Custom double buffer

[Kuba Florczyk]

Hi

I've got some problem doing double buffer.
Here is my problem:
I've got custom control on which i paint some data (chat messages, lets call
it ChatControl), this control is puted on a scrollable panel.
Of course i've set right styles on a ChatControl:

//styles
this.SetStyle(ControlStyles.AllPaintingInWmPaint, true);
this.SetStyle(ControlStyles.DoubleBuffer, true);
this.SetStyle(ControlStyles.UserPaint, true);
this.SetStyle(ControlStyles.ResizeRedraw, true);

Everything is ok,but i've got some performance problems. Chat messages
arrived in every 5 seconds, and i call on ChatControl Refresh(), so my
OnPaint method is called - and thats ok. But control is repainted more times
than on in every 5 second refresh: user used scroll, or something like that.

And now i want to made some additional double buffer, because i want to draw
remembered graphic (thru bitmap), than draw it again - because its neccesery
when i only refresh control. I know i should do something like this:

Bitmap bmp = new Bitmap(this.ClientRectangle.Witdh,
this.ClientRectangle.Height);
Graphics g = Graphics.FromImage(bmp);

and than i should draw on g

but there is a "small" problem - beacuse i know control size after i draw
something (thats depends at chat messages count)! so how i can get a bitmap
from my base graphics or how to create bitmap that will resize automaticly
to my graphic size ? Or .... maybe somebody got any idea?

regards
kuba florczyk

 

[Bob Powell [MVP]]

You should possibly consider manual double buffering. What you're doing is
essentially double buffering and then writing that the the systems
back-buffer so you might as well do it yourself.

Windows Forms Tips and Tricks has an article on double buffering and shows
you how to manage a back-buffer that changes size in response to the
OnSizeChanged method calls.

--
Bob Powell [MVP]
Visual C#, System.Drawing

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