Added dynamic starfield tiling

src/main.rs

@@ -26,6 +26,9 @@ pub const STARFIELD_COUNT: u64 = 100;
 // will completely cover a (square) screen. This depends on zoom!
 pub const STARFIELD_SIZE: u64 = STARFIELD_PARALLAX_MAX as u64 * 500;
 
+pub const ZOOM_MIN: Pfloat = 200.0;
+pub const ZOOM_MAX: Pfloat = 2000.0;
+
 use crate::{
 	doodad::Doodad,
 	inputstatus::InputStatus,
@@ -84,9 +87,6 @@ struct Game {
 }
 
 impl Game {
-	const ZOOM_MIN: Pfloat = 200.0;
-	const ZOOM_MAX: Pfloat = 2000.0;
-
 	fn new() -> Self {
 		Game {
 			last_update: Instant::now(),
@@ -128,8 +128,7 @@ impl Game {
 		}
 
 		if self.input.v_scroll != 0.0 {
-			self.camera.zoom =
-				(self.camera.zoom + self.input.v_scroll).clamp(Self::ZOOM_MIN, Self::ZOOM_MAX);
+			self.camera.zoom = (self.camera.zoom + self.input.v_scroll).clamp(ZOOM_MIN, ZOOM_MAX);
 			self.input.v_scroll = 0.0;
 		}
 
@@ -165,7 +164,7 @@ pub async fn run() -> Result<()> {
 	let mut gpu = GPUState::new(window).await?;
 	let mut game = Game::new();
 
-	gpu.on_new_system(&game);
+	gpu.update_starfield_buffer(&game);
 
 	event_loop.run(move |event, _, control_flow| {
 		match event {
@@ -175,7 +174,7 @@ pub async fn run() -> Result<()> {
 				match gpu.render(&game) {
 					Ok(_) => {}
 					// Reconfigure the surface if lost
-					Err(wgpu::SurfaceError::Lost) => gpu.resize(gpu.window_size),
+					Err(wgpu::SurfaceError::Lost) => gpu.resize(&game, gpu.window_size),
 					// The system is out of memory, we should probably quit
 					Err(wgpu::SurfaceError::OutOfMemory) => *control_flow = ControlFlow::Exit,
 					// All other errors (Outdated, Timeout) should be resolved by the next frame
@@ -205,17 +204,17 @@ pub async fn run() -> Result<()> {
 						..
 					} => game.process_key(state, key),
 					WindowEvent::MouseInput { state, button, .. } => {
-						game.process_click(state, button)
+						game.process_click(state, button);
 					}
 					WindowEvent::MouseWheel { delta, phase, .. } => {
-						game.process_scroll(delta, phase)
+						game.process_scroll(delta, phase);
 					}
 					WindowEvent::Resized(physical_size) => {
-						gpu.resize(*physical_size);
+						gpu.resize(&game, *physical_size);
 					}
 					WindowEvent::ScaleFactorChanged { new_inner_size, .. } => {
 						// new_inner_size is &&mut so we have to dereference it twice
-						gpu.resize(**new_inner_size);
+						gpu.resize(&game, **new_inner_size);
 					}
 					_ => {}
 				}

src/render/gpustate.rs

@@ -5,7 +5,7 @@ use std::{iter, rc::Rc};
 use wgpu;
 use winit::{self, dpi::PhysicalSize, window::Window};
 
-use crate::{Game, STARFIELD_COUNT, STARFIELD_SIZE};
+use crate::{Game, STARFIELD_COUNT, STARFIELD_PARALLAX_MIN, STARFIELD_SIZE, ZOOM_MAX};
 
 use super::{
 	globaldata::{GlobalData, GlobalDataContent},
@@ -46,6 +46,8 @@ impl GPUState {
 	// We can draw at most this many sprites on the screen.
 	// TODO: compile-time option
 	pub const SPRITE_INSTANCE_LIMIT: u64 = 100;
+
+	// Must be small enough to fit in an i32
 	pub const STARFIELD_INSTANCE_LIMIT: u64 = STARFIELD_COUNT * 9;
 
 	pub async fn new(window: Window) -> Result<Self> {
@@ -188,7 +190,7 @@ impl GPUState {
 		&self.window
 	}
 
