为什么 PenAlignment.Inset 在用户控件绘图中不生效？答案

【问题标题】：Why Doesn't PenAlignment.Inset Take Effect in User Control Drawing?为什么 PenAlignment.Inset 在用户控件绘图中不生效？
【发布时间】：2014-01-10 00:43:00
【问题描述】：

我做了一个自定义的可移动控件，但像素计算有问题。

控件大小为100、100，Padding和Margin均为0,0,0,0。

我认为从控件宽度（和高度）中减去笔宽两次就可以了，但是当我这样做时 DrawRectangle 中的底线和右线被部分或全部剪裁，具体取决于 pen.Width 的值和 size.Width size.Height 的减量因子

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);

        var pen = new Pen(Color.Black);
        pen.Width = 16;
        pen.Alignment = System.Drawing.Drawing2D.PenAlignment.Inset;
        var brush = Brushes.Aquamarine;
        var size = this.Size;
        size.Width -= (int)(pen.Width * 2);  
        size.Height -= (int)(pen.Width * 2);
        var rec = new Rectangle(this.Location, this.Size);
        e.Graphics.FillRectangle(brush, rec);
        e.Graphics.DrawRectangle(pen, rec);
    }

无论选择什么 pen.Width 值，似乎 (90, 90) 点之外的整个图像都会被剪裁。

编辑：我刚刚发现，当 control.Location 设置为 (0, 0) 时，不会发生 unwatned 剪辑。

public partial class Form1 : Form
{
    MTC control;
    public Form1()
    {
        InitializeComponent();

        control = new MTC();
        control.Parent = panel1;
        control.Width = 100; control.Height = 200;
        //control.Left = 100; control.Top = 100;
        control.Location = new Point(0, 0);
        panel1.Controls.Add(control);

【问题讨论】：

绘画相对于控件的客户区。因此，您必须使用var rec = new Rectangle(Point.Empty, size);

标签： c# winforms user-controls

【解决方案1】：

线宽可以是可变的，但整个粗线中心的精确 1 像素线是沿着矩形绘制的。所以你应该像这样计算矩形：

protected override void OnPaint(PaintEventArgs e)
{
    base.OnPaint(e);

    var pen = new Pen(Color.Black);
    pen.Width = 16;
    pen.Alignment = System.Drawing.Drawing2D.PenAlignment.Inset;
    var brush = Brushes.Aquamarine;
    var halfPenWidth = pen.Width/2;
    var rec = new RectangleF(Location, Size);
    rec.Width -= pen.Width;
    rec.Height -= pen.Width;
    rec.X += halfPenWidth;
    rec.Y += halfPenWidth;
    e.Graphics.FillRectangle(brush, rec);
    //Graphics.DrawRectangle does not support RectangleF directly
    e.Graphics.DrawRectangle(pen, rec.Left, rec.Top, rec.Width, rec.Height);
}

【讨论】：

【解决方案2】：

通过引入另一个面板控件并将其添加到 real 容器中解决了这个问题。

public class Movable : Control
{
    public Panel ContainerPanel { get; set; }    
    public Movable(Point location, Size size) : base()
    {
        var pan = new Panel();
        pan.Margin = new Padding(0);
        pan.Padding = new Padding(0);
        pan.Location = location;
        pan.Size = size;
        this.ContainerPanel = pan;
        this.Location = new Point(0, 0);
        this.Size = size;
        pan.Controls.Add(this);
        pan.Height = size.Height; // Resize again after addition of 'content'
        this.movable = isMovable;
    }
    // codes for OnMouseDown, OnMouseUp, OnMouseMove, ...
}

public class MovableTest : Movable
{
    public MovableTest(Point location, Size size)
        : base(location, size) { }
    protected override void OnPaint(System.Windows.Forms.PaintEventArgs e)
    {
        base.OnPaint(e);
        // user drawing code comes here
    }
}

public partial class Form1 : Form
{
    MovableTest ctrl2;
    ctrl2 = new MovableTest(new Point(75, 50), new Size(100, 100));

    // add .ContainerPanel, NOT ctrl2 itself!
    this.Controls.Add(ctrl2.ContainerPanel); 
}

【讨论】：