AlphaTransparent Image as form background

[vigge89]

My current project allows the user to skin the application. I'm using GDI+ for painting an image as the background for the program. The image is either an 32bit bitmap or an 24bit PNG. I want to paint the image directly on the screen (so alphatransparency is keeped, pixels which is semi-transparent in the image should be it on the screen). I'm currently painting the image on the form, which makes the image painted overlap the form, so it doesn't keep it's transparency. So you can say that i want to make the form-background invisible, while keeping the painted image and the controls on the form visible.

this is how it should look like (taken from another app):

The image isn't painted on the form, it's painted directly on the screen or whatever you should call it.

this is the image which should be painted (24bit png with transparency):


This is how it currently looks like:

The reason why i got pink/purple background is becuase i'm using SetLayeredWindowAttributes() to make the color pink/purple go invisible. But since the image is painted on the form, the image's parts where it is semi-transparent is chaning the pink behind it to another color. I would like to scrap the "pink is invisible"-function and instead use images with transparency to decide the invisibility of the pixels.

I have no idea on how to solve this. Are there anyone who is familiar with this? I've looked after a solution for one week, but i can't find anything regarding this.

Thanks in advance.

[cyborg]

I think you could probably get the desktop DC and blend the two images together and then paint it to the form.
You should also hide the form before getting the desktop DC...

[vigge89]

yeah, i guess, but that's not the real way, it must be some way else
what if there's a window under the app?

[cyborg]

If I'm not wrong, the desktop DC holds an image of the entire screen. You should be able to do it this way:

1) Hide the program
2) Copy the desktop DC to a local DC
3) Mix it with the skin
4) Paint it on the form
5) Show the program

Also everytime you move the form you'll have to remix the skin with the other DC. And everytime your program loses/gets focus, you should update the desktop DC, because other windows might have been moved.
(You don't have to get the whole DC, just the part that's behind the program)

Just as vigge89 says, there should be another way, but I don't know it. I know there is a way to make the program fully transparent in different regions, but you can not make it partially transparent using that method.

[vigge89]

that way would be kinda slow, laggy, and it would probably flicker alot, so it wouldn't look to good

[cyborg]

Originally posted by vigge89
that way would be kinda slow, laggy, and it would probably flicker alot, so it wouldn't look to good

That's probably true.

I've heard that the new windows "longhorn" will keep separate buffers for each windows which allows them to be blended with the other windows. Maybe you should wait for longhorn

[vigge89]

it is possible right now, i've seen lots of system-monitoring apps and stuff do this

[cyborg]

Originally posted by vigge89
it is possible right now, i've seen lots of system-monitoring apps and stuff do this

I know that in 3D Mark when you load it, the splash screen fades in and blends with the background. But I think it does it using my method... Is it those kind of windows you're talking about? Or are you talking about those that you can move around?

[vigge89]

yeah, the form/window should be moveable

[vigge89]

The image on how it should look like is taken from RainLendar, which is written in C++.
I just saw that he had released the source code for it, which can be found at:
http://www.ipi.fi/~rainy/index.php?pn=projects&project=rainlendar

I downloaded the code and looked trhough it, but i don't know C++ at all, so i can't "read" the code. If anyone could find the code for using the trans, could you tell me how it's done?
thanks...

[SLH]

From looking at rainwindow.cpp, it looks like it takes a pic of the desktop (inc. windows), draws itself on it, then displays it.

[vigge89]

hmm, can you see how it paints itself?

[SLH]

In that file the updatetransparency function seems to be the one. It uses a C++ function called 'UpdateLayeredWindow' It has the following parameters:

( HWND hwnd,
HDC hdcDst,
POINT *pptDst,
SIZE *psize,
HDC hdcSrc,
POINT *pptSrc,
COLORREF crKey,
BLENDFUNCTION *pblend,
DWORD dwFlags
);

Have checked and it's not an API function.

