Fixed a bug when using rectangular vector field
Fixed a bug when using rectangular vector field

When calculating the row and column indices, there was a division by shape.y instead of shape.x, causing bugs when using a non-square vector field.
jdreaver/vispy,drufat/vispy,drufat/vispy,dchilds7/Deysha-Star-Formation,ghisvail/vispy,jdreaver/vispy,bollu/vispy,inclement/vispy,QuLogic/vispy,ghisvail/vispy,michaelaye/vispy,julienr/vispy,Eric89GXL/vispy,dchilds7/Deysha-Star-Formation,bollu/vispy,QuLogic/vispy,Eric89GXL/vispy,bollu/vispy,inclement/vispy,julienr/vispy,jdreaver/vispy,julienr/vispy,michaelaye/vispy,Eric89GXL/vispy,QuLogic/vispy,drufat/vispy,dchilds7/Deysha-Star-Formation,inclement/vispy,ghisvail/vispy,michaelaye/vispy