Project: svg
Task (challenging): When click label triangle, use mouse in canvas to draw a svg polygon triangle (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 triangle's left-bottom is the rect left-bottom, right-bottom is the rect right-bottom, and top is the center of rect top edge. Polygon points sequence is left-bottom, right-bottom, top.