From acf1b10e6674fc27526ba3ee76ab0900088ffaf6 Mon Sep 17 00:00:00 2001
From: Rekai Musuka <musukarekai@gmail.com>
Date: Mon, 13 Jul 2020 22:16:42 -0500
Subject: [PATCH] Move where CHIP-8 Program Counter is updated

---
 src/emu.rs  | 12 +++++-------
 src/main.rs | 18 +++++++++---------
 2 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/src/emu.rs b/src/emu.rs
index b346942..72666e2 100644
--- a/src/emu.rs
+++ b/src/emu.rs
@@ -59,7 +59,8 @@ impl Chip8 {
 
     pub fn execute_cycle(&mut self) {
         let opcode = self.get_opcode();
-        // println!("{:#x}", self.opcode);
+        self.pc += 2; // Immediately increment the Program Counter
+
         self.execute_opcode(opcode);
 
         self.delay.tick();
@@ -82,7 +83,6 @@ impl Chip8 {
 
     fn get_opcode(&self) -> u16 {
         let pc = self.pc as usize;
-
         ((self.memory[pc] as u16) << 8) | self.memory[pc + 1] as u16
     }
 
@@ -105,8 +105,6 @@ impl Chip8 {
         let y = nib_3;
         let n = nib_4;
 
-        self.pc += 2;
-
         match (nib_1, nib_2, nib_3, nib_4) {
             // CLS
             (0x0, 0x0, 0xE, 0x0) => self.cls(),
@@ -197,7 +195,7 @@ impl Chip8 {
 
     fn jmp_addr(&mut self, nnn: u16) {
         // sets the program counter to addr (nnn)
-        self.pc = nnn - 2; // We want to execute nnn so decrement pc by 2;
+        self.pc = nnn; // We want to execute nnn so decrement pc by 2;
     }
 
     fn call_addr(&mut self, nnn: u16) {
@@ -205,7 +203,7 @@ impl Chip8 {
         // pc is then set to addr
         self.sp += 1;
         self.stack[self.sp as usize] = self.pc;
-        self.pc = nnn - 2; // see Chip8#jmp_addr()
+        self.pc = nnn; // see Chip8#jmp_addr()
     }
 
     fn se_vx_byte(&mut self, x: u8, kk: u8) {
@@ -323,7 +321,7 @@ impl Chip8 {
 
     fn jmp_addr_with_offset(&mut self, nnn: u16) {
         // set program counter to addr + V0
-        self.pc = nnn + self.v[0] as u16 - 2; // see Chip8#jmp_addr
+        self.pc = nnn + self.v[0] as u16; // see Chip8#jmp_addr
     }
 
     fn rand(&mut self, x: u8, kk: u8) {
diff --git a/src/main.rs b/src/main.rs
index 34a68f8..eb3a156 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -15,17 +15,15 @@ static WIDTH: u32 = 64;
 static HEIGHT: u32 = 32;
 
 fn main() {
+    let mut chip8: Chip8 = Default::default();
+    let mut input = WinitInputHelper::new();
     let event_loop = EventLoop::new();
     let window = init_window(&event_loop);
+    let mut hidpi_factor = window.scale_factor();
     let mut pixels = init_pixels(&window);
 
-    let mut hidpi_factor = window.scale_factor();
-    let mut input = WinitInputHelper::new();
-
-    let mut chip8: Chip8 = Default::default();
-    chip8
-        .load_rom(Path::new("./games/ibm_logo.ch8"))
-        .expect("Unable to load ROM");
+    let rom_path = Path::new("./games/ibm_logo.ch8");
+    chip8.load_rom(rom_path).expect("Unable to load ROM");
 
     event_loop.run(move |event, _, control_flow| {
         if let Event::RedrawRequested(_) = event {
@@ -67,11 +65,13 @@ fn init_pixels(window: &Window) -> Pixels {
 }
 
 fn init_window(event_loop: &EventLoop<()>) -> Window {
-    let size = LogicalSize::new(WIDTH as f64, HEIGHT as f64);
+    const SCALE: u32 = 10;
+    let min_size = LogicalSize::new(WIDTH as f64, HEIGHT as f64);
+    let size = LogicalSize::new((WIDTH * SCALE) as f64, (HEIGHT * SCALE) as f64);
     WindowBuilder::new()
         .with_title("Chip8 Emulator")
         .with_inner_size(size)
-        .with_min_inner_size(size)
+        .with_min_inner_size(min_size)
         .build(event_loop)
         .unwrap()
 }