Transparency of picture box

问题:

Im just looking for an answer in my simple problem. Here it is

I have a pricturebox that has image with transparent background i Set the picturebox backcoloras transparent.

and after that, the picture has transparent bg. But after i added this code

ìmg1.Left = windows.forms.cursor.Position.X - me.Left ìmg1.Top= windows.forms.cursor.Position.Y - me.Top

'code for using img as cursor

the image bg is not really transparent like this

I think the transaparent backcoloris not really transparent. it will only get the backcolorof form and use it as backcolorof image instead of transparent.

Is there any solution to make it fully transparent?

回答1:

You are correct in your assumption.
Transparency in winforms does not mean that the object is actually transparent. Instead, it means that it will display it's parent object instead of it's background, including it's background, images and text, but not including any other controls on it, hence your problem.
Since the parent control of your top most picture box is not and can not be the other picture boxes, the fact that your top most picture box have a transparent background will not help.

Unfortunately, using the form's TransparencyKey property will also not help for this. (It will make the selected color transparent, but will yield unexpected (and usually undesired) results.

In order to achieve your goal, you will have to follow OneFineDay's advice in the comments, and use Graphics to draw the image yourself.
Fortunately, this is very easy to do:

Public Sub DrawImage(Image as Image, Location As Point)     Using(Dim g as Graphics = Me.CreateGraphics())         g.DrawImage(Image, Location)     EndUsing End Sub 

回答2:

Drawing the image using a graphics object is the recommended procedure if you're going to use it as a cursor. But if you sometime want to use a PictureBox (for reasons like being able to quickly change image using it's Image property, etc), that is possible too.

This code will draw a better "transparent" background, by drawing each control behind your PictureBox on it's background.

How to use:

1) Create a custom component.

2) Put Inherits PictureBox below the Public Class ... line.

3) Paste this code inside the class:

Protected Overrides Sub OnPaintBackground(e As System.Windows.Forms.PaintEventArgs)     MyBase.OnPaintBackground(e)      If Parent IsNot Nothing Then         Dim index As Integer = Parent.Controls.GetChildIndex(Me)          For i As Integer = Parent.Controls.Count - 1 To index + 1 Step -1             Dim c As Control = Parent.Controls(i)             If c.Bounds.IntersectsWith(Bounds) AndAlso c.Visible = True Then                 Dim bmp As New Bitmap(c.Width, c.Height, e.Graphics)                 c.DrawToBitmap(bmp, c.ClientRectangle)                 e.Graphics.TranslateTransform(c.Left - Left, c.Top - Top)                 e.Graphics.DrawImageUnscaled(bmp, Point.Empty)                 e.Graphics.TranslateTransform(Left - c.Left, Top - c.Top)                 bmp.Dispose()             End If         Next     End If End Sub 

4) Build your project.

5) Select your class from the toolbox and add it to your form/usercontrol.

回答3:

This blog article inspired this SO answer. These were the basis for a more robust control with scaling, text, contentalignment etc.

The following is a scaled back version (in VB) to primarily implement the appearance of true transparency. The core painting is nearly identical to the original SO post except to account for a border in the painting. A few control level features have also been retained.

