func (dc *DrawContext) UpperLeft() image.Point {
	return dc.upperLeft
}
UpperLeft returns the point which indicates the upper left position.
package qrcode
import (
	"image"
	"image/color"
	"github.com/fogleman/gg"
)
var (
	_shapeRectangle IShape = rectangle{}
	_shapeCircle    IShape = circle{}
)
type IShape interface {
	Draw(ctx *DrawContext)
	DrawFinder(ctx *DrawContext)
}
type DrawContext struct {
	*gg.Context
	upperLeft image.Point  
	w, h      int
	color color.Color
}