func moveTriangle(t *spec.Triangle) { t.Dy = t.Dy - gravity t.X = t.X + t.Dx*timeBetweenPaints t.Y = t.Y + t.Dy*timeBetweenPaints if t.Y <= -1 { t.Dy = -1 * t.Dy t.Y = -1 } else if maxY := 1 - triangleCenterHeight; t.Y >= maxY { t.Dy = -1 * t.Dy t.Y = maxY } }