byte-engine 0.1.0

A composable Rust game engine focused on graphics, input, audio, physics, and retained UI.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147

use math::Base as _;

use super::{LayoutElement, Location3, Size};
use crate::ui::Transform;

#[derive(Clone, Copy)]
pub(super) struct Affine2 {
	a: f32,
	b: f32,
	c: f32,
	d: f32,
	tx: f32,
	ty: f32,
}

impl Affine2 {
	pub(super) fn identity() -> Self {
		Self {
			a: 1.0,
			b: 0.0,
			c: 0.0,
			d: 1.0,
			tx: 0.0,
			ty: 0.0,
		}
	}

	pub(super) fn from_transform(transform: Transform, element: &LayoutElement) -> Self {
		let center_x = element.position.x() + element.size.x() * 0.5;
		let center_y = element.position.y() + element.size.y() * 0.5;
		let scale_x = sanitize_scale(transform.scale_x);
		let scale_y = sanitize_scale(transform.scale_y);

		Self {
			a: scale_x,
			b: 0.0,
			c: 0.0,
			d: scale_y,
			tx: center_x + sanitize_offset(transform.translate_x) - center_x * scale_x,
			ty: center_y + sanitize_offset(transform.translate_y) - center_y * scale_y,
		}
	}

	pub(super) fn compose(self, rhs: Self) -> Self {
		Self {
			a: self.a * rhs.a + self.c * rhs.b,
			b: self.b * rhs.a + self.d * rhs.b,
			c: self.a * rhs.c + self.c * rhs.d,
			d: self.b * rhs.c + self.d * rhs.d,
			tx: self.a * rhs.tx + self.c * rhs.ty + self.tx,
			ty: self.b * rhs.tx + self.d * rhs.ty + self.ty,
		}
	}

	fn transform_point(self, x: f32, y: f32) -> (f32, f32) {
		(self.a * x + self.c * y + self.tx, self.b * x + self.d * y + self.ty)
	}

	pub(super) fn transform_rect(self, element: &LayoutElement) -> (Location3, Size) {
		let left = element.position.x();
		let top = element.position.y();
		let right = left + element.size.x();
		let bottom = top + element.size.y();

		let corners = [
			self.transform_point(left, top),
			self.transform_point(right, top),
			self.transform_point(right, bottom),
			self.transform_point(left, bottom),
		];

		let mut min_x = f32::INFINITY;
		let mut min_y = f32::INFINITY;
		let mut max_x = f32::NEG_INFINITY;
		let mut max_y = f32::NEG_INFINITY;

		for (x, y) in corners {
			min_x = min_x.min(x);
			min_y = min_y.min(y);
			max_x = max_x.max(x);
			max_y = max_y.max(y);
		}

		// Preserve fractional visual bounds so display scaling cannot magnify logical-pixel snapping.
		let x = clamp_coordinate(min_x);
		let y = clamp_coordinate(min_y);
		let width = clamp_coordinate(max_x - min_x);
		let height = clamp_coordinate(max_y - min_y);

		(Location3::new(x, y, element.position.z()), Size::new(width, height))
	}
}

fn sanitize_offset(value: f32) -> f32 {
	if value.is_finite() {
		value
	} else {
		0.0
	}
}

fn sanitize_scale(value: f32) -> f32 {
	if value.is_finite() {
		value.max(0.0)
	} else {
		1.0
	}
}

fn clamp_coordinate(value: f32) -> f32 {
	if !value.is_finite() || value <= 0.0 {
		0.0
	} else {
		value
	}
}

#[cfg(test)]
mod tests {
	use std::num::NonZeroU32;

	use super::*;

	#[test]
	fn transformed_rect_preserves_subpixel_motion_at_retina_scale() {
		let element = LayoutElement {
			id: NonZeroU32::new(1).unwrap(),
			position: Location3::new(10, 10, 0),
			size: Size::new(100, 40),
			hit_testable: false,
		};
		let physical_positions = (0..=10)
			.map(|step| {
				let transform = Transform::identity().translate_x(step as f32 * 0.1);
				let (position, _) = Affine2::from_transform(transform, &element).transform_rect(&element);
				position.x() * 2.0
			})
			.collect::<Vec<_>>();

		assert!(
			physical_positions
				.windows(2)
				.all(|positions| (positions[1] - positions[0] - 0.2).abs() < 0.0001),
			"smooth motion was quantized into physical positions: {physical_positions:?}"
		);
	}
}