In this application we shall learn how to draw over the desktop. To do this we shall make use of the following windows api functions.
[DllImport("GDI32.dll")]
private static extern bool DeleteDC(int hdc);
[DllImport("GDI32.dll")]
private static extern bool DeleteObject(int hObject);
[DllImport("GDI32.dll")]
private static extern int SelectObject(int hdc, int hgdiobj);
[DllImport("User32.dll")]
private static extern int GetDesktopWindow();
[DllImport("User32.dll")]
private static extern int GetWindowDC(int hWnd);
[DllImport("GDI32.dll")]
private static extern int LineTo(int hdc, int x, int y);
[DllImport("GDI32.dll")]
private static extern int MoveToEx(int hdc, int x, int y,ref Point lppoint);
[DllImport("GDI32.dll")]
private static extern int CreatePen(int penstyle, int width, int color);
Using these functions I have developed a class called DesktopDrawing
which contains a static method public static void DrawALine(int x1,int y1,int x2,int y2,int width,Color clr)
The parameters are self explanatory.
The method makes use of the following Windows API functions:-
1) GetDesktopWindow gets a handle to the Desktop.
2) GetWindowDC gets the Device Context to a window given it's handle.
3) CreatePen Creates a Pen for drawing, given a DrawMode, width and Color.
4) SelectObject Selects a Pen for drawing into a DeviceContext.
5) MoveToEx Moves the Current Point of a DeviceContext to a specified X,Y Position. It also returns the new Point by a reference Parameter.
6) LineTo Draws a Line from the Current Point in a DeviceContext to a given X,Y Position .
7) DeleteDC Deletes a DeviceContext and releases the resources used.
8) DeleteObject Deletes an Object and releases the used resources.
The Application
DesktopDrawing.cs
using System;
using System.Collections.Generic;
using System.Text;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;
namespace DesktopPainter
{
public static class DesktopDrawing
{
[DllImport("GDI32.dll")]
private static extern bool DeleteDC(int hdc);
[DllImport("GDI32.dll")]
private static extern bool DeleteObject(int hObject);
[DllImport("GDI32.dll")]
private static extern int SelectObject(int hdc, int hgdiobj);
[DllImport("User32.dll")]
private static extern int GetDesktopWindow();
[DllImport("User32.dll")]
private static extern int GetWindowDC(int hWnd);
[DllImport("GDI32.dll")]
private static extern int LineTo(int hdc, int x, int y);
[DllImport("GDI32.dll")]
private static extern int MoveToEx(int hdc, int x, int y,ref Point lppoint);
[DllImport("GDI32.dll")]
private static extern int CreatePen(int penstyle, int width, int color);
public static void DrawALine(int x1,int y1,int x2,int y2,int width,Color clr)
{
Point p=new Point ();
int hdcSrc = GetWindowDC(GetDesktopWindow());
int newcolor =System.Drawing .ColorTranslator.ToWin32 ( clr);
int newpen=CreatePen(0,width , newcolor);
SelectObject(hdcSrc,newpen );
MoveToEx(hdcSrc, x1, y1, ref p);
LineTo(hdcSrc,x2,y2);
DeleteDC(hdcSrc);
DeleteObject(newpen);
}
}
}
Program.cs
using System;
using System.Collections.Generic;
using System.Linq;
using System.Windows.Forms;
namespace DesktopPainter
{
static class Program
{
/// <summary>
/// The main entry point for the application.
