Add delay timer

src/chip8/display.rs

@@ -16,12 +16,33 @@ impl Screen {
     }
 
     pub fn pixel_set(&mut self, x: usize, y: usize) -> () {
-        self.pixels[y][x] = true;
+        self.pixels[y][x] ^= true;
     }
 
     pub fn is_pixel_set(&self, x: usize, y: usize) -> bool {
         self.pixels[y][x]
     }
+
+    pub fn draw_sprite(&mut self, x: usize, y: usize, sprite: &[u8]) -> bool {
+        let mut pixel_collission = false;
+
+        for ly in 0..sprite.len() {
+            let b = sprite[ly];
+            for lx in 0..8 {
+                if b & 0b10000000 >> lx > 0 {
+                    let dx = (x + lx) % WIDTH;
+                    let dy = (y + ly) % HEIGHT;
+                    if !pixel_collission && self.is_pixel_set(dx, dy) {
+                        pixel_collission = true;
+                    }
+
+                    self.pixel_set(dx, dy);
+                }
+            }
+        }
+
+        pixel_collission
+    }
 }
 
 #[cfg(test)]
@@ -34,4 +55,11 @@ mod tests {
         screen.pixel_set(5, 5);
         assert!(screen.is_pixel_set(5, 5));
     }
+
+    #[test]
+    fn it_returns_true_when_overwriting() {
+        let mut screen = Screen::new();
+        assert!(!screen.draw_sprite(0, 0, &[0xff]));
+        assert!(screen.draw_sprite(0, 0, &[0xff]));
+    }
 }

src/chip8/emulator.rs

@@ -1,7 +1,7 @@
 use crate::chip8::display::Screen;
 use crate::chip8::keyboard::Keyboard;
 use crate::chip8::memory::Memory;
-use crate::chip8::registers::Registers;
+use crate::chip8::registers::{Register, Registers};
 use crate::chip8::stack::Stack;
 
 pub struct Chip8 {
@@ -22,4 +22,12 @@ impl Chip8 {
             screen: Screen::new(),
         }
     }
+
+    pub fn delay_if_necessary(&mut self) -> () {
+        let delay_timer = self.registers.get(Register::DT);
+        if delay_timer > 0 {
+            ::std::thread::sleep(::std::time::Duration::new(0, 1_000_000_000u32 / 60));
+            self.registers.set(Register::DT, delay_timer - 1);
+        }
+    }
 }

src/chip8/memory.rs

@@ -49,6 +49,10 @@ impl Memory {
     pub fn get(&self, index: usize) -> u8 {
         self.memory[index]
     }
+
+    pub fn read(&self, start: usize, bytes: u8) -> &[u8] {
+        &self.memory[start..start + bytes as usize]
+    }
 }
 
 #[cfg(test)]
@@ -79,4 +83,12 @@ mod tests {
         let memory = Memory::new();
         assert_eq!(memory.memory[0..5], [0xf0, 0x90, 0x90, 0x90, 0xf0])
     }
+
+    #[test]
+    fn it_returns_a_slice_of_memory() {
+        let memory = Memory::new();
+        let slice = memory.read(0, 5);
+        assert_eq!(slice.len(), 5);
+        assert_eq!(slice, [0xf0, 0x90, 0x90, 0x90, 0xf0]);
+    }
 }

src/main.rs

@@ -12,9 +12,9 @@ const EMULATOR_WINDOW_TITLE: &str = "Rust CHIP-8";
 
 fn main() -> Result<(), String> {
     let mut chip8 = Chip8::new();
-    chip8.screen.pixel_set(0, 0);
-    chip8.screen.pixel_set(10, 2);
-    chip8.screen.pixel_set(42, 23);
+    chip8.screen.draw_sprite(24, 13, chip8.memory.read(20, 5));
+    chip8.screen.draw_sprite(29, 13, chip8.memory.read(10, 5));
+    chip8.screen.draw_sprite(34, 13, chip8.memory.read(40, 5));
 
     let sdl_context = sdl2::init()?;
     let video_subsystem = sdl_context.video()?;
@@ -85,7 +85,7 @@ fn main() -> Result<(), String> {
         }
 
         canvas.present();
-        ::std::thread::sleep(::std::time::Duration::new(0, 1_000_000_000u32 / 60));
+        chip8.delay_if_necessary();
     }
 
     Ok(())