Can't seem to print the contents of a buffer (getting 0 values)

[BLuchterhand]

Hey all! I've been following various resources (but mostly the wgpu repo's example for compute buffers https://github.com/gfx-rs/wgpu/tree/trunk/examples/hello-compute) to be able to access a buffer's contents.

I'm initializing a buffer with the contents of a vector of a single f32 value (12.0 as a random number) and I would expect this value to print out after it's been copied to the contents of the other buffer. All I'm seeing printed out is Some(0) as you can see below:

BufferView { slice: BufferSlice { buffer: Buffer { context: Context { type: "Native" }, id: ObjectId { id: Some(4611687899623063559) }, data: Any { .. }, map_context: Mutex { data: MapContext { total_size: 4, initial_range: 0..4, sub_ranges: [0..4] } }, size: 4, usage: MAP_READ | COPY_DST }, offset: 0, size: None }, data: BufferMappedRange { ptr: 0x10ff8c100, size: 4 } }
[0.0]

Here's my code:

        let size = std::mem::size_of::<f32>() as wgpu::BufferAddress;
        let staging_buffer = self.device.create_buffer(&wgpu::BufferDescriptor {
            label: None,
            size,
            usage: wgpu::BufferUsages::MAP_READ | wgpu::BufferUsages::COPY_DST,
            mapped_at_creation: false,
        });

        let initial_data = vec![12.0; 1];
        let storage_buffer = self.device.create_buffer_init(&wgpu::util::BufferInitDescriptor {
            label: Some("Storage Buffer"),
            contents: bytemuck::cast_slice(&initial_data),
            usage: wgpu::BufferUsages::STORAGE
                | wgpu::BufferUsages::COPY_DST
                | wgpu::BufferUsages::COPY_SRC,
        });

        let mut encoder = self
            .device
            .create_command_encoder(&wgpu::CommandEncoderDescriptor {
                label: Some("Render Encoder"),
            });

        encoder.copy_buffer_to_buffer(&storage_buffer, 0, &staging_buffer, 0, size);
        self.queue.submit(Some(encoder.finish()));

        let buffer_slice = staging_buffer.slice(..);
        let (sender, receiver) = futures_intrusive::channel::shared::oneshot_channel();
        buffer_slice.map_async(wgpu::MapMode::Read, move |v| sender.send(v).unwrap());
        self.device.poll(wgpu::Maintain::Wait);

        if let Some(Ok(())) = receiver.receive().await {
            let data = buffer_slice.get_mapped_range();

            let result: Vec<f32> = bytemuck::cast_slice(&data).to_vec();
            println!("{:?}", data);
            println!("{:?}", result);
            drop(data);
            staging_buffer.unmap();
        } else {
            panic!("failed to run compute on gpu!")
        }

And my cargo.toml if it's helpful

[package]
name = "rust_game"
version = "0.1.0"
edition = "2021"

[dependencies]
cfg-if = "1"
anyhow = "1.0"
bytemuck = { version = "1.12", features = [ "derive" ] }
cgmath = { version = "0.18", features = [ "swizzle" ] }
env_logger = "0.10"
pollster = "0.2"
log = "0.4"
tobj = { version = "3.2", features = ["async"]}
wgpu = { version = "0.15"}
winit = "0.27"
instant = "0.1"
futures-intrusive = "0.5.0"
futures = "0.3.28"

[dependencies.image]
version = "0.24"
default-features = false
features = ["png", "jpeg"]

[target.'cfg(target_arch = "wasm32")'.dependencies]
reqwest = { version = "0.11" }
console_error_panic_hook = "0.1"
console_log = "0.2"
wgpu = { version = "0.17", features = ["webgl"]}
wasm-bindgen = "0.2"
wasm-bindgen-futures = "0.4"
web-sys = { version = "0.3", features = [
    "Document",
    "Window",
    "Element",
    "Location",
]}

[build-dependencies]
anyhow = "1.0"
fs_extra = "1.2"
glob = "0.3"

Side note: I've tried running this on my M1 Mac (my primary machine) as well as my PC with a dedicated graphics card, both with the same results. I'm absolutely out of ideas and would appreciate any pointers if you have any for me!

[BLuchterhand]

I'll leave this up as a cautionary tale for "always double-check your data types"...
As you can see, I was casting this data into a Vec, when my data was actually of type Vec<64>. Because my number was so small and it was only gathering the first few bits of the floating point number, it was printing out 0...

solved :)