Filling a Partially Rounded Rectangle with GDI+

I have a rounded rectangle that I make like so

dc.RoundRect(textBorder, CPoint(20, 20));

Later on I draw a line through it about 1/3 of the way down.

dc.LineTo(textBorder.right, textBorder.top + 15);

Now I would like to fill just the part above the line with a solid color. In other words I need to fill a partially rounded rectangle, because the top of the rectangle is rounded, but the bottom of it is truncated by the line. Is there an easy way to do this?

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Have you tried using a combination of CreateRoundRectRegion and then FillRgn to fill the non-rectangular area?

This the example given in the docs for CreateRoundRectRegion:

CRgn   rgnA, rgnB, rgnC;

VERIFY(rgnA.CreateRoundRectRgn( 50, 50, 150, 150, 30, 30 ));
VERIFY(rgnB.CreateRoundRectRgn( 200, 75, 250, 125, 50, 50 ));
VERIFY(rgnC.CreateRectRgn( 0, 0, 50, 50 ));

int nCombineResult = rgnC.CombineRgn( &rgnA, &rgnB, RGN_OR );
ASSERT( nCombineResult != ERROR && nCombineResult != NULLREGION );

CBrush brA, brB, brC;
VERIFY(brA.CreateSolidBrush( RGB(255, 0, 0) ));  
VERIFY(pDC->FillRgn( &rgnA, &brA));      // rgnA Red Filled

VERIFY(brB.CreateSolidBrush( RGB(0, 255, 0) ));  
VERIFY(pDC->FillRgn( &rgnB, &brB));      // rgnB Green Filled
VERIFY(brC.CreateSolidBrush( RGB(0, 0, 255) ));  // rgnC Blue
VERIFY(pDC->FrameRgn( &rgnC, &brC, 2, 2 ));

In general, when you want to do something with non-rectangular areas you have to start looking into regions.

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