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CRgn::CreatePolygonRgn

Creates a polygonal region.

BOOL CreatePolygonRgn(
   LPPOINT lpPoints,
   int nCount,
   int nMode 
);

Parameters

lpPoints
Points to an array of POINT structures or an array of CPoint objects. Each structure specifies the x-coordinate and y-coordinate of one vertex of the polygon. The POINT structure has the following form:
typedef struct tagPOINT {
   int x;
   int y;
} POINT;
nCount
Specifies the number of POINT structures or CPoint objects in the array pointed to by lpPoints.
nMode
Specifies the filling mode for the region. This parameter may be either ALTERNATE or WINDING.

Return Value

Nonzero if the operation succeeded; otherwise 0.

Remarks

The system closes the polygon automatically, if necessary, by drawing a line from the last vertex to the first. The resulting region is stored in the CRgn object.

The size of a region is limited to 32,767 by 32,767 logical units or 64K of memory, whichever is smaller.

When the polygon-filling mode is ALTERNATE, the system fills the area between odd-numbered and even-numbered polygon sides on each scan line. That is, the system fills the area between the first and second side, between the third and fourth side, and so on.

When the polygon-filling mode is WINDING, the system uses the direction in which a figure was drawn to determine whether to fill an area. Each line segment in a polygon is drawn in either a clockwise or a counterclockwise direction. Whenever an imaginary line drawn from an enclosed area to the outside of a figure passes through a clockwise line segment, a count is incremented. When the line passes through a counterclockwise line segment, the count is decremented. The area is filled if the count is nonzero when the line reaches the outside of the figure.

When an application has finished using a region created with the CreatePolygonRgn function, it should select the region out of the device context and use the DeleteObject function to remove it.

Example

CRgn   rgnA, rgnB;

CPoint ptVertex[5];

ptVertex[0].x = 180;
ptVertex[0].y = 80;
ptVertex[1].x = 100;
ptVertex[1].y = 160;
ptVertex[2].x = 120;
ptVertex[2].y = 260;
ptVertex[3].x = 240;
ptVertex[3].y = 260;
ptVertex[4].x = 260;
ptVertex[4].y = 160;

VERIFY(rgnA.CreatePolygonRgn( ptVertex, 5, ALTERNATE));

CRect rectRgnBox;
int nRgnBoxResult = rgnA.GetRgnBox( &rectRgnBox );
ASSERT( nRgnBoxResult != ERROR || nRgnBoxResult != NULLREGION );

CBrush brA, brB;
VERIFY(brA.CreateSolidBrush( RGB(255, 0, 0) ));  // rgnA Red
VERIFY(pDC->FrameRgn( &rgnA, &brA, 2, 2 ));
VERIFY(brB.CreateSolidBrush( RGB(0, 0, 255) ));  // Blue
rectRgnBox.InflateRect(3,3);
pDC->FrameRect( &rectRgnBox, &brB );

See Also

CRgn Overview | Class Members | Hierarchy Chart | CRgn::CreatePolyPolygonRgn | CreatePolygonRgn

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