form1.cs

Windows mobile 图形编程例子

using System;
using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;

namespace MobileDevelopersHandbook.AlphaBlendExample
{
    public partial class Form1 : Form
    {
        protected Bitmap backBuffer;
        protected Image displayImage;
        byte transparencyValue = 0;
        Timer blendTimer;

        public Form1()
        {
            InitializeComponent();

            // Load the image to use with the AlphaBlend API.
            string path = System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().GetName().CodeBase);
            displayImage = new Bitmap(path + @"\Microsoft_Windows_Mobile_logo.bmp");

            blendTimer = new Timer();
            blendTimer.Interval = 50;
            blendTimer.Tick += new EventHandler(blendTimer_Tick);
            blendTimer.Enabled = true;
        }

        void blendTimer_Tick(object sender, EventArgs e)
        {
            transparencyValue += 10;
            if (transparencyValue == 250)
            {
                transparencyValue = 255; // opaque
                blendTimer.Enabled = false; // stop the tmer
            }

            // Force a repaint
            this.Refresh();
        }

        protected override void OnPaintBackground(PaintEventArgs e)
        {
            // Make this a no-op, to avoid flicker
        }

        private void Form1_Paint(object sender, PaintEventArgs e)
        {
            if (backBuffer != null)
            {
                // We need a Graphics object on the buffer to get an HDC
                using (Graphics gxBuffer = Graphics.FromImage(backBuffer))
                {
                    // Since we nop'd OnPaintBackground, take care of it here
                    gxBuffer.Clear(this.BackColor);

                    // AlphaBlend takes two HDC's - one source and one destination.  Here's the source.
                    using (Graphics gxSrc = Graphics.FromImage(displayImage))
                    {
                        IntPtr hdcDst = gxBuffer.GetHdc();
                        IntPtr hdcSrc = gxSrc.GetHdc();
 
                        BlendFunction blendFunction = new BlendFunction();
                        blendFunction.BlendOp = (byte)BlendOperation.AC_SRC_OVER;   // Only supported blend operation
                        blendFunction.BlendFlags = (byte)BlendFlags.Zero;           // Documentation says put 0 here
                        blendFunction.SourceConstantAlpha = transparencyValue;      // Constant alpha factor
                        blendFunction.AlphaFormat = (byte)0;                        // Don't look for per pixel alpha

                        int left = this.Width / 2 - (displayImage.Width / 2);   // Get x co-or based on bitmap width
                        int top = 100;                                              // y co-or
                        PlatformAPIs.AlphaBlend(hdcDst, left, top,
                            displayImage.Width, displayImage.Height, 
                            hdcSrc, 0, 0,
                            displayImage.Width, displayImage.Height, 
                            blendFunction);
 
                        gxBuffer.ReleaseHdc(hdcDst);    // Required cleanup to GetHdc()
                        gxSrc.ReleaseHdc(hdcSrc);       // Required cleanup to GetHdc()
                    }
                }

                // Put the final composed image on screen.
                e.Graphics.DrawImage(backBuffer, 0, 0);
            }
            else
                e.Graphics.Clear(this.BackColor);
        }

        private void Form1_Resize(object sender, EventArgs e)
        {
            if (backBuffer != null)
            {
                // dispose of the original one
                backBuffer.Dispose();
            }

            // Create a new backbuffer of the correct size
            backBuffer = new Bitmap(this.ClientSize.Width, this.ClientSize.Height, 
                System.Drawing.Imaging.PixelFormat.Format32bppRgb);
        }
    }
}