Method alloc_mapped_buffer

cake-core/src/backends/vulkan/mod.rs:472–517

(
        device: &ash::Device,
        allocator: &mut gpu_allocator::vulkan::Allocator,
        size: u64,
        usage: vk::BufferUsageFlags,
        _uma_memory_type: Option<u32>,
    )

    // ── Buffer allocation ────────────────────────────────────────────

    fn alloc_mapped_buffer(
        device: &ash::Device,
        allocator: &mut gpu_allocator::vulkan::Allocator,
        size: u64,
        usage: vk::BufferUsageFlags,
        _uma_memory_type: Option<u32>,
    ) -> std::result::Result<MappedBuffer, String> {
        let buf_ci = vk::BufferCreateInfo::default()
            .size(size.max(256))
            .usage(usage)
            .sharing_mode(vk::SharingMode::EXCLUSIVE);
        let buffer = unsafe {
            device
                .create_buffer(&buf_ci, None)
                .map_err(|e| format!("create_buffer: {e}"))?
        };
        let requirements = unsafe { device.get_buffer_memory_requirements(buffer) };

        let allocation = allocator
            .allocate(&gpu_allocator::vulkan::AllocationCreateDesc {
                name: "cake-buf",
                requirements,
                location: gpu_allocator::MemoryLocation::CpuToGpu,
                linear: true,
                allocation_scheme: gpu_allocator::vulkan::AllocationScheme::GpuAllocatorManaged,
            })
            .map_err(|e| format!("allocate: {e}"))?;

        unsafe {
            device
                .bind_buffer_memory(buffer, allocation.memory(), allocation.offset())
                .map_err(|e| format!("bind_buffer_memory: {e}"))?;
        }

        let mapped_ptr = allocation
            .mapped_ptr()
            .ok_or("buffer not mapped — UMA required")?
            .as_ptr() as *mut u8;

        Ok(MappedBuffer {
            buffer,
            allocation,
            mapped_ptr,
            size: size.max(256),
        })
    }

    fn alloc_output(&self, count: usize) -> MappedBuffer {
        let bytes = (count * 4) as u64;