GDI+程序设计 Chapter14

这里介绍BitBlt的应用。我把书上的代码重新写了一边，在该加注释的地方加了一些注释。这样大家读起来就会更加方便一些。这是第十四章的代码。

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Runtime.InteropServices;
using System.Drawing.Drawing2D;

namespace AlphaDragExample
{
    public partial class Form1 : Form
    {
        构造函数#region 构造函数
        public Form1()
        {
            InitializeComponent();
            dragString = "Dragging Me";
            DragMePosition = new Point(100, 100);
            dragStringFont = new Font("Times New Roman", 14, FontStyle.Bold);
        } 
        #endregion

        Windows API#region Windows API

        [DllImport("gdi32.dll")]
        private static extern bool BitBlt(
            IntPtr hdcDest,     // handle to desination DC (device context)
            int nXDest,         // x-coord of destination upper-left corner
            int nYDest,         // y-corrd of destination upper-left corner
            int nWidth,         // width of destination rectangle
            int nHeight,        // height of destination rectangle
            IntPtr hdcSrc,      // handle to source DC
            int nXSrc,          // x-coordinate of source upper-left corner
            int nYSrc,          // y-coordinate of source upper-left corner
            Int32 dwRop         // raster operation code
            );

        [DllImport("gdi32.dll")]
        private static extern IntPtr CreateDC(
            String driverName,
            String deviceName,
            String outPut,
            IntPtr lpInitData
            );

        [DllImportAttribute("gdi32.dll")]
        private static extern bool DeleteDC(
            IntPtr dc
        );
        /**//// <summary>
        /// 该方法用来取得鼠标在屏幕中的坐标
        /// </summary>
        /// <param name="hWnd">handle to window</param>
        /// <param name="lpPoint">screen coordinates</param>
        /// <returns></returns>
        [DllImportAttribute("user32.dll")]
        private static extern unsafe bool ClientToScreen(
            IntPtr hWnd,            //handle to window
            Point* lpPoint          //screen coordinates
            ); 
        #endregion

        私有变量#region 私有变量
        const int SRCCOPY = 0x00CC0020;
        private Point DragMePosition;
        private bool mouseDown = false;
        private Point mouseDelta;
        private Bitmap backingStore;
        private Point backingStorePos;
        private string dragString;
        private Graphics backingStoreGraphics;
        private IntPtr backingStoreDC;
        private Graphics displayGraphics;
        private IntPtr displayDC;
        private Size dragImageSize;
        private Font dragStringFont; 
        #endregion

        私有方法#region 私有方法
        //加载页面时，初始化dragImageSize
        private void Form1_Load(object sender, EventArgs e)
        {
            Graphics g = this.CreateGraphics();
            SizeF temp = g.MeasureString(dragString, dragStringFont);
            dragImageSize = new Size((int)temp.Width, (int)temp.Height);
            g.Dispose();
        }

        private void getDisplayDC()
        {
            // 创建显卡的DC
            displayDC = CreateDC("DISPLAY", null, null, (System.IntPtr)null);
            // 获得显卡的设备上下文的句柄
            displayGraphics = Graphics.FromHdc(displayDC);
        }

        private void disposeDisplayDC()
        {
            displayGraphics.Dispose();
            DeleteDC(displayDC);
        }

        private unsafe Point controlToScreen(int x, int y)
        {
            Point p = new Point(x, y);
            Point* pp = &p;
            ClientToScreen(Handle, pp);
            return p;
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = e.Graphics;
            g.FillRectangle(Brushes.Bisque, ClientRectangle);
            Font bf = new Font("Times New Roman", 32);
            g.DrawString("Bonjour Le Monde", bf, Brushes.Blue, 10, 10);
            bf.Dispose();
            drawDragImage(g, false, DragMePosition.X, DragMePosition.Y, dragString);
        }

        private void drawDragImage(Graphics g, bool alphablend, int x, int y, string s)
        {
            Rectangle r = new Rectangle(x, y, dragImageSize.Width, dragImageSize.Height);

            //draw background
            if (alphablend)
            {
                Color c1 = Color.FromArgb(0, Color.Red);
                Color c2 = Color.FromArgb(80, Color.Red);
                Rectangle r1 = new Rectangle(r.Left, r.Top, r.Width / 2, r.Height);
                Rectangle r2 = new Rectangle(r.Left + r.Width / 2, r.Top, r.Width / 2, r.Height);

