BufferedDC

This class provides a simple way to avoid flicker: when drawing on it, everything is in fact first drawn on an in-memory buffer (a Bitmap) and then copied to the screen, using the associated DC, only once, when this object is destroyed.

BufferedDC itself is typically associated with ClientDC, if you want to use it in your EVT_PAINT handler, you should look at BufferedPaintDC instead.

When used like this, a valid DC must be specified in the constructor while the buffer bitmap doesn’t have to be explicitly provided, by default this class will allocate the bitmap of required size itself. However using a dedicated bitmap can speed up the redrawing process by eliminating the repeated creation and destruction of a possibly big bitmap. Otherwise, BufferedDC can be used in the same way as any other device context.

There is another possible use for BufferedDC is to use it to maintain a backing store for the window contents. In this case, the associated DC may be None but a valid backing store bitmap should be specified.

Finally, please note that GTK+ 2.0 as well as OS X provide float buffering themselves natively. You can either use Window.IsDoubleBuffered to determine whether you need to use buffering or not, or use AutoBufferedPaintDC to avoid needless float buffering on the systems which already do it automatically.

See also

DC, MemoryDC, BufferedPaintDC, AutoBufferedPaintDC

Inheritance Diagram

Inheritance diagram for class BufferedDC

Known Subclasses

BufferedPaintDC

Methods Summary

__init__	Default constructor.
Init	Initializes the object created using the default constructor.

Class API

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class BufferedDC(MemoryDC)

This class provides a simple way to avoid flicker: when drawing on it, everything is in fact first drawn on an in-memory buffer (a Bitmap) and then copied to the screen, using the associated DC, only once, when this object is destroyed.

Possible constructors:

BufferedDC()

BufferedDC(dc, area, style=BUFFER_CLIENT_AREA)

BufferedDC(dc, buffer=NullBitmap, style=BUFFER_CLIENT_AREA)

Methods

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__init__(self, *args, **kw)

Overloaded Implementations:

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__init__ (self)

Default constructor.

You must call one of the Init methods later in order to use the device context.

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__init__ (self, dc, area, style=BUFFER_CLIENT_AREA)

Creates a buffer for the provided dc.

Init must not be called when using this constructor.

Parameters:

• dc (DC) – The underlying DC: everything drawn to this object will be flushed to this DC when this object is destroyed. You may pass None in order to just initialize the buffer, and not flush it.
• area (Size) – The size of the bitmap to be used for buffering (this bitmap is created internally when it is not given explicitly).
• style (int) – BUFFER_CLIENT_AREA to indicate that just the client area of the window is buffered, or BUFFER_VIRTUAL_AREA to indicate that the buffer bitmap covers the virtual area.

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__init__ (self, dc, buffer=NullBitmap, style=BUFFER_CLIENT_AREA)

Creates a buffer for the provided dc.

Init must not be called when using this constructor.

Parameters:

• dc (DC) – The underlying DC: everything drawn to this object will be flushed to this DC when this object is destroyed. You may pass None in order to just initialize the buffer, and not flush it.
• buffer (Bitmap) – Explicitly provided bitmap to be used for buffering: this is the most efficient solution as the bitmap doesn’t have to be recreated each time but it also requires more memory as the bitmap is never freed. The bitmap should have appropriate size, anything drawn outside of its bounds is clipped.
• style (int) – BUFFER_CLIENT_AREA to indicate that just the client area of the window is buffered, or BUFFER_VIRTUAL_AREA to indicate that the buffer bitmap covers the virtual area.

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Init(self, *args, **kw)

Initializes the object created using the default constructor.

Please see the constructors for parameter details.

Overloaded Implementations:

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Init (self, dc, area, style=BUFFER_CLIENT_AREA)

Parameters:

• dc (DC) –
• area (Size) –
• style (int) –

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Init (self, dc, buffer=NullBitmap, style=BUFFER_CLIENT_AREA)

Parameters:

• dc (DC) –
• buffer (Bitmap) –
• style (int) –

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