Per Pixel Alpha - Listing 2

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Listing 2. The DropShadow application.

Note that this simple application requires a copy of the Sunset.jpg image. You may substitute any image you like from your system.

using System;

using System.Drawing;

using System.Drawing.Drawing2D;

using System.Drawing.Imaging;

using System.Collections;

using System.ComponentModel;

using System.Windows.Forms;

using System.Data;

namespace DropShadow

{

/// <summary>

/// Summary description for Form1.

/// </summary>

public class Form1 : System.Windows.Forms.Form

{

/// <summary>

/// Required designer variable.

/// </summary>

private System.ComponentModel.Container components = null;

public Form1()

{

// Required for Windows Form Designer support

InitializeComponent();

SetStyle(ControlStyles.DoubleBuffer|

ControlStyles.AllPaintingInWmPaint|

ControlStyles.UserPaint|

ControlStyles.ResizeRedraw, true);

}

/// <summary>

/// Clean up any resources being used.

/// </summary>

protected override void Dispose( bool disposing )

{

if( disposing )

{

if (components != null)

{

components.Dispose();

}

base.Dispose( disposing );

}

#region Windows Form Designer generated code

/// <summary>

/// Required method for Designer support - do not modify

/// the contents of this method with the code editor.

/// </summary>

private void InitializeComponent()

{

System.Resources.ResourceManager resources = new System.Resources.ResourceManager(typeof(Form1));

this.trackBar1 = new System.Windows.Forms.TrackBar();

((System.ComponentModel.ISupportInitialize)(this.trackBar1)).BeginInit();

this.SuspendLayout();

// trackBar1

this.trackBar1.Dock = System.Windows.Forms.DockStyle.Right;

this.trackBar1.Location = new System.Drawing.Point(531, 0);

this.trackBar1.Maximum = 255;

this.trackBar1.Name = "trackBar1";

this.trackBar1.Orientation = System.Windows.Forms.Orientation.Vertical;

this.trackBar1.Size = new System.Drawing.Size(45, 342);

this.trackBar1.TabIndex = 0;

this.trackBar1.TickFrequency = 8;

this.trackBar1.Scroll += new System.EventHandler(this.trackBar1_Scroll);

// Form1

this.AutoScaleBaseSize = new System.Drawing.Size(5, 13);

this.BackgroundImage = ((System.Drawing.Image)(resources.GetObject("$this.BackgroundImage")));

this.ClientSize = new System.Drawing.Size(576, 342);

this.Controls.Add(this.trackBar1);

this.Name = "Form1";

this.Text = "Form1";

this.Load += new System.EventHandler(this.Form1_Load);

this.Paint += new System.Windows.Forms.PaintEventHandler(this.Form1_Paint);

((System.ComponentModel.ISupportInitialize)(this.trackBar1)).EndInit();

this.ResumeLayout(false);

}

#endregion

/// <summary>

/// The main entry point for the application.

/// </summary>

[STAThread]

static void Main()

{

Application.Run(new Form1());

}

private System.Windows.Forms.TrackBar trackBar1;

Bitmap bm;

private void Form1_Load(object sender, System.EventArgs e)

{

bm=(Bitmap)Image.FromFile("..\\..\\sunset.jpg");

this.ClientSize=new Size(bm.Width,bm.Height);

}

public void RectangleDropShadow(Graphics tg, Rectangle rc, Color shadowColor, int depth, int maxOpacity)

{

//calculate the opacities

Color darkShadow=Color.FromArgb(maxOpacity,shadowColor);

Color lightShadow=Color.FromArgb(0,shadowColor);

//Create a brush that will create a softshadow circle

GraphicsPath gp=new GraphicsPath();

gp.AddEllipse(0,0,2*depth,2*depth);

PathGradientBrush pgb=new PathGradientBrush(gp);

pgb.CenterColor=darkShadow;

pgb.SurroundColors=new Color[]{lightShadow};

//generate a softshadow pattern that can be used to paint the shadow

Bitmap patternbm=new Bitmap(2*depth,2*depth);

Graphics g=Graphics.FromImage(patternbm);

g.FillEllipse(pgb,0,0,2*depth,2*depth);

g.Dispose();

pgb.Dispose();

SolidBrush sb=new SolidBrush(Color.FromArgb(maxOpacity,shadowColor));

tg.FillRectangle(sb,rc.Left+depth,rc.Top+depth,rc.Width-(2*depth),rc.Height-(2*depth));

sb.Dispose();

//top left corner

tg.DrawImage(patternbm,new Rectangle(rc.Left,rc.Top,depth,depth),0,0,depth,depth,GraphicsUnit.Pixel);

//top side

tg.DrawImage(patternbm,new Rectangle(rc.Left+depth,rc.Top,rc.Width-(2*depth),depth),depth,0,1,depth,GraphicsUnit.Pixel);

//top right corner

tg.DrawImage(patternbm,new Rectangle(rc.Right-depth,rc.Top,depth,depth),depth,0,depth,depth,GraphicsUnit.Pixel);

//right side

tg.DrawImage(patternbm,new Rectangle(rc.Right-depth,rc.Top+depth,depth,rc.Height-(2*depth)),depth,depth,depth,1,GraphicsUnit.Pixel);

//bottom left corner

tg.DrawImage(patternbm,new Rectangle(rc.Right-depth,rc.Bottom-depth,depth,depth),depth,depth,depth,depth,GraphicsUnit.Pixel);

//bottom side

tg.DrawImage(patternbm,new Rectangle(rc.Left+depth,rc.Bottom-depth,rc.Width-(2*depth),depth),depth,depth,1,depth,GraphicsUnit.Pixel);

//bottom left corner

tg.DrawImage(patternbm,new Rectangle(rc.Left,rc.Bottom-depth,depth,depth),0,depth,depth,depth,GraphicsUnit.Pixel);

//left side

tg.DrawImage(patternbm,new Rectangle(rc.Left,rc.Top+depth,depth,rc.Height-(2*depth)),0,depth,depth,1,GraphicsUnit.Pixel);

patternbm.Dispose();

}

int opacity=128;

private void Form1_Paint(object sender, System.Windows.Forms.PaintEventArgs e)

{

RectangleDropShadow(e.Graphics,new Rectangle(30,30,bm.Width,bm.Height), Color.Black, 20, opacity);

e.Graphics.DrawImageUnscaled(bm,10,10);

}

private void trackBar1_Scroll(object sender, System.EventArgs e)

{

opacity=this.trackBar1.Value;

Invalidate();

}

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