feat: add aspect ratio demo bin

src/bin/aspect_demo.rs

@@ -0,0 +1,130 @@
+use std::time::{Duration, Instant};
+
+use sdl2::event::Event;
+use sdl2::keyboard::Keycode;
+use sdl2::pixels::Color;
+use sdl2::rect::Rect;
+
+// A self-contained SDL2 demo showing how to keep a consistent aspect ratio
+// with letterboxing/pillarboxing in a resizable window.
+//
+// This uses SDL2's logical size feature, which automatically sets a viewport
+// to preserve the target aspect ratio and adds black bars as needed.
+// We also clear the full window to black and then clear the logical viewport
+// to a content color, so bars remain visibly black.
+
+const LOGICAL_WIDTH: u32 = 320; // target content width
+const LOGICAL_HEIGHT: u32 = 180; // target content height (16:9)
+
+fn main() -> Result<(), String> {
+    // Initialize SDL2
+    let sdl = sdl2::init()?;
+    let video = sdl.video()?;
+
+    // Create a resizable window
+    let window = video
+        .window("SDL2 Aspect Ratio Demo", 960, 540)
+        .resizable()
+        .position_centered()
+        .build()
+        .map_err(|e| e.to_string())?;
+
+    let mut canvas = window.into_canvas().build().map_err(|e| e.to_string())?;
+
+    // Set the desired logical (virtual) resolution. SDL will letterbox/pillarbox
+    // as needed to preserve this aspect ratio when the window is resized.
+    canvas
+        .set_logical_size(LOGICAL_WIDTH, LOGICAL_HEIGHT)
+        .map_err(|e| e.to_string())?;
+    // Optional: uncomment to enforce integer scaling only (more retro look)
+    // canvas.set_integer_scale(true)?;
+
+    let mut events = sdl.event_pump()?;
+
+    let mut running = true;
+    let start = Instant::now();
+    let mut last_log = Instant::now();
+
+    while running {
+        for event in events.poll_iter() {
+            match event {
+                Event::Quit { .. }
+                | Event::KeyDown {
+                    keycode: Some(Keycode::Escape),
+                    ..
+                } => {
+                    running = false;
+                }
+                Event::Window { win_event, .. } => {
+                    // Periodically log window size and the computed viewport
+                    // to demonstrate how letterboxing/pillarboxing behaves.
+                    use sdl2::event::WindowEvent;
+                    match win_event {
+                        WindowEvent::Resized(_, _)
+                        | WindowEvent::SizeChanged(_, _)
+                        | WindowEvent::Maximized
+                        | WindowEvent::Restored => {
+                            if last_log.elapsed() > Duration::from_millis(250) {
+                                let out_size = canvas.output_size()?;
+                                let viewport = canvas.viewport();
+                                println!(
+                                    "window={}x{}, viewport x={}, y={}, w={}, h={}",
+                                    out_size.0,
+                                    out_size.1,
+                                    viewport.x(),
+                                    viewport.y(),
+                                    viewport.width(),
+                                    viewport.height()
+                                );
+                                last_log = Instant::now();
+                            }
+                        }
+                        _ => {}
+                    }
+                }
+                _ => {}
+            }
+        }
+
+        // 1) Clear the entire window to black (no viewport) so the bars are black
+        canvas.set_viewport(None);
+        canvas.set_draw_color(Color::RGB(0, 0, 0));
+        canvas.clear();
+
+        // 2) Re-apply logical size so SDL sets a viewport that preserves aspect
+        //    ratio. Clearing now only affects the letterboxed content area.
+        canvas
+            .set_logical_size(LOGICAL_WIDTH, LOGICAL_HEIGHT)
+            .map_err(|e| e.to_string())?;
+
+        // Fill the content area with a background color to differentiate from bars
+        canvas.set_draw_color(Color::RGB(30, 30, 40));
+        canvas.clear();
+
+        // Draw a simple grid to visualize scaling clearly
+        canvas.set_draw_color(Color::RGB(60, 60, 90));
+        let step = 20i32;
+        for x in (0..=LOGICAL_WIDTH as i32).step_by(step as usize) {
+            let _ = canvas.draw_line(sdl2::rect::Point::new(x, 0), sdl2::rect::Point::new(x, LOGICAL_HEIGHT as i32));
+        }
+        for y in (0..=LOGICAL_HEIGHT as i32).step_by(step as usize) {
+            let _ = canvas.draw_line(sdl2::rect::Point::new(0, y), sdl2::rect::Point::new(LOGICAL_WIDTH as i32, y));
+        }
+
+        // Draw a border around the logical content area
+        canvas.set_draw_color(Color::RGB(200, 200, 220));
+        let border = Rect::new(0, 0, LOGICAL_WIDTH, LOGICAL_HEIGHT);
+        canvas.draw_rect(border)?;
+
+        // Draw a moving box to demonstrate dynamic content staying within aspect
+        let elapsed_ms = start.elapsed().as_millis() as i32;
+        let t = (elapsed_ms / 8) % LOGICAL_WIDTH as i32;
+        let box_rect = Rect::new(t - 10, (LOGICAL_HEIGHT as i32 / 2) - 10, 20, 20);
+        canvas.set_draw_color(Color::RGB(255, 140, 0));
+        canvas.fill_rect(box_rect).ok();
+
+        canvas.present();
+    }
+
+    Ok(())
+}