Draw a triangle between three points with color.
Source
Future<bool> triangle(
int x0, int y0, int x1, int y1, int x2, int y2, int color,
{bool fill: false}) =>
proto.write(
fill ? 8 : 7,
_s2b(x0)
..addAll(_s2b(y0))
..addAll(_s2b(x1))
..addAll(_s2b(y1))
..addAll(_s2b(x2))
..addAll(_s2b(y2))
..addAll(_s2b(color)));