用鼠标移动矩形

Question

我写了这段代码：

private struct MovePoint
    {
        public int X;
        public int Y;
    }
private void Image_MouseDown(object sender, MouseEventArgs e)
    {
        FirstPoint = new MovePoint();
        FirstPoint.X = e.X;
        FirstPoint.Y = e.Y;
    }

    private void Image_MouseMove(object sender, MouseEventArgs e)
    {
        if(e.Button == MouseButtons.Left)
        {
            if(FirstPoint.X > e.X)
            {
                Rectangle.X = FirstPoint.X - e.X;
                //Rectangle.Width -= FirstPoint.X - e.X;
            } else
            {
                Rectangle.X = FirstPoint.X + e.X;
                //Rectangle.Width += FirstPoint.X + e.X;
            }

            if(FirstPoint.Y > e.Y)
            {
                Rectangle.Y = FirstPoint.Y - e.Y;
                //Rectangle.Height -= FirstPoint.Y - e.Y;
            } else
            {
                Rectangle.Y = FirstPoint.Y + e.Y;
                //Rectangle.Height += FirstPoint.Y + e.Y;
            }

            Image.Invalidate();
        }
    }
private void Image_Paint(object sender, PaintEventArgs e)
    {
        if(Pen != null) e.Graphics.DrawRectangle(Pen, Rectangle);
    }

矩形移动，但有反转（不应该）。你能帮忙吗？

Answer 1

鼠标移动处理程序中用于根据鼠标移动移动矩形的数学似乎很不合理；我想你想要这样的东西：

private void Image_MouseMove(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        int initialX = 0, initialY = 0; // for example.

        Rectangle.X = (e.X - FirstPoint.X) + initialX; 
        Rectangle.Y = (e.Y - FirstPoint.Y) + initialY;

        Image.Invalidate();
    }
}

这样，矩形的左上角将通过跟踪初始鼠标按下位置和当前鼠标位置之间的增量来跟随鼠标。但请注意，每次重新单击并拖动时，矩形都会移回其原始位置。

相反，如果您希望矩形在多次单击和拖动操作中“记住”其位置（即不要在鼠标按下时重新初始化到其初始位置），您可以执行以下操作：

private void Image_MouseMove(object sender, MouseEventArgs e)
{
    if (e.Button == MouseButtons.Left)
    {
        // Increment rectangle-location by mouse-location delta.
        Rectangle.X += e.X - FirstPoint.X; 
        Rectangle.Y += e.Y - FirstPoint.Y; 

        // Re-calibrate on each move operation.
        FirstPoint = new MovePoint { X = e.X, Y = e.Y };

        Image.Invalidate();
    }
}

另一项建议：无需创建当已经存在 System.Drawing.Point 类型时，您自己的 MovePoint 类型。另外，一般来说，尽量不要创建可变结构。