Hi,
opacity can only work on top-level windows. It uses a hardware feature of the video adapter, that doesn't support child windows, like Panel. The only top-level Control derived class in Winforms is Form.
Several of the 'pure' Winform controls, the ones that do their own painting instead of letting a native Windows control do the job, do however support a transparent BackColor. Panel is one of them. It uses a trick, it asks the Parent to draw
itself to produce the background pixels. One side-effect of this trick is that overlapping controls doesn't work, you only see the parent pixels, not the overlapped controls.
This sample form shows it at work:
public partial class Form1 : Form {
public Form1() {
InitializeComponent();
this.BackColor = Color.White;
panel1.BackColor = Color.FromArgb(25, Color.Black);
}
protected override void OnPaint(PaintEventArgs e) {
e.Graphics.DrawLine(Pens.Yellow, 0, 0, 100, 100);
}
}
Thx.
