Any trick to use opacity on a panel in Visual Studio Window Form?
I recently started exploring Visual Studio.
I was trying to create a slide menu. More specifically, when the user would press the button a submenu would pop up to the right. To achieve that i have placed a Panel
to resize itself. Apart from functionality i wanted to add a bit more design and make the Panel
appear a bit faded.
I know that Panels
in Visual studio do not have opacity, but i was thinking if anyone knows a way-trick-idea about how it can be achieved. I tried a Picture Box
but that too didn't have Opacity as a property. I avoided to use the regular Menu
object that visual studio offers because i wanted to add more design. Any ideas?
Solution 1:
- Create a class that inherits from
Panel
. - Set the
ControlStyle.Opaque
for control in constructor usingSetStyle
.
If true, the control is drawn opaque and the background is not painted.
- Override
CreateParams
and setWS_EX_TRANSPARENT
style for it.
Specifies that a window created with this style is to be transparent. That is, any windows that are beneath the window are not obscured by the window. A window created with this style receives WM_PAINT messages only after all sibling windows beneath it have been updated.
- Create an
Opacity
property that accepts values from 0 to 100 that will be used as alpha channel of background. - Override
OnPaint
and fill the background using an alpha enabledBrush
that is created fromBackGroundColor
andOpacity
.
Complete Code
public class ExtendedPanel : Panel
{
private const int WS_EX_TRANSPARENT = 0x20;
public ExtendedPanel()
{
SetStyle(ControlStyles.Opaque, true);
}
private int opacity = 50;
[DefaultValue(50)]
public int Opacity
{
get
{
return this.opacity;
}
set
{
if (value < 0 || value > 100)
throw new ArgumentException("value must be between 0 and 100");
this.opacity = value;
}
}
protected override CreateParams CreateParams
{
get
{
CreateParams cp = base.CreateParams;
cp.ExStyle = cp.ExStyle | WS_EX_TRANSPARENT;
return cp;
}
}
protected override void OnPaint(PaintEventArgs e)
{
using (var brush = new SolidBrush(Color.FromArgb(this.opacity * 255 / 100, this.BackColor)))
{
e.Graphics.FillRectangle(brush, this.ClientRectangle);
}
base.OnPaint(e);
}
}
Screenshot
Solution 2:
To make a control "transparent", you should paint the right area of its parent onto the control. That's what the Button
does before it draws its content so the rounded corners will be transparent.
To mimic semi-transparency, you can paint the form onto the panel, and then draw something with Alpha:
private void panel1_Paint(object sender, PaintEventArgs e)
{
PaintTransparentBackground(panel1, e);
using (Brush b = new SolidBrush(Color.FromArgb(128, panel1.BackColor)))
{
e.Graphics.FillRectangle(b, e.ClipRectangle);
}
}
private static void PaintTransparentBackground(Control c, PaintEventArgs e)
{
if (c.Parent == null || !Application.RenderWithVisualStyles)
return;
ButtonRenderer.DrawParentBackground(e.Graphics, c.ClientRectangle, c);
}
Please note that the ButtonRenderer.DrawParentBackground
does not paint the controls of the form, which overlap with the panel, but only the background of the form.