Struct GpuReadback 

pub struct GpuReadback;

GPU → CPU readback helper.

The current implementation operates as a CPU stub (identity copy). Replace the body of GpuReadback::download and GpuReadback::download_region with actual WGPU buffer-mapping logic when a live device is available.

Implementations

impl GpuReadback

pub fn download(width: u32, height: u32, gpu_data: &[u8]) -> Vec<u8>

Download a full frame from GPU-accessible memory to a CPU Vec<u8>.

On the CPU stub backend this is an identity copy of gpu_data.

Arguments

• width – Frame width in pixels.
• height – Frame height in pixels.
• gpu_data – GPU-accessible source buffer (RGBA packed, row-major).

Returns

A Vec<u8> containing a copy of the readback data.

pub fn download_region( src_width: u32, x: u32, y: u32, w: u32, h: u32, gpu_data: &[u8], ) -> Vec<u8>

Download a sub-region of a frame.

• src_width – Width of the full source frame in pixels.
• x, y – Top-left corner of the sub-region.
• w, h – Width/height of the sub-region in pixels.
• gpu_data – Full source frame data (RGBA, row-major).

Returns an empty Vec if the region is fully out of bounds.

pub fn expected_len(width: u32, height: u32) -> usize

Compute the expected byte length for a frame of width × height pixels in RGBA format.

pub fn validate_size(width: u32, height: u32, gpu_data: &[u8]) -> bool

Verify that gpu_data has exactly the expected length for a width × height RGBA frame.

pub fn split_channels(gpu_data: &[u8]) -> (Vec<u8>, Vec<u8>, Vec<u8>, Vec<u8>)

Split RGBA packed data into separate R, G, B, A channel planes.

Returns (r, g, b, a) each of length width * height.