Introducing the Powerful New Picture Object in VB 4.0

ID: Q129887

The information in this article applies to:

Microsoft Visual Basic Standard, Professional, and Enterprise Editions, 16-bit and 32-bit, for Windows, version 4.0

SUMMARY

In Visual Basic version 3.0, you had only the Picture property of the PictureBox control. Now, in Visual Basic version 4.0, you have a new Picture object that adds many capabilities. This article details some of these new capabilities.

MORE INFORMATION

Array of Picture Objects

You can use an array of Picture objects to keep a series of graphics in memory without using a form that contains multiple PictureBox or Image controls. For example, the following code loads a Picture object with a bitmap and uses that bitmap to set the Picture property of a PictureBox control:


   Private Sub Command1_Click()
      Dim x As Picture
      Set x = LoadPicture("cars")
      Set Picture1.Picture = x
   End Sub

Handle Property of Picture Object Differs from hDC Property of PictureBox

There is no direct relationship between a Picture.Handle and a PictureBox.hDC. The hDC property of the PictureBox is the handle provided by the operating system to the device context of the PictureBox control. The Handle property of the Picture object is actually the handle of the GDI object that is contained in the Picture object. If the Picture property contains a bitmap, its an HBITMAP. If it contains an icon, then its an HICON, or if it contains a metafile, then its an HMETAFILE.

Use the Picture Object Instead of the Windows API

There are lots of things you can do with an HBITMAP, an HICON, or an HMETAFILE in the Windows API, but the Picture object already does most of them for you. This means that you are better off using the Picture object instead of the Windows API whenever possible.

There are now two completely different ways to paint graphics on a window (or blit). You can use BitBlt or StretchBlt on the hDC of an object, or you can use the PaintPicture method on the Picture Object or Property. If you have an Image control, you can only use PaintPicture because Image controls do not have an hDC. For example:


   Private Sub Command1_Click()
      Dim x as Picture
      Set x = LoadPicture("cars.bmp")
      PaintPicture x, 0, 0
      PaintPicture Picture1.Picture, 0, 200
      PaintPicture Image1.Picture, 0, 500
   End Sub

The link between the Picture object and the PictureBox control is the Image property. You can draw something into the hDC of the PictureBox (with BitBlt, Polygon, LineTo, or other API functions), and then assign its Image property to the Picture property. This gives the PictureBox a bitmap with the same content as the hDC. This is useful for operations such as converting an icon or a metafile into a bitmap. However, you can only use raster operation (ROP) codes with PaintPicture on bitmaps, so this conversion is necessary for many blitting operations.

NOTE: For a list of Raster Operation (ROP) codes for use with PaintPicture, see WIN32API.TXT in your VB\WINAPI directory.

Additional query words: 4.00 vb4win vb4all

Keywords :
Version :
Platform :
Issue type :