Make a specific area on a HDC transparent
in [Win32 API]
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From: Sascha on 27 May 2010 06:00 Hello I am trying to find a Win32 function/way that can allow me to erase a HRGN from a HDC. What I am doing is double buffering; so I copy the window HDC to a buffer HDC, then I delete/erase a specific area of the buffer HDC, then draw what I need to. But I dont know how to erase a specific area of a HDC?. I cant use InvalidateRgn(NULL, ObjRegion, true) (because this function only erases the window HDC) or can I? Can I use FillRgn( hdc, ObjRegion, (HBRUSH)GetStockObject(NULL_BRUSH) ); ? If I can, do I use it in the message WM_ERASEBKGND or in WM_PAINT? To give an idea of what I am trying to do: I am trying to make my own simple 2d drawing engine (animation?) :P. So what I do is at each drawing_clock_interval I have a drawing controller object that copies the window HDC in a buffer HDC(STEP 1), erases an objects HRGN (from the buffer HDC) (erase the old position of an object), then I draw the objects new position (FillRegion) onto the bufferHDC, then I copy the buffer HDC to the main window HDC. I dont want to use InvalidateRgn() before STEP 1, because I think it may cause the flicker affect that you get without double buffering(Because of the delay between, erasing the region, copying the HDC, drawing on the HDC, then copying it back) . Am I right? Hope this makes sense :)
From: John H. on 27 May 2010 19:39
Sascha wrote: > I am trying to make my own simple 2d drawing engine (animation?) :P. > So what I do is at each drawing_clock_interval I have a drawing Not too sure about this, but you could try at each interval, invalidating the region you want to repaint, via InvalidateRgn. Then look for the WM_PAINT message. When it comes, see if there is an update area, via GetUpdateRect. If there is, BeginPaint, do your painting, and EndPaint. |