绘制可逆矩形

Question

我从http://support.microsoft.com/kb/314945获得了绘制可逆/橡皮筋矩形的代码。我给它添加了代码，这样当我离开鼠标左键时，图像上也会创建一个矩形，然后我就可以用它来裁剪图像。

这个很好用。唯一的问题是橡皮筋矩形不会从鼠标所在的位置开始或结束。虽然分歧很小，但仍然相当值得注意。之后，我使用相同的坐标来绘制矩形，该矩形将精确地绘制在鼠标开始和结束的位置。如果能帮上忙，我们将不胜感激。

以下是代码：(Got问题修复-添加代码，以便其他人可以从中受益)我已经使它成为一个控件，我在任何需要它的地方使用它！

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Drawing;
using System.Data;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace CroppingControl
{
    public partial class CroppingImage : UserControl
    {
        Rectangle rc = new Rectangle();
        Boolean bHaveMouse;
        Point ptOriginal = new Point();
        Point ptLast = new Point();
        Image Pic;

        public CroppingImage()
        {
            InitializeComponent();
            pictureBox1.MouseDown += new MouseEventHandler(MyMouseDown);
            pictureBox1.MouseUp += new MouseEventHandler(MyMouseUp);
            pictureBox1.MouseMove += new MouseEventHandler(MyMouseMove);
            bHaveMouse = false;
        }


        public Image Image
        {
            set
            {
                pictureBox1.Image = value;
                Pic = value;
            }
            get
            {
                return pictureBox1.Image;
            }
        }

        public void MyMouseDown(Object sender, MouseEventArgs e)
        {
            pictureBox1.Image = Pic;
            // Make a note that we "have the mouse".

            bHaveMouse = true;
            // Store the "starting point" for this rubber-band rectangle.
            ptOriginal.X = e.X;
            ptOriginal.Y = e.Y;
            // Special value lets us know that no previous
            // rectangle needs to be erased.
            ptLast.X = -1;
            ptLast.Y = -1;
        }

        // Convert and normalize the points and draw the reversible frame.
        private void MyDrawReversibleRectangle(Point p1, Point p2)
        {
            Point px = p1;
            Point py = p2;

            // Convert the points to screen coordinates.
            p1 = PointToScreen(p1);
            p2 = PointToScreen(p2);
            // Normalize the rectangle.
            if (p1.X < p2.X)
            {
                rc.X = p1.X;
                rc.Width = p2.X - p1.X;
            }
            else
            {
                rc.X = p2.X;
                rc.Width = p1.X - p2.X;
            }
            if (p1.Y < p2.Y)
            {
                rc.Y = p1.Y;
                rc.Height = p2.Y - p1.Y;
            }
            else
            {
                rc.Y = p2.Y;
                rc.Height = p1.Y - p2.Y;
            }
            // Draw the reversible frame.
            ControlPaint.DrawReversibleFrame(rc, Color.Black, FrameStyle.Dashed);

            rc.X = px.X;
            rc.Y = px.Y;

        }
        // Called when the left mouse button is released.
        public void MyMouseUp(Object sender, MouseEventArgs e)
        {
            // Set internal flag to know we no longer "have the mouse".
            bHaveMouse = false;
            // If we have drawn previously, draw again in that spot
            // to remove the lines.
            if (ptLast.X != -1)
            {
                Point ptCurrent = new Point(e.X, e.Y);
                MyDrawReversibleRectangle(ptOriginal, ptLast);
                Graphics graphics = pictureBox1.CreateGraphics();
                Pen pen = new Pen(Color.Gray, 2);
                pen.DashStyle = System.Drawing.Drawing2D.DashStyle.DashDot;
                graphics.DrawRectangle(pen, rc);

            }
            // Set flags to know that there is no "previous" line to reverse.
            ptLast.X = -1;
            ptLast.Y = -1;
            ptOriginal.X = -1;
            ptOriginal.Y = -1;
        }
        // Called when the mouse is moved.
        public void MyMouseMove(Object sender, MouseEventArgs e)
        {
            Point ptCurrent = new Point(e.X, e.Y);
            // If we "have the mouse", then we draw our lines.
            if (bHaveMouse)
            {
                // If we have drawn previously, draw again in
                // that spot to remove the lines.
                if (ptLast.X != -1)
                {
                    MyDrawReversibleRectangle(ptOriginal, ptLast);
                }
                // Update last point.
                ptLast = ptCurrent;
                // Draw new lines.
                MyDrawReversibleRectangle(ptOriginal, ptCurrent);
            }
        }

    }
}

Answer 1

ControlPaint.DrawReversibleFrame使用屏幕坐标在屏幕上绘制一个矩形(即，与应用程序的窗口无关)，这在执行拖动鼠标操作时非常有用，因为鼠标可能会移动到应用程序窗口之外。如果您在应用程序中使用相同的坐标raw进行绘制，那么它们将作为您要在其上绘制的控件上的坐标相对于控件的原点(通常是控件的左上角)而存在。

要使用屏幕坐标，首先需要在要绘制的控件上使用PointToClient()或RectangleToClient()方法将它们转换为控件坐标，例如

// panel`s OnPaint
Rectangle screenRectangle = ...
Rectangle clientRectangle = panel.RectangleToClient(screenRectangle);
graphics.DrawRectangle(Pens.Red, clientRectangle);