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use crate::*;
use std::sync::Arc;
/// Buffer arena that can grow as needed.
#[derive(Debug)]
pub struct GrowingBufferArena {
buffers: Vec<(Arc<wgpu::Buffer>, u64)>,
desc: wgpu::BufferDescriptor<'static>,
}
impl GrowingBufferArena {
/// Creates a new [GrowingBufferArena].
///
/// The arena will use `desc` to allocate buffers when it grows.
pub fn new(cx: &Context, desc: wgpu::BufferDescriptor<'static>) -> Self {
GrowingBufferArena {
buffers: vec![(Arc::new(cx.device.create_buffer(&desc)), 0)],
desc,
}
}
/// Allocates a sub-buffer of specified `size`.
///
/// Size *must* be less than `desc.size` (provided with [GrowingBufferArena::new]).
pub fn allocate(&mut self, cx: &Context, size: u64) -> ArenaAllocation {
assert!(size <= self.desc.size);
for (i, (buffer, cursor)) in self.buffers.iter_mut().enumerate() {
if size <= self.desc.size - *cursor {
let offset = *cursor;
*cursor += size;
return ArenaAllocation {
buffer: buffer.clone(),
offset,
index: i,
};
}
}
self.grow(cx);
self.allocate(cx, size)
}
/// Resets all the buffer allocations.
///
/// All `ArenaAllocation`s returned from this arena should now be considered invalid.
pub fn free(&mut self) {
for (_, cursor) in &mut self.buffers {
*cursor = 0;
}
}
fn grow(&mut self, cx: &Context) {
self.buffers
.push((Arc::new(cx.device.create_buffer(&self.desc)), 0));
}
}
/// Sub-buffer allocation returned from [GrowingBufferArena].
#[derive(Debug, Clone)]
pub struct ArenaAllocation {
pub buffer: Arc<wgpu::Buffer>,
pub offset: u64,
/// The internal buffer index in [GrowingBufferArena].
pub index: usize,
}