Question

Im actually trying to paint an elipse around my cursor when i moove it, I dont want it to leave a trail like it does actually.

Can someone help with this, I believe it has something to do with the invalidaterec option

Any example son using invalidate rec?

Here is my code, besides the trail it has to work the same way it does now.

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;
using System.Runtime.InteropServices;



namespace MouseTest
{
    public partial class Form1 : Form
    {
        [DllImport("user32.dll", EntryPoint = "GetDC")]
        private static extern IntPtr GetDC(IntPtr hWnd);

        [DllImport("user32.dll", EntryPoint = "ReleaseDC")]
        private static extern int ReleaseDC(IntPtr hWnd, IntPtr hDC);

        [System.Runtime.InteropServices.DllImport("Shell32.dll")]
        private static extern int SHChangeNotify(int eventId, int flags, IntPtr item1,         IntPtr item2);

        System.Timers.Timer t1 = new System.Timers.Timer(100);


        public Form1()
        {
        t1.Elapsed += new System.Timers.ElapsedEventHandler(t1_Elapsed);
        t1.Start();
        // System.Windows.Forms.Cursor.Current = System.Windows.Forms.Cursors.WaitCursor;
        //Mouse.OverrideCursor = System.Windows.Input.Cursors.Hand;
        InitializeComponent();


    }

    void t1_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
    {
        t1.Stop();

        //SolidBrush b = new SolidBrush(Color.Red);
        IntPtr desktopDC = GetDC(IntPtr.Zero);
        Graphics g = Graphics.FromHdc(desktopDC);
        g.FillEllipse(new SolidBrush(Color.BlueViolet), Cursor.Position.X, Cursor.Position.Y, 25, 25);
        g.Dispose();
        ReleaseDC(IntPtr.Zero, desktopDC);

       t1.Start();


    }



}

}

Answer 1

Yes, keeping the previous coordinate and calling InvalidateRect on the previous enclosing rectangle before drawing the new new ellipse would probably work. I don’t have any code lying around that calls InvalidateRect, but if this is exactly your goal:” to paint an elipse around my cursor when i moove it, I dont want it to leave a trail like it does actually.” there are other, more straight forward ways.

One way is to draw the ellipse on a transparent form and then move that form around based on the cursor’s movement:

Here, first is the form definition:

namespace MouseForm
{
    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.shapeContainer1 = new Microsoft.VisualBasic.PowerPacks.ShapeContainer();
            this.ovalShape1 = new Microsoft.VisualBasic.PowerPacks.OvalShape();
            this.timer1 = new System.Windows.Forms.Timer(this.components);
            this.SuspendLayout();
            // 
            // shapeContainer1
            // 
            this.shapeContainer1.Location = new System.Drawing.Point(0, 0);
            this.shapeContainer1.Margin = new System.Windows.Forms.Padding(0);
            this.shapeContainer1.Name = "shapeContainer1";
            this.shapeContainer1.Shapes.AddRange(new Microsoft.VisualBasic.PowerPacks.Shape[] {
            this.ovalShape1});
            this.shapeContainer1.Size = new System.Drawing.Size(74, 74);
            this.shapeContainer1.TabIndex = 0;
            this.shapeContainer1.TabStop = false;
            // 
            // ovalShape1
            // 
            this.ovalShape1.BorderColor = System.Drawing.Color.Red;
            this.ovalShape1.BorderWidth = 3;
            this.ovalShape1.FillColor = System.Drawing.SystemColors.Control;
            this.ovalShape1.FillStyle = Microsoft.VisualBasic.PowerPacks.FillStyle.Solid;
            this.ovalShape1.Location = new System.Drawing.Point(2, 2);
            this.ovalShape1.Name = "ovalShape1";
            this.ovalShape1.Size = new System.Drawing.Size(70, 70);
            // 
            // timer1
            // 
            this.timer1.Enabled = true;
            this.timer1.Tick += new System.EventHandler(this.timer1_Tick);
            // 
            // Form1
            // 
            this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
            this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
            this.ClientSize = new System.Drawing.Size(74, 74);
            this.ControlBox = false;
            this.Controls.Add(this.shapeContainer1);
            this.Enabled = false;
            this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;
            this.Name = "Form1";
            this.ShowIcon = false;
            this.ShowInTaskbar = false;
            this.Text = "Form1";
            this.TopMost = true;
            this.TransparencyKey = System.Drawing.SystemColors.Control;
            this.ResumeLayout(false);

        }

        #endregion

        private Microsoft.VisualBasic.PowerPacks.ShapeContainer shapeContainer1;
        private Microsoft.VisualBasic.PowerPacks.OvalShape ovalShape1;
        private System.Windows.Forms.Timer timer1;
    }
}

And here is the code:

using System;
using System.Windows.Forms;

namespace MouseForm
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
            this.Left = Cursor.Position.X - this.Width / 2;
            this.Top = Cursor.Position.Y - this.Height / 2;
        }
    }
}

I’ll leave it as an exercise to the reader to implement a way to close the transparent form 🙂