add functions to convert containers directly into packet

src/cp437_grid.rs

@@ -1,5 +1,5 @@
-use crate::{heap_drop, heap_move, heap_move_nonnull, ByteSlice};
-use servicepoint::{Cp437Grid, DataRef, Grid};
+use crate::{heap_drop, heap_move, heap_move_nonnull, heap_remove, ByteSlice};
+use servicepoint::{Cp437Grid, Cp437GridCommand, DataRef, Grid, Origin, Packet};
 use std::ptr::NonNull;
 
 /// Creates a new [Cp437Grid] with the specified dimensions.
@@ -132,3 +132,24 @@ pub unsafe extern "C" fn sp_cp437_grid_unsafe_data_ref(
 ) -> ByteSlice {
     unsafe { ByteSlice::from_slice((*cp437_grid.as_ptr()).data_ref_mut()) }
 }
+
+/// Creates a [Cp437GridCommand] and immediately turns that into a [Packet].
+///
+/// The provided [Cp437Grid] gets consumed.
+///
+/// Returns NULL in case of an error.
+#[no_mangle]
+pub unsafe extern "C" fn sp_cp437_grid_into_packet(
+    grid: NonNull<Cp437Grid>,
+    x: usize,
+    y: usize,
+) -> *mut Packet {
+    let grid = unsafe { heap_remove(grid) };
+    match Packet::try_from(Cp437GridCommand {
+        grid,
+        origin: Origin::new(x, y),
+    }) {
+        Ok(packet) => heap_move(packet),
+        Err(_) => std::ptr::null_mut(),
+    }
+}