BUG: Some ROP Codes Cause Inconsistent Polygon() Line Segments (111580)

SYMPTOMS

When a ROP (raster operation) such as R2_XORPEN or R2_NOT is used with the Polygon() function, the line segments may be inconsistent; they may appear highlighted or ragged when they should appear smooth. This may be more apparent when the polygon is filled with a gray brush (80h).

CAUSE

The border does not overlap the interior fill precisely. Polygonal filling works successfully, but the XOR operation with the pen shows that the overlap between border and fill is not completely consistent.

STATUS

Microsoft has confirmed this to be a bug in Windows versions 3.0 and 3.1. We are researching this problem and will post new information here in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

The following function demonstrates the problem:

int PASCAL TestProc( HWND hWnd )
{
    HDC hDC;
    HBRUSH hGrayBrush, hOldBrush;
    POINT aPoints[3];

    hGrayBrush = CreateSolidBrush(RGB(128,128,128));

    aPoints[0].x = 50;
    aPoints[0].y = 10;
    aPoints[1].x = 250;
    aPoints[1].y = 50;
    aPoints[2].x = 125;
    aPoints[2].y = 130;

    hDC = GetDC(hWnd);

    // default pen, brush, and ROP2
    Polygon(hDC, aPoints, sizeof(aPoints) / sizeof(POINT));

    // default pen, gray brush, XORPEN ROP2
    hOldBrush = SelectObject(hDC, hGrayBrush);
    SetROP2(hDC, R2_XORPEN);
    Polygon(hDC, aPoints, sizeof(aPoints) / sizeof(POINT));

    // clean up
    SelectObject(hDC, hOldBrush);
    ReleaseDC(hWnd, hDC);
    return 1;
}