C# .NET Control Transparency Problem

[Hristiyan]

Hello there ! I'm developing a Windows appliciation that involves so called "Transparent Controls". As you would probably know, the only ( as far as i know ) way to achieve a fully transparent control in C# is to add the so called "Transparent style" to your control ("WS_EX_TRANSPARENT"). There are numerous articles how to achieve this and the method is ALMOST always one and the same:

protected override CreateParams CreateParams
{
get
{
CreateParams cp=base.CreateParams;
cp.ExStyle|=0x00000020; //WS_EX_TRANSPARENT
return cp;
}
}
protected override void OnPaintBackground(PaintEventArgs pevent)
{
//do not allow the background to be painted
}

And that works fine! ( well .... at least all say that ..... and all the articles say so ), but am i missing something or that method has SOME SERIOUS problems that nobody can see ? For example the Z-order. The following piece of code creates simply a transparent control that draws a line accross itself with a random color:

using System;
using System.Collections.Generic;
using System.Text;
using System.Windows.Forms;
using System.Drawing;
namespace WindowsApplication16
{
public class HrisTranspControl : Control
{
private Pen _drawingPen;
public HrisTranspControl()
{
Random rnd = new Random();
this._drawingPen = new System.Drawing.Pen(new System.Drawing.SolidBrush(System.Drawing.Color.FromArgb(rnd.Next(0,255),rnd.Next(0,255), rnd.Next(0,255))),5);
}
protected override CreateParams CreateParams
{
get
{
CreateParams cp = base.CreateParams;
cp.ExStyle |= 0x00000020;
return cp;
}
}
protected override void OnPaintBackground(PaintEventArgs pevent)
{
// Do nothing
}
protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
e.Graphics.DrawLine(_drawingPen, new System.Drawing.Point(0, 0), new System.Drawing.Point(this.Width, this.Height));
}
}
}

And so ... when u put few "line controls" on top of each other the Z-ORDER goes to hell. You can't change it, its not corrent and it changes randomly each time u select a random "line control". I've tried A LOT of methods to fix that ( changing the z-order in background, repainting the actual background because i think its because the

[Phil J Pearson]

I think your problem stems from a misunderstanding of the meaning of WS_EX_TRANSPARENT. It has nothing to do with visual transparency; it makes a window 'transparent' to mouse clicks. In other words, the click goes through to the window underneath. If you're trying to use the mouse to select such a window you are bound to get confusing results! You probably don't need that style at all.

Phil

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