c# - 实现对齐 Canvas 网格线

Question

我对此有点困惑，但我有一个问题，就是试图让我的头脑围绕鼠标捕捉到网格。目前我正在通过覆盖 OnRender 来绘制网格像这样；

 protected override void OnRender(DrawingContext drawingContext)
        {

            int numberOfVerticalLines = 8;
            int numberOfHorizontalLines = 8;

            CellHeight = this.ActualHeight / numberOfVerticalLines;
            CellWidth = this.ActualWidth / numberOfHorizontalLines;

            double verticalOffset = 0;
            double horizontalOffset = 0;

            Pen pen = new Pen(Stroke, StrokeThickness);

            pen.DashStyle = DashStyle;

            for (int i = 0; i <= numberOfHorizontalLines; i++)
            {
                for (int j = 0; j <= numberOfVerticalLines; j++)
                {

                    drawingContext.DrawLine(pen, new Point(horizontalOffset, verticalOffset), new Point(horizontalOffset, CellHeight + verticalOffset));

                    verticalOffset += CellHeight;
                }

                horizontalOffset += CellWidth;
                verticalOffset = 0;
            }

            horizontalOffset = 0;
            verticalOffset = 0;

            for (int i = 0; i <= numberOfVerticalLines; i++)
            {
                for (int j = 0; j <= numberOfHorizontalLines; j++)
                {
                    drawingContext.DrawLine(pen, new Point(horizontalOffset, verticalOffset), new Point(CellWidth + horizontalOffset, verticalOffset));

                    horizontalOffset += CellWidth;
                }

                verticalOffset += CellHeight;
                horizontalOffset = 0;
            }
        }

这给出了以下结果；



但是，我在考虑将鼠标捕捉到最近的网格交叉点(水平线与垂直线交汇处)的路线时有点卡住了。显然，当我使用绘图上下文来绘制线条时，我在绘制这些线条后没有引用这些线条。

所以我想基本上我的问题是，我怎样才能实现鼠标捕捉到网格？这更像是一个数学问题而不是一个面向对象的控制问题吗？我已经通读了几乎所有我发现相关的堆栈溢出问题，但还没有得出任何现实的想法。

注意:虽然目前我已经硬编码了一个 8x8 网格，但这最终将由用户定义。

Answer 1

一种基本方法是通过以下方式将鼠标的 (x,y) 与十字架进行比较:
1.计算鼠标所在单元格的宽度和高度的起点和终点；和
2. 将这两个间隔(宽度和高度)与实际鼠标 (x,y) 进行比较以找到最近的单元格点。

下面是一些快速拼凑的示例代码来演示捕捉:

/// <summary>
/// When left shift key is pressed we snap the mouse to the closest
/// intersection
/// </summary>
void MainWindow_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Key == Key.LeftShift)
    {
        var p = GetSnappingPoint(Mouse.GetPosition(this), new Size(200, 200));
        SetCursorPos((int)p.X, (int)p.Y+20);
    }

}

[DllImport("User32.dll")]
private static extern bool SetCursorPos(int x, int y);

/// <summary>
/// Get snapping point by
/// </summary>
Point GetSnappingPoint(Point mouse,Size cellSize)
{
    //Get x interval based on cell width
    var xInterval = GetInterval(mouse.X, cellSize.Width);

    //Get y interal based in cell height
    var yInterval = GetInterval(mouse.Y, cellSize.Height);

    // return the point on cell grid closest to the mouseposition
    return new Point()
    {
        X = Math.Abs(xInterval.Lower - mouse.X) > Math.Abs(xInterval.Upper - mouse.X) ? xInterval.Upper : xInterval.Lower,
        Y = Math.Abs(yInterval.Lower - mouse.Y) > Math.Abs(yInterval.Upper - mouse.Y) ? yInterval.Upper : yInterval.Lower,
    };
}

/// <summary>
///  Find an interval of the celsize based on mouse position and size
/// </summary>
Interval GetInterval(double mousePos,double size)
{
    return new Interval()
    {
        Lower = ((int)(mousePos / size)) * size,
        Upper = ((int)(mousePos / size)) * size + size
    };
}

/// <summary>
/// Basic interval class
/// </summary>
class Interval
{
    public double Lower { get; set; }
    public double Upper { get; set; }
}