vb@rchiv · Tipps & Tricks · Transparente Bitmaps

Rubrik: Grafik und Font · Bilder & Icons | VB-Versionen: VB6

08.10.09

Transparente Bitmaps Eine Funktion, mit der sich ein Bild anhand einer frei definierbare Farbe transparent darstellen lässt.
Autor: Dieter Otter	Bewertung:	Views: 10.256
www.tools4vb.de	System: Win2k, WinXP, Win7, Win8, Win10, Win11	Beispielprojekt auf CD

Heute stellen wir Ihnen eine Funktion vor, mit der sich ein Bild anhand einer frei definierbaren Farben transparent darstellen lässt. Für die Ausgabe des transparenten Bildes wird ein Control mit einer hDC-Eigenschaft benötigt (bspw. Form oder PictureBox).

Fügen Sie nachfolgenden Code in ein Modul ein:

Option Explicit
 
' benötigte API-Deklarationen
Private Declare Function GdiTransparentBlt Lib "gdi32.dll" ( _
  ByVal hDC As Long, _
  ByVal x As Long, _
  ByVal y As Long, _
  ByVal nWidth As Long, _
  ByVal nHeight As Long, _
  ByVal hSrcDC As Long, _
  ByVal xSrc As Long, _
  ByVal ySrc As Long, _
  ByVal nSrcWidth As Long, _
  ByVal nSrcHeight As Long, _
  ByVal crTransparent As Long) As Boolean
 
Private Declare Function GetObject Lib "gdi32" _
  Alias "GetObjectA" ( _
  ByVal hObject As Long, _
  ByVal nCount As Long, _
  lpObject As Any) As Long
 
Private Declare Function GetDesktopWindow Lib "user32" () As Long
 
Private Declare Function GetDC Lib "user32.dll" ( _
  ByVal hWnd As Long) As Long
 
Private Declare Function CreateCompatibleDC Lib "gdi32.dll" ( _
  ByVal hDC As Long) As Long
 
Private Declare Function CreateCompatibleBitmap Lib "gdi32.dll" ( _
  ByVal hDC As Long, _
  ByVal nWidth As Long, _
  ByVal nHeight As Long) As Long
 
Private Declare Function SelectObject Lib "gdi32.dll" ( _
  ByVal hDC As Long, _
  ByVal hObject As Long) As Long
 
Private Declare Function DrawState Lib "user32" _
  Alias "DrawStateA" ( _
  ByVal hDC As Long, _
  ByVal hBrush As Long, _
  ByVal lpDrawStateProc As Long, _
  ByVal lData As Any, _
  ByVal wData As Long, _
  ByVal x As Long, _
  ByVal y As Long, _
  ByVal cx As Long, _
  ByVal cy As Long, _
  ByVal fuFlags As Long) As Long
 
Private Declare Function DeleteObject Lib "gdi32.dll" ( _
  ByVal hObject As Long) As Long
 
Private Declare Function DeleteDC Lib "gdi32.dll" ( _
  ByVal hDC As Long) As Long
 
Private Declare Function ReleaseDC Lib "user32.dll" ( _
  ByVal hWnd As Long, ByVal hDC As Long) As Long
 
' Bitmap-Inforamtionen
Private Type Bitmap
  bmType As Long
  bmWidth As Long
  bmHeight As Long
  bmWidthBytes As Long
  bmPlanes As Integer
  bmBitsPixel As Integer
  bmBits As Long
End Type
 
Private Const DST_BITMAP = &H4

' Erstellt ein transparentes Bitmap und zeichnet dieses 
' in den angegebenen Device-Context
'
' Optionale Parameter: x, y
'   = Ausgabeposition (linkere obere Ecke)
Private Function DrawTransparentBmp(ByVal hDC As Long, ByVal hBitmap As Long, _
  ByVal TransColor As Long, Optional ByVal x As Long = 0, Optional ByVal y = 0)
 
  Dim bmp As Bitmap
  Dim DeskDC As Long
  Dim TempDC As Long
  Dim TmpBmp As Long
  Dim OldBmp As Long
 
  ' Bitmap-Struktur ermitteln
  Call GetObject(hBitmap, Len(bmp), bmp)
 
  ' Device-Context erstellen
  DeskDC = GetDC(GetDesktopWindow)
  TempDC = CreateCompatibleDC(DeskDC)
 
  ' Kompatibles Bitmap erstellen
  TmpBmp = CreateCompatibleBitmap(DeskDC, bmp.bmWidth, bmp.bmHeight)
  OldBmp = SelectObject(TempDC, TmpBmp)
 
  ' Bitmap zeichnen
  Call DrawState(TempDC, 0, 0, hBitmap, 0, 0, 0, 0, 0, DST_BITMAP)
 
  ' Transaprenz erzeugen
  GdiTransparentBlt hDC, x, y, bmp.bmWidth, bmp.bmHeight, TempDC, 0, 0, _
    bmp.bmWidth, bmp.bmHeight, TransColor
 
  ' Objekte freigeben
  DeleteObject SelectObject(TempDC, OldBmp)
  DeleteDC TempDC
  ReleaseDC GetDesktopWindow, DeskDC
End Function

Aufrufbeispiel:

' Bild mit "Magenta" als transparente Farbe anzeigen
DrawTransparentBmp Picture1.hDC, LoadPicture("d:\bild1.bmp"), vbMagenta