[GDI+] Why doesnt this save transparent png? [Solved]

[PAEz]

#include <WinAPI.au3>
#include <GDIPlus.au3>
_GDIPlus_Startup()
Local $width=100, $height=100, $ch_image, $ch_graphic, $ch_bitmap
 
$ch_bitmap = _WinAPI_CreateBitmap( $width , $height , 1 , 32 )
;$ch_image = _GDIPlus_ImageLoadFromFile (@MyDocumentsDir & "\123.png")
$ch_image = _GDIPlus_BitmapCreateFromHBITMAP($ch_bitmap)
$ch_graphic = _GDIPlus_ImageGetGraphicsContext($ch_image)
_GDIPlus_GraphicsClear($ch_graphic, 0x00FFFFFF)
_GDIPlus_ImageSaveToFile($ch_image, @MyDocumentsDir & "\11111.png")
_GDIPlus_Shutdown()

As the title asks, why doesnt this save a transparent png?

If I set the image by loading a png with transparency then it does as expected, but if I use CreateBitmap then it saves a black picture.

Im on XP incase that makes a difference.

Edited August 31, 2011 by PAEz

[monoscout999]

I don´t know why happend that.. i will do something like this

#include <GDIPlus.au3>
#include <Constants.au3>
Global Const $STM_SETIMAGE = 0x172

_CreateClearPNG(@DesktopDir & "\MyPNG.png", 0x55FF0000)

Func _CreateClearPNG($sFile, $iColor)
    _GDIPlus_Startup()
    Local $hImage = _GDIPlus_BitmapCreateFromScan0(100, 100)
    Local $hGraphics = _GDIPlus_ImageGetGraphicsContext($hImage)
    _GDIPlus_GraphicsClear($hGraphics, "0x" & Hex($iColor, 8))
    _GDIPlus_ImageSaveToFile($hImage, $sFile)
    _GDIPlus_GraphicsDispose($hGraphics)
    _GDIPlus_BitmapDispose($hImage)
    _GDIPlus_Shutdown()
EndFunc   ;==>_CreateClearPNG
Func _GDIPlus_BitmapCreateFromScan0($iWidth, $iHeight, $iStride = 0, $iPixelFormat = 0x0026200A, $pScan0 = 0)
    Local $aResult = DllCall($ghGDIPDll, "uint", "GdipCreateBitmapFromScan0", "int", $iWidth, "int", $iHeight, "int", $iStride, "int", $iPixelFormat, "ptr", $pScan0, "int*", 0)
    If @error Then Return SetError(@error, @extended, 0)
    Return $aResult[6]
EndFunc   ;==>_GDIPlus_BitmapCreateFromScan0

EDITED

Edited August 30, 2011 by monoscout999

[smashly]

Hi,

Use _GDIPlus_BitmapLockBits() to play with the pixels.

This code will actually generate a blank transparent png in xp , or at least it does for me

#include <WinAPI.au3>
#include <GDIPlus.au3>

Global $iW = 100, $iH = 100, $hBitmap, $hBMP, $tBitmapData, $tPixels

_GDIPlus_Startup()
$hBitmap = _WinAPI_CreateBitmap($iW, $iH , 1 , 32)
$hBMP = _GDIPlus_BitmapCreateFromHBITMAP($hBitmap)
_WinAPI_DeleteObject($hBitmap)
$hBitmap = _GDIPlus_BitmapCloneArea($hBMP, 0, 0, $iW, $iH, $GDIP_PXF32ARGB)
_GDIPlus_BitmapDispose($hBMP)
$tBitmapData = _GDIPlus_BitmapLockBits($hBitmap, 0, 0, $iW, $iH, $GDIP_ILMWRITE, $GDIP_PXF32ARGB)
$tPixels = DllStructCreate("byte[" & $iH * $iW * 4 & "]", DllStructGetData($tBitmapData, "Scan0")) ; Create DLL structure for all pixels
DllStructSetData($tPixels, 1, StringReplace(DllStructGetData($tPixels, 1), "000000FF", "00000000"))
_GDIPlus_BitmapUnlockBits($hBitmap, $tBitmapData)
$tPixels = 0
$tBitmapData = 0
_GDIPlus_ImageSaveToFile($hBitmap, @MyDocumentsDir & "\11111.png")
_GDIPlus_BitmapDispose($hBitmap)
_GDIPlus_Shutdown()

Cheers

[PAEz]

Oh Thank You Both SOOOOO Much!.....that was driving me nuts ;P

As to why it happens I think its because when you define it as having 32bits it thinks you mean 32bits without alpha...I had a look at the msdn (think thats what its called) and they mentioned that theres a 32bit without alpha, seems silly to me.

_GDIPlus_BitmapCreateFromScan0

....should be added to the UDF, very clean solution.

One thing, why do you convert the color in GraphicsClear to a string?...using a number like 0x00FFFFFF worked fine.

And thanks for the tip on LockBits I had been looking at that. Saw some routines on the forum that use that to change the alpha of a bitmap and Im going to need that later and I like to know how things work.

[monoscout999]

One thing, why do you convert the color in GraphicsClear to a string?...using a number like 0x00FFFFFF worked fine.

my mistake.. i didn`t try that simple way, because when i pass the string like this 0x55ff0000 whitout the quotes "" in the function is transformed to a integer

[wakillon]

monoscout999's solution give a real transparency effect in a photo editor but not smashly's script.

[PAEz]

Hows that?

I changed

DllStructSetData($tPixels, 1,StringReplace(DllStructGetData($tPixels,1),"000000FF","00000000"))

to

DllStructSetData($tPixels, 1,StringReplace(DllStructGetData($tPixels,1),"000000FF","00000088"))

and got what I would expect an image that was semitransparent...loaded it in Paint.Net and it seemed fine.

Prefer the first way tho, nice and clean.