Project: svg
Task (easy): When click label ellipse, use mouse in canvas to draw a svg ellipse (fill color is white, line width is '.line-width' value, line color is '.color' value). There is a rect whose left-top is the point when mouse pressing down and right-bottom is the point when mouse pressing up. The ellipse's center is the rect center, x radius is the half rect width, y radius is the half rect height.