'Namespace omitted to reduce indentation Imports System.Windows.Forms Imports System.Drawing Imports System.ComponentModel Imports System.Drawing.Drawing2D  Public Class TransPicBox     Inherits PictureBox      Public Enum ImageSizing         None         Stretch         Scale     End Enum      Public Sub New()         ' defaults for a new one         MyBase.BackColor = Color.Transparent         MyBase.InitialImage = Nothing         MyBase.ErrorImage = Nothing         MyBase.Image = Nothing      End Sub      Public Overloads Property Image As Image         Get             Return MyBase.Image         End Get         Set(value As Image)             MyBase.Image = value             InvalidateParent()         End Set     End Property      Private imgSizing As ImageSizing = ImageSizing.None     Public Property ImageSizing As ImageSizing         Get             Return imgSizing         End Get         Set(value As ImageSizing)             imgSizing = value             InvalidateParent()         End Set     End Property      ' because the child control displays are interdependent     ' tell the parent to update when some things change     ' Image, Scaling, Border, Text, BackColor etc     Private Sub InvalidateParent()         Invalidate()         If MyBase.Parent IsNot Nothing Then             MyBase.Parent.Invalidate()         End If     End Sub      ' since the display depends on ZOrder, provide     ' a control method to alter it     Public Sub MoveUpZOrder()          ChangeZOrder(-1)     End Sub      Public Sub MoveDownZOrder()          ChangeZOrder(+1)     End Sub      Private Sub ChangeZOrder(value As Int32)         Dim ndx As Integer = Parent.Controls.GetChildIndex(Me)          If ((ndx + value) >= 0) AndAlso ((ndx + value)      Public Shadows Property ErrorImage As Image      Protected Overrides Sub OnPaintBackground(pevent As PaintEventArgs)         If MyBase.BackColor = Color.Transparent Then             ' magic happens here!             PaintSiblings(pevent)         Else             ' do nothing special when the backcolor is not Transparent             MyBase.OnPaintBackground(pevent)         End If      End Sub      ' code for painting the image     Protected Overrides Sub OnPaint(pe As PaintEventArgs)         Dim rect As Rectangle          If (MyBase.Image IsNot Nothing) Then             rect = GetImgRect(Bounds)             pe.Graphics.InterpolationMode = Drawing2D.InterpolationMode.HighQualityBicubic             pe.Graphics.CompositingQuality = CompositingQuality.HighQuality             pe.Graphics.SmoothingMode = SmoothingMode.HighQuality             pe.Graphics.DrawImage(Image, rect)         End If     End Sub      Private Sub PaintSiblings(e As PaintEventArgs)         ' need to access the parent' controls collection          If (Parent IsNot Nothing) Then             Dim borderSize As Integer = 0             Dim thisLeft As Single = -Left             Dim thisTop As Single = -Top              ' fix             Select Case MyBase.BorderStyle                 Case BorderStyle.FixedSingle                     borderSize = SystemInformation.BorderSize.Width                 Case BorderStyle.Fixed3D                     borderSize = SystemInformation.Border3DSize.Width             End Select              ' Shift ClipBounds to form relative coords             e.Graphics.TranslateTransform(thisLeft, thisTop)              ' Get Parent to paint the part behind us:             ' we cant know if thats been done or not             Using pea As New PaintEventArgs(e.Graphics, e.ClipRectangle)                 InvokePaintBackground(Parent, pea)                 InvokePaint(Parent, pea)             End Using              ' shift back             e.Graphics.TranslateTransform(-thisLeft, -thisTop)              ' starting control index is...well, ours             Dim startAt As Integer = Parent.Controls.GetChildIndex(Me)             Dim ctl As Control              ' Controls are in z-Order, so loop              ' thru the controls "behind" me             For n As Int32 = Parent.Controls.Count - 1 To startAt + 1 Step -1                 ctl = Parent.Controls(n)                  ' skip if they are invisible, too small or do not overlap me                 If (ctl.Visible = False OrElse                              ctl.Width = 0 OrElse                              ctl.Height = 0 OrElse                             Bounds.IntersectsWith(ctl.Bounds) = False) Then                     Continue For                 Else                      Using bmp As New Bitmap(ctl.Width, ctl.Height, e.Graphics)                         ' draw this sibling to a bitmap                         ctl.DrawToBitmap(bmp, New Rectangle(0, 0, ctl.Width, ctl.Height))                          ' shift the orientation relative to sibling and draw it                         thisLeft = ctl.Left - Left                         thisTop = ctl.Top - Top                          'offset, then draw the image, reset                         e.Graphics.TranslateTransform(thisLeft - borderSize,                                                  thisTop - borderSize)                         e.Graphics.DrawImageUnscaled(bmp,                                                  New Point(0, 0))                         e.Graphics.TranslateTransform(-thisLeft + borderSize,                                                 -thisTop + borderSize)                      End Using                 End If             Next         Else             ' not sure how this could happen             Using br As New SolidBrush(MyBase.BackColor)                 e.Graphics.FillRectangle(br, ClientRectangle)             End Using         End If      End Sub      ' image scaling is mainly a matter of the size and location     ' of the img rect we use in Paint     Private Function GetImgRect(destRect As Rectangle) As Rectangle         Dim pt As New Point(0, 0)         Dim sz As Size          If MyBase.Image IsNot Nothing Then             Select Case Me.ImageSizing                 Case ImageSizing.None                     sz = Image.Size                  Case ImageSizing.Scale                     If Width > Height Then                         sz = New Size(GetScaledWidth(Height), Height)                     Else                         sz = New Size(Width, GetScaledHeight(Width))                     End If                  Case ImageSizing.Stretch                     sz = Me.Size             End Select         End If         ' ToDo: move the pt if you add an Image ContentAlignment         ' (Top, TopLeft, BottomRight...) property         Return New Rectangle(pt, sz)      End Function      Private Function GetScaledWidth(h As Integer) As Integer         Dim scale As Single = CSng(Image.Width / Image.Height)         Return CInt(h * scale)     End Function      Private Function GetScaledHeight(w As Integer) As Integer         Dim scale As Single = CSng(Image.Height / Image.Width)         Return CInt(w * scale)     End Function End Class 

How to Use It

1. Create a Class Library
2. Replace the new class boilerplate code with the above
3. Add references for the NameSpaces listed in the Imports statements
4. Build the Library. A new TransPicBox should show in the toolbox.

You can also just include the class code file in your project and rebuild to avoid a DLL dependency which includes just one thing. Results:

• Four small PNGs under a larger one; all are on a Panel (rose BG)
• The TopLeft and BottomRight images use a Transparent BG, the other 2 do not
• They all have the border turned on to show the client area; the BL Clock uses a 3D border
• The larger PNG uses ImageSizing.Scale to be about 150% larger

The parent backcolor shows thru the TL and BR images as well as the overlapping larger one in front. The control will display BMP and JPGs normally and still show whats behind empty areas (if any) when the control's back color is Transparent.

Notes:

1. This is a fairly expensive Paint. Each time one of these needs to be painted, at least a portion of the parent and every control under it must be repainted as well.
2. When moving a TransPicBox in the form designer, VS temporarily brings the control to the front, so the display is temporarily whacked
3. Windows ambles on normally so things behind your special control are still hidden as far as it is concerned. The image below shows that the portions of a button partially behind a TransPicBox will not 'glow' when the mouse is over it. As far as Windows knows, that portion of it cant be seen so it is not repainted.

文章来源: Transparency of picture box