extmod/modframebuf: Fix FrameBuffer get-buffer implementation.

This wasn't correctly accounting for the bits-per-pixel and was returning a
bufinfo struct with the incorrect length.  Instead, just forward directly
to the underlying buffer object.

Fixes issue #12563.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

extmod/modframebuf.c

@@ -336,12 +336,8 @@ STATIC void framebuf_args(const mp_obj_t *args_in, mp_int_t *args_out, int n) {
 }
 
 STATIC mp_int_t framebuf_get_buffer(mp_obj_t self_in, mp_buffer_info_t *bufinfo, mp_uint_t flags) {
-    (void)flags;
     mp_obj_framebuf_t *self = MP_OBJ_TO_PTR(self_in);
-    bufinfo->buf = self->buf;
-    bufinfo->len = self->stride * self->height * (self->format == FRAMEBUF_RGB565 ? 2 : 1);
-    bufinfo->typecode = 'B'; // view framebuf as bytes
-    return 0;
+    return mp_get_buffer(self->buf_obj, bufinfo, flags) ? 0 : 1;
 }
 
 STATIC mp_obj_t framebuf_fill(mp_obj_t self_in, mp_obj_t col_in) {

tests/extmod/framebuf1.py

@@ -109,3 +109,9 @@ except ValueError:
 fbuf = framebuf.FrameBuffer1(buf, w, h)
 fbuf = framebuf.FrameBuffer1(buf, w, h, w)
 print(framebuf.MVLSB == framebuf.MONO_VLSB)
+
+# test get-buffer (returns the original buffer)
+fbuf = framebuf.FrameBuffer(bytearray(2), 8, 1, framebuf.MONO_HLSB)
+fbuf.pixel(0, 0, 1)
+fbuf.pixel(4, 0, 1)
+print(bytearray(fbuf))

tests/extmod/framebuf1.py.exp

@@ -66,3 +66,4 @@ bytearray(b'\n\x15\n\x15\n\x15\n\x15\x00\x00\x00\x00\x00\x00\x00\x00')
 
 ValueError
 True
+bytearray(b'\x88\x00')