpu.rs  | 47 ++++++++++++++++++++++++++++++++++++++++++++---
 src/main.rs | 22 ++++++++++++----------
 src/mmu.rs  |  7 ++++---
 src/mode.rs |  1 +
 5 files changed, 63 insertions(+), 18 deletions(-)

diff --git a/src/cpu.rs b/src/cpu.rs
index c98fc06..5ca2887 100644
--- a/src/cpu.rs
+++ b/src/cpu.rs
@@ -4,7 +4,7 @@ use crate::registers::{Registers, Flags};
 
 pub struct CPU {
     reg: Registers,
-    mem: MMU,
+    pub mem: MMU,
     halted: bool,
     // Enabled Interrupts
     ei: bool
@@ -14,7 +14,7 @@ impl CPU {
     pub fn new(mode: GBMode, rom: Vec<u8>) -> Self {
         Self {
             reg: Registers::new(mode),
-            mem: MMU::new(rom),
+            mem: MMU::new(mode, rom),
             halted: false,
             ei: true
         }
diff --git a/src/gpu.rs b/src/gpu.rs
index 79285ae..1d92f45 100644
--- a/src/gpu.rs
+++ b/src/gpu.rs
@@ -1,9 +1,11 @@
 use bitflags::{bitflags, Flags};
+use crate::mode::GBMode;
 
 pub const SCREEN_W: usize = 160;
 pub const SCREEN_H: usize = 144;
 
 pub struct GPU {
+    mode: GBMode,
     sy: u8,
     sx: u8,
     ly: u8,
@@ -12,7 +14,8 @@ pub struct GPU {
     wx: u8,
     lcdc: LCDC,
     lcds: LCDS,
-    ram: [u8; 0x4000]
+    ram: [u8; 0x4000],
+    frame_buffer: [[[u8; 3]; SCREEN_W]; SCREEN_H]
 }
 
 bitflags! {
@@ -52,8 +55,9 @@ bitflags! {
     }
 }
 impl GPU {
-    pub fn new() -> Self {
+    pub fn new(mode: GBMode) -> Self {
         Self {
+            mode,
             sy: 0,
             sx: 0,
             ly: 0,
@@ -62,10 +66,47 @@ impl GPU {
             wx: 0,
             lcdc: LCDC::empty(),
             lcds: LCDS::empty(),
-            ram: [0; 0x4000]
+            ram: [0; 0x4000],
+            frame_buffer: [[[0; 3]; SCREEN_W]; SCREEN_H]
         }
     }
 
+    pub fn cycle(&mut self) {
+        self.draw_bg();
+    }
+
+    fn grey_to_l(v: u8, i: usize) -> u8 {
+        match v >> (2 * i) & 0x03 {
+            0x00 => 0xFF,
+            0x01 => 0xFC,
+            0x02 => 0x60,
+            _ => 0x00
+        }
+    }
+
+    fn set_rgb(&mut self, x: usize, r: u8, g: u8, b: u8) {
+        // TODO: Color mapping from CGB -> sRGB
+        self.frame_buffer[self.ly as usize][x] = [r, g, b];
+    }
+
+    fn draw_bg(&mut self) {
+        for x in 0..SCREEN_W {
+            if self.mode == GBMode::Color {
+                let r = 0;
+                let g = 0;
+                let b = 0;
+                self.set_rgb(x, r, g, b);
+            } else {
+                let lightness = Self::grey_to_l(0, 0);
+                self.set_rgb(x, lightness, lightness, lightness);
+            }
+        }
+    }
+
+    fn draw_sprites(&mut self) {
+
+    }
+
     pub fn read(&self, a: u16) -> u8 {
         match a {
             0xFF40 => self.lcdc.bits(),
diff --git a/src/main.rs b/src/main.rs
index 0c965e8..3ba5581 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -44,6 +44,16 @@ async fn main() -> Result<(), impl std::error::Error> {
     let game_name = std::str::from_utf8(&name_data[0..index]).expect("Failed to get game name!");
     println!("Starting \"{game_name}\"...");
 
+    let event_loop = EventLoop::new().unwrap();
+
+    let window = WindowBuilder::new()
+        .with_title(format!("gb-rs - {:}", game_name))
+        .with_inner_size(winit::dpi::LogicalSize::new(160, 144))
+        .build(&event_loop)
+        .unwrap();
+
+    let mut context = Context::new(window).await;
+
     let buffer_copy = buffer.clone();
     // Start CPU
     tokio::spawn(async move {
@@ -51,20 +61,12 @@ async fn main() -> Result<(), impl std::error::Error> {
 
         while true {
             let cycles = cpu.cycle();
+            cpu.mem.gpu.cycle();
+
             sleep(Duration::from_millis((1000_f64 / 4_194_304_f64 * cycles as f64) as u64)).await;
         }
     });
 
-    let event_loop = EventLoop::new().unwrap();
-
-    let window = WindowBuilder::new()
-        .with_title(format!("gb-rs - {:}", game_name))
-        .with_inner_size(winit::dpi::LogicalSize::new(160, 144))
-        .build(&event_loop)
-        .unwrap();
-
-    let mut context = Context::new(window).await;
-
     let mut modifiers = ModifiersState::default();
 
     event_loop.run(move |event, elwt| {
diff --git a/src/mmu.rs b/src/mmu.rs
index a1e1645..6768224 100644
--- a/src/mmu.rs
+++ b/src/mmu.rs
@@ -1,8 +1,9 @@
 use crate::gpu::GPU;
+use crate::mode::GBMode;
 
 pub struct MMU {
     rom: Vec<u8>,
-    gpu: GPU,
+    pub gpu: GPU,
     wram: [u8; 0x8000],
     hram: [u8; 0x7F],
     interrupt: u8,
@@ -10,10 +11,10 @@ pub struct MMU {
 }
 
 impl MMU {
-    pub fn new(rom: Vec<u8>) -> Self {
+    pub fn new(mode: GBMode, rom: Vec<u8>) -> Self {
         Self {
             rom,
-            gpu: GPU::new(),
+            gpu: GPU::new(mode),
             wram: [0; 0x8000],
             hram: [0; 0x7f],
             interrupt: 0,
diff --git a/src/mode.rs b/src/mode.rs
index 00de0a3..478db7a 100644
--- a/src/mode.rs
+++ b/src/mode.rs
@@ -1,3 +1,4 @@
+#[derive(Clone, Copy, PartialEq)]
 pub enum GBMode {
     Classic,
     Color,