Here's it being used:

LONG style = GetWindowLong(m_Window, GWL_EXSTYLE);
SetWindowLong(m_Window, GWL_EXSTYLE, style | WS_EX_LAYERED);

RECT r;
GetWindowRect(m_Window, &r);
typedef BOOL (WINAPI * FPUPDATELAYEREDWINDOW)(HWND hWnd, HDC hdcDst,
 POINT *pptDst, SIZE *psize, HDC hdcSrc, POINT *pptSrc, COLORREF crKey,
 BLENDFUNCTION *pblend, DWORD dwFlags);
HINSTANCE h = LoadLibrary("user32.dll");
FPUPDATELAYEREDWINDOW UpdateLayeredWindow = (FPUPDATELAYEREDWINDOW)GetProcAddress(h, "UpdateLayeredWindow");

BLENDFUNCTION blendPixelFunction= {AC_SRC_OVER, 0, 255, AC_SRC_ALPHA};
POINT ptWindowScreenPosition = {r.left, r.top};
POINT ptSrc = {0, 0};
SIZE szWindow = {m_Width, m_Height};
			
HDC dcScreen = GetDC(GetDesktopWindow());
HDC dcMemory = CreateCompatibleDC(dcScreen);
HBITMAP oldBitmap = (HBITMAP)SelectObject(dcMemory, m_DoubleBuffer.GetBitmap());
UpdateLayeredWindow(m_Window, dcScreen, &ptWindowScreenPosition, &szWindow, dcMemory,
 &ptSrc, 0, &blendPixelFunction, ULW_ALPHA);
			ReleaseDC(GetDesktopWindow(), dcScreen);
SelectObject(dcMemory, oldBitmap);
DeleteDC(dcMemory);
FreeLibrary(h);

[vigge89]

Hmm, i'm using SetLayeredWindowAttributes() which is an API in my project for setting alphatransparency, maybe they're related?
How i call the function:

SetLayeredWindowAttributes hWnd, RGB(255, 0, 255), bAlpha, LWA_COLORKEY Or LWA_ALPHA

Does anyone know what the UpdateLayeredWindow() does, and what it "is"?

It's called with:

UpdateLayeredWindow(m_Window, dcScreen, &ptWindowScreenPosition, &szWindow, dcMemory, &ptSrc, 0, &blendPixelFunction, ULW_ALPHA);

what is "&blendPixelFunction" and "ULW_ALPHA"?

[SLH]

&PixelBlendFunction looks like it wants a pointer to the address of a blend function.
The blend function has this structure:

{
  BYTE     BlendOp;
  BYTE     BlendFlags;
  BYTE     SourceConstantAlpha;
  BYTE     AlphaFormat;
}

Judging by C++ naming conventions i'd guess that ULW_ALPHA was a constant (unsigned long) value.

Sorry i can't help more.

[vigge89]

Originally posted by SLH
&PixelBlendFunction looks like it wants a pointer to the address of a blend function.
The blend function has this structure:

{
  BYTE     BlendOp;
  BYTE     BlendFlags;
  BYTE     SourceConstantAlpha;
  BYTE     AlphaFormat;
}

Judging by C++ naming conventions i'd guess that ULW_ALPHA was a constant (unsigned long) value.

Sorry i can't help more.

yea, i knew it was a constant, but what is it for?

thanks for answering btw

[SLH]

Well according to the declaration of 'updatelayeredwindow' it's its flags.
From the MSDN help:

dwFlags
This parameter can be one of the following values.
ULW_ALPHA
Use pblend as the blend function. If the display mode is 256 colors or less, the effect of this value is the same as the effect of ULW_OPAQUE.
ULW_COLORKEY
Use crKey as the transparency color.
ULW_OPAQUE
Draw an opaque layered window.
If hdcSrc is NULL, dwFlags should be zero.

[vigge89]

I looked at the function on MSDN, seems to act exactly like SetLayeredWindowAttributes(), so that's not what i'm looking for. I'll keep searching...

