How can I set the opacity or transparency of a Panel in WinForms

Question

I was wondering how to change or modify the transparency of a Panel in C   not the whole form  but the panel only   I ve seen many C  tutorials on Opacity  but its for the Form  im looking for how it could be possible with the Panel only  Thank You

User · Answer

Don t forget to bring your Panel to the Front when dynamically creating it in the form constructor   Example of transparent panel overlay of tab control   panel1   new TransparentPanel    panel1 BackColor   System Drawing Color Transparent  panel1 Location   new System Drawing Point 0  0   panel1 Name    panel1   panel1 Size   new System Drawing Size 717  92   panel1 TabIndex   0  tab2 Controls Add panel1   panel1 BringToFront           lt    otherwise the other controls paint over top of the transparent panel

User · Answer

Based on information found at http   www windows-tech info 3 53ee08e46d9cb138 php  I was able to achieve a translucent panel control using the following code   public class TransparentPanel   Panel       protected override CreateParams CreateParams               get                       var cp   base CreateParams              cp ExStyle    0x00000020     WS EX TRANSPARENT              return cp                       protected override void OnPaint PaintEventArgs e    gt          e Graphics FillRectangle new SolidBrush this BackColor   this ClientRectangle       The caveat is that any controls that are added to the panel have an opaque background  Nonetheless  the translucent panel was useful for me to block off parts of my WinForms application so that users focus was shifted to the appropriate area of the application

User · Answer

Try this   panel1 BackColor   Color FromArgb 100  88  44  55     change alpha A  to get desired opacity

User · Answer

Yes  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             If that s not good enough then you need to consider stacking forms on top of each other   Like this   Notable perhaps is that this restriction is lifted in Windows 8   It no longer uses the video adapter overlay feature and DWM  aka Aero  cannot be turned off anymore   Which makes opacity transparency on child windows easy to implement   Relying on this is of course future-music for a while to come   Windows 7 will be the next XP

User · Answer

I just wanted to add to the William Smash solution as I couldn t get to his blog so answers which may have been in there to my simple questions could not be found   Took me a while to realise  but maybe I was just having a moment     If you haven t had to do so already you ll need to add a reference to System Windows Forms in the project properties   Also you ll need to add   Imports System Windows Forms    to the file where you re adding the override class   For OnPaintBackground you ll need to add a reference for System Drawing then   Imports System Drawing Printing PrintEventArgs

User · Answer

This does work for me  In below example  Alpha range can be a value between 0 to 255  Previously  I made a mistake by thinking that it must be a value of percentage   Dim x as integer   230 Panel1 BackColor   Color FromArgb x  Color Blue

User · Answer

As far as I know a Panel can have a transparent color only  you can not control the opacity of the panel  So  you can have some parts of a panel completely transparent but not a 50  to say something   To use transparency you must define the transparent color property

User · Answer

For whoever is still looking for a totally transparent panel  I found a nice solution in this blog by William Smash who in turn has taken it from Tobias Hertkorn on his T  blog  I thought its worth posting it as an answer here   C  code   public class TransparentPanel   Panel       protected override CreateParams CreateParams                            get               CreateParams cp    base CreateParams              cp ExStyle    0x00000020     WS EX TRANSPARENT             return cp                          protected override void OnPaintBackground PaintEventArgs e                   base OnPaintBackground e              VB Net code   Public Class TransparentPanel Inherits Panel     Protected Overrides ReadOnly Property CreateParams   As System Windows Forms CreateParams         Get             Dim cp As CreateParams   MyBase CreateParams             cp ExStyle   cp ExStyle Or  amp H20    WS EX TRANSPARENT             Return cp         End Get     End Property     Protected Overrides Sub OnPaintBackground ByVal e As System Windows Forms PaintEventArgs         MyBase OnPaintBackground e      End Sub End Class

User · Answer

Panel with opacity   public class GlassyPanel   Panel       const int WS EX TRANSPARENT   0x20         int opacity   50       public int Opacity               get                       return opacity                    set                       if  value  lt  0    value  gt  100  throw new ArgumentException  Value must be between 0 and 100                opacity   value                       protected override CreateParams CreateParams               get                       var cp   base CreateParams              cp ExStyle   cp ExStyle   WS EX TRANSPARENT               return cp                       protected override void OnPaint PaintEventArgs e                using  var b   new SolidBrush Color FromArgb opacity   255   100  BackColor                          e Graphics FillRectangle b  ClientRectangle                      base OnPaint e

User · Answer

some comments says that it works and some say it doesn t It works only for your form background not any other controls behind

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