code: func b8(img *image.Paletted, x, y, size float64, angle int) {
  	points := pool.Get().([]float64)[:0]
  	m := size / 2
  	mm := m / 2
  
  	// 顶部三角形
  	drawBlock(img, x, y, size, angle, append(points,
  		x+m, y,
  		x+3*mm, y+m,
  		x+mm, y+m,
  		x+m, y,
  	))
  
  	// 底下左边
  	drawBlock(img, x, y, size, angle, append(points[:0],
  		x+mm, y+m,
  		x+m, y+size,
  		x, y+size,
  		x+mm, y+m,
  	))
  
  	// 底下右边
  	drawBlock(img, x, y, size, angle, append(points[:0],
  		x+3*mm, y+m,
  		x+size, y+size,
  		x+m, y+size,
  		x+3*mm, y+m,
  	))
  
  	pool.Put(points)
  }
docs: // b8 三个堆叠的三角形
  //
  //  -----------
  //  |    #    |
  //  |   ###   |
  //  |  #####  |
  //  |  #   #  |
  //  | ### ### |
  //  |#########|
  //  -----------