c++ repaint part of window

Question

i want to repaint part of the window not the whole thing. i have no idea how to. im using win32 please no mfc........
thanks in advance

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// create rect structure
RECT rect2;
rect2.left=0;
rect2.top=0;
rect2.right=225;
rect2.bottom=300;
// calling invalidateRect when left mouse button is donw
case WM_LBUTTONDOWN:
    InvalidateRect(hWnd, &rect2, false);
    break;

Answer 1

What's wrong with RedrawWindow ?

Answer 2

Pass the rectangle of the portion of window, which you want to re-paint, in InvalidateRect() method. Read here for details.

Answer 3

Is this for a game engine? It appears so since you are concerned about cpu usage on a full redraw.

If it is, then I'd recommend blitting to a back buffer image, keeping track of what portion of your back buffer has changed and copying only that portion to the screen once you are done rendering. This is called double buffering and will also take care of flickering issues you might see.

Answer 4

As other answers have pointed out; when handling WM_PAINT you need to get the update rectangle/region and draw/blit accordingly.

see:
+ The WM_PAINT Message
+ Retrieving the Update Region
+ Invalidating and Validating the Update Region
+ Synchronous and Asynchronous Drawing