c# - 在给定矩形的情况下在 GDI+ 中绘制三角形

Question

我正在尝试创建一个函数，该函数将在给定 Rectangle 结构的情况下创建一个三角形。我有以下代码:

public enum Direction {
    Up,
    Right,
    Down,
    Left
}

private void DrawTriangle(Graphics g, Rectangle r, Direction direction)
{
    if (direction == Direction.Up) {
        int half = r.Width / 2;

        g.DrawLine(Pens.Black, r.X, r.Y + r.Height, r.X + Width, r.Y + r.Height); // base
        g.DrawLine(Pens.Black, r.X, r.Y + r.Height, r.X + half, r.Y); // left side
        g.DrawLine(Pens.Black, r.X + r.Width, r.Y + r.Height, r.X + half, r.Y); // right side
    }
}

只要方向朝上，这个就可以工作。但是我有两个问题。首先，有没有一种方法可以始终绘制它，而只是分别将其旋转 0 度、90 度、180 度或 270 度，从而避免使用四个 if 语句？其次，如何用黑色填充三角形？

Answer 1

您可以绘制一个统一的三角形，然后使用矩阵变换对其进行旋转和缩放以适合矩形内部，但老实说，我认为这比定义每个点的工作量更大。

    private void DrawTriangle(Graphics g, Rectangle rect, Direction direction)
    {            
        int halfWidth = rect.Width / 2;
        int halfHeight = rect.Height / 2;
        Point p0 = Point.Empty;
        Point p1 = Point.Empty;
        Point p2 = Point.Empty;          

        switch (direction)
        {
            case Direction.Up:
                p0 = new Point(rect.Left + halfWidth, rect.Top);
                p1 = new Point(rect.Left, rect.Bottom);
                p2 = new Point(rect.Right, rect.Bottom);
                break;
            case Direction.Down:
                p0 = new Point(rect.Left + halfWidth, rect.Bottom);
                p1 = new Point(rect.Left, rect.Top);
                p2 = new Point(rect.Right, rect.Top);
                break;
            case Direction.Left:
                p0 = new Point(rect.Left, rect.Top + halfHeight);
                p1 = new Point(rect.Right, rect.Top);
                p2 = new Point(rect.Right, rect.Bottom);
                break;
            case Direction.Right:
                p0 = new Point(rect.Right, rect.Top + halfHeight);
                p1 = new Point(rect.Left, rect.Bottom);
                p2 = new Point(rect.Left, rect.Top);
                break;
        }

        g.FillPolygon(Brushes.Black, new Point[] { p0, p1, p2 });  
    }