[RESOLVED] [2005] GDI drawing disappears with DoubleBuffer on

[mpdeglau]

I have created my own control using GDI+. I have overriden the OnPaint event of the user control. The problem is there is a lot of flickering, so I added doublebuffering. But when I do that the control flashes info drawn with GDI flashed twice and disappears. What am I doing wrong?

[wossname]

I've done loads of .net graphics now and I have never seen any evidence that the DoubleBuffer property does anything at all.

I say turn it off again and handle low level drawing yourself. This is easier than it sounds really although it is harder than VB6's AutoRedraw property...

Not sure how much you already know about backbuffering (the proper name for doublebuffering ) but basically it means tha you have an image hidden away in RAM tha is the same size as the dimensions of your control. The thing about this RAM buffer is that it never gets messed up by other forms getting in the way o anything like that.

The ram buffer is completely under your control. From your control's perspective all it has to do to implement backbuffering is to copy the ram buffer onto its own surface in it paint event. Thats it!

So if you want to (for example) draw a line on the control all you have to do is draw it onto the RAM buffer INSTEAD and then simply invalidate() the control and as if by magic you have persistent graphics.

If you want higher speed redrawing then you need to use control.SetStyle(...) to set a few flags in the control that determine how much control MS Windows has over your own drawing procedures. You need to set the UserPaint flag and a few others (i can't remember the names offhand, i'll get back to you if you PM me).

[Kasracer]

Not sure how much you already know about backbuffering (the proper name for doublebuffering )

Proper name? Wouldn't the "proper name" be BitBlt?

[mpdeglau]

Thanks for the info Woss, I think I found a good how to for dealing with the low level drawing. I'll try that out.

[maged]

Proper name? Wouldn't the "proper name" be BitBlt?

no, i dont think so

because the doublebuffer technique is about drawing all the things in memory before displaying the final version of the graphics once on screen ( that is how it prevents flickering while drawing several details on screen).

so according to this discription i think it is back buffereing than bitbilt

[Kasracer]

no, i dont think so

because the doublebuffer technique is about drawing all the things in memory before displaying the final version of the graphics once on screen ( that is how it prevents flickering while drawing several details on screen).

so according to this discription i think it is back buffereing than bitbilt

Back buffering and double buffering are the same as BitBlit. They all draw everything off the screen and then load it onto the screen.

[mpdeglau]

It worked like a charm Woss. This is going to help me udles.

[maged]

yes i know,

we were just arguing about the proper name.

anyway i just answered to teaze him

[wossname]

Back buffering and double buffering are the same as BitBlit. They all draw everything off the screen and then load it onto the screen.

Kasracer, get a grip. BitBlt is the name of a Function in GDI. It means "Bit Block Transfer". It is often used during the backbufferig process but it is only PART of that process.

You can quite easily use BitBlt between 2 onscreen buffers, there is no reason to assume that BitBlt is only used for backbuffering. Thats like saying that a screwdriver is only ever used in building Ikea coffee tables.

mpdeglau, great I'm glad to help.