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How can I make the picture or text I am dragging on top of a larger picture semi transparent

Posted on 2009-06-29
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Last Modified: 2012-05-07
In the last question you showed me how to drag 1 image on top of a larger image is it possible to make the draggable image semi transparent so you can see the bottom image through it some what?
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Question by:Dov_B
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by:mohan_sekar
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Use
filter: alpha(opacity = 100); - for Internet Explorer
    -moz-opacity: 1.0; - for Firefox
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by:mohan_sekar
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Sorry, I thought the question was posted in asp.net zone!
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by:Mike Tomlinson
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The crux of the question:

    "...is it possible to make the draggable image semi transparent so you can see the bottom image through it some what?"

My answer:

   Yes...and No.

Transparency in .Net is a funny beast.   =\

(a) If you want to keep each overlaid image in its own container (picturebox) then you have to place it into its OWN window (borderless form) and literally "float" the image OVER the original form.  This allows you to set the Opacity() property of the floating window to less than 1 thus making it semi-transparent.  So you would create the new form, set the image and opacity, and then calculate the necessary location to make it appear in the correct position relative to the original form.  This obviously brings up a slew of other issues that you must now deal with such as "syncing" the movement of all the overlay windows with the main form when it is moved/resized by the user.  The overlay form must be limited to move "within" the confines of the original image as well.  You must also setup communication between the forms so that you can make things happen in the main form in response to the overlay forms.  The advantage to this approach is that it is relatively easy to MOVE the smaller image around by simply moving the overlay form itself.

(b) Another option is to build ONE composite image consisting of the original image and then the smaller images drawn on top.  With Graphics.DrawImage() it is possible to specify an alpha channel which would blend the smaller image on top of the underlying image.  The disadvantage here is that it now becomes difficult to seamlessly move the image around in response to user interaction since now the entire image has to be REDRAWN everytime you want to move just one image.  This can be a processor intensive operation and may cause some "sluggishness" if you wanted to let a user drag an image around in real time.  This could be alleviated by not dragging the actual image around but instead making the user drag around just a rectangle border (think rubberbanding!).

Which approach do you want to explore?...
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by:Dov_B
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gee...I am not sure
I guess either option a or
option b but moving just the rectangle bordere
either way thank you
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by:Mike Tomlinson
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Basically there isn't an "easy" solution here and integrating either concept into an existing project will probably require a lot of code changes.

So let's take baby steps shall we?  I'll post up a simplified example showing how to draw a smaller image with semi-transparency on top of a larger image and then we'll go from there...
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by:Dov_B
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thank you
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Mike Tomlinson earned 500 total points
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Try this out with a BLANK form...

Select a Background Image when the form opens then Double Click somewhere on the image and select a smaller image to "overlay" on it:
Imports System.Drawing.Imaging

Public Class Form1
 

    Private WithEvents PB As New PictureBox
 

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

        PB.SizeMode = PictureBoxSizeMode.Normal

        PB.Dock = DockStyle.Fill

        Me.Controls.Add(PB)

    End Sub
 

    Private Sub Form1_Shown(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Shown

        SelectBackgroundImage()

    End Sub
 

    Private Sub SelectBackgroundImage()

        Using ofd As New OpenFileDialog

            With ofd

                .Title = "Select a BACKGROUND Image"

                .Filter = "Image Files(*.BMP;*.JPG;*.GIF)|*.BMP;*.JPG;*.GIF|All files (*.*)|*.*"

                If .ShowDialog = Windows.Forms.DialogResult.OK Then

                    Try

                        Using fs As New System.IO.FileStream(.FileName, IO.FileMode.Open)

                            PB.Image = Image.FromStream(fs)

                        End Using

                    Catch ex As Exception

                        MessageBox.Show("Image File" & .FileName, "Error Opening Image File", MessageBoxButtons.OK, MessageBoxIcon.Error)

                    End Try

                End If

            End With

        End Using

    End Sub
 

    Private Sub PB_DoubleClick(ByVal sender As Object, ByVal e As System.EventArgs) Handles PB.DoubleClick

        If Not IsNothing(PB.Image) Then

            Dim pt As Point = PB.PointToClient(Cursor.Position)

            Using ofd As New OpenFileDialog

                With ofd

                    .Title = "Select a smaller OVERLAY Image"

                    .Filter = "Image Files(*.BMP;*.JPG;*.GIF)|*.BMP;*.JPG;*.GIF|All files (*.*)|*.*"

                    If .ShowDialog = Windows.Forms.DialogResult.OK Then

                        Dim cm As New ColorMatrix

                        cm.Matrix33 = 0.5 ' values range from 0 --> 1

                        Dim IA As New ImageAttributes

                        IA.SetColorMatrix(cm)
 

                        Try

                            Dim overlay As New Bitmap(.FileName)

                            Dim bmp As New Bitmap(PB.Image)

                            Using G As Graphics = Graphics.FromImage(bmp)

                                G.DrawImage(overlay, New Rectangle(pt, overlay.Size), 0, 0, overlay.Width, overlay.Height, GraphicsUnit.Pixel, IA)

                            End Using

                            PB.Image = bmp

                        Catch ex As Exception

                            MessageBox.Show(ex.ToString, "Error Adding Overlay")

                        End Try

                    End If

                End With

            End Using

        Else

            MessageBox.Show("Please select a background image first...")

            SelectBackgroundImage()

        End If

    End Sub
 

End Class

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Author Comment

by:Dov_B
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very cool
thanks
I will be gone for about an hour
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Author Closing Comment

by:Dov_B
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Sorry away so long
I am asking a related question if you get a chance to look at it
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