How to get pixel color from the buffer ?

[sak96]

previously using this worked.

let buffer_slice = self.output_buffer.slice(..);
let buffer_future = buffer_slice.map_async(wgpu::MapMode::Read);
self.device.poll(wgpu::Maintain::Wait);
if futures::executor::block_on(buffer_future).is_ok() {
    let padded_buffer = buffer_slice.get_mapped_range();
    todo!();
}
output_buffer.unmap();

with wgpu = "0.15.0" how do i achieve the same?

i tried this:

let buffer_slice = self.output_buffer.slice(..);
buffer_slice.map_async(wgpu::MapMode::Read, |_| ());
self.device.poll(wgpu::Maintain::Wait);
// if futures::executor::block_on(buffer_future).is_ok() {
let padded_buffer = buffer_slice.get_mapped_range();
todo!();
output_buffer.unmap();

i got error

thread 'main' panicked at 'unable to remove range from map context',

may be related is discussion here
related example here

[sak96]

adding padded_buffer to scope seems to have fixed issue but not sure if that is really a fix.

let buffer_slice = self.output_buffer.slice(..);
let (tx, rx) = channel::oneshot::channel();
buffer_slice.map_async(wgpu::MapMode::Read, move |result| {
    tx.send(result).unwrap();
});
self.device.poll(wgpu::Maintain::Wait);
if block_on(async {rx.await}).is_ok() {
  let padded_buffer = buffer_slice.get_mapped_range();
  todo!();
}
output_buffer.unmap();