                // 定义一个渐变的笔刷，利用该笔刷可以实现渐变
                LinearGradientBrush lgb1 = new LinearGradientBrush(r1, c1, c2, 0f);
                LinearGradientBrush lgb2 = new LinearGradientBrush(r2, c2, c1, 0f);

                // 用渐变的笔刷来填充矩形
                g.FillRectangle(lgb1, r1.Left + 1, r1.Top, r1.Width + 1, r1.Height);
                g.FillRectangle(lgb2, r2);

                lgb1.Dispose();
                lgb2.Dispose();
            }
            else
                g.FillRectangle(Brushes.Red, r);

            //Draw the text
            Color c;
            if (alphablend)
                c = Color.FromArgb(80, Color.Black);
            else
                c = Color.Black;
            Brush blackBrush = new SolidBrush(c);
            g.DrawString(s, this.dragStringFont, blackBrush, r);
        }

        private void Form1_MouseDown(object sender, MouseEventArgs e)
        {
            //Rectangle 
            Rectangle dragMeRectangle = new Rectangle(DragMePosition, new Size(dragImageSize.Width, dragImageSize.Height));
            //Point screenPoint2 = controlToScreen(e.X, e.Y);
            if (dragMeRectangle.Contains(e.X, e.Y))
            {
                mouseDown = true;
                mouseDelta = new Point(e.X - DragMePosition.X, e.Y - DragMePosition.Y);

                // 得到在显示器中的位置
                Point screenPoint = controlToScreen(e.X, e.Y);

                // 算出所绘的图片顶点在屏幕中的坐标
                screenPoint.X -= mouseDelta.X;
                screenPoint.Y -= mouseDelta.Y;

                // 取得屏幕的DC
                getDisplayDC();

                backingStore = new Bitmap(dragImageSize.Width, dragImageSize.Height);
                backingStoreGraphics = Graphics.FromImage(backingStore);
                //backingStoreGraphics.FillRectangle(Brushes.Red, 0, 0, backingStore.Width, backingStore.Height);
                backingStoreDC = backingStoreGraphics.GetHdc();

                // 把屏幕上的图片考到位图上
                BitBlt(backingStoreDC, 0, 0, backingStore.Width, backingStore.Height, displayDC, screenPoint.X, screenPoint.Y, SRCCOPY);
                // 利用BitBlt方法，可以直接往显示器上绘图，这个和DrawString方法都是差不多的。
                BitBlt(displayDC, screenPoint.X, screenPoint.Y, backingStore.Width, backingStore.Height, backingStoreDC, 0, 0, SRCCOPY);
                //BitBlt(displayDC, screenPoint.X+30, screenPoint.Y+30, backingStore.Width, backingStore.Height, backingStoreDC, 0, 0, SRCCOPY);
                backingStorePos = new Point(screenPoint.X, screenPoint.Y);

                drawDragImage(displayGraphics, true, screenPoint.X, screenPoint.Y, dragString);
            }
        }

        private void Form1_MouseMove(object sender, MouseEventArgs e)
        {
            if (mouseDown)
            {
                Point screenPoint = controlToScreen(e.X, e.Y);

                screenPoint.X -= mouseDelta.X;
                screenPoint.Y -= mouseDelta.Y;

                // 通过循环，重新覆盖背景图片
                // 先覆盖
                BitBlt(displayDC, backingStorePos.X, backingStorePos.Y, backingStore.Width, backingStore.Height, backingStoreDC, 0, 0, SRCCOPY);
                // 后取，把screenPoint范围内的全部存下来
                BitBlt(backingStoreDC, 0, 0, backingStore.Width, backingStore.Height, displayDC, screenPoint.X, screenPoint.Y, SRCCOPY);
                backingStorePos = new Point(screenPoint.X, screenPoint.Y);

                // 利用DrawString方法绘出字符串
                drawDragImage(displayGraphics, true, screenPoint.X, screenPoint.Y, dragString);
            }
        }

        private void Form1_MouseUp(object sender, MouseEventArgs e)
        {
            if (mouseDown)
            {
                mouseDown = false;
                BitBlt(displayDC, backingStorePos.X, backingStorePos.Y, backingStore.Width, backingStore.Height, backingStoreDC, 0, 0, SRCCOPY);

                disposeDisplayDC();

                backingStoreGraphics.ReleaseHdc(backingStoreDC);
                backingStoreGraphics.Dispose();

                backingStore.Dispose();
                backingStore = null;
            }
        } 
        #endregion
    }
}

BitBlt是GDI中的方法，它通过各个对象的句柄来直接实现绘图操作，是一个十分重要的方法。