inline void initialize(device_context* dc, rect pr)
{
dc_ = dc;
rect_ = pr = pr.normalize();
poffset_ = -pr.left_top();
prect_ = pr;
mask_ = nullptr;
canvas_ = std::make_shared<canvas_type>(pr.width(), pr.height());
}
inline void paint_area(const point& offset, rect rect)
{
poffset_ += offset;
prect_ = rect.normalize();
mask_ = nullptr;
}