如何增加或减少圆圈

Question

我在Load事件上绘制了一个圆圈，并且我有两个按钮可以增加和减小圆圈的大小。但是我无法沿圆心缩小或放大大小。

private Draw draw = new Draw();
private int width = 150;
private int height = 150;
private int xLocation = 300;
private int yLocation = 100;

private void Form1_Load(object sender, EventArgs e)
{
}

protected override void OnPaint(PaintEventArgs e)
{
    draw.circle(xLocation, yLocation, width, height, e.Graphics);
}

private void enlarge_Click_1(object sender, EventArgs e)
{
    width = width + 5;
    height = height + 5;
    draw.circle(xLocation, yLocation, width, height, this.CreateGraphics());
}

private void Shrink_Click_1(object sender, EventArgs e)
{
    width = width - 5;
    height = height - 5;
    draw.circle(xLocation, yLocation, height, height, this.CreateGraphics());
} 

internal class Draw
{
    public int x { get; set; }
    public int y { get; set; }
    public int width { get; set; }
    public int height { get; set; }
    public Graphics g { get; set; }

    public void circle(int x, int y, int width, int height, Graphics g)
    {
        this.x = x;
        this.y = y;
        this.width = width;
        this.height = height;
        Pen color = new Pen(Color.Red);
        this.g = g;
        g.Clear(Color.White);
        Rectangle circle = new Rectangle(x, y, width, height);
        g.DrawEllipse(color, circle);
        g.Dispose();
    }
}

Answer 1

使用Rectangle.Inflate方法在长轴的两个方向上放大或缩小Rectangle。

您可以用width类型的单个变量替换height，xLocation，yLocation和Rectangle类成员，并在窗体的Load事件中实例化它：

private Rectangle drawRect;

private void Form1_Load(object sender, EventArgs e)
{
    //Set the default size and location...
    drawRect = new Rectangle(
        (ClientRectangle.Width - 150) / 2,
        (ClientRectangle.Height - 150) / 2, 150, 150);
}

如果在Form调整大小时需要重新调整绘图矩形的位置，请按以下方式处理Resize事件：

private void Form1_Resize(object sender, EventArgs e)
{
    //Assuming you want to center the drawing rectangle...
    drawRect = new Rectangle(
        (ClientRectangle.Width - drawRect.Width) / 2,
        (ClientRectangle.Height - drawRect.Height) / 2,
        drawRect.Width, drawRect.Height);
}

放大和缩小尺寸：

private void enlarge_Click(object sender, EventArgs e)
{
    var cr = ClientRectangle;
    cr.Inflate(-50, -50);

    //Optional check to draw within the ClientRectangle with some margins
    if (cr.Contains(drawRect))
    {
        drawRect.Inflate(5, 5);
        Invalidate();
    }
}

private void Shrink_Click(object sender, EventArgs e)
{
    //Optional check to have a minimum size for the Rectangle.
    if (drawRect.Width >= 15 && drawRect.Height >= 15)
    {
        drawRect.Inflate(-5, -5);
        Invalidate();
    }
}

Draw类可以简化为：

internal class Draw
{
    public static void Circle(Graphics g, int x, int y, int width, int height) =>
        Circle(g, new Rectangle(x, y, width, height));

    public static void Circle(Graphics g, Rectangle rect)
    {
        g.Clear(Color.White);
        g.DrawEllipse(Pens.Red, rect);
    }
}

因此您可以在任何Paint事件中调用静态方法，就像这样简单：

private void Form1_Paint(object sender, PaintEventArgs e) =>
    Draw.Circle(e.Graphics, drawRect);

旁注：

• 调用Control.Invalidate方法以通知绘图画布（在您的情况下为Form）以刷新绘图/绘画例程，并避免重复调用。

• 在这种情况下没有理由创建新的Graphics对象。

• Pen也是一次性物品，应丢弃。用于在using块中创建一次性对象，以帮助您完成此任务。