def _move_viewport(self, dx=0, dy=0, x=None, y=None, force_draw=False):
if x is None:
x = self._view_col0 + dx
if y is None:
y = self._view_row0 + dy
ncol0 = clamp(x, 0, self._max_col0)
nrow0 = clamp(y, 0, self._max_row0)
if ncol0 != self._view_col0 or nrow0 != self._view_row0 or force_draw:
self._view_col0 = ncol0
self._view_row0 = nrow0
self._draw()
def _fetch_data(self):
"""
Retrieve frame data within the current view window.
This method will adjust the view window if it goes out-of-bounds.
"""
self._view_col0 = clamp(self._view_col0, 0, self._max_col0)
self._view_row0 = clamp(self._view_row0, 0, self._max_row0)
self._view_ncols = clamp(self._view_ncols, 0,
self._frame_ncols - self._view_col0)
self._view_nrows = clamp(self._view_nrows, 0,
self._frame_nrows - self._view_row0)
return self._data_callback(self._view_row0,
self._view_row0 + self._view_nrows,
self._view_col0,
self._view_col0 + self._view_ncols)
