From c0db69bd7600d21970b07fb063d83e7ba206e59f Mon Sep 17 00:00:00 2001
From: Mark <mark@betalupi.com>
Date: Fri, 22 Dec 2023 22:10:38 -0800
Subject: [PATCH] Added basic parallax

---
 src/doodad.rs              |  2 ++
 src/main.rs                | 29 ++++++++++++++++++++++++++---
 src/render/gpustate.rs     | 13 +++++++------
 src/render/texturearray.rs |  2 +-
 src/ship.rs                |  1 +
 src/system.rs              | 10 +++++++++-
 6 files changed, 46 insertions(+), 11 deletions(-)

diff --git a/src/doodad.rs b/src/doodad.rs
index f123aa2..f949c66 100644
--- a/src/doodad.rs
+++ b/src/doodad.rs
@@ -5,6 +5,7 @@ use crate::{physics::Pfloat, Sprite, Spriteable};
 pub struct Doodad {
 	pub sprite: String,
 	pub pos: Point2<Pfloat>,
+	pub parallax: Pfloat,
 }
 
 impl Spriteable for Doodad {
@@ -14,6 +15,7 @@ impl Spriteable for Doodad {
 			name: self.sprite.clone(),
 			angle: Deg { 0: 0.0 },
 			scale: 1.0,
+			parallax: self.parallax,
 		};
 	}
 }
diff --git a/src/main.rs b/src/main.rs
index 82cdc2f..7b8e5e0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,5 +1,5 @@
 use anyhow::Result;
-use cgmath::{Deg, Point2};
+use cgmath::{Deg, EuclideanSpace, Point2};
 use winit::{
 	event::{
 		ElementState, Event, KeyboardInput, MouseButton, MouseScrollDelta, TouchPhase,
@@ -51,6 +51,22 @@ struct Sprite {
 	// This sprite's rotation
 	// (relative to north, measured ccw)
 	angle: Deg<Pfloat>,
+
+	// Parallax factor.
+	// More positive => farther away
+	// More negative => closer
+	// Zero: no parallax.
+	parallax: Pfloat,
+}
+
+impl Sprite {
+	const PARALLAX_STRENGTH: Pfloat = 0.1;
+
+	// Returns post-parallax position in game coordinates.
+	pub fn post_parallax_position(&self, camera: Camera) -> Point2<f32> {
+		let v = camera.pos.to_vec() - self.pos.to_vec();
+		return self.pos + (v * self.parallax * Self::PARALLAX_STRENGTH);
+	}
 }
 
 struct Game {
@@ -95,11 +111,11 @@ impl Game {
 		}
 
 		if self.input.key_right {
-			self.player.body.rot(Deg { 0: 15.0 } * t);
+			self.player.body.rot(Deg { 0: 35.0 } * t);
 		}
 
 		if self.input.key_left {
-			self.player.body.rot(Deg { 0: -15.0 } * t);
+			self.player.body.rot(Deg { 0: -35.0 } * t);
 		}
 
 		if self.input.v_scroll != 0.0 {
@@ -119,6 +135,13 @@ impl Game {
 		sprites.append(&mut self.system.sprites());
 		sprites.push(self.player.sprite());
 
+		// Make sure sprites are drawn in the correct order
+		// (note the reversed a, b in the comparator)
+		//
+		// TODO: use a gpu depth buffer with parallax as z-coordinate?
+		// Might be overkill.
+		sprites.sort_by(|a, b| b.parallax.total_cmp(&a.parallax));
+
 		return sprites;
 	}
 }
diff --git a/src/render/gpustate.rs b/src/render/gpustate.rs
index 7bd12ac..c5e3b1a 100644
--- a/src/render/gpustate.rs
+++ b/src/render/gpustate.rs
@@ -260,13 +260,15 @@ impl GPUState {
 
 		let mut instances: Vec<SpriteInstance> = Vec::new();
 		for s in sprites {
-			let pos = s.pos - camera.pos.to_vec();
+			let pos = s.post_parallax_position(camera) - camera.pos.to_vec();
 			let texture = self.texture_array.get_texture(&s.name[..]);
 
-			// Game dimensions of this sprite post-scale
-			// We really need height / 2 to check if we're on the screen,
-			// but we omit the division so we get a small "margin"
-			// and so we can re-use this value.
+			// Game dimensions of this sprite post-scale.
+			//
+			// We only need height / 2 to check if we're on the screen,
+			// but we omit the division.
+			// This gives us a small margin, and lets us re-use the value
+			// without an extra multiply.
 			let height = texture.height * s.scale;
 			let width = height * texture.aspect;
 
@@ -277,7 +279,6 @@ impl GPUState {
 				|| pos.x > clip_sw.x + width
 				|| pos.y < clip_sw.y - height
 			{
-				println!("skip {}", s.name);
 				continue;
 			}
 
diff --git a/src/render/texturearray.rs b/src/render/texturearray.rs
index 280aa69..a1a935f 100644
--- a/src/render/texturearray.rs
+++ b/src/render/texturearray.rs
@@ -11,7 +11,7 @@ pub struct TextureArray {
 	texture_indices: HashMap<String, u32>,
 }
 
-const TEX: &[&str] = &["error", "red", "gypsum", "earth", "a0"];
+const TEX: &[&str] = &["error", "small", "gypsum", "earth", "a0"];
 
 pub struct Texture {
 	pub index: u32,  // Index in texture array
diff --git a/src/ship.rs b/src/ship.rs
index f811eac..3a1bf78 100644
--- a/src/ship.rs
+++ b/src/ship.rs
@@ -35,6 +35,7 @@ impl Spriteable for Ship {
 			name: self.kind.sprite().to_owned(),
 			angle: self.body.angle,
 			scale: 1.0,
+			parallax: 0.0,
 		};
 	}
 }
diff --git a/src/system.rs b/src/system.rs
index 477c519..5344a53 100644
--- a/src/system.rs
+++ b/src/system.rs
@@ -12,6 +12,7 @@ impl System {
 		s.bodies.push(Doodad {
 			pos: (0.0, 0.0).into(),
 			sprite: "a0".to_owned(),
+			parallax: 3.0,
 		});
 
 		s.bodies.push(Doodad {
@@ -22,11 +23,18 @@ impl System {
 			}
 			.to_cartesian(),
 			sprite: "earth".to_owned(),
+			parallax: 1.0,
 		});
 
 		s.bodies.push(Doodad {
-			pos: (1000.0, 1000.0).into(),
+			pos: Polar {
+				center: (0.0, 0.0).into(),
+				radius: 200.0,
+				angle: Deg { 0: 270.0 },
+			}
+			.to_cartesian(),
 			sprite: "small".to_owned(),
+			parallax: -1.0,
 		});
 
 		return s;