-	pub fn resize(&mut self, new_size: PhysicalSize<u32>) {
+	pub fn resize(&mut self, game: &Game, new_size: PhysicalSize<u32>) {
 		if new_size.width > 0 && new_size.height > 0 {
 			self.window_size = new_size;
 			self.window_aspect = new_size.width as f32 / new_size.height as f32;
@@ -196,6 +198,7 @@ impl GPUState {
 			self.config.height = new_size.height;
 			self.surface.configure(&self.device, &self.config);
 		}
+		self.update_starfield_buffer(game)
 	}
 
 	pub fn update(&mut self) {}
@@ -253,27 +256,56 @@ impl GPUState {
 	/// Make a StarfieldInstance for each star that needs to be drawn.
 	/// Will panic if STARFIELD_INSTANCE_LIMIT is exceeded.
 	///
-	/// This is only called inside self.render()
-	fn make_starfield_instances(&mut self, game: &Game) -> Vec<StarfieldInstance> {
-		let mut instances = Vec::new();
+	/// Starfield data rarely changes, so this is called only when it's needed.
+	pub fn update_starfield_buffer(&mut self, game: &Game) {
 		let sz = STARFIELD_SIZE as f32;
-		for offset in [
-			Vector2 { x: 0.0, y: 0.0 },
-			Vector2 { x: 0.0, y: sz },
-			Vector2 { x: sz, y: sz },
-			Vector2 { x: sz, y: 0.0 },
-			Vector2 { x: sz, y: -sz },
-			Vector2 { x: 0.0, y: -sz },
-			Vector2 { x: -sz, y: -sz },
-			Vector2 { x: -sz, y: 0.0 },
-			Vector2 { x: -sz, y: sz },
-		] {
-			for s in &game.system.starfield {
-				instances.push(StarfieldInstance {
-					position: (s.pos + offset).into(),
-					parallax: s.parallax,
-					height: s.height,
-				})
+
+		// Compute window size in starfield tiles
+		let mut nw_tile: Point2<i32> = {
+			// Game coordinates (relative to camera) of nw corner of screen.
+			let clip_nw = Point2::from((self.window_aspect, 1.0)) * ZOOM_MAX / 2.0;
+
+			// Adjust for parallax
+			let v: Point2<f32> = clip_nw * STARFIELD_PARALLAX_MIN;
+
+			// We don't need to adjust coordinates here, since clip_nw is always positive.
+
+			#[rustfmt::skip]
+			// Compute m = fmod(x, sz)
+			let m: Vector2<f32> = (
+				(v.x - (v.x / sz).floor() * sz),
+				(v.y - (v.y / sz).floor() * sz)
+			).into();
+
+			// Now, remainder and convert to "relative tile" coordinates
+			// ( where (0,0) is center tile, (0, 1) is north, etc)
+			let rel = (v - m) / sz;
+
+			// relative coordinates of north-east tile
+			(rel.x.round() as i32, rel.y.round() as i32).into()
+		};
+
+		// Truncate tile grid to buffer size
+		// (The window won't be full of stars if we don't have a large enough instance limit)
+		while (nw_tile.x * 2 + 1) * (nw_tile.y * 2 + 1) > Self::STARFIELD_INSTANCE_LIMIT as i32 {
+			nw_tile -= Vector2::from((1, 1));
+		}
+
+		// Add all tiles to buffer
+		let mut instances = Vec::new();
+		for x in (-nw_tile.x)..=nw_tile.x {
+			for y in (-nw_tile.y)..=nw_tile.y {
+				let offset = Vector2 {
+					x: sz * x as f32,
+					y: sz * y as f32,
+				};
+				for s in &game.system.starfield {
+					instances.push(StarfieldInstance {
+						position: (s.pos + offset).into(),
+						parallax: s.parallax,
+						height: s.height,
+					})
+				}
 			}
 		}
 
@@ -284,16 +316,10 @@ impl GPUState {
 		}
 
 		self.starfield_count = instances.len() as u32;
-		return instances;
-	}
-
-	pub fn on_new_system(&mut self, game: &Game) {
-		// Create starfield instances
-		let starfield_instances = self.make_starfield_instances(game);
 		self.queue.write_buffer(
 			&self.vertex_buffers.starfield.instances,
 			0,
-			bytemuck::cast_slice(&starfield_instances),
+			bytemuck::cast_slice(&instances),
 		);
 	}
 

src/render/shaders/starfield.wgsl

@@ -27,7 +27,7 @@ struct GlobalUniform {
 
 
 fn fmod(x: vec2<f32>, m: f32) -> vec2<f32> {
-	return x - floor(x * (1.0 / m)) * m;
+	return x - floor(x / m) * m;
 }
 
 @vertex
@@ -64,7 +64,7 @@ fn vertex_shader_main(
 	// Translate
 	pos = pos + (
 		// Don't forget to correct distance for screen aspect ratio too!
-		(camera_pos / (global.camera_zoom * instance.parallax))
+		(camera_pos / (global.camera_zoom * (instance.parallax)))
 		/ vec2<f32>(global.window_aspect, 1.0)
 	);