update_brush_size: Update the brush size in the mouse move event
Description
The brush size is changed by the differences in two successive mouse
positions.
Usage
update_brush_size(meta, event)
Arguments
meta
the meta data containing the brush information (meta$pos,
meta$brush.size, meta$brush.move and meta$start)
event
the event in the callback (if missing, it will search in the
parent environment sys.frame(1) which is often the callback
function)
Value
a matrix of the coordinates of the brush rectangle, which can be
passed to qrect and used to query the brushed
elements by layer$locate(); as a side effect, the brush size is
updated, unless it is only a single click or the brush is not in the move
mode
Details
The current mouse position is obtained from event$pos(). If the brush
is in the move mode (meta$brush.move == TRUE; often set in a mouse
click event), the brush size is updated by the differences between
meta$start and meta$pos; the former is the starting position of
the mouse, and the latter is the current position.