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CURVE
typedefstructtagCurve{L_UINTuStructSize;L_INTnType;L_INTnPointCount;L_POINT*pPoints;L_UINTuFillMode;L_DOUBLEdTension;L_INTnClose;L_INTnReserved;} CURVE, *pCURVE;
TheCURVEstructure defines a curve for theL_SetBitmapRgnCurvefunction and theL_CurveToBezierfunction.
Members
uStructSize
Size of this structure in bytes, for versioning. Use the sizeof() operator to calculate this value.
nType
Flag that indicates the type of curve defined. Possible values are:
| Value | Meaning |
|---|---|
| CURVE_BEZIER | The points specified in thepPointsfield define a Bezier curve. |
| CURVE_STANDARD | The points specified in thepPointsfield define a standard curve. |
| CURVE_NATURAL_CUBIC_SPLINE | The points specified in thepPointsfield define a natural cubic spline curve. |
nPointCount
Number of points in thepPointsarray.
IfnTypeis:
CURVE_BEZIER, nPointCount must be 3n + 4, where n >= 0. For example, nPointCount can be 4, 7, 10, 13, and so on.
CURVE_STANDARD, nPointCount must be greater than or equal to 3. For example, nPointCount can be 3, 4, 5, 6, and so on.
CURVE_NATURAL_CUBIC_SPLINE, nPointCount must be greater than or equal to 3. For example, nPointCount can be 3, 4, 5, 6, and so on.
pPoints
Pointer to an array of L_POINT structures that contain the points that define the curve.
uFillMode
Flag that indicates how to handle complex crossing lines. The following are valid values, which are illustrated below:
| Value | Meaning |
|---|---|
| L_POLY_WINDING | [0] All pixels that are inside the resulting exterior lines are in the region. |
| L_POLY_ALTERNATE | [1] The region includes the area between odd-numbered and even-numbered polygon sides on each scan line. |
dTension
Value that indicates the "straightness" of the curves that connect points. This value is used only whennTypeCURVE_STANDARD。在0.0之间的有效值d 1.0, where 0.0 indicates straight lines, and 1.0 indicates lines with the highest curvature. A typical value for dTension is 0.5.
nClose
Value that indicates how the curve is closed. This value is used only whennTypeCURVE_STANDARD。可能的值是:
| Value | Meaning |
|---|---|
| CURVE_NO_CLOSE | [0x0] For n points, draw (n - 3) segments. For example, for points {P0, P1, P2, P3, P4}, draw segments P1P2 and P2P3. |
| CURVE_CLOSE | [0x1] For n points draw (n) segments. For example, for points {P0, P1, P2, P3, P4}, draw segments P0P1, P1P2, P2P3, P3P4, P4P0. |
| CURVE_PARTIAL_CLOSE | (0 x2) n个点绘制(n - 1)段。为考试ple, for points {P0, P1, P2, P3, P4}, draw segments P0P1, P1P2, P2P3, P3P4 (but not P4P0). |
In the following diagram, the resulting region is shown in gray.
nReserved
Reserved for future use.
Comments
The CURVE structure is used by theL_SetBitmapRgnCurvefunction to draw a curve using an array of POINT items. It is also used by theL_CurveToBezierfunction to convert a curve to a Bezier. The CURVE structure can define three types of curves:
nTypeis CURVE_STANDARD: A minimum of three points define a smooth curve that goes through all of the points. In this case,nPointCountmust be equal to or greater than three.nTypeis CURVE_BEZIER: A minimum of four points defines a series of one or more Bezier curves. In this case,nPointCountmust be 4+3n, where n is equal to or greater than 0. For example,nPointCountcan be 4, 7, 10, 13, and so on. The first four points define the first Bezier curve, and each subsequent group of three points defines the next Bezier curve, using the last point of the previous Bezier curve as the starting point.nTypeis CURVE_NATURAL_CUBIC_SPLINE: A minimum of three points define a smooth curve that imitates the behavior of a plastic rod bent around control pegs (an engineering spline). This behavior can be used to imitate or suggest three-dimensional bending and rotation. In this case,nPointCountmust be equal to or greater than three.
Some functions which take this structure as a parameter require that the structure be initialized prior to the function call. You must set theuStructSizemember to the total size, in bytes, of the structure. Use the sizeof() operator to calculate this value. Functions that do not require the structure be initialized will take the total size of the structure, in bytes, as an additional function parameter.
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