add "balls" example

examples/balls/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "balls"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+anyhow = "1.0.55"
+libretrogd = { path = "../../libretrogd" }
+sdl2 = { version = "0.34.5", features = ["static-link", "bundled", "unsafe_textures" ] }
+

examples/balls/src/main.rs

@@ -0,0 +1,124 @@
+use std::path::Path;
+
+use anyhow::Result;
+use sdl2::keyboard::Scancode;
+
+use libretrogd::utils::rnd_value;
+use libretrogd::*;
+
+const NUM_BALLS: usize = 128;
+const NUM_BALL_SPRITES: usize = 16;
+const BALL_WIDTH: u32 = 8;
+const BALL_HEIGHT: u32 = 8;
+
+struct Ball {
+    x: i32,
+    y: i32,
+    dir_x: i32,
+    dir_y: i32,
+    sprite: usize,
+}
+
+fn main() -> Result<()> {
+    let mut system = SystemBuilder::new()
+        .window_title("Flying Balls!")
+        .vsync(true)
+        .build()?;
+
+    let mut is_running = true;
+
+    let font = BitmaskFont::new_vga_font()?;
+
+    let (balls_bmp, balls_palette) = Bitmap::load_pcx_file(Path::new("./assets/balls.pcx"))?;
+    system.palette = balls_palette.clone();
+
+    let mut sprites = Vec::<Bitmap>::new();
+    let mut balls = Vec::<Ball>::new();
+
+    for i in 0..NUM_BALL_SPRITES {
+        let mut sprite = Bitmap::new(BALL_WIDTH, BALL_HEIGHT)?;
+        sprite.blit_region(
+            BlitMethod::Solid,
+            &balls_bmp,
+            &Rect::new(i as i32 * BALL_WIDTH as i32, 0, BALL_WIDTH, BALL_HEIGHT),
+            0,
+            0,
+        );
+        sprites.push(sprite);
+    }
+
+    for _ in 0..NUM_BALLS {
+        let speed = rnd_value(1, 3);
+        let ball = Ball {
+            x: rnd_value(0, SCREEN_WIDTH as i32 - 1),
+            y: rnd_value(0, SCREEN_HEIGHT as i32 - 1),
+            dir_x: if rnd_value(0, 1) == 0 { -speed } else { speed },
+            dir_y: if rnd_value(0, 1) == 0 { -speed } else { speed },
+            sprite: rnd_value(0, NUM_BALL_SPRITES - 1),
+        };
+        balls.push(ball);
+    }
+
+    while is_running {
+        system.do_events_with(|event| {
+            if let sdl2::event::Event::Quit { .. } = event {
+                is_running = false;
+            }
+        });
+
+        if system.keyboard.is_key_pressed(Scancode::Escape) {
+            is_running = false;
+        }
+
+        if system.keyboard.is_key_up(Scancode::S) {
+            for i in 0..NUM_BALLS {
+                let ball = &mut balls[i];
+                ball.x += ball.dir_x;
+                ball.y += ball.dir_y;
+
+                if ball.dir_x < 0 {
+                    if ball.x <= 0 {
+                        ball.dir_x = -ball.dir_x;
+                        ball.x = 0;
+                    }
+                } else {
+                    if ball.x >= (SCREEN_WIDTH - BALL_WIDTH) as i32 {
+                        ball.dir_x = -ball.dir_x;
+                        ball.x = (SCREEN_WIDTH - BALL_WIDTH) as i32;
+                    }
+                }
+
+                if ball.dir_y < 0 {
+                    if ball.y <= 0 {
+                        ball.dir_y = -ball.dir_y;
+                        ball.y = 0;
+                    }
+                } else {
+                    if ball.y >= (SCREEN_HEIGHT - BALL_HEIGHT) as i32 {
+                        ball.dir_y = -ball.dir_y;
+                        ball.y = (SCREEN_HEIGHT - BALL_HEIGHT) as i32;
+                    }
+                }
+            }
+        }
+
+        system.video.clear(2);
+
+        system
+            .video
+            .print_string("hello, world!", 10, 10, 15, &font);
+
+        for i in 0..NUM_BALLS {
+            system.video.blit(
+                BlitMethod::Transparent(0),
+                &sprites[balls[i].sprite],
+                balls[i].x,
+                balls[i].y,
+            );
+        }
+
+        system.display()?;
+    }
+
+    Ok(())
+}