Raise error if target(s) fit in board

stimuli/illusions/checkerboards.py

@@ -4,13 +4,24 @@
 
 
 def mask_from_idx(checkerboard_stim, check_idc):
+    board_shape = checkerboard_stim["board_shape"]
+
     check_size = checkerboard_stim["check_visual_size"]
     ppd = checkerboard_stim["ppd"]
 
     check_size_px = resolution.shape_from_visual_size_ppd(check_size, ppd)
 
     mask = np.zeros(checkerboard_stim["shape"])
     for coords in check_idc:
+        if (
+            coords[0] < 0
+            or coords[0] > coords[0]
+            or coords[1] < 0
+            or coords[1] > board_shape[1]
+        ):
+            raise ValueError(
+                f"Cannot provide mask for check {coords} outside board {board_shape}"
+            )
         ypos = int(coords[0] * check_size_px.height)
         xpos = int(coords[1] * check_size_px.width)
         mask[