1 files changed, 117 insertions, 0 deletions
diff --git a/wgpu/src/buffer/static.rs b/wgpu/src/buffer/static.rs
new file mode 100644
index 00000000..cf06790c
--- /dev/null
+++ b/wgpu/src/buffer/static.rs
@@ -0,0 +1,117 @@
+use bytemuck::{Pod, Zeroable};
+use std::marker::PhantomData;
+use std::mem;
+
+//128 triangles/indices
+const DEFAULT_STATIC_BUFFER_COUNT: wgpu::BufferAddress = 128;
+
+/// A generic buffer struct useful for items which have no alignment requirements
+/// (e.g. Vertex, Index buffers) & no dynamic offsets.
+#[derive(Debug)]
+pub(crate) struct Buffer<T> {
+    //stored sequentially per mesh iteration; refers to the offset index in the GPU buffer
+    offsets: Vec<wgpu::BufferAddress>,
+    label: &'static str,
+    usages: wgpu::BufferUsages,
+    gpu: wgpu::Buffer,
+    size: wgpu::BufferAddress,
+    _data: PhantomData<T>,
+}
+
+impl<T: Pod + Zeroable> Buffer<T> {
+    /// Initialize a new static buffer.
+    pub fn new(
+        device: &wgpu::Device,
+        label: &'static str,
+        usages: wgpu::BufferUsages,
+    ) -> Self {
+        let size = (mem::size_of::<T>() as u64) * DEFAULT_STATIC_BUFFER_COUNT;
+
+        Self {
+            offsets: Vec::new(),
+            label,
+            usages,
+            gpu: Self::gpu_buffer(device, label, size, usages),
+            size,
+            _data: PhantomData,
+        }
+    }
+
+    fn gpu_buffer(
+        device: &wgpu::Device,
+        label: &'static str,
+        size: wgpu::BufferAddress,
+        usage: wgpu::BufferUsages,
+    ) -> wgpu::Buffer {
+        device.create_buffer(&wgpu::BufferDescriptor {
+            label: Some(label),
+            size,
+            usage,
+            mapped_at_creation: false,
+        })
+    }
+
+    /// Returns whether or not the buffer needs to be recreated. This can happen whenever mesh data
+    /// changes & a redraw is requested.
+    pub fn resize(&mut self, device: &wgpu::Device, new_count: usize) -> bool {
+        let size = (mem::size_of::<T>() * new_count) as u64;
+
+        if self.size < size {
+            self.offsets.clear();
+            self.size = size;
+            self.gpu = Self::gpu_buffer(device, self.label, size, self.usages);
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Writes the current vertex data to the gpu buffer with a memcpy & stores its offset.
+    ///
+    /// Returns the size of the written bytes.
+    pub fn write(
+        &mut self,
+        device: &wgpu::Device,
+        staging_belt: &mut wgpu::util::StagingBelt,
+        encoder: &mut wgpu::CommandEncoder,
+        offset: u64,
+        content: &[T],
+    ) -> u64 {
+        let bytes = bytemuck::cast_slice(content);
+        let bytes_size = bytes.len() as u64;
+
+        if let Some(buffer_size) = wgpu::BufferSize::new(bytes_size) {
+            let mut buffer = staging_belt.write_buffer(
+                encoder,
+                &self.gpu,
+                offset,
+                buffer_size,
+                device,
+            );
+
+            buffer.copy_from_slice(bytes);
+
+            self.offsets.push(offset);
+        }
+
+        bytes_size
+    }
+
+    fn offset_at(&self, index: usize) -> &wgpu::BufferAddress {
+        self.offsets
+            .get(index)
+            .expect("Offset at index does not exist.")
+    }
+
+    /// Returns the slice calculated from the offset stored at the given index.
+    /// e.g. to calculate the slice for the 2nd mesh in the layer, this would be the offset at index
+    /// 1 that we stored earlier when writing.
+    pub fn slice_from_index(&self, index: usize) -> wgpu::BufferSlice<'_> {
+        self.gpu.slice(self.offset_at(index)..)
+    }
+
+    /// Clears any temporary data from the buffer.
+    pub fn clear(&mut self) {
+        self.offsets.clear()
+    }
+}