Remove some memory allocations

1 files changed, 99 insertions, 0 deletions

diff --git a/engine/src/stackvec.rs b/engine/src/stackvec.rs
new file mode 100644
index 0000000..9c00461
--- /dev/null
+++ b/engine/src/stackvec.rs
@@ -0,0 +1,99 @@
+use std::mem::MaybeUninit;
+use std::ops::{Deref, DerefMut};
+
+pub struct StackVec<T, const CAPACITY: usize> {
+	values: [MaybeUninit<T>; CAPACITY],
+	len: usize,
+}
+
+impl<T, const CAPACITY: usize> Deref for StackVec<T, CAPACITY> {
+	type Target = [T];
+
+	fn deref(&self) -> &Self::Target {
+		self.as_slice()
+	}
+}
+
+impl<T, const CAPACITY: usize> DerefMut for StackVec<T, CAPACITY> {
+	fn deref_mut(&mut self) -> &mut Self::Target {
+		self.as_mut_slice()
+	}
+}
+
+impl<T, const CAPACITY: usize> FromIterator<T> for StackVec<T, CAPACITY> {
+	fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
+		let mut this = Self::new();
+		for item in iter {
+			this.push(item);
+		}
+
+		this
+	}
+}
+
+impl<T, const CAPACITY: usize> StackVec<T, CAPACITY> {
+	pub fn new() -> Self {
+		Self {
+			values: MaybeUninit::uninit_array(),
+			len: 0,
+		}
+	}
+
+	pub fn capcity(&self) -> usize {
+		CAPACITY
+	}
+
+	pub fn len(&self) -> usize {
+		self.len
+	}
+
+	pub fn is_empty(&self) -> bool {
+		self.len == 0
+	}
+
+	pub fn as_slice(&self) -> &[T] {
+		// safety: the first `len` elements are guaranteed to be initialized
+		unsafe { MaybeUninit::slice_assume_init_ref(&self.values[..self.len]) }
+	}
+
+	pub fn as_mut_slice(&mut self) -> &mut [T] {
+		// safety: the first `len` elements are guaranteed to be initialized
+		unsafe { MaybeUninit::slice_assume_init_mut(&mut self.values[..self.len]) }
+	}
+
+	pub fn as_ptr(&self) -> *const T {
+		self.values.as_ptr().cast()
+	}
+
+	pub fn as_mut_ptr(&mut self) -> *mut T {
+		self.values.as_mut_ptr().cast()
+	}
+
+	pub fn try_push(&mut self, value: T) -> Option<()> {
+		self.values.get_mut(self.len)?.write(value);
+		self.len += 1;
+		Some(())
+	}
+
+	pub fn push(&mut self, value: T) {
+		self.values[self.len].write(value);
+		self.len += 1;
+	}
+
+	pub fn pop(&mut self) -> Option<T> {
+		if self.is_empty() {
+			return None;
+		}
+
+		// safety: this value will no longer be used, and the value is valid
+		//         because it appears in the valid part of the array
+		unsafe {
+			self.len -= 1;
+			Some(std::ptr::read(self.as_ptr().add(self.len())))
+		}
+	}
+
+	pub fn clear(&mut self) {
+		self.len = 0;
+	}
+}