Implemented character blinking.

src/main.rs

@@ -1,7 +1,7 @@
 extern crate sdl2;
 
 use std::thread::sleep;
-use std::time::Duration;
+use std::time::{Duration, SystemTime, SystemTimeError, UNIX_EPOCH};
 
 use bitvec::prelude::*;
 use sdl2::event::Event;
@@ -28,6 +28,9 @@ const TOTAL_GLYPH_TEXTURES: usize = 256 * 16 * 8;
 // Total screen blocks = GLYPH_COLUMNS * GLYPH_ROWS
 const TOTAL_SCREEN_BLOCKS: usize = 2000;
 
+const FPS_60_HERTZ: u32 = 1_000_000_000u32 / 60;
+const BLINK_RATE: u128 = 266666666;
+
 pub enum EgaColors {
     Black,
     Blue,
@@ -118,10 +121,10 @@ impl EgaColors {
 
 #[derive(Clone, Copy)]
 pub struct ScreenBlock {
-    blink: bool,
-    background: u8,
-    foreground: u8,
-    glyph: u8,
+    pub blink: bool,
+    pub background: u8,
+    pub foreground: u8,
+    pub glyph: u8,
 }
 
 impl ScreenBlock {
@@ -147,7 +150,7 @@ impl ScreenBlock {
 
     pub fn as_texture_index(&self) -> usize {
         let num = ScreenBlock::attrs_to_index(
-            self.blink,
+            false,
             self.background,
             self.foreground,
             self.glyph
@@ -166,9 +169,21 @@ pub fn block_to_canvas(
     textures: &Vec<Texture>,
     x: u8,
     y: u8,
-    block: &ScreenBlock) {
+    block: &ScreenBlock,
+    blink: &bool
+) {
 
-    let tex_idx = block.as_texture_index();
+    let tex_idx = match blink {
+        false => block.as_texture_index(),
+        true => match block.blink {
+            false => block.as_texture_index(),
+            true => ScreenBlock::new(block.blink, block.background, block.background, block.glyph).as_texture_index(),
+        },
+    };
+
+    // These next two assignments look odd mainly because of Rust's current
+    // issue with exclusive range patterns. See here:
+    // https://github.com/rust-lang/rust/issues/37854
 
     let dest_x = match x {
         n if (0..=GLYPH_COLUMNS - 1).contains(&n) => GLYPH_WIDTH as i32 * x as i32,
@@ -192,18 +207,30 @@ pub fn block_to_canvas(
     };
 }
 
-pub fn render(canvas: &mut WindowCanvas, textures: &Vec<Texture>, screen: &[ScreenBlock]) {
+pub fn update(elapsed: u128) {
+    //println!("Updated after {} nanoseconds.", elapsed);
+}
+
+pub fn render(canvas: &mut WindowCanvas, textures: &Vec<Texture>, screen: &[ScreenBlock], blink: &bool) {
     canvas.set_draw_color(EgaColors::from_enum(EgaColors::Black));
     canvas.clear();
 
     for (idx, block) in screen.iter().enumerate() {
         let x = (idx % GLYPH_COLUMNS as usize) as u8;
         let y = (idx / GLYPH_COLUMNS as usize) as u8;
-        block_to_canvas(canvas, &textures, x, y, block);
+        block_to_canvas(canvas, &textures, x, y, block, blink);
     }
     canvas.present();
 }
 
+pub fn get_timestamp_in_nanos() -> Result<u128, SystemTimeError> {
+    let current_systime = SystemTime::now();
+    let since_epoch = current_systime.duration_since(UNIX_EPOCH)?;
+    let nanos = since_epoch.as_nanos();
+
+    Ok(nanos)
+}
+
 pub fn main() {
     let sdl_context = match sdl2::init() {
         Ok(sdl_context) => sdl_context,
@@ -275,14 +302,30 @@ pub fn main() {
         dos_screen[idx] = ScreenBlock::new(false, EgaColors::as_u8(EgaColors::Black), EgaColors::as_u8(EgaColors::BrightYellow), 178);
     }
 
-    render(&mut canvas, &glyph_textures, &dos_screen);
+    dos_screen[1030] = ScreenBlock::new(true, EgaColors::as_u8(EgaColors::Blue), EgaColors::as_u8(EgaColors::LightGray), 178);
+
+    let mut blink_tick: u128 = 0;
+    let mut blink_state: bool = false;
+
+    render(&mut canvas, &glyph_textures, &dos_screen, &blink_state);
 
     let mut event_pump = match sdl_context.event_pump() {
         Ok(event_pump) => event_pump,
         Err(err) => panic!("Could not obtain SDL2 Event Pump! SDL_Error: {}", err),
     };
 
+    let mut prev_tick = match get_timestamp_in_nanos() {
+        Ok(prev_tick) => prev_tick,
+        Err(err) => panic!("Could not get the current timestamp: {}", err),
+    };
+
     'running: loop {
+        let curr_tick = match get_timestamp_in_nanos() {
+            Ok(curr_tick) => curr_tick,
+            Err(err) => panic!("Could not get the current timestamp: {}", err),
+        };
+        let elapsed = curr_tick - prev_tick;
+
         for event in event_pump.poll_iter() {
             match event {
                 Event::Quit {..} |
@@ -293,7 +336,18 @@ pub fn main() {
             }
         }
 
-        render(&mut canvas, &glyph_textures, &dos_screen);
-        sleep(Duration::new(0, 1_000_000_000u32 / 60));
+        update(elapsed);
+
+        if blink_tick >= BLINK_RATE {
+            blink_state = !blink_state;
+            blink_tick = 0;
+        } else {
+            blink_tick += elapsed;
+        }
+
+        render(&mut canvas, &glyph_textures, &dos_screen, &blink_state);
+        //sleep(Duration::new(0, FPS_60_HERTZ));
+
+        prev_tick = curr_tick;
     }
 }