1 files changed, 90 insertions, 1 deletions
diff --git a/src/instance.rs b/src/instance.rs
index eded8cf..dc1ee40 100644
--- a/src/instance.rs
+++ b/src/instance.rs
@@ -3,7 +3,7 @@ use std::mem::size_of;
 use bytemuck::{Pod, Zeroable};
 
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
-pub struct InstanceId(pub(crate) usize);
+pub struct InstanceId(usize);
 
 #[repr(C)]
 #[derive(Copy, Clone, Debug, PartialEq, Pod, Zeroable)]
@@ -58,3 +58,92 @@ impl Instance {
 		}
 	}
 }
+
+pub struct InstanceBuffer {
+	instances: Vec<Instance>,
+	instance_buffer: wgpu::Buffer,
+	instance_buffer_size: usize,
+}
+
+fn create_buffer(device: &wgpu::Device, instances: &Vec<Instance>) -> wgpu::Buffer {
+	device.create_buffer(&wgpu::BufferDescriptor {
+		label: Some("Sprite Instance Buffer"),
+		size: (instances.capacity() * size_of::<Instance>()) as wgpu::BufferAddress,
+		usage: wgpu::BufferUsages::VERTEX | wgpu::BufferUsages::COPY_DST,
+		mapped_at_creation: false,
+	})
+}
+
+impl InstanceBuffer {
+	pub(crate) fn new(device: &wgpu::Device, capacity: usize) -> Self {
+		let instances = Vec::with_capacity(capacity);
+		let instance_buffer_size = instances.capacity();
+		let instance_buffer = device.create_buffer(&wgpu::BufferDescriptor {
+			label: Some("Sprite Instance Buffer"),
+			size: (instance_buffer_size * size_of::<Instance>()) as wgpu::BufferAddress,
+			usage: wgpu::BufferUsages::VERTEX | wgpu::BufferUsages::COPY_DST,
+			mapped_at_creation: false,
+		});
+
+		Self {
+			instances,
+			instance_buffer,
+			instance_buffer_size,
+		}
+	}
+
+	pub fn len(&self) -> u32 {
+		self.instances
+			.len()
+			.try_into()
+			.expect("expected less than 3 billion instances")
+	}
+
+	pub fn is_empty(&self) -> bool {
+		self.instances.is_empty()
+	}
+
+	pub const fn buffer_size(&self) -> usize {
+		self.instance_buffer_size
+	}
+
+	pub(crate) fn buffer_slice(&self) -> wgpu::BufferSlice {
+		self.instance_buffer.slice(..)
+	}
+
+	pub fn push_instance(&mut self, instance: Instance) -> InstanceId {
+		let index = self.instances.len();
+		self.instances.push(instance);
+		InstanceId(index)
+	}
+
+	pub fn get_instance(&self, id: InstanceId) -> Option<&Instance> {
+		self.instances.get(id.0)
+	}
+
+	pub fn get_instance_mut(&mut self, id: InstanceId) -> Option<&mut Instance> {
+		self.instances.get_mut(id.0)
+	}
+
+	pub fn clear(&mut self) {
+		self.instances.clear();
+	}
+
+	fn expand_buffer(&mut self, device: &wgpu::Device) {
+		self.instance_buffer_size = self.instances.capacity();
+		self.instance_buffer = create_buffer(device, &self.instances);
+	}
+
+	#[profiling::function]
+	pub(crate) fn fill_buffer(&mut self, device: &wgpu::Device, queue: &wgpu::Queue) {
+		if self.instances.len() > self.instance_buffer_size {
+			self.expand_buffer(device);
+		}
+
+		queue.write_buffer(
+			&self.instance_buffer,
+			0 as wgpu::BufferAddress,
+			bytemuck::cast_slice(&self.instances),
+		);
+	}
+}