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2.2.2.2.1.1.1.9 Fill Mode (FILL_MODE)

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The FILL_MODE structure specifies the algorithm used to determine if a given point is contained within a polygon.


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FillMode

FillMode (1 byte): An 8-bit, unsigned integer that specifies the fill mode. FillMode MUST be one of the following values.

Value

Meaning

ALTERNATE

0x01

Alternate fill mode. To test if a point is inside a polygon, a ray is drawn from that point parallel to the x-axis to infinity, and the number of intersections between the ray and the polygon outline is counted. If the number of intersections is odd, the point is inside the polygon, and, if it is even, the point is outside.

WINDING

0x02

Winding fill mode. To determine if a point is within a polygon, a ray is drawn from that point parallel to the x-axis to infinity, and its intersections with the outline are examined. A count that starts from 0 is kept for the ray. Each intersection with a clockwise polygon outline increments the count, and each intersection with a counterclockwise polygon outline decrements the count. If the final value of the count is nonzero, the point is inside the polygon; otherwise, it is outside.

For alternate and winding fill modes, see [YUAN] section 9.4 and [PETZOLD] pages 169–171.