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Bitmap Class

  + Object
    + Display
      + Bitmap

Description

The Bitmap class manipulates images in memory. Using the methods inherited from the Display class, you can draw an image in memory or on screen, and copy parts of an image into another image or onto the screen. This class is instantiable and cloneable but not derivable.

A Bitmap object can be associated with a resource. When you insert an image into your project, a global Bitmap type variable with the name of the image is automatically created, and associated with the corresponding image in the application resources. The first time you access methods and properties of this object, the associated image is loaded. When you no longer need the image, you can free up memory by calling the Destroy method or the Unload function.

On the other hand, when you instantiate the Bitmap class yourself, the object obtained is not associated with any resource. In this case, you must explicitly create the image contained in the object using the Create method, specifying the width, height, an optional bit depth and density. You can then destroy it with the Destroy method. The Unload function has no effect on a Bitmap object which is not associated with a resource.

You can also create a bitmap using the CreateFromResource and CreateFromBitmapType methods, which initialize the Bitmap object from data packed accordingly to the Palm OS^® resource format. This is typically used to access images or icons of a third party application, or to access images returned by a shared library such as a JPEG converter.

Starting with Palm OS^® 3.5, you can specify a transparency color for images using the TransparencyColor property. When copying an image to screen or another image, all the pixels whose color corresponds to that specified by this property are not copied.

When duplicating of a Bitmap object with the Clone keyword, the image contained in the object is an exact copy, including bit depth, density, and transparency color.

The following example creates an image dynamically, and displays it in the middle of the form:

Private bm as New Bitmap

Private Sub Form_Load()
  bm.Create 100, 40
  bm.BackColor=hbColorBlue
  bm.ForeColor=hbColorBlack
  bm.Rectangle 0, 0, 99, 39, hbRectBorderSolid+hbRectFillSolid,5
  bm.TextColor=hbColorWhite
  bm.DrawFont=hbFontLargeBold
  bm.TextOut 50, 20, "Sample Bitmap",hbTextAlignCenter+hbTextAlignVCenter
  bm.Flush
End Sub

Private Sub Form_Unload()
  bm.Destroy
End Sub

Private Sub Form_Paint()
  CopyArea 30, 60, 100, 40, bm, 0, 0
End Sub

Note: The maximum bit depth of an image depends on the Palm OS^® version, while the supported densities depends on the device your application is running on. Refer to the Create method for more information.

Members

System requirements