Bugzilla

Quoting Kvark:

```
Here is a rough plan:

    wgpu-hal expects platform-dependent draw/dispatch buffer.
    the only thing exposed to the outside is the size of that buffer (for each kind of draw/draw indexed/dispatch)
    wgpu-hal command encoder gets a new fn prepare_indirect(src_buffer, src_offset, dst_buffer, dst_offset, kind, count). Under the hood it will be a compute operation that does clamping as well as copies of first instance/vertex.
    wgpu-core spawns a separate encoder to prepare indirect calls whenever it sees one, and orders it accordingly. It also manages the destination buffer as a temporary thing.
```

To expand, if I understand correctly, What I'm planning to do is to:
 - have wgpu-core store some proxy indirect buffers (somewhere, maybe on the device). These will be used as input for the draw indirect commands instead of what is in the command. 
 - in `command_encoder_run_render_pass_impl`, when running into indirect commands, we allocate ranges into the proxy buffers and use them in the render pass instead of the original buffer/range, and record that we need to sanitize the content of the original buffer at its requested offset into the new range of the proxy buffer.
- After we are done with the render pass, we see if we have recorded any ranges to sanitize, if so we create a compute pass that will be submitted just before the render pass. It will dispatch a simple compute shader that reads from the indirect buffer/ranges and write the sanitized output into the proxy buffer.

Quoting Kvark:

```
Here is a rough plan:

    wgpu-hal expects platform-dependent draw/dispatch buffer.
    the only thing exposed to the outside is the size of that buffer (for each kind of draw/draw indexed/dispatch)
    wgpu-hal command encoder gets a new fn prepare_indirect(src_buffer, src_offset, dst_buffer, dst_offset, kind, count). Under the hood it will be a compute operation that does clamping as well as copies of first instance/vertex.
    wgpu-core spawns a separate encoder to prepare indirect calls whenever it sees one, and orders it accordingly. It also manages the destination buffer as a temporary thing.
```

To expand, if I understand correctly, What I'm planning to do is to:
 - have wgpu-core store some proxy indirect buffers (somewhere, maybe on the device). These will be used as input for the draw indirect commands instead of what is in the command. 
 - in `command_encoder_run_render_pass_impl`, when running into indirect commands, we allocate ranges into the proxy buffers and use them in the render pass instead of the original buffer/range, and record that we need to sanitize the content of the original buffer at its requested offset into the new range of the proxy buffer.
- After we are done with the render pass, we see if we have recorded any ranges to sanitize, if so we create a compute pass that will be submitted just before the render pass. It will dispatch a simple compute shader that reads from the indirect buffer/ranges and write the sanitized output into the proxy buffer.

Validating into a separate buffer instead of in-place is so that the validation cannot be observed by other means than the indrect draw itself.