Drawing graphics doesn't work

Question

I have this code where it makes the form always on top, transparent and click through.

    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.Diagnostics;
    using System.Runtime.InteropServices;

    namespace HyperBox
    {

public partial class Form1 : Form
{

    public Form1()
    {
        InitializeComponent();

        this.TopMost = true; // make the form always on top
        this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None; // hidden border
        this.WindowState = FormWindowState.Maximized; // maximized
        this.MinimizeBox = this.MaximizeBox = false; // not allowed to be minimized
        this.MinimumSize = this.MaximumSize = this.Size; // not allowed to be resized
        this.TransparencyKey = this.BackColor = Color.Red; // the color key to transparent, choose a color that you don't use

        // Set the form click-through
        int initialStyle = GetWindowLong(this.Handle, -20);
        SetWindowLong(this.Handle, -20, initialStyle | 0x80000 | 0x20);
    }

    [System.Runtime.InteropServices.DllImport("user32.dll", SetLastError = true)]
    static extern int GetWindowLong(IntPtr hWnd, int nIndex);





    [System.Runtime.InteropServices.DllImport("user32.dll")]
    static extern int SetWindowLong(IntPtr hWnd, int nIndex, int dwNewLong);


    [System.Runtime.InteropServices.DllImport("user32.dll")]
    static extern bool SetLayeredWindowAttributes(IntPtr hwnd, uint crKey, byte bAlpha, uint dwFlags);


    [System.Runtime.InteropServices.DllImport("user32.dll")]
    static extern int SetParent(int hWndChild, int hWndNewParent);


    [DllImport("user32.dll", CharSet = CharSet.Auto)]
    public static extern IntPtr FindWindow(
     [MarshalAs(UnmanagedType.LPTStr)] string lpClassName,
     [MarshalAs(UnmanagedType.LPTStr)] string lpWindowName);
    [DllImport("user32.dll")]
    public static extern IntPtr SetParent(
     IntPtr hWndChild,      // handle to window
     IntPtr hWndNewParent   // new parent window
     );

    protected override void OnPaint(PaintEventArgs e)
    {
        base.OnPaint(e);
        // draw what you want
        e.Graphics.FillRectangle(Brushes.Red, new Rectangle((SystemInformation.WorkingArea.Width / 2) - 4, (SystemInformation.WorkingArea.Height / 2) - 20, 8, 40));
        e.Graphics.FillRectangle(Brushes.Red, new Rectangle((SystemInformation.WorkingArea.Width / 2) - 20, (SystemInformation.WorkingArea.Height / 2) - 4, 40, 8));


    }
    private void Form1_MouseMove(object sender, MouseEventArgs e)
    {

    }

    private void Form1_Paint(object sender, PaintEventArgs e)
    {

    }

    private void Form1_Load(object sender, EventArgs e)
    {

        IntPtr hwndf = this.Handle;
        IntPtr hwndParent = FindWindow("chrome.exe", null);
        SetParent(hwndf, hwndParent);



    }

}
    }

The problem is when I draw the graphics, it draws nothing. When the coordinates are around 100~ it works. But when it does the method above nothing happens. At all, not even a pixel. Could someone please explain why this is happening and or repost a fixed snippet, thank you. Layne

Your transparency color is `Red` and you are drawing with `Red` also. Have you tried with different colors? — John Alexiou, Nov 10 '12 at 01:55
@ja72 The TransparencyKey is only used for BackColors of the form and controls. This is why he is able to see parts of his rectangles sometimes. http://msdn.microsoft.com/en-us/library/system.windows.forms.form.transparencykey(v=vs.100).aspx — TyCobb, Nov 10 '12 at 02:13

score 1 · Accepted Answer · edited May 23 '17 at 11:48

OnPaint is giving you a graphics object for your form, not the screen. You are filling rectangles based on the working area of the system, not the form. You will need to adjust your rectangle coordinates and position the form where you want your graphics to appear. A rectangle with a location of (0, 0) is the top-left corner of the form's client area. You should also be able to access that rectangle by calling ClientRectangle that is exposed on the base Form class.

Take a look at this question for drawing outside your form: Draw / Paint Outside Form That should get you started in the right direction if you don't want to paint on your form, but it would probably be easier to reposition and resize your form as needed.

EDIT It would probably be wise to at least add a some sort of border while you debug your issue. This will help you see where the form is positioned and what monitor it is on. You can then check your numbers as you break point in OnPaint to make sure you are creating your rectangles correctly, however, making sure you are painting within the form's client area should fix your issue.

Drawing graphics doesn't work

1 Answers1