/// </summary>
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new Form1());
}
}
}
Form1.cs
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace DesktopPainter
{
public partial class Form1 : Form
{
bool IsColorDialogOpened = false;
int px = 0, py = 0;
public Form1()
{
InitializeComponent();
}
private void timer1_Tick(object sender, EventArgs e)
{
if (!chkDraw.Checked || IsColorDialogOpened )
return;
int x = Cursor.Position.X;
int y = Cursor.Position.Y;
DesktopDrawing.DrawALine(px, py, x, y,50, lblDrawingColor.BackColor );
px = x;
py = y;
}
private void lblDrawingColor_Click(object sender, EventArgs e)
{
IsColorDialogOpened = true;
cld.Color = lblDrawingColor.BackColor;
cld.AllowFullOpen = true;
cld.ShowDialog(this);
lblDrawingColor.BackColor = cld.Color;
IsColorDialogOpened = false;
}
private void chkDraw_CheckedChanged(object sender, EventArgs e)
{
px = Cursor.Position.X;
py = Cursor.Position.Y;
}
}
}
Form1.Designer.cs
{
partial class Form1
{
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (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()
{
this.components = new System.ComponentModel.Container();
this.picDesktop = new System.Windows.Forms.PictureBox();
this.timer1 = new System.Windows.Forms.Timer(this.components);
this.cld = new System.Windows.Forms.ColorDialog();
this.lblDrawingColor = new System.Windows.Forms.Button();
this.chkDraw = new System.Windows.Forms.CheckBox();
((System.ComponentModel.ISupportInitialize)(this.picDesktop)).BeginInit();
this.SuspendLayout();
//
// picDesktop
//
this.picDesktop.Dock = System.Windows.Forms.DockStyle.Fill;
this.picDesktop.Location = new System.Drawing.Point(0, 0);
this.picDesktop.Name = "picDesktop";
this.picDesktop.Size = new System.Drawing.Size(782, 464);
this.picDesktop.SizeMode = System.Windows.Forms.PictureBoxSizeMode.StretchImage;
this.picDesktop.TabIndex = 0;
this.picDesktop.TabStop = false;
//
// timer1
//
this.timer1.Enabled = true;
this.timer1.Interval = 200;
this.timer1.Tick += new System.EventHandler(this.timer1_Tick);
//
// cld
//
this.cld.Color = System.Drawing.Color.Red;
//
// lblDrawingColor
//
this.lblDrawingColor.BackColor = System.Drawing.Color.Red;
this.lblDrawingColor.Location = new System.Drawing.Point(122, 71);
this.lblDrawingColor.Name = "lblDrawingColor";
this.lblDrawingColor.Size = new System.Drawing.Size(156, 33);
this.lblDrawingColor.TabIndex = 1;
this.lblDrawingColor.Text = "&Drawing Color";
this.lblDrawingColor.UseVisualStyleBackColor = false;
this.lblDrawingColor.Click += new System.EventHandler(this.lblDrawingColor_Click);
//
// chkDraw
//
this.chkDraw.AutoSize = true;
this.chkDraw.Location = new System.Drawing.Point(357, 86);
this.chkDraw.Name = "chkDraw";
this.chkDraw.Size = new System.Drawing.Size(79, 17);
this.chkDraw.TabIndex = 2;
this.chkDraw.Text = "Draw &Lines";
this.chkDraw.UseVisualStyleBackColor = true;
this.chkDraw.CheckedChanged += new System.EventHandler(this.chkDraw_CheckedChanged);
//
// Form1
//
this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.ClientSize = new System.Drawing.Size(782, 464);
this.Controls.Add(this.chkDraw);
this.Controls.Add(this.lblDrawingColor);
this.Controls.Add(this.picDesktop);
this.Name = "Form1";
this.Text = "Form1";
((System.ComponentModel.ISupportInitialize)(this.picDesktop)).EndInit();
this.ResumeLayout(false);
this.PerformLayout();
}
#endregion
private System.Windows.Forms.PictureBox picDesktop;
private System.Windows.Forms.Timer timer1;
private System.Windows.Forms.ColorDialog cld;
private System.Windows.Forms.Button lblDrawingColor;
private System.Windows.Forms.CheckBox chkDraw;
}
}
I have deliberately kept it a bit rough round the edges while still providing the basic requirements. Enter your E Mail in the comments if you want a zip of the Application.
