Device Contexts

A DC is a device context onto which graphics and text can be drawn. The device context is intended to represent a number of output devices in a generic way, with the same API being used throughout.

Some device contexts are created temporarily in order to draw on a window. This is true of ScreenDC, ClientDC, PaintDC, and WindowDC. The following describes the differences between these device contexts and when you should use them.

• ScreenDC. Use this to paint on the screen, as opposed to an individual window.
• ClientDC. Use this to paint on the client area of window (the part without borders and other decorations), but do not use it from within an PaintEvent.
• PaintDC. Use this to paint on the client area of a window, but only from within a PaintEvent.
• WindowDC. Use this to paint on the whole area of a window, including decorations. This may not be available on non-Windows platforms.

To use a client, paint or window device context, create an object on the stack with the window as argument, for example:

def OnMyCmd(self, event):

    dc = wx.ClientDC(window)
    DrawMyPicture(dc)

Try to write code so it is parameterised by DC - if you do this, the same piece of code may write to a number of different devices, by passing a different device context. This doesn’t work for everything (for example not all device contexts support bitmap drawing) but will work most of the time.