[TokersBall_CDXX]

Module

Option Explicit
Declare Function CreateRectRgn Lib "GDI32" (ByVal X1 As Long, ByVal Y1 As Long, ByVal X2 As Long, ByVal Y2 As Long) As Long
Declare Function CombineRgn Lib "GDI32" (ByVal hDestRgn As Long, ByVal hSrcRgn1 As Long, ByVal hSrcRgn2 As Long, ByVal nCombineMode As Long) As Long
Declare Function GetPixel Lib "GDI32" (ByVal hDC As Long, ByVal x As Long, ByVal Y As Long) As Long
Declare Function SetWindowRgn Lib "user32" (ByVal hWnd As Long, ByVal hRgn As Long, ByVal bRedraw As Long) As Long
Declare Function DeleteObject Lib "GDI32" (ByVal hObject As Long) As Long
 
Public Function createSkinnedForm(SkinnedForm As Form, skinSrc As PictureBox, Optional transparentColor As Long) As Long
Const RGN_OR = 2
Dim glSkinImage As Long
Dim glHeight    As Long
Dim glwidth     As Long
Dim lReturn     As Long
Dim lRgnTmp     As Long
Dim lSkinRgn    As Long
Dim lStart      As Long
Dim lRow        As Long
Dim lCol        As Long
skinSrc.AutoSize = True
With SkinnedForm
    .Hide
    .Picture = skinSrc.Picture
    .Width = skinSrc.Width
    .Height = skinSrc.Height
End With
lSkinRgn = CreateRectRgn(0, 0, 0, 0)
With skinSrc
    .AutoRedraw = True
    glHeight = .Height / Screen.TwipsPerPixelY
    glwidth = .Width / Screen.TwipsPerPixelX
    If transparentColor < 1 Then transparentColor = GetPixel(.hDC, 0, 0)
    For lRow = 0 To glHeight - 1
        lCol = 0
        Do While lCol < glwidth
            Do While lCol < glwidth And GetPixel(.hDC, lCol, lRow) = transparentColor
                lCol = lCol + 1
            Loop
            If lCol < glwidth Then
                lStart = lCol
                Do While lCol < glwidth And GetPixel(.hDC, lCol, lRow) <> transparentColor
                    lCol = lCol + 1
                Loop
                If lCol > glwidth Then lCol = glwidth
                lRgnTmp = CreateRectRgn(lStart, lRow, lCol, lRow + 1)
                lReturn = CombineRgn(lSkinRgn, lSkinRgn, lRgnTmp, RGN_OR)
                Call DeleteObject(lRgnTmp)
            End If
        Loop
    Next
End With
Call SetWindowRgn(SkinnedForm.hWnd, lSkinRgn, True)
skinSrc.Picture = LoadPicture("")
SkinnedForm.Show
End Function

form should contain a picturebox with the image

FORM

Call createSkinnedForm(Me, BackPic)

result?

[vigge89]

TokersBall: yeah, that's for a normal skinned form, i looking for code which allows semi-transparent images

[vigge89]

i've got another question now (don't forget the old one tho ):

I use this code to draw an image on an picturebox:

gfx.CreateFromHDC cmdExe.hDC
 
    gfx.DrawImageI img_btn_normal.Handle, 0, 0
    cmdExe.Refresh

gfx is the GDI+ graphics handle, and cmdExe is the picturebox (wrong name, i know). Now i'm wondering how to clear the drawn picture, so i can paint another image (which could be transprarent) on the picturebox. I've tried cmdExe.Cls, but that stops the picturebox from being painted on again. Does anyone know how to do it properly?

Edit: nevermind, got it to work by using:

cmdExe.Cls
    gfx.CreateFromHDC cmdExe.hDC
    gfx.DrawImageI img_btn_normal.Handle, 0, 0
    cmdExe.Refresh

ANy new ideas on the main problem?

[vigge89]

pulling this thread up again after i contacted the author of Rainlendar. He gave me an example source for doing this in C++.

Check the attachment for the Vc++ source. Now, i've studied some C++, but i'm not that good on it, so if anyone could take a look, if you could translate the code into english, so I can port the code into VB.

Thanks in advance...

[vigge89]

i finally found a working example, but it seems to be kinda complicated. I'll attach the code for the example and the project im trying to create.

Here's the example i found. Drag an image with alphatransparency onto the top slider, and it will create a window for it.

[vigge89]

Here's the program i'm trying to add the feuture to (just an simple example program which uses the current way of painting images which i got in my main project)

I can't get the UpdateLayeredWindow() function to work

Thanks in advance....